Anaerobic Co-Digestion of Municipal Sludge with High-Strength by SzYu1ey

VIEWS: 6 PAGES: 78

									                       DRAFT




MUNICIPAL ANAEROBIC DIGESTERS AS
  REGIONAL RENEWABLE ENERGY
           FACILITIES

                           For:

                       Larry Krom
                Research and Development
        Focus on Energy Renewable Energy Program
                       P.O. Box 687
                  Spring Green, WI 53588


                           By:

           Daniel Zitomer and Prasoon Adhikari
                   Marquette University
     Department of Civil and Environmental Engineering
                   Water Quality Center
                       P.O. Box 1881
                   Milwaukee, WI 53201




                        May, 2005
                                                                                          i


EXECUTIVE SUMMARY


Anaerobic co-digestion is defined as the microbiological production of methane from a

mixture of various wastes. The mixing of wastes can result in both synergistic and

antagonistic interactions that influence methane production. Successful application of co-

digestion therefore requires careful management.



Many municipal wastewater treatment plants have existing anaerobic digesters that may

be used to co-digest high-strength wastes with municipal wastewater solids. If used for

co-digestion, then the municipal digesters could become regional renewable energy

facilities.



Four high-strength wastes were studied in an effort to determine appropriate operating

conditions for co-digestion, and to perform a simple economic analysis. Municipal

wastewater solids from South Shore Wastewater Treatment Plant (SSWWTP), Oak

Creek, WI were co-digested with high strength waste from the following facilities (with

the range of waste COD in parentheses):



        ° Miller Brewery beer filter                        (3000 – 6000 mg/L)

        ° Lesaffre Yeast fermentation                       (40,000 –50,000 mg/L)

        ° Southeastern Wisconsin Products fermentation      (80,000 to 90,000 mg/L)

        ° Pandl’s Restaurant food                           (200,000 to 500,000 mg/L)
                                                                                          ii

The food waste was pretreated using the Rothenberg Wet Waste Recovery System

marketed by Ecology, LLC of Glendale, WI.



The project consisted of three phases. First, the high-strength wastes were tested for

biochemical methane potential (BMP) and also tested using anaerobic toxicity assays

(ATAs). Second, bench scale digesters were operated in the laboratory. Finally, a full-

scale demonstration was performed by feeding wastes to the anaerobic digesters at the

SSWWTP.



BMP Testing. The average maximum BMP values were as follows (ml CH4 per gram

COD):

        ° Miller Brewery                                     413

        ° Lesaffre Yeast                                     2274

        ° Southeastern Wisconsin Products                    943

        ° Pandl’s Restaurant                                 488

The maximum theoretical BMP for any waste is 395 ml CH4 per gram COD assuming all

the COD is converted to methane. The abnormally high values for Lasaffre Yeast and

Southeastern Wisconsin Products wastes indicates that they stimulate methane production

from background COD present in the biomass, which was digested sludge from the

SSWWTP. The COD in Miller Brewery and Pandl’s Restaurant waste is essentially

completely convertible to methane.
                                                                                            iii

ATA Testing. At the loadings tested (typically 0 to 2 g COD/L), the wastes do not pose

toxicity challenges. An unanticipated result was that doses of Lesaffre Yeast Corporation,

Southeastern Wisconsin Products, and Miller Brewery wastewaters actually caused

methane production rates to significantly increase by as much as 15 to 230%.



Bench-Scale Digester Testing. Fourteen bench scale, fill-and-draw anaerobic digesters

were operated. Each 2-liter digester was fed a different blend of one high strength waste

and municipal wastewater solids (70% primary sludge and 30% v/v thickened waste

activated sludge from SSWWTP). Each digester was completely mixed and operated at a

15-day solids residence time (SRT) at 37±1o C. It was determined that Lasaffre Yeast and

Southeastern Wisconsin Products wastewaters can be successfully co-digested with

municipal wastewater solids at all blend ratios tested (from 20 to 80% v/v wastewater in

municipal wastewater sludge). Similarly, the food waste can be successfully co-digested

at all blend ratios tested (from 3 to 11% v/v food waste in municipal wastewater sludge).



The Miller brewery wastewater was not successfully digested by itself in the fill-and-

draw digester utilized; however, it was successfully digested when blended with

municipal wastewater solids. Although the brewery wastewater was not successfully

digested alone, it is amenable to anaerobic treatment. If it is treated alone, then it is

recommended that reactor configurations other than a fill-and-draw digester should be

considered.
                                                                                           iv

All the wastes utilized in bench-scale testing had metals concentrations below the

Wisconsin Department of Natural Resources high quality limits for biosolids to be land

applied and will not limit the land application of digested biosolids.



Full-Scale Demonstration Testing. A full-scale demonstration test was performed by

feeding Southeastern Wisconsin Products and Pandl’s Restaurant wastes to the anaerobic

digesters at the SSWWTP at the same time municipal wastewater solids were also being

fed. There was a 70% increase in biogas production when Southeastern Wisconsin

Products wastewater was co-digested. The waste constituted 1% of the total COD loading

to the digesters. Therefore, the biogas production increase was not due to additional

COD, but may have been due to a synergistic effect resulting from the presence of

bioavailable nutrients (e.g., iron) required for microbial growth. The additional biogas

can be employed to produce 16,300 kw-hr/day of electricity worth over $200,000 per

year using an existing biogas-powered electric generator set at the treatment plant.



Pandl’s Restaurant food waste was also delivered to the digesters at the SSWWTP.

However, due to the relatively large solid particles (approximately 20% of solids greater

than 4.76-mm nominal diameter), the food waste solids could have damaged pumps and

appurtenances. Therefore, the Pandl’s food waste was discharged to the primary clarifiers

at the plant. The solids that settle in the primary clarifier are screened and pumped to the

anaerobic digesters. Laboratory settleability testing and sieve analyses data were used to

estimate that 67% of the food waste COD would be conveyed to the anaerobic digesters

at SSWWTP. It is estimated that the waste produced by Pandl’s Restaurant can be
                                                                                              v

converted to 780 standard cubic feet per day of methane. The methane can be used to

generate $992 per year of electricity or can be used to off-set the purchase of $1620 per

year of natural gas.



It should be noted that Pandl’s Restaurant food waste is currently disposed of in a

sanitary landfill. It is possible that anaerobic digestion with biogas utilization and safe

application of the stabilized biosolids would prove to be a more economical approach

than landfilling if a detailed lifecycle cost comparison of the two options was performed.

In addition, if more restaurants began to practice waste shredding and storage, then it is

probable that economy-of-scale savings could be accrued.



It is recommended that treatment plant personnel consider periodic or continuous co-

digestion of Southeastern Wisconsin Products wastewater and municipal wastewater

solids; this may lead to a sustained increase in biogas production. In addition,

investigations regarding the use of Southeastern Wisconsin Products and other similar

yeast production/fermentation wastes as supplements to increase biogas production at

other anaerobic digestion facilities are recommended.
                                                                     vi


ACKNOWLEDGEMENTS

The support of the following organizations is greatly appreciated:



Focus on Energy, Renewable Energy Program

Ecology, LLC, Glendale, Wisconsin

Marquette University, Milwaukee, Wisconsin

United Water Services, Inc., Milwaukee, Wisconsin

Lasaffre Yeast, Inc., Milwaukee, Wisconsin

Miller Brewing, Milwaukee, Wisconsin

Pandl’s Restaurant, Bayside, Wisconsin

Southeastern Wisconsin Products, Oak Creek, Wisconsin
                                                                                 vii



TABLE OF CONTENTS
EXECUTIVE SUMMARY……………………………………………….......…………….………... i
ACKNOWLEDGEMENTS……………………………………………………………………......…. vi
LIST OF TABLES………………………………………………………………………………….. ix
LIST OF FIGURES…………………………………………………………………………….….... x
CHAPTER 1: INTRODUCTION……………………………………………………………………..                                   1
 1.1  Anaerobic Digestion……………………………...………………………………….…..                              1
 1.2  Aanaerobic Co-Digestion………………………...………………………………………                              3
 1.3  Municipal Anaerobic Digesters as Regional Renewable Energy Facilities………….…..   4

CHAPTER 2: BIOCHEMICAL METHANE POTENTIAL (BMP) AND ANAEROBIC TOXICITY
            ASSAYS (ATA) OF HIGH –STRENGTH INDUSTRIAL WASTES………………….….                8
 2.1 Introduction……………………………………………………………………………….                                      8
 2.2 Materials and Methods………………………………………………………………...….                               9
   2.2.1 BMP…………………………………………………………………………………..                                         9
   2.2.2 ATA…………………………………………………………………………………..                                         11
 2.3 Results and Discussion………………………………………………………......……......                        12
   2.3.1 BMP…………………………………………………………………………………..                                         12
   2.3.2 ATA……………………………………….………………………………………….                                         20
 2.4 Conclusions…………………………………………….……………………………....…                                    26



CHAPTER 3: BENCH-SCALE TESTING OF ANAEROBIC CO-DIGESTION ……………………….. 27
  3.1 Introduction………………………………………………………………….…………… 27
  3.2 Bench-Scale Digester Description………………………………………………...…...… 29
  3.3 Sampling and Analyses……………………………………………..….………………… 31
  3.4 Results and Discussion………………………………………………….………………... 32
3.4.1 Average Seed Biomass and Feed Characteristics……………………..………………..... 32
3.4.2 Digester Loadings/Hydraulic Retention Time………………………..………………….. 34
3.4.3 pH and Alkalinity………………………………………………………………………… 35
3.4.4 Volatile Solid Destruction………………………………...………………………...……. 37
3.4.5 Biogas/Methane …………………………………………………….……………………. 39
  3.5 Conclusions………………………………………………………………………………. 40

CHAPTER 4: FULL-SCALE CO-DIGESTION TESTING AT SOUTH SHORE WASTEWATER
              TREATMENT PLANT……………………………………………………………….                                42
4.1 Introduction………………………………………………………………………..……….....                                 42
4.2 South Shore Wastewater Treatment Plant (SSWWTP)……………………………………..                   42
4.3 Anaerobic Digesters at SSWWTP………………………………………………..………...…                          43
4.4 Southeastern Wisconsin Yeast Wastewater (SEWYWW)………………...………………….                 44
4.5 Pandl’s Restaurant Food Waste ………………………………………………………………                            48
4.5.1 Settleability Testing…………………………………………………………………...…..                            50
4.5.2 Sieve Analysis………………………………………………………………………….....                                 51
4.6 Economic Analysis……………………………………………………………………………                                    52
4.6.1 Southeastern Wisconsin Yeast Wastewater (SEWYWW)………………………………                    54
4.6.2 Pandl’s Restaurant Food Waste…………………………………………………………                             56
                                                               viii

4.7 Conclusions……………………………………………………………...…………………                  56



CHAPTER 5: OVERALL CONCLUSIONS AND RECOMMENDATIONS………………...……….… 59
5.1 BMP and ATA Testing………………………………………………………………………                59
5.2 Bench-Scale Co-Digestion Testing………………………………………………………….       60
5.3 Full-Scale Co-Digestion Testing…………………………………………………………….       61


REFERENCES……………………………………………………………………………………... 64
BIBLIOGRAPHY…………………………………………………………………………………… 66
                                                                                          ix




                                    LIST OF TABLES

Table 2.1: BMP Miller Brewery Wastewater…………………………….……………………………                                  17
Table 2.2: BMP Lesaffre Yeast Corporation Wastewater………………………….…………………..                         17
Table 2.3: BMP Southeastern Wisconsin Products Wastewater………………………...……………..                     18
Table 2.4: BMP Pandl’s Restaurant Food Waste………………………………………...…………….                             18
Table 2.5: Overall BMP Results……………………………………….………………………………. 19
Table 2.6: ATA Miller Brewery Wastewater……………………………………….……...…………..                              24
Table 2.7: ATA Lesaffre Yeast Corporation Wastewater………………………….…………………..                         24
Table 2.8: ATA: Southeastern Wisconsin Products Wastewater………………..……………………..                     24
Table 3.1: Combinations of Municipal Wastewater Solids and High-Strength Waste Fed to            29
Digesters………...….…………………………………………………………………………...
Table 3.2: Sampling Schedule……………………………………………………….……………..…..                                     30
Table 3.3: Gas Chromatographic Conditions for Methane Analysis………………………………….                     31
Table 3.4: Average Characteristics of PS and WAS in Municipal Wastewater Solids …………..….         33
Table 3.5: Average Characteristics of High-Strength Wastes……………………………...…………..                   33
Table 3.6: Blend of Municipal Sludge and High Strength Waste and VS Loading Rates…………...         34
Table 3.7: Average pH of High-Strength Wastes …………………………………………….……….                             36
Table 3.8: Average pH and Alkalinity of Effluent from Digesters…………………………………...                  36
Table 3.9: Total Solids, Volatile Solids of the Effluent and Volatile Solids Destruction………….…   37
Table 3.10: Biogas Production, Rate of Biogas Production and Percentage Methane in Assays ……     39
Table 4.1: Average SEWYWW Addition: Date and Amount…………….……………………….…... 45
Table 4.2: Average Characteristics of SEWYWW ……………………………..………………..……                             45
Table 4.3: Biogas and Methane Production Before and After SEWYWW Co-Digestion…………..              47
Table 4.4: Pandl’s Restaurant Food Waste Characteristics………………………………………….…                       49
Table 4.5: Pandlt’s Food Waste and Wisconsin Land Application Limit Metals                       50
Concentrations……………………………………………………………………………………
Table 4.6: Sieve Analysis Results for Food Waste Solids……………………………………………..                       51
Table 4.7: Synopsis of the Biogas Production and Energy Savings During SEWYWW Co-
Digestion………………………………………………………………………………………....                                                   55
                                                                                         x



                                   LIST OF FIGURES

Figure 2.1: BMP: Miller Brewery Wastewater………………………………………………..                          13
Figure 2.2: BMP: Lesaffre Yeast Corporation Wastewater …………………………………                    14
Figure 2.3: BMP: Southeastern Wisconsin Products Wastewater………………….…………. 15
Figure 2.4: BMP: Food Waste…………………………………………………………………                                    16
Figure 2.5: ATA: Miller Brewery Wastewater…………………………….…………...……... 21
Figure 2.6: ATA: Lesaffre Yeast Corporation Wastewater…………..………………………. 22
Figure 2.7: ATA: Southeastern Wisconsin Products Wastewater…………………….……..                23
Figure 2.8 Rate of Methane Production versus Wastewater Dose (% v/v)……..……………..         25
Figure 3.1: Control Anaerobic Bench-Scale Digester (R#1) and Different Blends of MWS
                                                                                        28
and MBWW (R#2, R#3 and R#4)……………………………………………………………..
Figure 3.2: Control Anaerobic Bench-Scale Digester (R#1) and Different Blends of MWS
                                                                                        28
and LYWW (R#5, R#6 and R#7)……………………………………………………………...
Figure 3.3: Control Anaerobic Bench-Scale Digester (R#1) and Different Blends of MWS
                                                                                        28
and SEWYWW (R#8, R#9 and R#10)………………………………………………………...
Figure 3.4: Control Anaerobic Bench-Scale Digester (R#11) and Different Blends of MWS
                                                                                        28
and FW (R#12, R#13 and R#14)………………………………………………………………
Figure 4.1: Biogas Production from Full-Scale Co-Digestion of SEWYWW………………              48
                                                                                             1


CHAPTER 1: INTRODUCTION


1.1    ANAEROBIC DIGESTION

Anaerobic digestion (AD) is one of the standard technologies for stabilizing wastes. AD

is the biological decomposition of organic matter in the absence of molecular oxygen.

The AD process produces biogas principally composed of methane (CH4) and carbon

dioxide (CO2) and the undegraded solids and liquids (Lusk and Moser, 1996). Anaerobic

processes can either occur naturally or in a controlled environment such as a biogas plant.

Depending on the waste feedstock and the system design, biogas is typically 55 to 80

percent methane; the remaining composition is primarily carbon dioxide, with trace

quantities of potentially corrosive hydrogen sulfide and water vapor.



The process of anaerobic digestion can be considered to consist of three steps. The first

step is the decomposition (hydrolysis) of complex organic matter. This step breaks down

the organic material to smaller molecules such as sugars. The second step is the

conversion of smaller molecules to organic acids. Finally, the acids are converted to

biogas containing methane (Speece, 1995).



Process temperature affects the rate of digestion and is often maintained in the

mesophillic range (30 to 38oC or 95 to 105o F). It is also possible to operate in the

thermophillic range (50 to 57 oC or 122to 136o F (Metcalf and Eddy, 2003). There are

usually two reasons why the mesophilic and thermophilic temperatures are preferred over

lower temperatures. First, a higher loading rate of organic materials can be processed and
                                                                                              2

increased rates of biogas production typically result. Second, higher temperatures increase

the destruction rate of pathogens present in raw sanitary wastes.



Benefits of AD technology are listed below (Speece, 1995).

Waste Treatment Benefits

 Natural waste treatment process
           
 Can require less land than aerobic wastewater treatment, composting or landfilling
           
 Reduces disposed waste volume and weight of solid waste to be landfilled
           
           

Energy Benefits

 Can be a net energy producing process
           
 Generatesa renewable fuel

           

Economic Benefits

 Is sometimes more cost-effective than other treatment options, such as aerobic
           
  wastewater treatment


The major applications of AD are in the stabilization of concentrated sludges produced

from the treatment of municipal wastewater. However, the wastes that can be treated by

AD cover a wide range and include sewage sludge, agricultural wastes, municipal solid

wastes and industrial wastes (Metcalf and Eddy, 2003).



Many industries with organic waste streams use an AD process as a pretreatment step to

lower sludge disposal costs and reduce the cost of overall treatment. Some industries

using AD for wastewater treatment are listed below (Speece, 1995).
                                                                                             3


 Food process such as vegetable canning, milk and cheese manufacture, slaughterhouse

 wastes and potato processing wastes

 Drink industry, breweries, soft drinks, distilleries, coffee and fruit juices production

 Industrial products, paper and board, rubber, chemicals, starch and pharmaceuticals



1.2   ANAEROBIC CO-DIGESTION

In typical applications, an anaerobic digester is designed and operated to treat waste from

one facility only, such as a food production facility, soft drink bottling plant, or municipal

wastewater treatment plant. Co-digestion is a modification of this typical application.


                                                                                                 Comment [A1]: The font and spacing got a bit
Ahring et al. (1992) and others have described co-digestion as a waste treatment                 screwed in this paragraph.



method in which different wastes or wastewaters are mixed and treated together.


The term “co-fermentation” is synonymously used for “co-digestion”. When various


wastes are mixed and co-digested, both synergistic and antagonistic outcomes are


possible. Successful combinations of different types of wastes and wastewater


require careful management. For example, wastes low in nutrients or alkalinity can be


mixed with wastes with high concentrations of these required constituents to increase

overall biogas production. The potential advantages of co-digestion are presented


below (Braun, 2002).
                                                                                              4

Potential Advantages of Co-Digestion

   Improved nutrient balance and digestion
   Equalization of particulate, floating, settling, and acidifying wastes through dilution
    by manure, sewage sludge, or other wastes
   Additional biogas production




1.3 MUNICIPAL ANAEROBIC DIGESTERS AS REGIONAL RENEWABLE
    ENERGY FACILITIES


Wastewater and solid waste management is a challenge faced by communities around the

world. Rapid population growth, urbanization, and the associated population density

increase are factors that increase the waste disposal challenge. Methods of solid waste

management include recycling of paper, metal, and plastic, incineration and sanitary

landfilling. In the case of incineration, perceived air pollution and high capital cost are

potential disadvantages. Typically, a large fraction of solid waste is disposed of in

landfills. However, in some communities, landfills are approaching capacity. In addition,

landfills are not designed to maximize the rate of methane generation for renewable

energy. In comparison, anaerobic digestion systems achieve more rapid methane

generation.



Population growth and urbanization along with industrialization have also helped to

increase world energy demand. Conventional non-renewable sources of energy are
                                                                                            5

limited. Some researchers predict that petroleum deposits will be depleted in the next few

decades and coal deposits will be depleted within 150-200 years (Smil, 2003). Besides

this, the environmental damage (e.g., global warming, mercury pollution) caused by

improper combustion of fossil fuels is a matter of concern. Hence, it is prudent to develop

energy from a variety of sources, including sources of renewable energy.



In this regard, solid waste and industrial wastewater are potential energy sources worth

considering. Many industries dispose of solid wastes in landfills, or discharge high-

strength wastewater to sewers. If handled through landfills and sewers, the waste

materials are wasted since they are not typically used as feedstocks to produce renewable       Comment [A2]: Lanfills do recover energy so
                                                                                                they are not truly wasted

energy. If sludge or wastes are disposed of in a landfill, then wastes take up landfill

space, may lead to future groundwater pollution and may not be used to produce energy.

Biological treatment of wastewater and solid waste using anaerobic treatment may be

used to increase renewable energy production. In this process, wastes are converted to

biogas (an energy source) and stabilized biosolids.



Many of Wisconsin’s municipal wastewater treatment plants like Milwaukee, South

Milwaukee, Brookfield, Waukesha, Racine, Sheboygan, Burlington, Watertown, West

Bend, New London, Madison, Richland Center, Walworth County, Chilton,

Delafield/Hartland, Grafton, Kiel, Plymouth, and Port Washington use anaerobic

digesters to biologically convert municipal wastewater solids to biogas that contains

methane. The methane is often used as a renewable energy source to generate electricity,

run equipment, heat the digesters, and heat buildings. The digesters are often very large
                                                                                             6

and could, under the correct conditions, treat other high-strength industrial byproducts

and economically produce more methane. Therefore, existing municipal anaerobic

digesters could become regional renewable energy facilities.



Reports of co-digestion have recently become more numerous, and there have been

several applications or research projects regarding co-digestion of municipal wastewater

solids, agricultural wastes, animal wastes, olive oil, pig slurry, swine manure, cattle

manure, paper mill sludge, and municipal solid waste (Angelidaki et al., 1997; Carrieri et

al., 1993; Cecchi et al., 1993; Di Palma et al., 1999; Gavala et al., 1996; Gavala et al.,

1999; Hamzawi et al., 1998; McGrady, 1999; Mavinic et al., 1998; Rintala and Jaervinen,

1996; Sosnowski et al., 2003) . However, anaerobic co-digestion of municipal wastewater

solids with high strength wastewater and food waste has not been widely practiced in the

United States due to lack of information regarding implementation, correct operating

conditions, experience and costs.



In order to determine appropriate operating conditions and experience for co-digestion of

different high strength wastewaters, a practical demonstration project was performed and

is reported herein. Municipal wastewater solids from the South Shore Wastewater

Treatment Plant (SSWWTP), Oak Creek, WI were co-digested with high strength

wastewater from I-house beer filters from Miller Brewery, fermentation waste from                Comment [A3]: I don't know what an I-house is.
                                                                                                 Maybe a little explanation?

Lesaffre Yeast production facility, fermentation waste from Southeastern Wisconsin

Products and Food Wastes from Pandl’s Restaurant. The wastes were selected base upon
                                                                                       7

their high COD, probable anaerobic degradability, and generation in proximity of the

SSWWTP. Information regarding these facilities is presented below.



Miller Brewing Company

3939 W. Highland Blvd.

Milwaukee, WI 53201

Contact: James Surfus




Lasaffre Yeast Corporation

2702 W. Greves Street

Milwaukee, WI 53208

Contact: Tony Boyd



Southeastern Wisconsin Products Company, Inc.

500 W Edgerton Ave

Milwaukee WI 53207

Contact: Michael Malencore



Pandl’s Restaurant

8825 N Lake Dr

Milwaukee WI 53217
                                                                                         8

Contact James Pandl




CHAPTER 2: BIOCHEMICAL METHANE POTENTIAL (BMP) AND
          ANAEROBIC TOXICITY ASSAYS (ATA) OF HIGH-STRENGTH
          INDUSTRIAL WASTES


2.1    INTRODUCTION

Batch anaerobic bioassay techniques have been developed by others as simple and

inexpensive procedures to monitor relative biodegradability and possible toxicity of

wastes to be treated by AD. The biochemical methane potential (BMP) and anaerobic

toxicity assay (ATA) are relatively simple bioassays that can be conducted in laboratories

without the need for sophisticated equipment (Owen et al., 1979).
                                                                                           9

The BMP is a measure of sample biodegradability (Owen et al., 1979). Just as the

biochemical oxygen demand (BOD) assay indicates how much organic pollution can be

degraded in an aerobic process, the BMP is a measure of what fraction of a given wastes’

COD can be removed anaerobically and what volume of methane can be produced when

treating that waste (Speece, 1996). The assay provides a simple means to monitor relative

anaerobic biodegradability of substrates. Uses of the BMP are as follows (Speece, 1995).



 Assaying the concentration of organic pollutants in a wastewater which can be

 anaerobically converted to methane (CH4)

 Evaluating potential anaerobic process efficiency

 Measuring residual organic pollution amenable to further anaerobic treatment

 Testing for non-biodegradable chemical oxygen demand (COD) remaining after

 treatment



The ATA was developed to determine any toxic effect of a substance on the organisms

that convert acetate to methane (Owen et al., 1979). These organisms are typically

considered to be the microbes most sensitive to toxicants in the mixed microbial culture

that achieves methane production from complex substrates.



The significant difference between the BMP and ATA assays is that the ATA is

supplemented with a high concentration of acetate as well as varying wastewater

concentrations, whereas no acetate is added to the BMP system. The total amount of
                                                                                           10

biogas production is most important in the BMP test, whereas the initial rate of gas

production is of primary interest in the ATA test (Speece, 1996).



The BMP assay was conducted on all of the wastes used for co-digestion. The ATA assay

was conducted on I-house beer filter waste from Miller Brewery, fermentation waste

from Lesaffre Yeast Corporation and fermentation waste from Southeastern Wisconsin

Products.



2.2 MATERIAL AND METHODS

2.2.1 BMP

The BMP protocol of Owen et al. (1979) was used to determine the extent to which each

of the high-strength wastes might be converted to methane by Southshore Wastewater

Treatment Plant (SSWWTP) digester sludge microorganisms.

For the Miller Brewing Company and Lesaffre Yeast Corporation wastes, waste

concentrations of 0.5, 1.0, 2.0 and 2.5 grams of COD per liter (gCOD/l) and for

Southeastern Wisconsin Products waste concentrations of 0.4, 1.2, 1.8, and 2.4 gCOD/l

were fed to 40-mL aliquots of methanogenic biomass in 160-mL serum bottles. For the

Pandl’s food waste, serum bottles were organically loaded based upon volatile solids

values (and not COD) because the waste had a very high solids concentration. Nominal

loadings of 0.5, 1, 2, 5 and 10 grams of volatile solids per liter (gVS/L) were employed.

Also, control bottle receiving no waste were prepared. In order to maintain the pH at 7,

alkalinity in the form of sodium bicarbonate (NaHCO3) was added to all the systems at

the concentration of 5 g/L.
                                                                                        11




All systems were run in triplicate. Thus, 54 serum bottles were prepared for BMP testing.

Bottles were sparged with 30% CO2 /70% N2 gas to help establish anaerobic conditions,

then sealed with rubber septa. BMP bottles were placed on a shaker table (C25KC

Incubator Shaker, New Brunswick Scientific, Edison, NJ, USA) at 35o C and 150 rpm.

Total biogas production was measured over approximately 30 days using 50-ml or 100-

mL wetted barrel glass syringes, and biogas methane content was determined by gas

chromatography with a flame ionization detector (GowMac GC), an 8ft. x .124 in. o.d.

stainless steel column packed with 1%SP-1000 on 60/80 Carbopack B (Supelco, Inc.

Bellefonte, PA) and a nitrogen carrier flow of 20 ml/min at an oven temperature of 60oC.

The numerical data are presented herein as the average cumulative volume of gas

production from triplicate bottles.



2.2.2 ATA

The ATA protocol of Owen et al. (1979) was used to determine the extent to which each

of the high strength wastes might inhibit methane production by aceticlastic

methanogens.



For the Miller Brewing Company ATA, studies were run at four organic loadings of 0.5,

1, 2, and 2.5 gCOD/L. For Lesaffre Yeast Corporation wastes, the four organic loadings

were 0.5, 1, 2, 2.5 gCOD/L, and for Southeastern Wisconsin Products waste the loading

were 0.4, 1.2, 1.8, 2.4 gCOD/L. Calcium acetate was also added to provide an initial

concentration of 10,000 mg/L in the bottles. This is a non-limiting substrate concentration
                                                                                           12

for aceticlastic methanogenic organisms. Therefore, any decrease in the rate of biogas

production measured was due to the wastewater toxicity and not due to lack of acetate

needed by the anaerobic microorganisms. Also to ensure that pH was approximately 7,

alkalinity in the form of sodium bicarbonate (NaHCO3) was added to all the systems at

the concentration of 5g/l. A control bottle receiving no waste was also prepared.



All systems were run in triplicate. Thus, 39 serum bottles were prepared for ATA tests.

Bottles were sparged with 30% CO2 /70% N2 gas to establish anaerobic conditions, then

sealed with rubber septa. ATA bottles were placed on a shaker table (C25KC Incubator

Shaker, New Brunswick Scientific, Edison, NJ, USA) at 35o C and 150 rpm. Total biogas

production was measured daily over a period of approximately 30 days using 50-ml or

100-mL wetted barrel glass syringes, and biogas methane content was determined by gas

chromatography with a flame ionization detector (GowMac GC), an 8ft. x .124 in. o.d.

stainless steel column packed with 1%SP-1000 on 60/80 Carbopack B (Supelco, Inc.

Bellefonte, PA) and a nitrogen carrier flow of 20 ml/min at an oven temperature of 60oC.

The data are presented as the average initial rate of methane production from triplicate

bottles.



2.3 RESULTS AND DISCUSSION

2.3.1 BMP

Gas production in BMP serum bottles for Miller Brewing wastewater, Lesaffre Yeast

Corporation wastewater, Southeastern Wisconsin Products wastewater and Pandl’s

Restaurant food waste was monitored for 32, 30, 32 and 33 days respectively. Cumulative
                                                                                          13

methane production in BMP assays for the different wastes is illustrated in Figures 2.1

through 2.4. The COD of wastes used from BMP assays are as follows: Miller Brewery

wastewater (5,600mg/l), Lesaffre Yeast Corporation wastewater (47,300 mg/l),

Southeastern Wisconsin Products wastewater (83,000 mg/l), and Pandl’s Restaurant food

waste (233,800 mg/l).
                                             14




Figure 2.1: BMP: Miller Brewery Wastewater
                                                        15




Figure 2.2 BMP: Lasaffre Yeast Corporation Wastewater
                                                              16




Figure 2.3: BMP: Southeastern Wisconsin Products Wastewater
                              17




Figure 2.4: BMP: Food Waste
                                                                                         18

Methane production was observed at all the concentration of wastes tested (see Figures

2.1 through 2.4). The total amount of methane produced and the maximum specific

methane production rates at the various organic loadings are summarized in Table 2.1

through 2.4.



Table 2.1: BMP Miller Brewery Wastewater
          Vol.                           Max. Methane             Max. Specific
 Loadings      Methane   BMP      Biogas              Biomass
          WW                              production           methane production
(g COD/l)       (ml) (mlCH4/gCOD) % CH4                VS (g)
          (ml)                            rate (ml/d)         rate (ml CH4/gVS- d)
   0.0     0     31±0       NA         47         4
   0.5     4     40±1       409        52         6
   1.0     9     50±3       388        53         10
   2.0     23    85±2       429        62         14        0.48          35.4
   2.5     33    109±3      427        65         17
  Avg.                      413        58
  Std.                       19         6




Table 2.2: BMP Lesaffre Yeast Corporation Wastewater
          Vol.                           Max. Methane             Max. Specific
 Loadings      Methane   BMP      Biogas              Biomass
          WW                              production           methane production
(g COD/l)       (ml) (mlCH4/gCOD) % CH4                VS (g)
          (ml)                            rate (ml/d)         rate (ml CH4/gVS- d)
   0.0      0    45±4        NA         61        2
   0.5     0.4   86±3       2030        56        6
   1.0     0.9   142±1      2372        60        18
   2.0     1.8   211±1      1986        61        25        0.61          59.0
   2.5     2.2   331±6      2711        63        36
  Avg.                      2274        60
  Std.                      338         3
                                                                                              19


Table 2.3: BMP Southeastern Wisconsin Products Wastewater
          Vol.                           Max. Methane             Max. Specific
 Loadings      Methane   BMP      Biogas              Biomass
          WW                              production           methane production
(g COD/l)       (ml) (mlCH4/gCOD) % CH4                VS (g)
          (ml)                            rate (ml/d)         rate (ml CH4/gVS- d)

  0.00       0    100±2        NA          67         7
  0.05      0.2   126±1       1617         68        9
  0.10      0.5   131±2       638          68        11
  0.20      0.9   153±2       720          70        14              0.39           43.6
  0.25      1.2   179±1       799          70        17
  Avg.                        943          69
  Std.                        454          1




Table 2.4: BMP Pandl’s Restaurant Food Waste
                                                          Max. Methane                  Max. Specific
 Loading    Grams    Methane   BMP      Biogas %                            Biomass
                                                          production rate            methane production
 (g VS/l)   Waste     (ml) (mlCH4/gCOD)   CH4                                VS (g)
                                                              (ml/d)                rate (ml CH4/gVS-d)
    0.0        0     131±2           NA         66              8
    0.5     0.1089   139±7           182        66              9
    1.0     0.1819   136±11          228        67              10
    2.0     0.3762   186±4           626        69              12
                                                                             0.54          35.2
    5.0     0.9380   277±18          665        67              16
   10.0     1.8766   455±23          738        72              19
   Avg.                              488        68
   Std.                              262        2




The BMP values were calculated by subtracting the amount of methane produced in the

control bottles that received no waste from the amount of methane produced in the fed

bottles. The difference obtained was divided by the mass of COD added to the test

bottles to obtain BMP in terms of mlCH4/gCOD. Table 2.5 below presents the overall

BMP results.
                                                                                         20




Table 2.5: Overall BMP Results
                                 Miller      Lesaffre        SE WI
       Characteristics                                                     Food waste
                                Brewing        Yeast        Products
    BMP (mlCH4/gCOD)            41319       2274338       943454         488262
        Biogas % CH4             586          603           691           682
  Max. CH4 Production rate
                                  17            36             17              19
           (ml/day)
       VS Biomass (g)            0.48          0.61            0.39           0.54
 Max. Sp. CH4 Production rate
                                 35.4          59.0           43.60           35.2
      (mlCH4/g VS-day)



According to stoichiometric relationships, 395 ml of methane at 35oC is equivalent to 1 g

of COD removed from wastewater if the COD is removed via methane production only.

However, measured values sometimes vary slightly from that of the stoichiometric

relationship due to biomass growth, sulfate reduction, hydrogen gas generation,

experimental inaccuracies and other factors. Major variation from stoichiometric

relationships should be closely scrutinized, and indicate the existence of unique

mechanisms or experimental error.



Regarding the values observed and reported herein, the BMPs for Lesaffre Yeast

Corporation and Southeastern Wisconsin Products wastewaters are abnormally high (i.e.,

greater than 900 mL/g COD). On the other hand, the average BMP values for Miller

Brewery and Pandl’s Restaurant wastes are within 22% of the theoretical BMP. The

abnormally high BMP values for the two yeast-containing wastewaters may be due to the

presence of supplementary nutrients (e.g, iron) in the yeast wastewaters tested. In

addition, the presence of complexing agents that render the metals more soluble and

bioavailable could cause an increase in biogas production. Therefore, nutrients and/or

complexing agents may have stimulated fermentation of residual COD in the seed
                                                                                         21

biomass slurry employed in the tests. It is known that the addition of trace nutrients, such

as nickel, cobalt, and iron, can greatly increase methane production rates in nutrient

limited systems, including some municipal digesters (Speece, 1988). However, further

study is required to determine conclusively that trace nutrients in the yeast wastes caused

the extremely high BMP values.



2.3.2 ATA

The results of ATA trials for Miller Brewery wastewater, Lesaffre Yeast Corporation

wastewater, and Southeastern Wisconsin Products wastewater are presented in Figures

2.5 through 2.7 respectively. Gas production in serum bottles for Miller Brewing

wastewater, Lesaffre Yeast Corporation Wastewater, Southeastern Wisconsin Products

Wastewater and food waste was monitored for 32, 30, 32 and 33 days respectively. The

results of ATA tests are presented in Figures 2.5 through 2.7. The total amount of

methane produced and the rates of methane production for the wastes are presented in

Tables 2.6 through 2.8.
                                        22




Figure 2.5: ATA: Miller Brewery Waste
                                                         23




Figure 2.6: ATA: Lasaffre Yeast Corporation Wastewater
                                                              24




Figure 2.7: ATA: Southeastern Wisconsin Products Wastewater
                                                                                 25




Table 2.6: ATA Miller Brewery Wastewater
                          Vol.
                                                                  Max. Methane
  Loadings   Vol. WW     Calcium      Biogas   Biogas % Methane
                                                                   production
 (g COD/l)     (ml)      Acetate       (ml)      CH4     (ml)
                                                                   rate (ml/d)
                          (ml)
    0.0          0         5.5         220       63       138         27
    0.5          4         6.0         257       62       161         30
    1.0          9         7.0         343       62       213         37
    1.8         23         9.0         388       63       247         34
    2.2         33         10.0        422       64       263         31




Table 2.7: ATA Lesaffre Yeast Corporation Wastewater
                          Vol.                                    Max. Methane
  Loadings   Vol. WW                  Biogas   Biogas % Methane
                        Calcium                                    production
 (g COD/l)     (ml)                    (ml)      CH4     (ml)
                       Acetate (ml)                                rate (ml/d)

     0         0           5.5         309       66       205         17
    3.8        4           6.0         390       64       252         18
    7.6        9           7.0         451       63       286         45
    15         23          9.0         731       57       407         51
    19         33         10.0         845       55       490         56




Table 2.8: ATA: Southeastern Wisconsin Products Wastewater
                          Vol.                                    Max. Methane
  Loadings   Vol. WW                  Biogas   Biogas % Methane
                        Calcium                                    production
 (g COD/l)     (ml)                    (ml)      CH4     (ml)
                       Acetate (ml)                                rate (ml/d)

     0          0           5.5        241       64       154         27
    0.4        0.2          6.0        267       64       169         29
    0.9        0.5          7.0        363       63       227         31
    1.5        0.9          9.0        421       64       270         34
     2         1.2         10.0        470       62       289         38
                                                                                                                   26

Miller Brewing, Lesaffre Yeast, and Southeastern Wisconsin Products wastes did not

demonstrate any inhibitory effect on the methane production rates. In fact, the methane

production rate increased approximately 80% when Lasaffre yeast wastewater was added

at doses of more than 8% volume per volume (v/v) (see Figure 2.8). Similarly, as

Southeastern Wisconsin Products wastewater dose increased from zero to 40% v/v, the

methane production rate increased 40%. In addition, methane production rate also

increased with increasing Miller Brewery wastewater doses as high as 32% v/v. However

a dose of 40% Miller Brewery wastewater caused a decrease in methane production (see

Figure 2.8).



                                                   60
               Rate of Methane Production (ml/d)




                                                   50

                                                   40

                                                   30

                                                   20

                                                   10

                                                   0
                                                        0   5   10   15     20      25       30     35   40   45
                                                                            % Wastewater

                                                                     MBWW        LYWW      SEWYWW




Figure 2.8 Rate of Methane Production versus Wastewater Dose (% v/v)                                                    Comment [A4]: This table could use units on the
                                                                                                                        ordinate

       MBWW (Miller Brewery Wastewater)
       LYWW( Lasaffre Yeast Wastewater)
       SEWYWW (Southeastern Wisconsin Yeast Wastewater)
                                                                                             27


2.4    CONCLUSIONS

Anaerobic bioassay techniques (BMP and ATA) were used to determine that the four

high strength wastes, namely I-house beer filters from Miller Brewery, fermentation

waste from Lesaffre yeast production facility, fermentation waste from Southeastern

Wisconsin Products and Food Wastes from Pandl’s Restaurant, were amenable to

anaerobic treatment and demonstrated no discernable toxicity to anaerobic

microorganisms at the concentrations studied. Interestingly, Lesaffre Yeast Corporation

wastewater and Southeastern Wisconsin Products wastewater demonstrated abnormally

high BMP values. These values suggest that the two wastes stimulated methane

production from background COD present in the biomass used in the test, which was

digested sludge from the SSWWTP. In addition, doses of Lasaffre, Southeastern

Wisconsin Products, and Miller Brewery wastewaters caused methane production rates to

increase by as much as 20 to 80% in systems containing a non-limiting concentration of

acetate (i.e., ATA assays). The unanticipated stimulatory effects of the wastewaters may

be due to the presence and bioavailability of trace nutrients. The microbes that convert

substrates to methane require nutrients, such as nickel, cobalt, and iron. The addition of

these nutrients in bioavailable forms and/or the addition of complexing agents that render

the metal nutrients bioavailable often leads to an increase in methane production rate in

nutrient limited systems. Additional research to investigate this stimulatory affect of yeast

production waste is warranted. It may be that yeast wastes can be used as additives to

significantly increase biogas production in many anaerobic digesters.
                                                                                           28




CHAPTER 3: BENCH-SCALE TESTING OF ANAEROBIC CO-DIGESTION


3.1 INTRODUCTION

In order to determine appropriate operating conditions for co-digestion of high strength

wastes with municipal wastewater solids, research was performed at the Water Quality

Center of Marquette University. Municipal wastewater solids from South Shore

Wastewater Treatment Plant (SSWWTP) were co-digested with high strength wastewater

from Miller Brewing Company (MBWW), Lasaffre Yeast Corporation (LYWW),

Southeastern Wisconsin Products yeast (SEWYWW), and Pandl’s Restaurant food waste

(FW). These facilities are all within a 20-mile radius of the SSWWTP in Oak Creek,

Wisconsin. Their locations are given in Chapter 1.



A set of bench-scale anaerobic digesters was operated for each high-strength waste

mentioned above. Each digester in a set was fed a different volumetric blend of one high-

strength waste and municipal wastewater solids. The schematics of the bench scale

anaerobic digesters are shown in Figures 3.1 through 3.4.
                                                                 29




Note that “MWS” is an acronym for municipal wastewater solids.
                                                                                          30


3.2     BENCH-SCALE DIGESTER DESCRIPTION

Fourteen different digesters were constructed (2.5 L glass vessels) and seeded with 2 L of

digested sludge (from South Shore Wastewater Treatment Plant). Each digester was fitted

with a rubber stopper and a gas collection bag. Each had a magnetic stir bar inside and

was placed on a stirrer so that complete mixing was achieved (see Figures 3.1 through

3.4). The different combinations of high-strength waste and municipal wastewater solids

fed to each digester are shown in Table 3.1. Municipal wastewater solids were a mix of

30% thickened waste activated sludge (WAS) and 70% primary sludge (PS) by volume

from the SSWWTP.




Table 3.1: Combinations of Municipal Wastewater Solids and High-Strength Waste Fed
to Digesters
                            High Strength Waste             Municipal Wastewater Sludge
      Digester                            Volume Fed                        Volume Fed
                           %                                   %
                                            (ml/d)                             (ml/d)
         1                 0                   0             100                133
         2            20 MBWW                 27              80                106
         3            80 MBWW                106              20                 27
         4           100 MBWW                133              0                   0
         5            80 LYWW                106              20                 27
         6            60 LYWW                 80              40                 53
         7            20 LYWW                 27              80                106
         8          80 SEWYWW                106              20                 27
         9          60 SEWYWW                 80              40                 53
        10          20 SEWYWW                 27              80                106
        11                 0                   0             100                133
        12              11 FW                 15              89                118
        13               5 FW                  7              95                126
        14               3 FW                  4              97                129



All digesters were operated in a temperature-controlled room at 371oC. Each was a

batch fed, completely mixed stirred tank reactor (CMSTR) operated for at least 2.3

months . Every day, 133 mL of digester content was removed and immediately replaced
                                                                                         31

with an equivalent volume of digester feed. In addition, alkalinity in the form of sodium

bicarbonate (NaHCO3) was added to the feed at a concentration of 2.5 g/l. The solids

retention time (SRT) and the hydraulic retention time (HRT) for all the digesters were

maintained at 15 days. This SRT was employed because the full-scale digesters at the

SSWWTP operated at an HRT of approximately 15 days.



The sampling schedule of frequently measured parameters is shown in Table 3.2. In

addition, the concentrations of the following constituents were measured three times for

each waste: arsenic, cadmium, chromium, copper, lead, mercury, molybdenum, nickel,

selenium, zinc, waste COD, total Kjeldahl nitrogen (TKN), ammonia, total phosphorus

and potassium. Metals measurements were performed since land application of digested

biosolids is regulated in Wisconsin, in part, based upon the concentration of these

constituents.



Table 3.2: Sampling Schedule
                   Parameters                            Measurement Frequency
Temperature                                                        Daily
pH (effluent)                                                      Daily
Biogas production volume                                           Daily
% CH4 in headspace                                      Once every one to two weeks
Influent solid content (TS, VS)                             Three times a week
Effluent solid content (TS, VS)                             Three times a week
Alkalinity (PA, IA)                                         Three times a week
Effluent SCOD                                                  Once a week



Every seven to fifteen days, assays were performed to determine digester biogas

production rate. A 50-mL aliquot was removed from each digester before digester

feeding and placed in a serum bottle (160-ml total volume), sparged with gas (30/70

CO2/N2 volume per volume blend) to help establish anaerobic conditions, sealed, and
                                                                                            32

placed on a shaker table in a 35°C incubator. Biogas production from these bottles was

measured daily over approximately 20 days with a 50- or 100-ml glass syringe.



3.3     SAMPLING AND ANALYSES

Temperature was measured with a thermometer placed in the temperature-controlled

room. Sample pH was measured using a pH probe and meter (Orion Model 720A). The

percentage of methane present in the biogas was measured using a gas chromatograph.

Table 3.3 shows the gas chromatograph conditions. The total and volatile solids

concentration of the samples was determined by standard methods 2540 B and 2540 E

(APHA et. al, 1998).



Table 3.3: Gas Chromatographic Conditions for Methane Analysis
Chromatograph:         GowMac GC
Data Acquisition:      EZ Chrom with Pentium PC
Injector:              Packed column injector, Temperature=200oC
Column:                (Packed Column) Supelco, Carbopack 1-1825, 60/80 Carbopack C/0.3%
                       Carbowax 20M/0.1% H3PO4
Oven:                  150oC
Detector:              Flame ionization detector at 200 oC
Carrier Gas:           Ultra high purity Helium 50 ml/min.




Alkalinity in wastewater results from the presence of hydroxides [OH-], carbonates

[CO32-], and bicarbonates [HCO3-] and other salts of weak acids. Calcium and magnesium

bicarbonates are most common. Borates, silicates, and phosphates can also contribute to

the alkalinity. The alkalinity in wastewater helps to resist a decrease in pH caused by

addition of acids (Metcalf and Eddy, 2003). Titration and buffer intensity curves can

show the relative magnitudes of bicarbonate and volatile acids (VA), but the development

of such curves is tedious for routine operation. Therefore, titration to two endpoints is
                                                                                           33

more attractive. Titration from the original sample pH to pH 5.75, or partial alkalinity

(PA), results in an alkalinity that corresponds roughly to bicarbonate alkalinity. Titration

from pH 5.75 to 4.3, or intermediate alkalinity (IA), approximates the VA alkalinity.

Successful digester operation depends on maintenance of adequate bicarbonate buffering

and avoidance of excessive VA concentration; the VA-to-alkalinity ratio (VA: Alkalinity

or IA: PA) has been used to monitor anaerobic digestion of municipal sludge (Ripley et

al., 1986). The alkalinity titrations were conducted as per standard method 2320B (APHA

et. al., 1998).



Soluble chemical oxygen demand (SCOD) was measured by placing 20 ml of effluent in

a centrifuge tube, centrifuging for 30 minutes and then filtering the centrate through a

0.45-µm cellulose nitrate membrane filter. The filtrate was then used for the COD test as

per standard method 5220A (APHA et. al, 1998).



3.4 RESULTS AND DISCUSSION

3.4.1 AVERAGE SEED BIOMASS AND FEED CHARACTERISTICS

All Digesters were seeded with sludge from the anaerobic digesters at the SSWWTP.

Digesters 1 through 10 were started using sludge having TS and VS concentrations of

43.8 and 28.0 g/l, respectively. Digesters 11 through 14 were started later with sludge

having TS and VS concentrations of 41.2 and 25.8 g/l, respectively.

The characteristics of PS and WAS from SSWWTP and the individual high-strength

wastes used during bench-scale studies are presented in Tables 3.4 and 3.5, respectively.

Control digesters (Digester 1 and 11) were not fed industrial waste, but only fed a
                                                                                                    34

mixture of 70% PS and 30% WAS, which is referred to herein as municipal wastewater

solids.

Table 3.4: Average Characteristics of PS and WAS in Municipal Wastewater Solids
                      pH                      TS (g/l)            VS (g/l)                 %VS
                     (n= 3)                   (n=120)             (n=120)                (n= 120)
  1
PS                  5.8±0.2                    42±12                31±9                   75±5
PS2                 6.2±0.3                    35±12                23±7                  67±10
WAS1                6.2±0.1                     8±5                  5±4                   62±8
WAS2                6.0±0.2                     9±3                 5±27                   59±4
PS1 and WAS1 were used for digesters 1 to 10 and PS2 and WAS2 were used for digesters 11 to 14.
n= number of samples




Table 3.5: Average Characteristics of High-Strength Wastes
Characteristics             MBWW                   LYWW                 SEWYWW                       FW
Total Solids (g/l)    4±3 (n= 84)          61±2 (n=74)        16±2 (n=35)                248±38
Volatile Solids (g/l) 1±1 (n= 84)          36±2 (n=74)        14±2 (n=35)                217±37
% Volatile            48±28                59±3               88±3                       88±3
COD (mg/l)            4280±1780            45600±3980         85600±2360                 462800±13400
NH3-N (mg/l)          8.7±4.5              280±248            55±32                      5430±2890
Org N (mg/l)          85.5±35.3            2180±46.9          715±43                     49400±18300
TKN (mg/l)            94±38                2470±250           770 ±74                    54900±19900
TP (mg/l)             13 ±5.0              53±18              160±41                     6100±4186
Cd (µg/l)             4.00±6.93            30.7±12.7          <6                         <4.1>
Cr (µg/l)             <10                  93.7±121           <10                        <3.6
Cu (µg/l)             148±45.7             524±91.5           660±622                    <47>
Pb (µg/l)             53.3±92.4            290±253            <65                        <23>
Ni (µg/l)             <66                  676±275            <66                        <23>
Zn (µg/l)             372±535              3430±677           16±28                      76±63
K (µg/l)              22400±15900          30700±7740         296000±163000              11400±11700
Hg (µg/l)             0.53±0.92            <0.6               <0.6                       <0.03
As (µg/l)             2.47±2.45            2.47±2.45          <0.2                       <0.04
Se (µg/l)             <2                   <2                 0.67±1.15                  <0.06
Mo (µg/l)             9.67±8.74            56.67±73.71        <0.2                       0.67±1.15
Three samples were measured to determine COD, TKN, ammonia TP and the metals concentrations.




Regarding metal concentrations, none of the wastes tested contained metals at

concentrations greater than the Wisconsin Department of Natural Resources high quality

limits for biosolids to be land applied. Therefore, it is probable that land application of
                                                                                         35

residuals would not be problematic. However, it should be pointed out that the

concentration of metals in the residuals could theoretically increase due to sorption onto

the surface of sludge solids.



3.4.2 DIGESTER LOADINGS /HYDRAULIC RETENTION TIME

Digesters 1 and 11 (receiving only municipal wastewater solids) were maintained as

controls and were operated for 276 days (18.4 SRTs) and 104 days (6.9 SRTs),

respectively. Digesters 2 through 4 (receiving MBWW) and Digesters 5 through 7

(receiving LYWW) were operated for 206 days (13.7 SRTs). Digesters 8 through 10

(receiving SEWYWW) were operated for 71 days (4.7 SRTs). Digesters 12 through 14

(receiving FW) were operated for 104 days (6.9 SRTs). Loading rates and the blend of

municipal wastewater solids and different high strength wastes fed are presented in Table

3.6.




Table 3.6: Blend of MWS and High Strength Waste and VS Loading Rates
                                Waste/MWS         Days of             Loading Rate
Digester      Waste
                              %          ml      Operation       gVS/l-d        lbVS/ft3-d
   1          MWS           0/100       0/133        276        1.52±0.46       0.10±0.03
   2         MBWW           20/80      27/106                   1.28±0.41       0.08±0.03
   3         MBWW           80/20      106/27        206        0.37±0.10       0.02±0.01
   4         MBWW           100/0       133/0                   0.08±0.04      0.005±0.002
   5         LYWW           80/20      106/27                   2.23±0.14       0.14±0.01
   6         LYWW           60/40       80/53        206        2.07±0.21       0.13±0.01
   7         LYWW           20/80      27/106                   1.74±0.41       0.11±0.03
   8        SEWYWW          80/20      106/27                   1.03±0.11       0.06±0.01
   9        SEWYWW          60/40       80/53        70         1.12±0.12       0.07±0.01
   10       SEWYWW          20/80      27/106                   1.30±0.20       0.08±0.01
   11         MWS           0/100       0/133                   1.13±0.32       0.07±0.02
   12          FW           11/89      15/118                   1.12±0.29       0.07±0.02
                                                     104
   13          FW            5/95       7/126                   1.10±0.28       0.07±0.02
   14          FW            3/97       4/129                   1.09±0.29       0.07±0.02
                                                                                        36

The feeding of bench-scale digesters was not based on volatile solid loading rates per se,

but on hydraulic retention time (HRT). All the digesters employed an HRT of 15 days.



The results obtained from Digesters 1 and 11 are useful to make comparisons with the

results obtained from other digesters. The percentage of FW fed to Digesters 12, 13 and

14 are low compared to the percentage of high-strength waste fed to other reactors

because the COD and VS of the FW were relatively high (refer to Table 3.5).



3.4.3 pH AND ALKALINITY

Unacclimated methane-producing organisms require a neutral environment (pH 6.8 to

8.5) in order to produce methane (Speece, 1995). Acid-forming bacteria often grow

faster than methane forming organisms. Acid-producing bacteria may produce acid faster

than methane-producing microorganisms can consume it, and excess acid can build up in

the system, causing a drop in the pH which inhibits the activity of methane-forming

bacteria. In case of low pH, methane production may stop entirely.



To help ensure proper pH, alkalinity in the form of NaHCO3 was added to all the

digesters at a concentration of 2.5 g/l. Most digesters were stable as far as pH was

concerned, but Digesters 8 and 9 had average pH values less than 6.8 and high average

IA/PA ratios irrespective of addition of NaHCO3. The standard deviation of pH and

IA:PA values were also high. There were periods when the digesters pH values were

above 6.8 and methane production was not inhibited by low pH. It appears that these

digesters acclimated to the relatively low pH since their methane production rates were
                                                                                               37

relatively high. Tables 3.7 and 3.8 show the pH of the wastes as well as the temperature,

pH, and alkalinity (PA, IA and total alkalinity (TA)) of digester effluent, respectively.



Table 3.7: Average pH of High-Strength Wastes
                  Wastes                                            pH (n=3)
                  MBWW                                              5.00.20
                  LYWW                                              5.90.10
                 SEWYWW                                             6.10.20
                   FW                                               4.30.30




Table 3.8: Average pH, and Alkalinity of Effluent from Digesters
                                                PA          IA           TA
                       Days of
Digester    Waste                   pH        mg/l as     mg/l as      mg/l as      IA/PA
                      Operation
                                              CaCO3       CaCO3        CaCO3
   1         MWS         276      7.00.1    2508455    1821628     4329918     0.730.21
   2        MBWW                  7.00.1   25651136   16301244    41952294     0.620.21
   3        MBWW         206      7.00.1   21841130    1126653    33101545     0.530.17
   4        MBWW                  7.00.2   14751106    8621015    23321827     2.234.89
   5        LYWW                  7.20.2   56761647   57561508    114321802    1.150.58
   6        LYWW         206      7.20.2   48101349   50571400    98671299     1.250.85
   7        LYWW                  7.20.2    4058701    2586658     6647717     0.690.35
   8       SEWYWW                 6.31.0   10451384   24341100    34792391     5.837.40
   9       SEWYWW         70      6.00.9    8551453    2785496    36401898    8.8811.97
   10      SEWYWW                 7.00.1    2495792    1696521    41911289     0.680.09
   11        MWS                  7.40.2   59831324    2288432    82701646     0.400.12
   12        FW                   7.50.2   82851486   37331941    120182330    0.470.30
                         104
   13        FW                   7.60.2   76771527    3836886    115132222    0.510.10
   14        FW                   7.50.2   73571729    3148670    105041815    0.490.46




IA: PA values for the bench scale digesters are above 0.35. Notably, Digesters 8 and 9

that received SEWYWW had IA: PA ratios above 5.0. These digesters also had low

average pH values. The high IA:PA ratios and low pH values may be due to high organic

loading rate (OLR) resulting from the high COD of the SEWYWW and the relatively

high volume of waste in the feed. The average temperature of all digesters was 37 ± 1°C.
                                                                                             38


3.4.4 VOLATILE SOLIDS DESTRUCTION

In general, volatile solid destruction is used to measure the performance of municipal

anaerobic digesters. At mesophilic conditions in full-scale appplicaitons, 40% volatile

solid destruction is a reasonable value in the municipal sludge digestion process (De La

Rubia et al., 2002).



Tables 3.4 and 3.5 present the solid concentrations in PS, WAS and the different high

strength wastes used for co-digestion. Table 3.9 presents total solids and volatile solids

concentrations of digester effluents and volatile solid destruction achieved in each

digester during the steady-state period (i.e., after 45 days had passed).



Table 3.9: Total Solids, Volatile Solids of the Effluent and Volatile Solid Destruction
                          Waste/MWS              Effluent Solid           VS Destruction
Digester     Waste                                                        During Steady
                          %        ml     TS (%)     VS (%)       %VS       State (%)
    1        MWS        0/100     0/133   1.90.4    1.00.2      544        6613
    2       MBWW        20/80    27/106   1.70.4    0.90.2      526        567
    3       MBWW        80/20    106/27   1.2 0.4   0.60.2      457        519
    4       MBWW        100/0     133/0   0.80.4    0.20.2      3112      -5441
    5       LYWW        80/20    106/27   3.60.4    1.80.3      496        464
    6       LYWW        60/40     80/53   3.30.3    1.80.3      542        405
    7       LYWW        20/80    27/106   2.30.3    1.20.2      514        546
    8      SEWYWW       80/20    106/27   1.70.7    1.10.3      646        561
    9      SEWYWW       60/40     80/53   1.90.5    1.10.3      624        511
   10      SEWYWW       20/80    27/106   1.70.5    1.00.3      552        621
   11        MWS        0/100     0/133   2.20.6    0.70.2      3513       588
   12         FW        11/89    15/118   3.40.4    1.50.2      453        614
   13         FW         5/95     7/126   3.10.4    1.30.3      424        527
   14         FW         3/97     4/129   2.90.3    1.10.2      396        536



If 40% volatile solid reduction is considered to be an acceptable value in the performance

of municipal sludge digestion (De La Rubia et al., 2002) then all digesters except for

Digester 4 demonstrated good VS destruction. Digester 4 which received 100% Miller
                                                                                         39

Brewery wastewater demonstrated a negative VS destruction value, meaning that there

was an increase in VS, ostensibly due to growth of biomass. The digester also had a low

pH and produced very little methane. Therefore, methane production in the system was

inhibited.



Digestion of 100% Miller Brewery wastewater was not successful in the fill-and-draw

digester configuration employed. However, co-digestion of Miller Brewery wastewater

and 20% v/v or more of municipal wastewater solids lead to acceptable solids destruction

and biogas production. Therefore, Miller Brewery wastewater can be successfully treated

in a fill-and-draw digester if it is co-digested with approximately 20% v/v or more of

municipal wastewater solids.



It should be noted that 100% Miller Brewery wastewater is not intrinsically a poor

candidate for anaerobic treatment without co-digestion of municipal wastewater solids.

However, the fill-and-draw digester configuration employed is typically not appropriate

for the comparatively low, mostly soluble COD present in the Miller Brewery wastewater

since no form of biomass immobilization is utilized. As demonstrated by BMP results in

Chapter 2, Miller Brewery wastewater may be treated anaerobically without co-digestion,

but other reactor configurations, such as a fluidized bed or upflow anaerobic sludge

blanket would be more appropriate reactor configurations.
                                                                                        40


3.4.5 BIOGAS/METHANE

Table 3.10 presents biogas production, percentage methane, and rate of biogas production

results measured in serum bottle assays for biomass from each digester during the steady

state period. Steady state was assumed after 45 days (i.e., 3 SRTs) had passed.



Table 3.10: Biogas Production, Rate of Biogas Production and Percentage Methane in
Assays
                                                                Steady       Steady
                         Waste/                                  State        State
                                                    Steady
                        Municipal         Steady               Methane      Specific
                                                     State
                        Wastewater         State              Production    Methane
                                                    % CH4
Digester    Wastes        Solids          Biogas                 Rate      Production
                                        Produced                              Rate
                                         (ml/l-d)                          (ml /g VS-
                        %       ml                           (ml/l-d)      day)

    1        MWS       0/100   0/133    865367     662     571± 242      57
    2       MBWW       20/80   27/106   653229     613     398 ± 140     44
    3       MBWW       80/20   106/27   432202     583     251± 117      42
    4       MBWW       100/0   133/0    12887      0±0      0±0           0
    5       LYWW       80/20   106/27   928346     612     566 ± 211     31
    6       LYWW       60/40   80/53    863315     632     543± 198      30
    7       LYWW       20/80   27/106   1018424    682     692± 288      58
    8      SEWYWW      80/20   106/27   840430     642     538± 276      49
    9      SEWYWW      60/40   80/53    840396     622     521± 246      47
   10      SEWYWW      20/80   27/106   54077      591     319± 45       32
   11        MWS       0/100   0/133    429210     633     270± 132      39
   12        FW        11/89   15/118   1154572    655     750± 372      50
   13        FW         5/95   7/126    960387     663     634± 255      49
   14        FW         3/97   4/129    554173     612     338± 106      31



During the steady state period, most of the co-digestion reactors produced biogas at

rates that were not statistically different from those of the control digesters. The

exceptions were Digesters 3, 4 and 10, which had lower biogas production rates than the

control (Digester 1), and Digesters 12 and 13, which had higher biogas production rates

than the control (Digester 11). The lower rates from Digester 3 and 4 are probably

because the Miller Brewery waste had a relatively low COD. In addition, the COD was

mostly soluble. Again, the fill-and-draw digester configuration employed is typically not
                                                                                          41

appropriate for low COD, soluble wastes. The reason for the lower rate in Digester 10 is

unknown.



3.5 CONCLUSIONS

All high-strength wastes tested had metals concentrations lower than the Wisconsin

Department of Natural Resources high quality limits for biosolids to be land applied.

Therefore, most likely, none of the wastes will limit land application of resulting

biosolids based upon metal criteria. The Lasaffre Yeast, Southeastern Wisconsin

Products, and Pandl’s Restaurant wastes were successfully co-digested at all blend ratios

tested (from 20 to 80% by volume). The Southeastern Wisconsin Products waste did,

however, cause a decrease in digester pH (to below 6.8) and an increase in IA:PA ratio

(to above 5) at waste: municipal wastewater solids ratios greater than 20:80. However,

the systems acclimated to these conditions and produce methane at significant rates.



The Miller Brewery wastewater was difficult to co-digest in the fill-and-draw digesters

employed and at the ratios tested due to its relatively low and soluble COD. Therefore,

although the Miller Brewery waste is amenable to anaerobic digestion (as evidenced by

BMP results of Chapter 2), co-digestion at lower ratios of waste: municipal wastewater

solids, or in a reactor configuration other than a fill-and-draw digester would be more

appropriate.



Co-digestion of municipal sludge with Lasaffre Yeast, Southeastern Wisconsin Products,

and Pandl’s Restaurant wastes at waste: municipal wastewater solids ratios from 20 to
                                                                                               42

80% by volume is feasible. Based on the results of bench-scale digester tests as well as

BMP, ATA, and COD testing, Food waste from Pandl’s restaurant, Lesaffre Yeast

Corporation Wastewater, and Southeastern Wisconsin Products Wastewater are good

candidates for full-scale co-digestion. In addition, Miller Brewery Wastewater may also

be co-digestible at waste: municipal wastewater solids ratios lower than 20:80; however

more testing is required to verify this assertion. It should be noted that issues other than

waste characteristics and digestibility, most notably the distance from the waste

production source to the co-digestion facility, significantly affect the economics of co-

digestion and should be considered when investigating co-digestion plans.
                                                                                          43



CHAPTER 4: FULL-SCALE CO-DIGESTION TESTING AT SOUTH SHORE
WASTEWATER TREATMENT PLANT


4.1    INTRODUCTION

Southeastern Wisconsin Products Yeast Wastewater (SEWYWW) and Pandl’s Restaurant

food waste were selected and used in full-scale co-digestion testing at the South Shore

Wastewater Treatment Plant (SSWWTP), Oak Creek, Wisconsin. These wastes were

selected based upon their high COD and BMP, appropriate metals concentrations for

land applicaiton, successful bench-scale digester testing, and production within a 20-mile

radius from the SSWWTP. Each waste was fed to the existing digesters at the plant along

with primary sludge. Participants in the study included Wisconsin Focus on Energy,

Marquette University, Ecology, LLC, marketers of the wet waste recovery system used at

Pandl’s Restaurant to mechanically shred and store the waste, as well as the Milwaukee

Metropolitan Sewerage District (MMSD) and United Water Services, Inc. (UWS), the

owner and contract operator of the treatment plant, respectively. Results of full-scale co-

digestion testing and an economic analysis are presented in this chapter.



4.2    SOUTHSHORE WASTEWATER TREATMENT PLANT (SSWWTP)

SSWWTP is located south of Milwaukee along the Lake Michigan shoreline in Oak

Creek, Wisconsin, and was put into operation in 1968. The plant treats an average of 90

million gallons of wastewater each day, most of it from the southern and western portions

of the MMSD service area. The facility has a peak capacity to treat approximately 300

million gallons per day of municipal wastewater.
                                                                                            44

Raw wastewater flows through primary, secondary and disinfection treatment processes.

Biosolids are conveyed to anaerobic digesters where microorganisms stabilize the solids

and create biogas containing methane. This biogas is collected, and is typically used to

continuously run blowers for the activated sludge process as well as produce electricity

using an engine generator set for approximately eight hours per day. If more biogas was

produced, then the engine generator set could be operated for more than eight hours per

day. This may help reduce energy costs at the treatment plant. Stabilized biosolids are

applied to farmland as a fertilizer and soil conditioner known as Agri-Life or dried to

produce a commercial soil amendment called Milorganite.



4.3    ANAEROBIC DIGESTERS AT SSWWTP

SSWWTP has 12 single-stage, high-rate, anaerobic digesters. At the time of this study,

Digesters 1 through 5 and 7 were being used to store digested biosolids, Digesters 6 and 8

were out of service, and the remaining four digesters (9 through 12) were active.

Digesters 9 through 12 are 125 feet in diameter and have a side water depth of 38 feet.

Recirculation pumps direct sludge through spiral heat exchangers at each digester to

maintain sludge temperatures in the range of 90 to 95 oF (32 to 35 oC) for mesophilic

digestion. Typically, waste heat from the blowers and engine generator set is used to heat

the digesters. When the ambient temperature is very low, natural gas is also used to fire

boilers providing additional heat for the digesters.



The digesters have fixed concrete covers with a gas dome, access manholes and sample

ports. Each of the gas domes has a pressure relief valve and a flame trap. The gas domes
                                                                                           45

collect the biogas produced in the anaerobic digestion process. Digester biogas is

recirculated through compressors and forced back into draft tube mixers to mix digester

contents. Excess gas is withdrawn from the digester cover through a gas header. In

addition, some biogas can be stored in pressurized storage vessels for later use.



Historically, primary sludge (PS) and thickened waste activated sludge (WAS) has been

fed to the digesters. However, at the time of this study, PS from both SSWWTP and

another treatment plant (Jones Island Wastewater Treatment Plant, Milwaukee,

Wisconsin) was fed, whereas no WAS was fed. PS from primary clarifiers was pumped

and fed, alternately, to each of the four operating digesters by automatic opening and

closing of appropriate valves. During the study, the PS total and volatile solids

concentrations were 42±12 and 31±9 g/L, respectively. The PS pH value was 5.8±0.2.



4.4 SOUTHEASTERN WISCONSIN YEAST WASTEWATER (SEWYWW)

The first addition of SEWYWW to the anaerobic digesters commenced on June 7, 2004.

The SEWYWW was stored in an unmixed tank at the plant and added into the PS feed

line using a metering pump. The tank and pump are employed in cold months to handle

waste aircraft deicing fluid from General Mitchell International Airport (Milwaukee,

Wisconsin) which is seasonally co-digested (Zitomer et al., 2001). The used deicer is

trucked to the treatment plant and stored in the unmixed tank. The waste aircraft deicing

fluid solids content is low. Therefore, most of the deicer constituents are soluble and,

therefore, mixers are not present in the storage tank since there are very few solid
                                                                                         46

particles to keep in suspension. Table 4.1 presents the date and the average amount of

SEWYWW added to the digesters.

The average characteristics of SEWYWW added to the digesters are presented in Table

4.2.

Table 4.1: Average SEWYWW Addition: Date and Amount
                           Average SEWYWW Addition
              Date
                                      (gal/min)
           7-June-04                     2.4
           9-June-04                     4.1
          10-June-04                     3.4
          11-June-04                     2.5
          16-June-04                     4.1
          17-June-04                     4.0
          18-June-04                     2.2
          23-June-04                     3.2
          24-June-04                     5.0
          25-June-04                     2.1
           9-July-04                     6.0
          10-July-04                     2.2


                  Table 4.2: Average Characteristics of SEWYWW
               Characteristics     Frequency of
                                         measurement       SEWYWW

                  Total Solids (g/l)         35                16±2
                 Volatile Solids (g/l)       35                14±2
                     % Volatile              35                88±3
                    COD (mg/l)               3             85619±2357
                   NH3-N (mg/l)              3               55±31.94
                   Org N (mg/l)              3             715.33±42.78
                    TKN (mg/l)               3             770.33±74.39
                     TP (mg/l)               3             160.00±41.76
                     Cd (µg/l)               3                  <6
                      Cr (µg/l)              3                 <10
                     Cu (µg/l)               3            660.00±622.25
                      Pb (µg/l)              3                 <65
                      Ni (µg/l)              3                 <66
                      Zn (µg/l)              3             16.00±27.71
                      K (µg/l)               3         295500.00±163341.67
                     Hg (µg/l)               3                 <0.6
                      As (µg/l)              3                 <0.2
                      Se (µg/l)              3              0.67±1.15
                     Mo (µg/l)               3                 <0.2
                                                                                           47



The SEWYWW contributed less than 1% of the flow and 1% of the total COD loading to

the digesters. Biogas production is often proportional to COD loading, assuming COD

removal efficiency does not decline. Due to the relatively low COD contribution of the

SEWYWW, it was anticipated that the additional biogas would not be measurable using

the treatment plant biogas flow meters which are accurate to ±5%.



However, a significant increase in biogas production of 70% was observed when

SEWYWW was co-digested. Figure 4.1 presents the biogas production during and after

addition of SEWYWW to the digesters. Table 4.3 presents the biogas and methane

production at periods during and after addition of SEWYWW. The average biogas

methane content during all periods was 59±1.3%. The average biogas production for 32

days (Period 1: 6/4/04 to 7/9/04) during the addition of SEWYWW to the digester was

approximately1200 standard cubic feet per minute (SCFM), whereas the biogas

production for 45 days (Period 3: 7/5/4 to 8/19/04) when SEWYWW was not added to

the system was only approximately 700 SCFM (see Figure 4.1). The extremely large

increase in biogas production was not expected. It was considered that the increase in

biogas production could have been due to an increase in the mass loading rate of sludge

solids. However, the total solids loading to the digesters was approximately 80 tons per

day during both Periods 1 and 3 (see Figure 4.1). Therefore, the increase in biogas

production was not a result of a significant increase in solids loading to the digesters. In

addition, the increase in biogas production could not have been a result of the additional

COD provided by the SEWYWW since it was negligible in comparison to the primary

sludge COD loading.
                                                                                                     48




The unexpected increase in biogas production may have been due to the presence of trace

nutrients and/or complexing agents in the SEWYWW that increased the activity of the

anaerobic microbes. Others have reported that addition of trace nutrients, such as nickel,

cobalt, and iron, can dramatically increase the rate of biogas production in some

anaerobic digesters that are nutrient limited (Speece, 1995). In addition, it is possible that

complexing agents (i.e., ligands) can form soluble complexes with metals and render the

metals more bioavailable. The biogas production rate of biomass from many municipal

anaerobic digester has been shown to increase upon addition of bioavailable iron and

other nutrients (Speece, 1988). The microorganisms responsible for anaerobic digestion

require these and other nutrients for optimal growth. However, trace nutrients are

sometimes not present in optimal concentrations or are not present in bioavailable forms

that microbes can utilize, even in municipal digesters (Speece, 1995). In this regard, yeast

extract, which is similar to SEWYWW, is often used in microbiology studies to provide

bioavailable nutrients.

Table 4.3: Biogas and Methane Production During and After SEWYWW Addition
                            Biogas              Biogas               Methane                Methane
            No. of                            Production                                   Production
Period*                   production                               Production
            days
                       (ft3CH4/tVS-d)      (ft3CH4/lb VS-d)      (ft3CH4/tVS-d)        (ft3CH4/lb VS-d)
  1           32      26316.0±6664.0           13.2±3.3         15802.7±4066.7              7.9±2.0
  2           45      17853.9±4033.4            8.9±2.0         10481.8±2471.0              5.2±1.2
  3           31      17187.7±3373.4            8.6±1.7         10312.6±2024.0              5.2±1.0
      * Period 1: 32 days during which SEWYWW was added to the digester (6/4/04 to 7/9/04).
          Period 2: The 45 days after addition of SEWYWW (i.e., 3 SRTs) (7/9/4 to 8/19/04).
          Period 3: The 31 days after Period 2 (8/19/04 to 9/20/04).
                                                                                         49




Figure 4.1: Biogas Production from Full-Scale Co-Digestion of SEWYWW
               TPD = tons per day
               SCFM = standard cubic feet per minute




When SEWYWW was added to the anaerobic digesters at the treatment plant, no

adverse affects were observed with regards to the operation of the storage tank, metering

pump, or anaerobic digesters.



4.5 PANDL’S RESTAURANT FOOD WASTE


Regarding Pandl’s food waste, treatment plant operators expressed initial concern that

large solid particles in the waste could potentially damage pumps and other equipment as

well as settle in the unmixed waste storage tank and/or the digesters at the treatment

plant. In comparison, the SEWYWW did not contain significant settleable, suspended
                                                                                              50

solids and these problems were not anticipated nor observed when it was co-digested. To

preclude potential equipment damage, the food waste was added to the primary clarifiers

at the treatment plant, and not directly to the digesters. It was likely that settleable solids

in the food waste would be removed from the bottom of the clarifier as primary sludge.

The sludge would be pumped with other primary solids through an existing sludge screen

to remove particles greater than 5 mm and then safely conveyed to the anaerobic

digesters. To explore this concept, testing including settleability and sieve analyses were

performed on the food waste.



The general data presented in Tables 4.4 and 4.5 were measured for Pandl’s food waste

samples collected on April 16, 2004 and March 22, 2004, respectively. The samples were

collected from the Ecology LLC wet waste recovery system (WWRS), a vacuum system

with grinding that collects and prepares food waste for disposal or recycling. This unit

was installed at Pandl’s restaurant in Bayside, WI.



Table 4.4: Pandl’s Restaurant Food Waste Characteristics
Parameter                                            Value
Density (Kg/l)                                       1.028
COD (mg/l)                                          462,800
TS (%)                                                26
VS (% of TS)                                          90
Solids retained on 4.76-mm screen (%)                 20
                                                                                          51

Table 4.5: Pandl’s Food Waste and Wisconsin Land Application Limit Metals
Concentrations –(mg/kg dry mass) unless otherwise stated
                                           Wisconsin Biosolids Land Application High
    Metal          Food Waste Value
                                                        Quality Limits
   TS (%)                35.3                                   -*
  TKN (%)                 7.5                                   -*
 Total P (%)              1.1                                   -*
     Cd                  <4.1                                  39
     Cr                  <3.6                                   -*
     Cu                    24                                 1500
     Pb                   <48                                  300
     Ni                    21                                  420
     Zn                    31                                 2800
     Hg                 <0.03                                  17
     As                 <0.07                                  41
     Se                 <0.13                                  100
     Mo                    2                                  75**
* There is presently no limit.
** Mo has no “high quality” limit. The normal limit is given.




4.5.1 SETTLEABILITY TESTING

A 100-gram wet sample of the food waste described in Table 4.5 was mixed with tap

water to bring the total volume to 1 liter. The suspension was thoroughly mixed and

allowed to settle for 30 minutes in a 1-liter graduated cylinder. A sample of the

supernatant was then removed with pipette and analyzed for COD. The result was that the

settled solids (i.e., sludge) volume was 600 ml, and the supernatant COD was 18,400

mg/l. Approximately 16% of the waste COD was in the supernatant. Therefore, most of

the COD was in the sludge blanket that would presumably end up at the bottom of the

primary clarifier. There was some floatable fat, oil, and grease observed (about a 1-cm

layer in the graduated cylinder).
                                                                                            52


4.5.2 SIEVE ANALYSIS

A 1-liter aliquot (total dry solids mass = 262 grams) of the food waste described in Table

4.5 was passed through a series of standard sieves. The mass and percent of solids

retained on each sieve are reported in Table 4.6. The percent of food solids retained on a

4.76-mm screen is similar to that which would be retained on the primary sludge screens

at SSWWTP, which have a 5-mm opening. A 5-mm sieve is not a standard size and,

therefore, was not available. Sludge from the primary clarifier is pumped through the

primary sludge screen at the treatment plant before entering the digesters to remove large

particles that may damage pumps or collect at the bottom of the digesters. Approximately

20% of the food particles were retained on the 4.76-mm sieve and would be retained on

the sludge screens. Therefore, most of the solids would be conveyed to the digester at the

treatment plant.


Table 4.6: Sieve Analysis Results for Food Waste Solids
Sieve opening size (mm)   % Recovered on Sieve   % Retained    % Passing
         25.0                     1.0               1.0          99.0
         19.1                     1.9               2.9          97.1
         9.50                     7.4               10.3         89.7
         4.76                     9.5               19.8         80.2
         2.38                     6.6               26.4         73.6
         2.00                     1.4               27.8         72.2
         1.68                     1.1               28.9         71.1
         <1.68                   71.1               100           -



The Pandl’s Restaurant food waste fed to the digesters represented less than 3% of the

total COD load fed to the digesters. Since biogas production is typically proportional to

COD load and the biogas flow meters are accurate to approximately ± 5%, the extra

biogas produced from food waste was below detection using existing plant gas flow

meters. However, the value of biogas that was generated from the waste can be estimated

as follows. Pandl’s restaurant produced approximately 260 liters of food waste per day
                                                                                           53

having an average COD concentration of 233.8 g/L. The food waste biochemical methane

potential was 540 mL of methane (35°C, 1 atmosphere) per gram of COD as reported in

Chapter 2. Therefore, the restaurant produced 60 Kg of COD per day. It is estimated from

settleability testing that 84% of the food COD can settle as primary sludge. It is

estimated from sieve analysis that 80% of the food waste solids in the primary sludge

pass through the sludge screen. Therefore, approximately 67% of the food waste COD

may be conveyed to the digesters, assuming that 1 g VS is equivalent to 1 g COD and the

soluble COD in the food waste is negligible in comparison to the particulate COD.

Therefore, approximately 40 Kg of food waste COD per day may be conveyed to the

anaerobic digesters and can be theoretically converted to 680 standard cubic feet of

methane per day. This has an energy value of 680,000 Btu per day.



When food waste was added to the primary clarifiers at the treatment plant, no adverse

affects were observed with regards to the operation of primary clarifiers, sludge screens,

or anaerobic digesters.



4.6 ECONOMIC ANALYSIS

When high-strength wastes are not co-digested at the SSWWTP, it is typical for digester

biogas to be utilized to continuously run blowers for the activated sludge process and run

an existing engine generator set for approximately 8 hours per day. The typical rate of

biogas production is not sufficient to run the engine generator set continuously. Excess

heat from the blower engines and generator set is used to heat the digesters. Under this

typical scenario, the blowers consume 475 SCFM of biogas continuously and the

generator set consumes 390 SCFM of biogas for 8 hours a day. Therefore, typical biogas
                                                                                              54

utilization is 871200 standard cubic feet per day. It should be noted that this is simply a

typical scenario, and biogas utilization scenarios can vary depending on how much

biogas is produced and what equipment is shut down for maintenance. For example,

natural gas is purchased to run blowers if biogas production falls short of requirements.

In addition, if the generator set is not operating or the ambient temperature is extremely

low, then biogas or natural gas is used to fuel boilers that heat the digesters. A typical

maximum biogas utilization rate is estimated assuming both the blowers and the engine

generator set are operated 24 hours per day, and this typical maximum biogas utilization

rate is 1245600 standard cubic feet per day. When co-digestion is not practiced, the

digesters produce approximately 871200 standard cubic feet per day of biogas. Therefore,

existing equipment can typically utilize an additional 374400 standard cubic feet per day

of biogas.



It should be noted that SSWWTP operators paid $ 0.03 per kw-hr of electricity during

peak hours (10:00 am to 10:00 pm) and $ 0.02 per kw-hr of electricity during off-peak

hours (10:00 pm to 10.00 am) during the study. Peak and off peak demand charges are                Comment [A5]: I think it's likely that they also
                                                                                                   pay a demand change, which could be substantial,
                                                                                                   especially if the biogas generation can be operated
also paid. The cost scenarios presented below assume electricity generated from biogas is          fairly constantly.


worth an average of $0.04 per kw-hr considering peak and off-peak demand charges as

well as the cost per kw-hr. In addition, a natural gas cost of $6.50 per decatherm (where

a decatherm is equivalent to one million British thermal units) was assumed based upon

New York Mercantile Exchange futures prices for natural gas in June 2004. A trucking

cost of $300 per 5000-gallon truckload was paid during the full-scale testing.
                                                                                             55

The following simple economic analysis considers waste trucking costs and the value of

methane generated form the high-strength wastes. Landfill tipping fees and wastewater

treatment plant user fees can be significant and vary from facility to facility. The tipping

fees and user fees have not been considered herein.



4.6.1 SOUTHEASTERN WISCONSIN YEAST WASTEWATER (SEWYWW)

The energy value of the SEWYWW co-digested can initially be estimated from

biochemical methane potential results of Chapter 2. The waste can be added to the

digesters at an average rate of 1.0 gallon per minute (2 truckloads per week) and had an

average COD concentration of 85.6 g/L. The SEWYWW biochemical methane potential

was 943 mL of methane (35°C, 1 atmosphere) per gram of COD as reported in Chapter 2.

Therefore, the SEWYWW COD could be fed at an average rate of 468 Kg per day that

will theoretically be converted to 13,800 standard cubic feet of methane per day. This has

an energy value of 1.38 * 107 Btu per day. Assuming this is utilized to generate

electricity, the biogas is worth $20,200/year. If the biogas is used in place of natural gas,

then the energy is estimated to be worth $ 32,800 per year. The yearly transportation cost

to transport two truckloads per week would be approximately $31,200. Based upon the

BMP results of Chapter 2, the trucking cost is more than the worth of electricity

generated from the extra biogas as well as the worth of the biogas if it is used to reduce

natural gas purchase.



However, when the SEWYWW was actually added to the digesters at the treatment plant,

the average methane production increase was nearly 10 times greater than that predicted
                                                                                          56

by BMP results. When the SEWYWW was added to the digesters, the biogas production

increased by 400,000 standard cubic feet per day (see Figure 4.1). Table 4.7 presents the

digester biogas production, treatment plant biogas utilization, excess biogas available for

energy generation, and worth of energy generated from excess biogas from the anaerobic

digesters when SEWYWW was co-digested.


Table 4.7: Synopsis of Biogas Production and Energy Savings During SEWYWW Co-
Digestion
                                     Maximum                  Potential
              Digester     Digester               Excess                    Worth of
                                     Treatment                electricity
               biogas      methane                Usable                   electricity
                                    plant biogas             generation
    Stage   production   production                biogas                 from excess
                                       usage                from excess
             (standard    (standard              (standard                   biogas2
                                     (standard             biogas 1 (kw-
              ft3/day)       3
                           ft /day)     3
                                                    3
                                                  ft /day)                    ($/yr)
                                      ft /day)                 hr/day)

     1      1640000       985000      1245600     272600       16300         237800
     3       973000       585000      1245600        0            0             0
1
  Assuming 1 kw-hr generated per 10,000 Btu and a maximum possible biogas                      Comment [A6]: This figure appears way too
                                                                                               efficient for typical IC engines. I suggest a heat rate
utilization of 1245600 standard cubic feet per day                                             of 15,000 Btu.kWh
2
  Assuming $0.04 per kw-hr
3
  Assuming $6.50 for 106 Btu.                                                                  Comment [A7]: I don't see a column for the gas
                                                                                               economics



During the period when SEWYWW waste was added to the digester, biogas production

increased; electricity worth in excess of $200,000 per year could be generated from the

usable additional biogas. If the extra biogas was used to off-set natural gas purchase, then

the plant operators could save $616,900 on natural gas purchases per year. The cost to

transport 2 truckloads per week of SEWYWW to the treatment plant would be $31,200.

Therefore, the worth of the electricity generated or natural gas saved as estimated by the

full-scale testing data, is significantly greater than the trucking cost.
                                                                                            57


4.6.2 PANDL’S RESTAURANT FOOD WASTE

The restaurant produced 60 Kg of COD per day, of which it is estimated that 40 Kg settle

in the primary clarifier, pass the sludge screen, and proceed to the anaerobic digesters.

The 40 Kg of COD is theoretically converted to 780 standard cubic feet of methane per

day. This has an energy value of 680,000 Btu per day.



The methane can be used to generate $992/year of electricity. If the biogas is used to off-

set the purchase of natural gas, then the energy is worth $1620 per year. The yearly

transportation cost would be approximately $1500 per year. Therefore, the trucking cost

is more than the worth of the electricity generated, whereas the trucking cost is slightly

less than the worth of the biogas if it is used to reduce natural gas purchase.



It should be noted that economic benefits not considered herein may be accrued if food

waste is anaerobically digested. For example, Pandl’s Restaurant food waste is presently

disposed of in a sanitary landfill. The waste occupies landfill volume and remains as a          Comment [A8]: Wouldn't there be an avoided tip
                                                                                                 fee? For SEWYWW too?

potential source of groundwater pollution. Anaerobic digestion with biogas utilization

and safe land application of biosolids may be a more economical solution based upon a

detailed life cycle cost comparison. However, a more detailed cost comparison is not

within the scope of this report.



4.7    CONCLUSIONS

Based on the results of BMP, ATA, COD and bench-scale testing as well as proximity to

the treatment plant, Pandl’s food waste and SEWYWW were chosen and used in full-
                                                                                            58

scale pilot tests of anaerobic co-digestion at the SSWWTP in Oak Creek, Wisconsin.

During the full-scale testing, no adverse impacts were observed regarding operation of

digesters, pumps, heat exchangers or other digestion appurtenances.



SEWYWW was trucked to the treatment plant and stored in an existing unmixed tank.

When SEWYWW was added to the digesters along with primary sludge, there was a 70%

increase in biogas production. The extra biogas could be used to generate electricity

worth in excess of $200,000 per year or off-set natural gas purchase worth $616,900 per

year. The yearly cost to transport 2 truckloads per week of the waste to the wastewater

treatment plant would be $31,200. Therefore, the worth of the electricity generated or

natural gas saved is significantly greater than the trucking cost.



The extremely large increase in biogas production during SEWYWW co-digestion was

not anticipated based on the increased COD loading from the waste alone. It is possible

that trace nutrients in the SEWYWW stimulated microbes in the digesters to produce

more biogas from COD in the primary sludge. Others have reported that biogas

production can significantly increase when trace nutrients are added to anaerobic

biological systems. It is possible that SEWYWW could be used as a trace nutrient

supplement to significantly increase biogas production at anaerobic digestion facilities.

However, additional research is required to verify the trace nutrient hypothesis.



Food waste from Pandl’s Restaurant was added to the treatment plant primary clarifiers

and not directly to the anaerobic digesters. This was done to prevent potential damage to
                                                                                             59

the existing metering pump due to particles in the food waste. In addition, the larger

particles could adversely affect existing plant operations by settling in the unmixed

storage tank as well as the digesters themselves. For these reasons, the food waste was

added to the primary clarifiers where it was ostensibly incorporated into primary sludge.

The primary sludge was passed through a sludge screen with a 5-mm opening, and then

conveyed to the anaerobic digesters. The increase in biogas production due to the

addition of the food waste was estimated from BMP testing, settleability tests, and sieve

analysis to be relatively low as compared to the total treatment plant biogas production,

and could not be observed using existing gas flow meters at the treatment plant which

have an accuracy of ±5%. Based upon the amount of food waste produced at Pandl’s

restaurant and results of BMP, settleability, and sieve analysis it is estimated that 680

standard cubic feet per day of methane can be produced from the restaurant waste. This

could be used to generate approximately $992 per year of electricity or off-set the

purchase of $1620 per year of natural gas. The estimated cost to truck the restaurant

waste to the treatment plant is $1500 per year. Therefore, the worth of the electricity

generated is less than the trucking cost, whereas the worth of the natural gas saved is

greater than the trucking cost. It should be noted that Pandl’s Restaurant food waste is

currently disposed of in a sanitary landfill. It is possible that anaerobic digestion with

biogas utilization and safe application of the stabilized biosolids would prove to be a

more economical approach than landfilling if detailed lifecycle cost comparison of the

options was performed.
                                                                                          60




CHAPTER 5: OVERALL CONCLUSIONS AND RECOMMENDATIONS

The research reported herein pertains to co-digestion of three high-strength wastewaters

(i.e., Miller Brewing Company, Lasaffre Yeast Corporation, and Southeastern Wisconsin

Products wastewaters) as well as restaurant food waste with municipal wastewater solids.

First, biochemical methane potential (BMP) tests and anaerobic toxicity assays (ATA) of

the wastes were performed. Second, bench-scale testing of anaerobic co-digestion was

performed for each waste. Finally, full-scale anaerobic co-digestion pilot testing of

Southeastern Wisconsin Products wastewater and food waste was accomplished using

existing digesters at the South Shore Wastewater Treatment Plant, Oak Creek, Wisconsin.

Conclusions and recommendations based on results of these tests follows.



5.1 BMP AND ATA TESTING

Results of BMP and ATA testing indicate that all four wastes are amenable to anaerobic

digestion and, at the concentrations studied, exhibit no significant toxicity to the

aceticlastic methanogenic organisms that convert acetate to methane. An unanticipated

outcome was that doses of Lasaffre, Southeastern Wisconsin Products, and Miller

Brewery wastewaters cause methane production rates to increase by as much as 20 to

80% in ATA tests. In addition, Lasaffre and Southeastern Wisconsin Products

wastewaters yielded abnormally high BMP values (i.e., greater than 900 mL methane per

gram COD). Therefore, each of the two wastes had a synergistic effect when digested

with municipal sludge biomass, increasing methane production from background COD

present in the sludge biomass use in the test. The unanticipated synergistic effect of these
                                                                                              61

wastes may be due to the presence and bioavailability of trace nutrients, such as iron. In

addition, the wastes may contain ligands that form complexes with trace metals and

render them more bioavailable, thus stimulating methanogenic organisms and increasing

the rate of methane production from all substrates present.



5.2 BENCH-SCALE CO-DIGESTION TESTING

Regarding bench-scale co-digestion testing, the Lasaffre Yeast and Southeastern

Wisconsin Products wastewaters can be successfully co-digested with municipal

wastewater solids at all blend ratios tested (from 20 to 80% v/v wastewater in municipal

wastewater sludge). Similarly, the food waste can be successfully co-digested at all blend

ratios tested (from 3 to 11% v/v food waste in municipal wastewater sludge).



The Miller brewery wastewater was not successfully digested by itself in the fill-and-

draw digester configuration utilized; however, it was successfully digested when blended

with municipal wastewater solids. Although the Miller Brewery wastewater was not

successfully digested alone, it is amenable to anaerobic digestion, as indicated by BMP

test results. If it is treated alone, then it is recommended that a reactor configuration other

than a fill-and-draw digester should be considered.



It is notable that all the wastes utilized in bench-scale testing had metals concentrations

below the Wisconsin Department of Natural Resources high quality limits for biosolids to

be land applied. Therefore, it is likely that none of the wastes will limit the land

application of digested biosolids.
                                                                                            62


5.3 FULL-SCALE CO-DIGESTION TESTING

Wisconsin Products wastewater and restaurant food waste were selected for full-scale co-

digestion testing at the South Shore Wastewater Treatment Plant. During the full-scale

co-digestion testing, no adverse impacts were observed regarding operation of digesters,

pumps, heat exchangers or other digester appurtenances. When Southeastern Wisconsin

Products wastewater was added to the digesters in addition to primary sludge, there was a

70% increase in biogas production. Again, the extremely large increase in biogas

production during Southeastern Wisconsin Products wastewater co-digestion was not

anticipated based on the increased COD loading from the waste alone. As mentioned

above, it is possible that trace nutrients, including iron, or ligands that render trace metals

more bioavailable in the Southeastern Wisconsin Products wastewater stimulated

microbes in the digesters to produce more biogas from COD in the primary sludge.

Speece (1995, 1988) has reported that biogas production can significantly increase when

bioavailable trace nutrients are added to anaerobic biological systems, including

municipal digesters.



The extra biogas can be used to generate electricity worth in excess of $200,000 per year

or off-set natural gas purchase worth $616,900 per year. The yearly cost to transport two

truckloads per week of the waste to the wastewater treatment plant would be $31,200.

Therefore, the worth of the electricity generated or natural gas saved is significantly

greater than the trucking cost. It is recommended that treatment plant personnel consider

repeating the full-scale co-digestion investigation of Southeastern Wisconsin Products

wastewater. Continuous co-digestion of Southeastern Wisconsin Products wastewater and
                                                                                              63

municipal wastewater solids may lead to a sustained increase in biogas production. In

addition, full-scale investigations regarding the use of Southeastern Wisconsin Products

and other similar yeast production/fermentation wastes as supplements to increase biogas

production at other anaerobic digestion facilities is recommended.



Food waste from Pandl’s Restaurant was added to the treatment plant primary clarifiers

and not directly to the anaerobic digesters. This was done to prevent potential damage to

the existing equipment and appurtenances due to large particles in the food waste. The

increase in biogas production due to the addition of the food waste was estimated from

BMP testing, settleability tests, and sieve analysis. It is estimated that 680 standard cubic

feet per day of methane can be produced from the restaurant waste. This could be used to

generate approximately $992 per year of electricity or off-set the purchase of $1620 per

year of natural gas. The estimated cost to truck the restaurant waste to the treatment plant

is $1500 per year. Therefore, the worth of the electricity generated is less than the

trucking cost, whereas the worth of the natural gas saved is greater than the trucking cost.



It should be noted that Pandl’s Restaurant food waste is currently disposed of in a

sanitary landfill. It is possible that anaerobic digestion with biogas utilization and safe

application of the stabilized biosolids would prove to be a more economical approach

than landfilling if a detailed lifecycle cost comparison of the two options was performed.

In addition, if more restaurants, markets, cafeterias, and similar facilities began to

practice waste shredding and storage, then it is probable that economy-of-scale savings
                                                                                     64

could be accrued, and that anaerobic digestion of food residuals would become more

cost-effective.
                                                                                         65



REFERENCES


Ahring, B. K., Angelidaki, I., and Johansen, K. (1992). Anaerobic treatment of manure
together with industial waste. Wat. Sci. Tech., vol. 25, no. 7, pp. 311-318.

Angelidaki, I., Ellegaard, L., and Ahiring, B.K. (1997). Modelling anaerobic co-digestion
of manure with olive oil mill effluent. Wat. Sci. Tech., vol. 36, no. 6-7, pp. 263-270.

APHA (American Public Health Association), AWWA (American Waterworks
Association), and WEF (Water Environment federation) (1998). Standard Methods for
the Examination of Water and Wastewater, 20th Edition.

Carrieri, C., Di Pinto, A., Rozzi, A., and Santori, M. (1993). Anaerobic co-digestion of
sewage sludge and concentrated soluble wastewaters. Wat. Sci. Tech., vol. 28, no. 2, pp.
187-189.

Cecchi, F., Pavan, P., and Mata-Alvarez, J. (1996). Anaerobic co-digestion of sewage
sludge: application to the macroalgae from the Venice lagoon. Resources, Conservation
and Recycling, vol. 17, no.1, pp. 57-66.

De La Rubia, M.A., Perez, M., Romero, L.I., Sales, D. (2002). Anaerobic mesophilic and
thermophilic municipal sludge digestion. Chem. Biochem. Eng., vol. 16, no. 3, pp. 119-
124.

Di Palma, L., Medici, F., Merli, C., and Petrucci, E. (1999). Anaerobic co-digestion of
sewage sludge and municipal solid waste from markets: experimental results. Journal of
Solid Waste Technology and Management, vol.26, no. 1, pp. 10-13.

Gavala, H., Skiadas, I., and Lyberatos, G. (1996). Anaerobic co-digestion of agricultural
industires’ wastewater. Wat. Sci. Tech., vol.34, no. 11, pp. 67-75.

Gavala, H., Skiadas, I., and Lyberatos, G. (1999). On the performance of a centralised
digestion facility receiving seasonal agroindustrial wastewaters. Wat. Sci. Tech., vol.40,
no. 1, pp. 339-346.

Hamzawi, N., Kennedy, K., and McLean, D.D. (1998). Anaerobic digestion of co-
mingled municipal solid waste and sewage sludge. Wat. Sci. Tech., vol. 38, no. 2, pp.
127-132.

Lusk, P. and Moser, M. (1996). Anaerobic Digestion- Yesterday, Today and Tomorrow.
Ninth European Bioenergy Conference; June 24-27, 1996, Copenhagen, Denmark. UK:
Pergamon Press; pp. 284-289.
                                                                                         66

Mavinic, D. S., Koch, F. A., Hall, E. R., Abraham, K., and Niedbala, D. (1998).
Anaerobic co-digestion of combined sludges from a BNR wastewater treatment plant.
Environmental Technology., vol.19, no.1, pp. 35-44.

Metcalf and Eddy (2003). Wastewater Engineering: Treatment and Reuse, McGraw Hill,
Boston, MA.

Owen, W. F., Stuckey, D. C., Healy Jr, J. B., Young, L. Y., and McCarty, P. L. (1979).
Bioassay for monitoring biochemical methane potential and anaerobic toxicity. Water
Research, vol. 13, pp. 485-492.

Rintala, J. A., and Jaervinen, K. T. (1996). Full-scale mesophilic anaerobic co-digestion
of municipal solid waste and sewage sludge: methane production characteristics. Waste
Management & Research, vol. 14, no. 2, pp. 163-170.

Ripley, L. E., Boyle, W. C., and Converse, J. C. (1986). Improved alkalimetric
monitoring for anaerobic digestion of high-strength wastes. Journal WPCF, vol. 58, no.
5, pp. 406-411.

Smil, V. (2003). Energy at the Crossroads: Global Perspectives and Uncertainties. The
Massachusetts Institute of Technology Press, Cambridge, MA.

Sosnowski, P., Wieczorek, A., and Ledakowicz, S. (2003). Anaerobic co-digestion of
sewage sludge and organic fraction of municipal solid wastes. Advances in
Environmental Research, vol. 7, no.3, pp. 609-616.

Speece, R. E. (1988). A survey of municipal anaerobic sludge digesters and diagnostic
activity assays. Wat. Res., vol. 22, no. 3, pp. 365-372.

Speece, R. E. (1995). Anaerobic Biotechnology for Industrial Wastewaters. Archae Press,
Nashville, TN.

Zitomer, D., Ferguson, N., McGrady, K., and Schilling, J. (2001). Anaerobic co-digestion
of aircraft deicing fluid and municipal wastewater sludge. Water Environment Research,
vol.73, no.6, pp. 645 – 654.
                                                                                          67


BIBLIOGRAPHY




Cecchi, F., Vallini, G., Pavan, P., Bassetti, A., and Mata-Alvarez, J. (1993). In Cecchi, F.,
Mata-Alvarez J. and Pohland F. G.(Eds.), Management of macroalgae from Venice
lagoon through anaerobic co-digestion and co-composting with municipal solid waste
(MSW).

Demirer, G.N., Duran, M., Erguder, T.H., Tezel, U., Gueven, E., and Ugurul, O. (2000).
Anaerobic treatibility and biogas production potential studies of different agro-industrial
wastewaters in Turkey. Proceeding of the 4th International Symposium on Environmental
Biotechnology.

E. P. A. (Environmental Protection Agency) (2004). A Plain English Guide to the EPA
part 503 Biosolids Rule, EPA 832/R-93-003, Washington, D. C.

Ferguson, L.N. (1999). Anaerobic Co-Digestion of Aircraft Deicing Fluid and
Microaerobic Studies. M. S. thesis, Department of Civil and Environmental Engineering,
Marquette University, Milwaukee, WI.

Fruteau de Laclos, H., Desbois, S. and Saint-Joly, C. (1997). Anaerobic digestion of
municipal organic waste: Calorga full-scale plant in Tilburg, The Netherlands. Wat. Sci.
Tech., vol. 36, no. 6-7, pp. 457-462.

McCarty, P.L. (2001). The development of anaerobic treatment and its future, Wat. Sci.
Tech., vol. 44, no. 8, pp.149-156.

McGrady, K. (1999). Anaerobic Co-Digestion and Phasing for Aircraft De-Icing Fluid
Treatment. M. S. thesis, Department of Civil and Environmental Engineering, Marquette
University, Milwaukee, WI.

Nagel, P., A. Urtubia, A., Aroca, G., Chamy, R. and Achiappacasse, M. (1999).
Methanogenic toxicity and anaerobic biodegradation of chemical products in use in a
brewery. Wat. Sci. Tech., vol. 40, no. 8, pp. 169-176.

Oleszkiewicz, J., and Mavinic, D. S. (2002). Wastewater biosolids: an overview of
processing, treatment, and management. J. Environ. Eng. Sci., vol. 1, pp. 75-88.

Switzenbaum, M. S. (1995). Obstacles in the implementation of anaerobic treatment
technology. Bioresource Technology, vol. 53, pp. 255-262.

Wellinger, A., Baserga, U. and Egger, K. (1992). New systems for the digestion of solid
wastes. Wat. Sci. Tech., vol. 25, no. 7, pp. 319-325.

								
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