Odor Control in Biosolids Management by qru89250

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									                               United States                Office of Water                  EPA 832-F-00-067
                               Environmental Protection     Washington, D.C.                 September 2000

                               Biosolids and Residuals
                               Management Fact Sheet
                               Odor Control in Biosolids Management
DESCRIPTION                                                Nuisance odors can have detrimental effects on
                                                           aesthetics, property values, and the quality of life in
This Fact Sheet provides information on the control        communities subjected to them. There are odorous
of odors from biosolids production facilities, and         compounds that are classified as toxic pollutants,
the prevention of odors from the storage,                  but emissions of these compounds are restricted by
distribution, and application of the biosolids             air quality regulations and their control is not part
product. The level of detail is intended to provide        of this discussion. An odorous biosolids product,
an overview for decision-makers including                  or a biosolids treatment process that results in odor
wastewater treatment plant managers and authority          emissions, may be perceived as unhealthy due to the
managers. The information provided is not                  origin of the solids. The cause of health complaints
intended to be design guidance.                            in the absence if irritation or toxicity is poorly
                                                           understood. (Schiffman et, al.) Tangential
Nuisance odors are a common occurrence at                  information is available from other industries but
wastewater treatment plants, biosolids processing          there is no necessarily direct relevance to biosolids
facilities, and biosolids recycling locations where        odors. More research is needed to identify potential
proper management and control are not                      health effects of biosolids odors.
implemented. Failure to acknowledge the potential
for odors and to work to prevent odor emissions can        Odor complaints at operating facilities can lead to
result in complaints, shutdowns, expensive retrofits,      long term problems. Local public opposition can
and non-acceptance of the finished product. Every          delay or prevent expansions or upgrades to facilities
operation should keep a systematic record of odor          required to improve water quality. The anticipation
complaints.(Chlupsa)        Proper facility design,        of nuisance odors from proposed land application
operation, management, control and careful                 programs can limit the implementation of a
oversight are necessary to minimize odors. Water           worthwhile beneficial reuse program.
quality professionals have a responsibility to
mitigate nuisance odors.                                   Why Do Biosolids Generate Odors?

The most successful odor control programs are              The beauty of biosolids is that is an abundant
those that take a holistic approach and examine the        source of food for microorganisms including
complete system from sewer users to land                   protiens amino acids and carbohydrates. These
application practices. Just as a good physician can        beasts in biosolids degrade these energy sources
identify the cause of the illness and not just treat the   and odorous compounds are formed. (Walker,
symptoms, effective odor management will identify          1991) Organic and inorganic forms of sulfur,
and manage the source of odors and not just attempt        mercaptans, ammonia, amines, and organic fatty
to mask or hide the offensive odors. In addition, a        acids are identified as the most offensive odor
holistic approach will encompass effective                 causing compounds associated with biosolids
communications with those groups that may be               production.    These compounds typically are
negatively impacted by odors.                              released from the biosolids by heat, aeration and
                                                           digestion. The odors vary by the type of residual
                                                           solids processed and the method of processing.
Anaerobic digestion of primary wastewater               assurance that capital and operating dollars are
residuals produces hydrogen sulfide and other           spent wisely. Facility owners should look for a
sulfur-containing gases, while alkaline stabilization   consultant who specializes in biosolids odor control
of the solids volatilizes ammonia along with other      when initiating an odor audit. An odor audit will
volatile compounds. Composting odors can be             accomplish the following:
caused by (Walker) ammonia, amine, sulfur-based
compounds, fatty acids, aromatics and                   •       Quantify odors from each odor emissions
hydrocarbons such as terpenes from the wood                     source.
products used as bulking agents. Aerobically
digested and air-dried biosolids may contain little     •       Analyze for odor causing compounds.
hydrogen sulfide, but have mercaptan and dimethyl
sulfide odors.(Bertucci, Dodd, Hatfield, Williams)      •       Determine the processes by which odor
                                                                causing compounds are formed.
The five independent factors that are required for
the complete odor assessment are:                       •       Identify the most significant odor sources.

1.     Intensity or pervasiveness- a measure of the     •       Obtain data for odor emissions air
       perceived strength of the odor compared to               dispersion modeling.
       concentrations of a standard compound.
                                                        •       Determine the most cost effective odor
2.     Character - which relates to the mental                  management plan.
       association made by the subject in sensing
       the odor.                                        Good management practices or modification to the
                                                        operation may reduce odor emissions; however,
3.     Hedonics - the relative pleasantness or          odor containment and treatment at the biosolids
       unpleasantness of an odor sensed by the          processing facility may be necessary to control
       subject.                                         downwind effects.

4.     Detectability or quantity - the number of        The value of air dispersion modeling prior to final
       dilutions required to reduce an odor to its      design should not be underestimated. Information
       minimum detectable threshold odor                obtained from modeling may result in design
       concentration (Switzenbaum et al., 1997,         changes such as; increasing stack height, increasing
       Walker).                                         stack velocity, providing reheat to increase thermal
                                                        buoyancy, or dilution with ambient air. (Haug,
5.     Mass - total mass per unit time or the           1990)      These low cost features can save
       volume of odorous air produced.                  significantly on capital and operating costs and
                                                        improve effectiveness.
                                                        Likewise, effective communication with the
Odor Control at Biosolids Processing Facilities         affected community is important to enhance odor
                                                        management and reduce the number of complaints.
Biosolids processors are faced with odors during
thickening, digestion, dewatering, conveying,           Odor Control at Land Application Sites
storage, truck loading, air drying, composting, heat
drying, alkaline stabilization, and/or incineration.    The biosolids producer should accept responsibility
The odors may be point sources or ambient air (in       for odor control at land application sites. Even if
a belt press room for example.) The odors may           the producer hires a contractor to provide
emanate from point sources or be present in             transportation, storage, or land application services,
ambient air from area sources. A comprehensive          the terms of the agreement should include
odor audit and air dispersion modeling is the best      management practices to minimize odors. In
addition, the generator and contractor should have      •      Clean tanks, trucks, and equipment daily.
an odor response plan in place to provide guidance
and policy on documenting and responding to odor        •      Whenever possible, subsurface inject or
complaints. The land applier should have the                   incorporate biosolids into the soil (WEF
ability and responsibility to divert biosolids from a          1997).
site that is experiencing odor problems.
                                                        •      Minimize the length of time biosolids are
Biosolids producers should make every effort to                stored (USEPA & USDA,2000).
minimize odors at the application site because the
long term efficacy of land application depends on it.   •      Reduce visibility and maximize the distance
A dramatic increase in local ordinances that ban or            of the storage area from occupied dwellings
restrict the use of biosolids has been observed in             (USEPA & USDA,2000).
recent years as a result of odor complaints. A
nationwide survey (Biocycle 1999 revealed that          •      Avoid land application when wind
odors at land application sites were usually the               conditions favor transport of odors to
initial operating problem that resulted in                     residential areas (USEPA & USDA,2000).
complaints, which were followed by questions and
often, organized public opposition.                     •      Plan field storage of biosolids based on the
                                                               stability, quantity, and length of time
Federal Biosolids Regulations do not regulate odors            biosolids are stored in addition to the
because it was believed that odors from land                   location of the site with respect to nearness
application did not present human health effects. It           to neighbors and the meteorological
has been said, however; “Biosolids odors may not               conditions (USEPA & USDA,2000).
pose a health threat, but odors are killing public
support for biosolids recycling programs.” (Toffey,     •      Avoid land application when nearby
1999)                                                          residential areas are planning outdoor
                                                               activities or around holidays such as
The most cost-effective approach to odor control               Memorial Day, Independence Day, and
may be to examine the operation and maintenance                Labor Day WEF 1997).
practices at the processing facility.          Septic
conditions may result in a biosolids product that is    •      Develop an odor control plan and train all
more offensive than necessary. Some polymers                   staff to identify and mitigate odors.
break down into odor forming compounds under
high heat and elevated pH. Incomplete anaerobic         •      Have alternate management including land-
digestion can result in worse odors than no                    filling for particularly malodorous batches
digestion at all. Blending of raw and WAS prior to             of biosolids.
liquid storage can result in higher concentrations of
Dimethyl Sulfide. (Hentz and Cassel, 2000)              Process Management

Methods to reduce odors at land application sites       The degree of odor control necessary for biosolids
include:                                                processing facilities is determined by site-specific
                                                        criteria such as:
•      Properly stabilize, condition and manage
       biosolids at the treatment works to              •      The current and future proximity of a site to
       minimize odors from the final product.                  residential or commercial developments.

•      Select remote sites and fields away from         •      Local wind patterns, air mixing and
       neighbors (USEPA & USDA,2000).                          dispersion (air stability) factors.

•      Apply well stabilized material.                  •      Temperature and humidity.
•       The variability of the above factors on a          off-site odors as the criteria for violation of
        daily and seasonal basis.                          nuisance standards.

•       The amount of biosolids being processed.           Sources of Odor

A computerized air dispersion model that addresses         Wastewater collection systems with long detention
magnitude, frequency, and duration of events, and          times can result in septic conditions throughout the
is calibrated and verified with on-site monitoring,        wastewater treatment plant and subsequent odor
can be an effective tool to predict the impact of          problems in biosolids handling and end use.
odor emissions. This type of model may determine           Aerated static pile, windrow and in-vessel
how much and what type of control will be                  composting processes can produce objectionable
necessary to prevent or minimize the impact. To            odors if anaerobic conditions occur and even with
accomplish this task with some certainty of success,       aerobic conditions. Ventilation of air through the
a formal odor study should be commissioned.                compost material helps to control composting
                                                           temperature, maintain aerobic conditions, and
During the planning or preliminary design of a             provide a means to direct the exhaust air stream
proposed biosolids processing facility, an odor            into an odor control device.           The alkaline
study should be conducted in light of the knowledge        pasteurization process produces ammonia as well as
and experience gained from successful operations           other odor-causing compounds. Large scale
at similar facilities. For existing facilities that have   facilities are often enclosed and ventilated to a wet
nuisance odor problems, the study should determine         chemical scrubber. Heat drying facilities usually
the degree to which specific unit processes or area        use wet scrubbers and/or afterburners such as
sources contribute to the offsite impact. A detailed       regenerative thermal oxidizers.
sampling and monitoring program should be
conducted to determine a not-to-exceed nuisance            Biosolids processing facilities can be operated and
odor level. Liquid and gas samples can be                  managed to reduce odor generation and emissions.
chemically analyzed for specific odor compounds.           The quantity and intensity of odorous compounds
Both direct sensory measurements of odor intensity         can be reduced by:
and odor strength are also useful to identify the
sources of the complex mixture of odor compounds           •      Operation and maintenance procedures to
typically responsible for nuisance complaints.                    prevent anaerobic conditions.
Direct sensory measurements are conducted by a
panel of trained observers (expert noses) which            •      Addition of oxidizing agents to prevent
analyzes and rates air samples in terms of odor                   formation of hydrogen sulfide.
intensity (n-butanol scale) and odor strength
(dilution to threshold or D/T scale.)                 A    •      Selection of polymers which are resistant to
comprehensive odor study should result in a full                  breakdown at high temperatures and pH.
understanding of the source and nature of the odor
emissions, identify available methods of odor              •      Optimizing all stabilization processes such
control, and establish criteria to measure the                    as anaerobic digestion, aerobic digestion, or
effectiveness of the control technology.                          alkaline stabilization.

Local ordinances may establish the degree of odor          •      Evaluate the impacts of blending different
control required. Generally, the ordinances are                   types of solids and storage. (Hentz and
written to prevent nuisance conditions at and                     Cassel)
beyond the facility property lines. Numerical limits
of allowable concentrations of odorous compounds           •      Scrubbing with a properly           operated
are specified in some localities, while others specify            chemical scrubber or biofilter.
the frequency and/or duration of the detection of
Addressing O&M optimization may result in dual           Disadvantages
benefits. First, it will reduce the amount and
intensity of odors generated at the site, minimizing     A major limitation of biofilters is the large land area
costs of odor control equipment. Second, it will         required for installations. The size of the biofilter
generate a less odorous product, which will be           surface area is directly related to the airflow to be
easier to store, transport, utilize, or market.          treated and the need to provide about a 45 to 60
                                                         second detention time. Poor biofilter performance
OVERVIEW OF ALTERNATIVES                                 is usually attributed to lack of moisture in the filter
                                                         media. Other performance inhibitors are short-
Current Status                                           circuiting, pH depression, and high temperatures.
                                                         A concentration of ammonia greater than 35 ppm in
Current methods to control odors from biosolids          the foul air stream may cause a toxic accumulation
production facilities include biofilters, activated      of ammonium in the media, leading to reduced
sludge basins, wet chemical scrubbers, regenerative      ammonia removal efficiency. The need to keep the
thermal oxidizers, and odor counteractant or             biofilters moist results in a significant amount of
neutralizing agents. The method chosen should be         water usage and the need to treat or dispose of
based on the results of an odor audit and the type of    leachate and condensate. Design criteria are not
odor causing compounds present.                          well established and biofilters may not be
                                                         appropriate for very strong odors.
Biofilters- Description
                                                         Biofilters -Design Criteria
Biofilters remove odors from a foul air stream by
the adsorption and absorption of odor causing            The medium is a mixture of materials that may
compounds onto a natural media bed where                 include bark, wood chips, yard waste or agricultural
microorganisms oxidize the compounds. The                waste compost, peat moss, sand, pulverized
indigenous bacteria and other microorganisms of          volcanic rock, or oyster shells.
the media acclimate to the compounds present and
are sufficient to provide the "scrubbing" action; no     Oyster shells, or similar materials, can provide pH
bacterial innoculation or chemical addition is           control within the media. (Haines et al). Rock, sand
required. Biofilters commonly are used to treat the      and bark are necessary to provide and maintain
air from all types of composting operations.             porosity of the bed. The medium may be kept
                                                         moist by spray nozzles in the foul air collection
Biofilters-Advantages and Disadvantages                  system and at the top of the biofilter
                                                         surface.(Haines et al).
                                                         Sometimes, water is also added inside the filter
Biofilters provide significant reduction of overall      through drip piping. The media bed is placed over
odor emissions including Volatile Organic Carbon         an air distribution system consisting of perforated
emissions. It is a simple technology with minimum        piping installed within a bed of gravel. An
moving parts and low energy requirements. Cold           impermeable membrane, such as a HDPE or PVC
winter temperatures do not affect            biofilter   liner, is placed under the gravel to facilitate leachate
performance. Biofilters have a low profile and are       collection and disposal. The biofilter can be
not as visible to neighbors as a system requiring a      constructed within a compacted soil trench or
stack. All the above advantages are true if biofilters   between soil berms. If the biofilter is installed
are properly sized, kept moist, and renewed              within a concrete, masonry, plastic or similar
periodically.                                            container, the container must be designed to prevent
                                                         short-circuiting at the side walls and to resist
                                                         corrosion from the acidic leachate.
The size of the biofilter is determined by the airflow   wastewater treatment plants can provide odor
to be treated. The accepted loading rate of a            removal by adsorption, absorption, condensation
biofilter is 3 to 4 cfm per square foot of media bed,    and microbial oxidation.
with a media bed depth of 3 to 4 feet. Design
should provide for ease of removal because               Activated Sludge Basins -Advantages and
biannual replacement or replenishment of the media       Disadvantages
may be required. Periodic mixing or turning of the
media may be required to maintain the design air         Advantages
flow and head loss through the odor control
ventilation system.                                      This can be a very cost effective alternative for
                                                         facilities which operate aeration basins. (Bowker)
Biofilters are widely regarded as an effective, low      Costs are usually lower for both capital and
cost method of treating low to moderate odorous          operating expenses.         Systems have been in
air. A well operated and maintained biofilter can        operation for over 40 years, and more than 25
reduce odors by 95% or greater (Schiffman et al)         facilities have used this technology. This system is
(Boyette and Bergstedt). In some cases, biofilters       effective in treating moderate to high strength
have resulted in the elimination of odor complaints.     odors. Activated-sludge basins are simple, with
(Alix). In other cases, improved composting              low operation and maintenance considerations
operations and biofilter renovation combined             (WEF MOP 24).
resulted in a reduction of odor complaints. (Haines
et al).                                                  Disadvantages

Biofilters -Operation and Maintenance                    Concerns about blower corrosion have been the
                                                         major impediment to use of activated sludge basins.
It is important that biofilters be kept moist so that    However, steel inlet filters and piping are more
the microbial community remains healthy and              common points of corrosion. There are reports of
effective. The goal is to operate the biofilters as      accumulation of a tar-like substance or greasy film
close to 100 percent humidity as possible. It is also    on the internal components of blowers, and the
important to keep sufficient void space and avoid        volume of foul air to be treated may exceed the
air channeling, which results in short circuiting the    demand of the aeration tanks. The method may not
media. Large amounts of dust and particulate             be appropriate for very strong odors.(WEF MOP
matter in the foul air will build up in the biofilter    24)
media and shorten the replacement time. In
addition, back pressure on the blowers will increase     Design Criteria - Activated Sludge Basins
maintenance requirements.           An appropriate
temperature range must be maintained to keep the         The foul air is ventilated through a dedicated
microbial organisms healthy and functioning. High        blower and diffuser system or through the process
temperature air (130-140 deg F) from composting          air distribution system. The foul air diffuser should
processes contains high concentrations of ammonia        be submerged at least eight feet to achieve high
that may be toxic to microorganisms. A typical           odor removal efficiency. The blower and diffuser
biofilter life expectancy is one to seven years with     equipment must be designed to withstand the
biofilter replacement every two years. Operators         corrosive nature of the air stream. Use of stainless
should develop a biofilter performance monitoring        steel, PVC, and moisture traps will minimize
protocol for routine assessment of odor control          corrosion. The foul air volume can be minimized
efficiency.                                              by using flat gasketed covers on tanks or individual
                                                         enclosures for dewatering or blending equipment.
Activated Sludge Basins -Description                     Inlet covers will prevent particulate accumulation in
                                                         fine bubble diffusers. Deep bed nitrification
Similar to biofilters, the activated sludge basins       biotowers are also used for odor control.(Lutz et al)
used for secondary treatment at municipal
Operation and Maintenance - Activated Sludge              controlled. Chemicals, power, and maintenance can
Basins                                                    be expensive, and large amounts of water are
                                                          needed. The spent chemical must be properly
If a diffused aeration system already exists, little or   disposed, and softening is required for the water.
no increase in O&M costs should be expected. The
blowers and air filters must be cleaned periodically      Design Criteria - Wet Scrubbers
and the system monitored for odor causing
compounds.                                                The three most common types of wet scrubbers are
                                                          packed bed scrubbers, mist scrubbers and venturi
Wet Chemical Scrubbers                                    scrubbers.

Wet Scrubbers are best suited to treating high            Packed beds use a shower of scrubbing liquid over
intensity odor emission and large air volumes.            a bed of high-surface-area plastic media to promote
They are usually used at alkaline stabilization           droplet and film contact within a reaction chamber.
facilities, biosolids drying facilities and               The foul air is ventilated through the plastic media
incinerators. There are several types of wet              in a direction that is co-current or counter-current to
scrubbers, the most commonly used in biosolids            the liquid flow. The advantage of a packed
facilities include packed bed, mist, and venturi          scrubber is that the concentration of the scrubbing
scrubbers. All are designed to maximize the               solution can be varied in response to fluctuating
contact between the odorous compounds of the foul         odor levels. These units are usually the least costly
air stream and a "scrubbing" chemical solution.           method of treating high intensity odors at
The compounds are absorbed and then oxidized by           dewatering and storage facilities. Mist scrubbers
the chemicals. The performance of a wet scrubbing         use compressed air to atomize a stream of
system depends on the solubility of the odors in the      scrubbing liquid and a controlled ventilation pattern
scrubbing solution. This should be determined by          within the reaction chamber to promote contact
testing or from previous installations.(Heller and        without the use of media. Advantages of mist
Heller) Multiple stage systems, using water or            scrubbers include a lower water usage and the
acid in the first stage to remove the ammonia,            ability to handle a wide range of flow rates. The
followed by a chlorine or caustic and chlorine in the     disadvantages of mist scrubbers are O&M costs of
second stage to remove sulfur based compounds,            the air compressor, larger space requirements, and
are used to treat composting odors and more               the small clearances on the spray nozzles require
commonly the ventilated air from alkaline                 water softening and occasional acid washes (Heller
pasteurization facilities.                                and Heller). Venturi scrubbers are similar in
                                                          operation to mist scrubbers, but atomize a
Advantages and Disadvantages - Wet Chemical               high-pressure stream of scrubbing liquid without
Scrubbers                                                 compressed air. The type of scrubbing liquid used
                                                          depends on the odor compounds to be treated. A
Advantages                                                combination of sodium hydroxide and sodium
                                                          hypochlorite is effective for sulfide odors, while
A two or three stage scrubber system can remove a         dilute sulfuric acid is effective for ammonia odors.
wide variety of odor-causing compounds. The units
have proven to have variable chemical consumption         Effective cooling of the scrubber gasses is also
and to be effective and reliable.                         needed for ammonia removal (Horst et al, 1991).

Disadvantages                                             Operation and Maintenance - Wet Chemical
There is a potential for emission of chlorinated
compounds and particulate from the scrubber               Wet scrubbers require pumps, compressors, valves,
exhaust stack, as well as a potential for emission of     and instrumentation. As a result, operation and
a bleach odor if chemical feed is not properly            maintenance costs are significant. Occasional
maintenance and calibration is required for the          Design Criteria - RTO’s
chemical supply system, liquid distribution nozzles
and ORP (oxidation reduction potential) and pH           The required temperature in the combustion
probes. System maintenance can normally be               chamber is 1,350 to 1,600 degrees F with a
performed without interrupting the treatment.            detention time in the range of 0.3 to 3 seconds. It is
However, mist scrubbers may require slightly more        also important to configure the system to provide
nozzle maintenance because of the use of finer           sufficient turbulence and oxygen for efficient
spray nozzles.                                           combustion. (Heller and Heller, 1999) The RTO
                                                         may be fueled with fuel oil or natural gas, and heat
Variable odor concentrations and constituents in the     exchangers recover much of the exhaust gas heat to
process air will make scrubber operations difficult      preheat the incoming air.
and reduce effectiveness. Composting operations
have found that improving compost operations,            Operation and Maintenance - RTO’s
specifically mixing and uniform aeration, results in
less variability in dimethyl disulfide concentrations    RTO’s are an expensive odor control technology to
in the scrubber feed air. Fewer and smaller              operate and maintain. High temperatures result in
operating adjustments are required to maintain           significant fuel costs and frequent maintenance
optimum scrubbing conditions. (Murray et al, 1991)       and/or replacement of instrumentation.

Regenerative Thermal Oxidizers (RTO’s)                   Counteractants, Neutralizing          Agents     and
                                                         Oxidizang Agents
RTOs use a high temperature to incinerate airborne
compounds in a short residence time combustion           These products are used to reduce the impact of
chamber. This technology is usually used for             odors from area sources, such as biosolids curing or
biosolids heat dryers, incinerators, or evacuation air   storage piles and point sources such as ventilation
from biosolids storage tanks.                            exhaust stacks. Essential oils and proprietary
                                                         compounds are used as odor masking agents and as
Advantages and Disadvantages - RTO’s                     odor neutralizing or counteracting agents. These
                                                         materials generally are non-toxic and
Advantages                                               non-hazardous to humans and the environment.
                                                         They may be dispersed as a fine mist into the air at
RTOs typically are used for VOC emission control,        processing facilities or added to the liquid waste
with odor removal being incidental.             This     streams.
equipment is compact compared to the area needed
for wet scrubbers or biofilters. They are well suited    Oxidizing agents released into the wastewater react
to treating low volume, high strength air streams.       with odor causing compounds to form a more
RTO’s are more energy efficient than conventional        stable, odor free compound.
afterburners requiring only 10 to 20 percent of the
energy. Thermal efficeincies are often 90 to 95%         Advantages and Disadvantages -
and the use of digester gas can reduce fuel costs.       Counteractants, Neutralizing Agents and
                                                         Oxidizing Agents
There are relatively few applications of RTOs
specifically for the control of biosolids processing     The use of counteractants and neutralizing agents
odors. Operators report these units are a significant    can be initiated quickly at a low capital cost. The
fuel cost. The system is only economical for high-       use of oxidizing agents, or counteractants, in the
strength, difficult-to-treat air streams.                waste stream can greatly reduce odors in the
                                                         workplaces especially around thickening and
                                                         dewatering equipment. At some facilities the
addition of potassium permanganate, an oxidizing          Operation and Maintenance - Counteractants,
agent, temporarily reduces odors in the biosolids         Neutralizing Agents and Oxidizing Agents
product,(Pisarczyk and Rossi) thereby making land
application less objectionable to a farmer’s              Once the proper dosage is determined, operation
neighbors. Some plants also observe improved              and maintenance is relatively simple. Routine
dewatering when using potassium permanganate.             maintenance of pumps, spray nozzles and
                                                          automated systems is required.
It is possible that the perfume-like odor from some
neutralizing agents may be perceived as an                The following table shows removal efficiency for a
objectionable or nuisance odor. The effectiveness         variety of odor control technologies. Within the
of neutralizing agents are limited to the area in         past 5 years, the design and operation of biofilters
which they can be dispersed. Oxidizing agents can         has been optimized and is now better understood
act as a bactericides and inhibit biological              than ever. Most work on biofilter is for use at
processes. The presence of non-odorous substances         composting facilities but due to their low cost, they
that react with the oxidizer, will greatly increase the   are also being examined for heat drying facilities.
cost of treatment.(WEF) Oxidizing agents are not
always effective and are sometimes expensive. The
system has a poor database and limited information                TABLE 1 REPORTED REMOVAL
on odor removal efficiency.                                              EFFICIENCIES

Design Criteria - Counteractant, Neutralizing                                                                 Odor
                                                           System                   H2S          NH3          Units
Agents and Oxidants

Essential oils and proprietary compounds are               Biofilter               > 98%        > 80%         > 95%
dispersed into the foul air stream as a vapor or fine      Activated Sludge       < 85% -       > 90%       90 - 95%
mist. Either a reaction chamber is provided to             (coarse bubble)          92%
maintain a contact and residence time or the               Activated Sludge       > 99.5%         N/A        > 99.5%
ventilation ductwork or exhaust tower is used to           (Fine Bubble)
apply the agent. Some products are claimed to              Wet Scrubbers           > 95%        > 95%        < 80%-
polymerize and precipitate odor molecules from the                                                            99%
air stream. The neutralizing agents are sometimes          RTO                      N/A           N/A         > 95%
sprayed continuously in the vicinity of odorous
tanks, truck loading or storage areas.                     Chemical                >99%1          N/A       up to 99%

Another design uses oxidizing agents such as               Counteractants           30%          30%           N/A
                                                           and neutralizing
chlorine, hypochlorite, chlorine dioxide, hydrogen         agents
peroxide or potassium permanganate to prevent              1
                                                            Hydrogen sulfide concentration measured above the
septic conditions and the resultant hydrogen sulfide       conveyor leaving the centrifuge.
odors. A small amount of oxidant is blended with
wastewater or liquid wastewater solids.           A        Source: Schiffman et,al, Williams, Ostojic & O’Brien,
                                                           Giggey et al, Solomon, LeBeau & Milligan, Pisotti,
potassium permanganate dose of 0.3% can reduce             Singleton et al; Vaith et al; Ficek.
the Threshold Odor Number from 1500 to 200. The
required dosage is dependent on pH. Less
potassium permanganate is needed at pH 5 or 7 than
at pH 9 (Pisarczyk. and Rossi, 1992).                     As with any odor control equipment, removal
                                                          efficiency is only one aspect of effectiveness. Odor
                                                          modeling will identify odor receptors and determine
                                                          the likelihood of odors being detected off site.

                                                  Operation/         Electrical or          Supplies/
 System              Overall       Capital                                                                      Effectiveness
                                                 Maintenance             fuel               Chemicals
 Biofilter          Moderate     Moderate-       Moderate            Low                 Water needed          High>95% in
                                 but land                                                                      compost

 Activated          Low, if      Low, if         Low, if existing    Low , if existing   Low                   High 90-95% for
 Sludge Basins      existing     existing        system, may         system and                                H2S and
                    system       system          corrode blowers     biosolids                                 Ammonia
                                                                     facility is close

 Wet Chemical       High         High-up to      High - much         High - must         High - chemical       High <80%-99%
 Scrubbers                       50% of          high speed          move water at       costs and water       handles alkaline
                                 total plant     equipment +         high pressure       demand                stab and all plant
                                 costs           instrumentat’n                                                odors

 Regenerative       High         Moderate        High- due to        High -              High - oil or gas     Good for organic
 Thermal                                         high temp           tremendous                                odorants from
 Oxydizers                                       equipment           heat demand                               incinerators, and
                                                                                                               heat dryers

 Oxidizing          Varies-      Low             Low- just mat’l     Low - small         High - potassium      Varies from one
 Agents             moderate                     handling issues     pumps required      permanaganate         plant to another
                    to high                                                              can be expensive

 Counteractant      Moderate     Low-            Varies from one     Low                 High - usually        Varies, but may
 & Neutralizing                  moderate        plant to another                        patented              help at end use
 Agents                                                                                  compounds             site.

 Source: Hentz et al, Haines et al, Giggey, Ostojic and O’Brien, Pisarczyk and Rossi, Ponte, Bowker, Vaith et al, Williams,

                                                                    solids, evaluate polymers and liquid blending and
COSTS                                                               storage practices, maintain records of odor
                                                                    complaints and conditions, and incorporate
Costs for odor control will vary significantly from                 language in land application contracts to assure best
one location to another and from one technology to                  management practices.
another. At the Hoosac Water Quality District
(HWQD) composting facility the biofilter was less                   REFERENCES
than 3% of the capital cost and media replacement
was about 7% of O&M costs (Alix,1998) .                             Other Related Fact Sheets
Multistage wet scrubbers and RTO’s can result in
30 to 50% of capital and operating costs of a                       Alkaline Stabilization of Biosolids
biosolids processing facility.           Potassium                  EPA 832-F-00-052
permanganate costs $1M per year at a facility that                  September 2000
dewaters and incinerates 60 dry tons per day
(DTPD) which equates to $45 per dry ton.                            In-Vessel Composting
                                                                    EPA 832-F-00-061
The following table compares the cost factors for                   September 2000
each technology. In addition, biosolids processing
facilities should budget funds to conduct a facility                Land Application of Biosolids
wide odor audit, use odor modeling whenever                         EPA 832-F-00-064
possible, avoid septic conditions in wastewater and                 September 2000
Centrifugal Dewatering and Thickening                   7.    Bowker, Robert P.G. “Activated sludge
EPA 832-F-00-053                                              Diffusion; Clearing the air on an overlooked
September 2000                                                odor control technique.” Water
                                                              Environment and Technology, WEF Feb.
Filter Belt Press Dewatering                                  1999
EPA 832-F-00-057
September 2000                                          8.    Boyette, R.A and Bergstedt, Loren,
                                                              “Wastewater Treatment Plant Odor Control
Recessed Plate Filter Press Dewatering                        Using a Biofiltration System in Diluth,
EPA 832-F-00-058                                              MN” The ninth International Conference on
September 2000                                                Cold Regions Engineering Sponsored by the
                                                              american Society of Civil Engineers,
Other EPA Fact Sheets can be found at the                     September, 1998
following web address:
http://www.epa.gov/owmitnet/mtbfact.htm                 9.    Brown, T.M. "Multiple Contracts Provide
                                                              for Complete Regenerative Thermal
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Post Buckley Schuh & Jernigan, Inc.
Larry Hentz, V.P. Wastewater Program Manager
One Town Center, Suite 302
4201 North View Drive
Bowie, MD 20716

National Biosolids Partnership
Peter S. Machno, Ph.D.
601 Wythe Street
Alexandria, VA 22313

Steve T, Welch
Assistant Executive to the Director
University Area Joint Authority
1576 Spring Valley Road                                         For more information contact:
State College, PA 16801
                                                                Municipal Technology Branch
U.S. EPA,                                                       U.S. EPA
John Walker                                                     Mail Code 4204
Mail Code 4204                                                  1200 Pennsylvania Avenue, NW
401 M St., S.W.                                                 Washington, D.C. 20460
Washington, DC 20460

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