In-Situ Leachate Management in a Tropical Landfill by ... - CiteSeerX

Proceedings of the International Conference on Sustainable Solid Waste Management, 5 - 7 September 2007, Chennai, India. pp.444-451

In-Situ Leachate Management in a Tropical Landfill by Storage and Recirculation Operation Techniques Chart Chiemchaisri, Wilai Chiemchaisri, Salinee Sittichoktum, Taweesak Tantichanthakarun and Sunya Tangsri Department of Environmental Engineering, Faculty of Engineering, Kasetsart University, Bangkok, Thailand ABSTRACT This paper presents the application of storage and recirculation techniques to leachate management in tropical climate. Four pilot-scale landfill lysimeters were operated under different operational mode, i.e. 1) conventional landfill operation (control) 2) leachate recirculation 3) internal storage with recirculation and 4) internal storage without recirculation. The experiment was carried out to quantify the amount and characteristics of leachate produced from landfill lysimeters operated in tropical climatic rainfall event. Variation in leachate characteristics, methane content in landfill gas was studied. The study revealed that leachate re-circulation and storage operation yielded lower organic concentration in leachate and highest methane content in landfill gas. Leachate re-circulation practice enhanced degree of waste stabilization. Rainfall intensity and leachate re-circulation practice affected leachate quantity as well as organic and nitrogen leaching from wastes. Partially degraded wastes in landfill lysimeters was further stabilized by in-situ aeration method. The aeration helped reducing stabilizing nitrogen in wastes. Leachate recirculation with aeration could produce leachate with its characteristics similar to those of matured leachate. The stabilized waste matrix was then successfully applied to the treatment of fresh leachate under aerobic condition. Keywords: Bioreactor landfill, leachate recirculation, leachate storage, submerged landfill, tropical climate. 1.0 INTRODUCTION Landfill has been widely used for municipal solid waste disposal all over the world. Conventionally, landfill is designed to contain or store the wastes so that the exposure to human and environment could be minimized. Under the containment landfill concept, water infiltration into the landfill is minimized to reduce emission of leachate and gases into the environment. However, severe impacts are occasionally found in these landfills due to the failure of their containment system. Sanitary landfills in many tropical countries are designed as shallow type with only 3-4 lifts (6-8 m. depth) in order to prevent severe contamination to subsurface water especially in low lying area. Huge amount of leachate generated during rainy or monsoon season provides severe environmental threats and difficulties in their management.

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Due to advance knowledge of landfill behavior and decomposition process of solid wastes, several researches focusing on upgrading existing landfill from storage/containment to process-based approach called bioreactor landfill. In contrary to conventional landfill, bioreactor landfill is designed to maximize the infiltration of water into the wastes in order to minimize leachate migration into subsurface environment and maximize landfill gas generation rates under controlled conditions (Reinhart and Townsend 1998). A bioreactor landfill is managed to accelerate decomposition of organic wastes by controlling moisture content of wastes, recycling of nutrients and seeding of microorganisms by leachate re-circulation. Several researches on landfill bioreactor in laboratory, pilot and full scale have been conducted during the past 30 years (Reinhart and Townsend 1998). Most of them have agreed that leachate circulation could enhance waste stabilization, leachate quality and landfill gas production (Pohland 1980; Titlebaum 1982; Barlaz et al. 1987; Stegmann and Ehrig 1989; Lay et al. 1998). However, some operational problems associated with leachate circulation were lack of appropriate circulation technique, leachate channeling and leachate ponding (Buivid et al. 1981). Municipal solid wastes from developing countries are composed mainly of easily biodegradable organic matter with high moisture content especially in tropical climate, therefore, providing different environmental conditions from the landfill in developed countries. This study focused on the application of partially submerged bioreactor landfill concept in tropical landfill by using leachate recirculation and internal storage techniques to enhance waste degradation while minimizing leachate discharge from landfill. The produced leachate during rainy season can be stored inside the waste cell for increasing the moisture content of wastes. It could be re-circulated back to maintain moisture content in top cover layer during dry period. As majority of leachate will be evaporated during irrigation, quantity of leachate needed to be treated could be minimized. The experiment was carried out over three-year period in which the first two year organic waste degradation took place under anaerobic condition. Aeration was supplied after the organic wastes in the system have been exhausted in order to enhance the maturity of the wastes. After completion, stabilized waste matrix was utilized to the treatment of young leachate coming from other new landfill cell area. 2.0 MATERIALS AND METHODS 2.1 Experimental System The experiment was conducted in pilot-scale landfill lysimeters. Four experiment units made of steel pipe of 0.90 m. diameter and 2.7-m height were used (Figure 1). The leachate drainage system was provided at the bottom of each lysimeter with a drainage pipe connected with 1-inch valve. Gravel layer (10-30 mm.) of 200 mm. thickness and geo-textile sheet were provided at the bottom of lysimeter to prevent clogging of suspended solids at the outlet. Leachate was circulated back to the lysimeter in the gravel layer placed below cover soil at the top of waste layer. Distribution of leachate was accomplished through perforated PVC pipe of 1-inch diameter installed in the gravel layer. Gas collection system was installed at the top of waste layer. It was made from perforated 1-inch diameter PVC pipe placed into a gravel pack to prevent clogging from small particles containing in solid wastes. 2.2 Solid Waste Materials Municipal solid waste obtained from a waste transfer station in Bangkok, Thailand was used. It was mixed with digested sludge at a ratio of 4:1 (solid: digested sludge) before being filled into the

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lysimeters. Solid waste was placed in the lysimeter at 200 – 250 mm. thickness each time and compacted to an average density of 621 kg/m3 until total height of 2 m was reached. The characteristics of solid wastes are shown in Table 1. Clay loam layer of 300 mm. was used to cover the top of each cell to prevent the release of gas through the cover soil layer.

Lysimeter 1 Control

Lysimeter 2 Re-circulation

Lysimeter 3 Re-circulation & Storage

Lysimeter 4 Storage

Figure 1 Schematic of Lysimeter Operations Table 1. Physical and Chemical Characteristics of Solid Wastes

Components Food wastes Plastic Paper Textile Wood Metals Foam & rubber Bone & shell Glass Others

Percentage (%w/w) 41.38 22.33 14.78 6.86 4.83 0.76 0.96 1.11 2.06 4.93

Parameters Moisture content Total solids Volatile solids Ash Carbon Hydrogen Oxygen Nitrogen Phosphorus Sulfur

Value (% w/w) 62.5 37.5 70.1 29.9 38.9 4.4 24.5 1.9 0.21 0.19

2.3 Lysimeter Operations Different experimental conditions were applied in the lysimeters, i.e. 1) conventional landfill operation 2) leachate recirculation once a week. 3) leachate recirculation once a week with internal storage at 50% of waste height and 4) internal storage of leachate at 50% of the waste height w/o recirculation. The lysimeters operated under each condition are referred to hereafter as lysimeter 1, 2, 446


3 and 4 respectively. During the first year experiment (day 1-320), rainwater was added into the lysimeters to simulate wet period for 140 days followed by a dry period. Simulated rainfall (using rainwater) was applied daily on the top cover soil based on average at a rate of 70% that of average rainfall amount in Thailand. In the second year (day 360-620), the amount of rainwater addition to each lysimeter was varied according to actual rainfall data of Bangkok. The third year (day 720-930) was operated to stabilize the waste matrix by providing in-situ aeration to maintain DO in drained leachate at about 1 mg/l. The solid waste and leachate characteristics from the semi-aerobic lysimeters were compared with those operated under anaerobic condition. 2.4 Sample Analysis Solid waste samples were analyzed for their temperature, density, moisture content, field capacity, total and volatile solids and chemical composition. Leachate samples from the lysimeters were collected once a week and analyzed for pH, alkalinity, BOD, COD, VFA, alkalinity, TKN and monitoring of leachate quantities. All analyses were performed according to Standard Methods for the Examination of Water and Wastewater. Gas samples were collected once a week and analyzed for their composition (CO2, O2, N2, CH4) using gas chromatography. 3.0 RESULTS AND DISCUSSION 3.1 Solid Waste Biodegradation in the Lysimeters Physical and chemical compositions of solid waste remained in the lysimeters after three years operations are shown in Table 2. As compared to their initial composition, most of the easily biodegradable waste components disappeared especially food wastes and paper. The majority of remaining materials were plastic (38.53-46.64%) and unidentifiable components (46.93-52.32%). Comparing solid wastes among the lysimeters, it was found that lysimeter 2 with leachate recirculation had highest reduction of volatile solids (VS) from 70.1% to 44.6%. Degree of waste degradation was also varied along the depth, being highest at the bottom of the lysimeter. High VS reduction was also observed in lysimeter 3 and 4 whereas the control lysimeter had lower degree of organic reduction. These observations could be explained by the fact that higher moisture content through leachate recirculation and storage promoted waste biodegradation by accelerating the hydrolysis step in waste stabilization process. In term of waste settlement rate, it was found that the lysimeter 2 with leachate re-circulation had highest settlement of 10.8% followed by lysimeter 3 during the experiment. The major part of settlement took place during rainy season as a result of higher waste degradation in that period. Leachate re-circulation helped promoting the waste settlement by allowing the leaching of hydrolyzed wastes into the bottom part of the lysimeters. The leaching of hydrolyzed wastes created higher porosity within the waste layer and the settlement took place once leachate had been drained out from the lysimeters. The lysimeter 3 and lysimeter 4 with leachate storage had relatively low settlement because their bottom part was under water-saturated condition. 3.2 Leachate Characteristics and Organic Leaching from the Lysimeters Figure 2 shows the variation of BOD, COD, TKN in leachate sampled from the lysimeters. Initial BOD and COD concentrations in leachate were found in a range of 40,000-60,000 mg/l and 40,00070,000 mg/l respectively. High BOD/COD ratio suggested that the leachate was highly biodegradable which is normal for young landfill. TKN concentration in the lysimeters were in the range between 447


2,000-3,500 mg/l. During the operation, BOD and COD in leachate from lysimeter 3 decreased significantly after 200 days of operation whereas TKN was maintained at the same level as the others. These results suggested that the application of leachate re-circulation and storage practice helped stabilizing organic substances in leachate and yielding low pollutant load if leachate were to be discharged from the landfill. BOD/COD ratios in leachate from the lysimeters were 0.51, 0.57, 0.49 and 0.58 respectively. As the operation reached its second years, BOD and COD in leachate from other lysimeters started decreasing at 400 days for lysimeter 2 and 500 days for lysimeter 1 and 4. TKN concentrations also had a similar decreasing trend as BOD and COD, but at much slower rate. They were reduced from 2000-2500 mg/l at the beginning to about 1500 mg/l at the end of the second year period. There was not much difference in term of TKN concentration in leachate among the lysimeters. During the operation, pH of leachate was maintained relatively constant at about 6 in all lysimeters while VFA/Alkalinity were maintaining in a range of 2-3. Further operation of the lysimeters to the third years in which in-situ aeration was supplied yielded slightly lower BOD and COD in leachate from all lysimeters, though not significantly different from those obtained during the latter stage of the second year, but could substantial reduce TKN level to a lower level. This was due to the development of nitrification in the lysimeters. As most of the nitrified nitrogen was denitrified back to nitrogen gas under anoxic condition in the lysimeter, total nitrogen concentration in leachate could be lowered than those operated under complete anaerobic condition. Table 3 shows final leachate characteristics obtained from the lysimeters after 3 years operation. There were not much difference in the characteristics of leachate among the lysimeters. They exhibited the characteristics of stabilized and matured wastes as BOD, COD and TKN were low. Table 2. Physical and Chemical Characteristics of Solid Wastes After 3 Years Operations

Components Physical composition - Food wastes - Paper - Plastic - Textile - Rubber & Foam - Yard wastes - Bone and shell - Glass - Metals - Others Chemical Characteristics - Moisture content - Total solids - Volatile solids - Ash - Carbon - Nitrogen

% by weight Lysimeter2 Lysimeter3

Lysimeter1

Lysimeter4

ND ND 46.41 0.10 0.01 0.99 ND 0.02 0.15 52.32

ND 1.53 46.64 0.07 0.20 2.94 ND ND ND 48.63

ND 0.07 44.92 2.00 3.69 1.00 ND 0.62 ND 47.70

ND 2.16 38.53 3.70 ND 7.28 1.18 0.22 ND 46.93

54.38 45.62 56.01 43.99 31.12 2.0

63.24 36.76 44.56 55.44 24.76 1.0

66.35 33.65 48.64 51.36 27.02 1.0

64.35 35.65 47.99 52.01 26.66 0.7

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Figure 2 Variation of BOD, COD and TKN in Leachate from the Lysimeters

Leaching of organic pollutants in terms of COD and TKN from the lysimeters was evaluated. It was found that the lysimeters with leachate re-circulation had lower COD leaching than the others. It was due to lower organic concentrations remaining in the drained leachate as they became more stabilized during re-circulation. The lysimeters with leachate re-circulation also gradually released organic substances at relatively constant rate over time whereas those without re-circulation flushed off major part of organic load at the beginning of rainy season. The leaching of TKN had similar pattern with those of COD. However, TKN leaching in the lysimeters with leachate re-circulation was found higher in the second year. Table 3. Leachate Characteristics from the Lysimeters

Parameters pH BOD COD NH3-N TKN PO4 EC

Lysimeter1 Range Avg. 7.3-7.8 7.5 23-120 47 120-620 269 92-652 296 187-759 339 4.6-10.3 7.1 3.0-9.8 4.9

Lysimeter2 Range Avg. 7.3-7.8 7.5 58 26-265 178-1060 370 94-735 237 111-1612 304 5.8 1.1-15.3 3.7-17.0 6.7

Remark: Unit in mg/l expect pH (-) and EC (mS/cm)

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Lysimeter3 Range Avg. 7.3-7.9 7.5 22-155 52 314 160-820 123-652 268 140-794 305 3.2-25.7 8.1 3.8-13.9 6.2

Lysimeter4 Range Avg. 7.5 7.2-7.9 65 4-187 207-1560 425 111-1185 295 123-1245 341 2.0-14.0 4.7 3.3-14.1 6.1


COD and TKN mass balance in the lysimeters were determined over 30 weeks during the final year of experiment. It was found that anaerobic lysimeters had 177.1 and 204.7 kg leached out from the lysimeter operated without leachate re-circulation and with leachate re-circulation whereas those from semi-aerobic lysimeters were 262.7 and 337.5 kg in the same period. TKN leached out from the lysimeters were 218.5 and 264.0 kg for anaerobic lysimeters versus 194.4 and 188.0 kg for semiaerobic lysimeters. From these results, it can be concluded that the operation of lysimeters under semiaerobic condition could substantial reduce nitrogen discharge from the lysimeters. 3.3 Gas Production from Solid Waste Biodegradation During the start-up period, methane content in produced gas was gradually increased and remained in the range between 5-20%. It was found that the lysimeter operated with leachate storage (lysimeter 3 and lysimeter 4) has produced slightly higher methane content than the others. As the operation entered the dry period, the methane production in most of the lysimeters has been increased to about 30% but slightly higher in lysimeter 3. It was found that leachate re-circulation in combination with leachate storage could enhance waste biodegradation as it could help retaining high moisture content of wastes, especially during dry period, and improving the biodegradation of solid wastes. Methane content in gas varied according to the rainfall patter during the second year experiment. The methane content in the lysimeter 1 was lowest at about 10%, comparable lower than the others (20-30%). As the operation entered raining period, methane content were raised to 24% in lysimeter 1 and 38% in lysimeter 3. Subsequent operation in dry period lowered methane content to about 13-17%. It is clearly show that rainwater affect the activities of methanogenic bacteria in the lysimeters. The lysimeter operation with re-circulation practice helped increased the moisture content in wastes especially during dry period and enhanced the microbial activities in such period. 3.4 Utilization of Stabilized Waste Matrix for Leachate Treatment Subsequent study was conducted to utilize the stabilized waste matrix for the treatment of fresh leachate from a landfill. The leachate application rate was varied at 10 and 20 L/m3.d. Table 4 shows the summary of experimental results. At leachate application rate of 10 L/m3.d, influent BOD and COD concentrations were 2755-3494 mg/L and 3116-4028 mg/L respectively. Over 9 weeks of experimental period, BOD and COD removal were 95.2-98.0% and 91.5-94.4% for aerobically stabilized wastes. These removal efficiencies were considered higher than those of anaerobically stabilized wastes which used as the control. When the loading was increased to 20 L/m3.d, BOD removal were 98.7% at the beginning but gradually declined to 75% after 9 weeks. It is still higher than that of control case (58.0-81.8%). No TKN removal was observed in both cases. From these Table 4. Organic and Nitrogen Removal from Fresh Leachate by Stabilized Waste Matrix

Conditions @ 10 L/m3.d - BOD (mg/L) - COD (mg/L) @ 20 L/m3.d - BOD (mg/L) - COD (mg/L)

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2755-3494 3116-4028

88-260 300-494

90.0-97.0 84.2-91.3

55-168 209-266

95.2-98.0 91.5-94.4

1153-3256 3520-4475

339-1051 481-1560

58.0-81.8 59.0-89.0

38-661 295-1030

75.0-98.7 73.9-93.4

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results, it can be concluded that the treatment of fresh leachate by stabilized waste matrix was effective in term of organic removal. Nevertheless, nitrogen removal was not possible with this operation technique. 4.0 CONCLUSIONS From the experimental results obtained, the following conclusions can be drawn. 1. Leachate circulation in combination with leachate storage was found to be an effective operating technique for tropical landfill for enhancing solid waste biodegradation. Leachate recirculation enhanced degree of waste degradation in landfill whereas the incorporation of leachate storage reduced organic and nitrogen concentrations and eliminated the discharge of leachate from the landfill. 2. Rainfall intensity and leachate recirculation affected leaching behavior of organic substances from the waste layer. The leaching of organic carbon from the wastes took place much faster than the organic nitrogen. In order to control nitrogen pollution, in-situ aeration at the latter stage helped promoting nitrification and producing leachate with its characteristics similar to those of matured leachate. 3. The utilization of stabilized waste matrix for leachate treatment was found effective. High organic removal was achieved when applying leachate at an appropriate loading rate but no TKN removal was observed. ACKNOWLEDGEMENT This research work is supported by Swedish International Development Cooperation Agency (SIDA) through Asian Regional Research Program on Environmental Technology (ARRPET). REFERENCES Barlaz, M.A., Milke M.W. and Ham R.K., Gas Production Parameters in Sanitary Landfill Simulators, J. Waste Manage. Res., Vol.5, pp.27-39 (1987). Buivid, M.G., Wise D.L. and Blanchet M.J., Fuel Gas Enhancement by Controlled Landfilling of Municipal Solid Waste, J. Resources Conserv., Vol.6, pp.3-20 (1981). Lay, J.J., Li Y.Y. and Noike T., Developments of Bacterial Population and Methanogenic Activity in a Laboratory Scale Landfill Bioreactor, Wat. Res., Vol.32, No.12, pp.3673-3679 (1998). Pohland, F.G., Leachate Recycle as Landfill Management Option, J. of Env. Eng. Div. ASCE, Vol.106, No.EE6, pp.1057-1069 (1980). Reinhart, D.R. and Townsend T.G., Landfill Bioreactor Design and Operation, Lewis Publishers, New York (1998). Stegmann, R. and Ehrig H.J., Enhancement of Gas Production in Sanitary Landfill Sites- Experiences in West Germany, In Resource Recovery from Solid Waste, pp.425-434 (1989). Titlebaum, M.E., Organic Carbon Content Stabilization Through Landfill Leachate Recirculation, J. WPCF, Vol.54, No.5, pp.428-433 (1982).

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