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EFFECT OF LEACHATE RECIRCULATION ON ORGANIC WASTE AND LEACHATE STABILIZATION IN ANAEROBIC BIOREACTOR-5

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EFFECT OF LEACHATE RECIRCULATION ON ORGANIC WASTE AND LEACHATE STABILIZATION IN ANAEROBIC BIOREACTOR-5 Powered By Docstoc
					International Journal of Civil Engineering
 International Journal of Civil Engineering and Technology (IJCIET) ISSN 0976 – 6308(Print),
and Technology (IJCIET), ISSN 09761, May - June (2010), © IAEME
 ISSN 0976 – 6316(Online) Volume 1, Number – 6308(Print)
ISSN 0976 – 6316(Online) Volume 1
                                                                          IJCIET
Number 1, May - June (2010), pp. 87-101                                       © IAEME
© IAEME, http://www.iaeme.com/ijciet.html

       EFFECT OF LEACHATE RECIRCULATION ON ORGANIC
      WASTE AND LEACHATE STABILIZATION IN ANAEROBIC
                                       BIOREACTOR
                                      Sandip T. Mali
                             Department of Civil Engineering
                     Sinhgad College of Engineering, Pune, Maharashtra

                                    Kanchan C. Khare
                              Department of Civil Engineering
                     Sinhgad College of Engineering, Pune, Maharashtra
                             E-mail: kanchankhare@gmail.com
                              viceprincipal.scoe@sinhgad.edu

                                        A.H. Biradar
                               Department of Civil Engineering
                       College of Engineering, Kopergaon, Maharashtra

 ABSTRACT
         In present study lab scale anaerobic bioreactor of 0.0742 m3 was used to
 investigate the effect of leachate recirculation on degradation of organic matter and
 stabilization of leachate. Reactor was filled with 34.10 kg of organic waste. Leachate
 quality was regularly monitored by means of pH, alkalinity, conductivity, oxidation
 reduction potential (ORP), biochemical oxygen demand (BOD3), chemical oxygen
 demand (COD), solids, total nitrogen, volatile fatty acids (VFA), sulphate, chloride,
 sodium, calcium and potassium. Reactor was also monitored for physical observations as
 temperature, settlement, quantity of leachate generated and recirculated. Observation
 indicates that pH was significant parameter for anaerobic digestion process. Total
 settlement of waste was 37.21%. There was gradual degradation of leachate quality with
 the time. Leachate recirculation shows that optimum moisture content was maintained in
 required range and microbial activity was accelerated to degrade the organic matter.
 Reduction in BOD3, COD and volatile solids of leachate were 84.92%, 82.12% and 76.90
 % respectively. Leachate recirculation reduces post treatment of leachate.



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Key Words: leachate recirculation, organic waste, anaerobic bioreactor.
1. INTRODUCTION
        There is tremendous increase in the amount of municipal solid waste (MSW) in
cities, all over the world. Population increase, economic progress, expansion in urban
areas, rapid industrial development and rising standards of living have contributed to
sharp rise in solid waste generation. Landfill has been widely used for MSW disposal all
over the world. Especially in developing countries it is considered to be a reliable and
cost effective method if adequate land is available. The volume of waste has increased
due to the lack of control and treatment alternatives and lack of effective implementation
of MSW rules and regulations in India. Improper management and operation of landfill
could create several environmental impacts such as groundwater pollution, frequent
landfill fires and nuisance odor etc. (C. Chiemchaisri et al., 2002). In India waste
received at landfill is majorly organic waste, from residential area, markets, commercial
areas, hotels and restaurants etc. The organic matter founds in different forms and sizes
and sometimes only one type of composition. Some of the organic materials having low
pH such as lemon, onion, pickle etc. This create acidic zone where it is dumped. Waste at
the landfill can be treated by bioreactor landfill. A bioreactor landfill is a sanitary landfill
site that uses enhanced microbiological process to transform and stabilize the readily and
moderately decomposable organic wastes. The bioreactor landfill significantly increases
the extent of organic waste decomposition, conversion rates of complex organic
compounds and process effectiveness over the traditional landfill sites (Reinhart D.R et
al., 2002). Leachate is recirculated in to the bioreactor landfill system to maintain
moisture, nutrient and microbial activity. Therefore there is need to study the effect of
leachate recirculation for acidic zone. In present study, effect of leachate recirculation on
biodegradation of organic matter for acidic condition was investigated.
2. MATERIALS AND METHODS

2.1 EXPERIMENTAL SETUP
        Lab scale anaerobic bioreactor was made of synthetic material with an internal
diameter of 0.3 m and height of 1.05 m (volume 0.0742 m3 or 74.22 L) as shown in Fig.
1. Thickness of cylinder was 5mm. A plastic ball (70 mm diameter, 4 mm thick and 75


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holes of 5 mm diameter) was kept at centre of bottom above the leachate outlet to prevent
the clogging of leachate outlet. Coarse gravel of 10 mm thick layer (gravel of particle size
of 12.5 mm at bottom and 10 mm size of gravel above 12.5 mm gravel) was placed to
facilitate leachate drainage at the bottom of reactor.




           Figure 1 Schematic representation of labscale anaerobic bioreactor
        The prepared waste of 34.10 kg was filled in layers, with density of 635 kg m-3.
The waste was placed and compacted manually in 100 to 150 mm lift. The height of
waste was 0.86 m and free board of 0.19 m. Soil layer of 50 mm thick was provided at
top of waste for equal distribution of moisture in waste mass. Gas collection pipe was
provided at the middle of waste mass (height 1m, diameter of PVC pipe 40 mm, diameter
of holes 5 mm and number of holes 430). Sampling port was provided for sampling and
temperature measurement (0.40 m above from bottom and 25 mm diameter). The reactor
was kept at college building terrace open to atmospheric conditions, but covered from the
top. Leachate was collected in plastic bucket at bottom (volume 5 L). The leachate was
pumped through submersible pump into leachate storage bucket (20 L)                           at top for



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recirculation (submersible pump make Futura Industries (cooler pump) India, model –
KR 1900, Max. head 2.5 m, Voltage 165-250 V/ 50 Hz, power – 40 W and output 1800 L
per hr.). Leachate was injected in reactor through the upper soil layer, using a perforated
PVC pipe (Figure 1).        Leachate control valve was provided between leachate storage
bucket and leachate distribution system to control the required flow rate. Water
displacement assembly was prepared for gas measurement.
2.2 PREPARATION OF WASTE SAMPLE
        Organic waste was collected from residential society, vegetable market and
college mess to get representative organic waste. The inorganic materials from the waste
were removed. Waste was shredded manually to size of 40 to 60 mm. Cow dung slurry of
10 L of was added and mixed before filling the reactor to inoculate anaerobic
microorganism. The characteristics of waste feed to reactor are given in Table 1.
2.3 ANALYTICAL METHOD
        Leachate was analyzed weekly for chemical parameters                          pH, electrical
conductivity, total solids (TS), total dissolved solids (TDS), total volatile solids (TVS),
total fixed solids (TVS), chemical oxygen demand (COD), biochemical oxygen demand
(BOD3), total nitrogen (TN), chloride, oxidation reduction potential (ORP), sulphate,
sodium (Na), calcium (Ca), potassium (K), volatile fatty acids (VFA) and alkalinity. All
these analysis were performed according to Standard Methods (APHA AWWA, 1998).
Atmospheric and reactor temperature was also measured. Settlement of waste was
measured initially before closing the reactor and at the end of experimentation.
           Table 1 Characteristics of waste at starting and end of experimentation
              Total quantity Total         Volatile Fixed           Organic      Moisture
              of wet waste,     solids,    solids,      solids      Matter, % content, %
              kg                %          %            %
 At starting 34.10              21.119     85.414       14.586      94.473       45.97
 At end       23.60             23.081     67.581       32.419      73.117       46.759
2.4 OPERATIONAL PROTOCOL
        The experimentation was carried out from 10 July 2009 to 7 September 2009 (90
days). Leachate generated and recirculated was measured regularly. Intermediately pH of
recirculated leachate was increased by adding alkaline solution (CaOH) to increase the
pH of waste mass, to maintain the anaerobic condition. Waste was containing sufficient



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moisture content at starting; so leachate was recirculated after 23 days. The volume of
leachate recycled after every 7 days was 3 to 6 % (v/v) of the waste in the reactor or 2 to
3 L. Total quantity of leachate generated and recirculated throughout the experimentation
was 32.30 L and 21.9 L respectively. Intermediately tap water was added to maintain 50
% moisture content. Total quantity of tap water added to reactor was 11.3 L. About 600
to 700 ml of leachate was taken for analysis every week.
3. RESULTS AND DISCUSSION
3.1 SETTLEMENT AND DEGRADATION OF WASTE
        Initial settlement of waste in the reactor was 5.81% and 18.60% after 1 and 4 days
respectively .Total settlement of waste was 37.21%. Initial settlement was due to self
weight of waste and further settlement was due to degradation of waste, which was
19.61%. Settlement during actual landfill operations will impact the performance of the
final surface grade, surface drainage, roads, gas collection piping system and leachate and
air distribution piping system (A. Suna Erses et al., 2008).The initial weight of wet waste
was 34.10 kg and which reduced to 23.60 kg. Weight reduction of waste was 30.79%
after 90 days. It indicates time span required for degradation of organic waste was more
as compared to composting. Anaerobic digestion process had not occurred effectively as
waste was in acidic condition. Initial organic matter was 94.47 % which had reduced to
73.11%. Similarly volatile solids reduced from 85.14% to 67.58%.
3.2 BOD and COD
        Biochemical oxygen demand (BOD) and chemical oxygen demand (COD) were
measured as indicators of leachate organic strength. The trend of leachate BOD and COD
is shown in Figure 2. The COD value at starting was 74400 mg/L and it reduces to
20600 mg/L after 46 days. COD were again increasing from 20600 to 32400 mg/L due to
acidogenic stage in which volatile fatty acids (VFA) formation were increased (Fig.6).
COD concentration decreased to 12000 mg/L on day 81 due degradation of the waste.
COD values on 67 days onwards starts to reduce and it becomes almost stable, indicating
less reduction in COD. BOD shows similar trend with COD removal (Fig.2). BOD3 to
COD ratio is often used to assess the biodegradability of the organic matter in leachate




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(Alvarez Vazquez et al., 2004). In the present study BOD3 to COD ratio reduced from
0.63 to 0.40.

                                                                                            COD
                                    80000                                                   BOD
                                    75000
                                    70000
                                    65000
                                    60000
                                    55000
                                    50000
                                    45000




                             mg/L
                                    40000
                                    35000
                                    30000
                                    25000
                                    20000
                                    15000
                                    10000
                                     5000
                                        0
                                            0   10   20   30     40   50     60   70   80     90

                                                               Time (Days)


                                Figure 2 BOD and COD variation with time
3.3 SOLIDS
        Kylefors and Lagerkvist (1977) reported that total solids (TS) concentration is
expected to decrease as the leachate moves from acdiogenic to methanogenic. S.T.S.
Yuen (1999), reported the same results for total solids, but indicated that there was not
considerable change in dissolved solids concentration as total solids. Figure 3 shows all
solids measurement results for anaerobic reactor. Total solids varied from 53800 to
17520 mg/L, TDS from 47160 to 14680 mg/L and TVS from 40520 to 9360 mg/L. The
percentage reduction in TS, TDS and TVS was 67.43%, 68.87% and 76.90%
respectively. The decrease in concentrations of all types of solids was due to consumption
of organic matter in leachate by bacteria to produce new cells and carbon dioxide. It
indicates that there was substantial degradation of solids in leachate through the leachate
recirculation. TVS followed the same trend of COD concentration as shown in Fig.3.
The increase in TVS was observed after 60 days due to addition of cowdung slurry in
recirculated leachate to increase the microbial activity. TVS concentration after 67 days
was reducing due to degradation of organic matter.




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                                                                                          TS
                                                                                          TVS
                                 55000                                                    TFS
                                                                                          TDS
                                 50000

                                 45000

                                 40000

                                 35000




                          mg/L
                                 30000

                                 25000

                                 20000

                                 15000

                                 10000

                                 5000
                                         0    10   20   30     40   50     60   70   80     90

                                                             Time (Days)


                                             Figure 3 Solids variation with time
3.4 PH AND ALKALINITY
        The change of pH of leachate in reactor is shown in Figure 4. The pH of leachate
on first day was 3.37. Alkaline solution (CaOH) was added intermediately in recirculated
leachate to increase the pH. The pH was increased after 81 days to 4.92. Observations
show that increasing the pH in the reactor by recirculating leachate was very slow
process. In anaerobic digestion process, volatile fatty acid formation takes place initially
which affects the increasing pH. Therefore for the anaerobic digestion process, pH of
waste material should be checked at time of feeding and it should be in range 6.5 to 7.5.
The pH of the waste can be adjusted to required range by adding suitable acidic or
alkaline solution. In the current study pH was not increased upto required mark, it was be
due to total quantity of waste was 34.10 kg and which contain substances such as lemon,
onion etc. whose pH was already less. Throughout the experimentation there was no gas
formation due to waste was in acidic condition. For the methanogenesis stage pH should
be in the range of 6.8 to 7.4. The pH of waste was very important operational parameter
to maintain the anaerobic condition, otherwise entire process gets affected. Study
indicates that degradation rate of waste was reduced in acidic condition, which increases
the time span of waste treatment without the gas formation.




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                                              8.0
                                              7.5
                                              7.0
                                              6.5
                                              6.0
                                              5.5
                                              5.0
                                              4.5
                                              4.0




                          pH
                                              3.5
                                              3.0
                                              2.5
                                              2.0
                                              1.5
                                              1.0
                                              0.5
                                              0.0
                                                    0       10    20    30    40    50     60   70   80   90

                                                                             Time(Days)


                                 Figure 4 pH variation with time
        Adequate alkalinity is necessary to maintain a stable pH in the reactor for optimal
biological activity. Alkalinity in range of 1000 to 5000 mg/L as CaCO3 was
recommended by G.J. Farquhar et al., (1973) and Tchbanoglous and Burton (1979).
Figure 5 shows the variation of alkalinity for leachate. Alkalinity was higher at initially
and by the time it gets reduced from 8480 to 3200 mg/L as CaCO3.

                                              9000

                                              8000

                                              7000

                                              6000
                           Alkalinity, mg/L




                                              5000

                                              4000

                                              3000

                                              2000

                                              1000


                                                        0    10    20   30     40   50     60   70   80   90

                                                                             Time (Days)


                     Fig. 5 Alkalinity variation with time
3.5 VOLATILE FATTY ACIDS (VFA)
        The organic waste in anaerobic reactor first hydrolyzed into aqueous organic
acids and consumed by acidogenic bacteria to produce VFA and carbon dioxide. Figure 6
shows the variation of VFA with the time. VFA concentration was varying with the time
due to variation in acid formation upto 67 days and then further reduced. The fluctuations



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of VFA were reflected in COD observations. Salem Alkaabi et al., (2009) reported that
VFA concentration increased at the beginning as a result of accumulation of organic
acids from the hydrolysis and acidogenic process.

                                                               50000

                                                               45000




                            Volatile Fatty Acids (VFA), mg/L
                                                               40000

                                                               35000

                                                               30000

                                                               25000

                                                               20000

                                                               15000

                                                               10000

                                                               5000

                                                                              0                       10        20    30      40        50    60    70        80   90

                                                                                                                           Time (Days)


                                                                       Figure 6 VFA variations with time
3.6 CONDUCTIVITY
        The conductivity of leachate reflects its total concentrations of ionic solutes and is
a measure of solutions ability to convey electric current (A. Suna Erses et al., 2008). The
variation of conductivity for present study was 16.38 mS/cm to 18.5 mS/cm as shown in
Figure 7.

                                                                                             19
                                                                                             18
                                                                                             17
                                                                                             16
                                                                                             15
                                                                       Conductivity, mS/cm




                                                                                             14
                                                                                             13
                                                                                             12
                                                                                             11
                                                                                             10
                                                                                              9
                                                                                              8
                                                                                              7
                                                                                              6
                                                                                              5
                                                                                              4
                                                                                              3
                                                                                              2
                                                                                              1
                                                                                              0
                                                                                                  0        10    20   30     40    50    60   70   80    90

                                                                                                                           Time (Days)



                                                               Figure 7 Conductivity variation with time




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3.7 OXIDATION REDUCTION POTENTIAL (ORP)
        The redox potential within a landfill determines the mechanism of waste
degradation. It has been suggested in literature, that there is an optimum oxidation-
reduction potential (ORP) requirement for methanogenesis, which generally ranges from
-100 to -300 mV (Farquhar et al., 1973, F.G. Pohland, 1975, G.J. T.H. Christensen et al.,
1989). ORP tests are very sensitive to sample storage time. The reading may rise fairly
rapidly and become a lot more positive when tested only hours after sampling (M. Sinan
Bilgili et al., 2007). ORP tests were done immediately at the time of sampling. Figure 8
shows that ORP values began to decrease, after the consumption of available oxygen
initially, indicating the degradation was shifting from acidogenic phase to methanogenic
phase. ORP value after 23 days was varying upto 67 days and afterwards increased upto -
45mV.

                                       20
                                       10
                                        0
                                       -10
                                       -20
                                       -30
                                       -40
                            ORP, mV




                                       -50
                                       -60
                                       -70
                                       -80
                                       -90
                                      -100
                                      -110
                                      -120
                                             0    10   20   30     40   50     60   70   80   90

                                                                 Time (Days)


                                                 Figure 8 ORP variation with time
3.8 NITROGEN
        Nitrogen in leachate is causing soil and water pollution. Variation of the total
nitrogen (TN) is shown in Figure 9. Total nitrogen in the study varies from 1379.50 to
140 mg/L. Total nitrogen of leachate at beginning was high due to mixture of organic
matter and cow dung slurry. Fig. 9 shows that from 39 days onwards variation in TN
value was very less. The recirculation of leachate into reactor reintroduces ammonia to
the system, keeping its value almost constant as it reached to stable stage (A. Suna Erses
et al., 2008). Pohland et al., (1987) stated that TN concentrations between 200 to 1500
mg/L have shown no adverse effects on anaerobic process, concentration ranging from



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1500 to 3000 mg/L were shown inhibitory effects at higher pH levels and concentration
above 3000 mg/L were very toxic.

                                                                 1400


                                                                 1200




                                           Total Nitrogen,mg/L
                                                                 1000


                                                                  800


                                                                  600


                                                                  400


                                                                  200


                                                                     0
                                                                         0        10    20   30     40   50     60        70    80   90

                                                                                                  Time (Days)


                   Figure 9 Total nitrogen variations with time
3.9 CHLORIDE AND SULPHATE
        Chloride was monitored as a conservative tracer in order to estimate the dilution
and washout effects (A. Suna Erses et al., 2008). The chloride value was reduced from
4763 to 1617 mg/L after 32 days and then increased continuously, may be due to
recirculation of leachate (Figure 10). The sulphate concentration was varying with time
as shown in Figure 13. Sulphate concentration at beginning was 2695 mg/L, which
increased to 6131 mg/L upto 60 days and then continuously reduced.

                                          5000

                                          4500

                                          4000

                                          3500
                        Chlorides, mg/L




                                          3000

                                          2500

                                          2000

                                          1500

                                          1000

                                          500

                                                       0
                                                                 0           10        20    30     40    50         60        70    80   90

                                                                                                  Time (Days)


                                                                     Figure 10 Chloride variations with time




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3.10 NA, CA AND K
        The change in alkali metal (Na, Ca, and K) is shown in Figure 11. Initial values of
alkali metals were higher and declining upto 39 days, due to recirculation of diluted
leachate before 39 days and further it increases upto 90 days.

                                                                                                           Na
                                    7000                                                                   K
                                                                                                           Ca
                                    6000


                                    5000


                                    4000
                              ppm

                                    3000


                                    2000


                                    1000


                                               0
                                                     0       10   20   30     40     50   60   70     80        90

                                                                            Time (Days)


                               Figure 11 Na, K and Ca variation with time
3.11 TEMPERATURE
        Variations in temperature reflect the degree of solid waste degradation. The
variation of temperature ranged from 22.9 to 32.2oC (Figure 13). According to Mehta et
al., (2002) observations, leachate recirculation accelerates the anaerobic reactions in
landfills and increased the temperatures inside the bioreactor landfill. Rees (1980)
observed that the optimum temperature for methane production from domestic refuse in a
conventional anaerobic digester is about 40oC.

                                                     3500


                                                     3000


                                                     2500
                                    Sulphate, mg/L




                                                     2000


                                                     1500


                                                     1000


                                                     500


                                                         0
                                                             0    10   20     30     40   50     60    70        80   90

                                                                                   Time (Days)



                                      Figure 12 Sulphate variation with time



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                                                  32
                                                  30
                                                  28
                                                  26
                                                  24
                                                  22




                                 Temperature, c
                                O
                                                  20
                                                  18
                                                  16
                                                  14
                                                  12
                                                  10
                                                   8
                                                   6
                                                   4
                                                   2
                                                   0
                                                       0   10   20   30    40   50   60   70   80   90

                                                                          Time(Days)


                               Figure 13 Temperature variations with time
4. CONCLUSION
        In present study, the impact of leachate recirculation on the biodegradation of
organic matter and stabilization of leachate was investigated using laboratory scale
anaerobic bioreactor. Leachate recirculation maintains the optimum moisture content in
the required range and accelerates the microbial activity which enhances degradation of
organic matter. The organic matter in acidic condition hampers the anaerobic digestion
process. The waste mass had lower pH value (3.37) at the start of experimentation and it
was very difficult to increase the pH value by addition of alkaline solutions. Reduction in
BOD3, COD and volatile solids of leachate were 84.92%, 82.12% and 76.90 %
respectively. Chemical characteristic of leachate gets reduced with the time during acidic
condition but the higher removal efficiency was not achieved with less time. Therefore
for anaerobic digestion process or anaerobic bioreactor landfill operational parameters
should be maintained for better performance of reactors.
Acknowledgement
        The authors wish to acknowledge the financial support provided by the Board of
College and University Development, University of Pune, Pune, India (BCUD 14,
ENGG-71).
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1. C.Chiemchaisri, W. Chiemchaisri, U.Nonthapund and S. Sittichoktam (2002),
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    Landfill Concept”, 5Th Asian Symposium on Academic Activities for Waste
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2. Reinhart, D.R., McCreanor, P.T., Townsend, T.( 2002), “The bioreactor landfill: its
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13. M. Sinan Bilgili, Ahmet Demir, Bestamin Ozkaya (2007), “Influence of leachate
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