Refuse Decomposition Research Articles

Impact of low temperature on ex situ nitritation/in situ denitritation in field pilot-scale landfill for postclosure care of leachate treatment and gas content.

Leachates and landfill gas (LFG) are the major problems for closed landfills (CL) and cause significant threats to receiving waterbody and ambient air quality. In this study, a field pilot-scale CL with ex situ nitritation/in situ denitritation process was constructed and operated continuously under wide temperature variations. The effect of low temperature on leachate treatment, and LFG content was studied. Results showed that the combined process can efficiently remove nitrogen and organic matters from leachate, and change LFG content under low-temperature condition. In the ex situ nitritaion, maximum removal efficiencies of ammonia and chemical oxygen demand (COD) were over 99% and 85%, respectively. The loading rate of nitrogen and COD reached 0.5kgNm-3 d-1 and 0.7kg COD m-3 d-1, respectively. The inhibitions of free ammonia (FA) and free nitrous acid (FNA), and low temperature were the key factors affecting nitritation. With recirculating nitrified leachate, total oxidized nitrogen (TON) was completely reduced, and the refuse decomposition was accelerated. Denitritation was the main reaction responsible in the CL. Additionally, methane content was observed lowly at non-inhibitory TON loading rate of 5.8±3.7gN ton-1 TS d-1. This decrease was not caused by the increased of TON loading, but a carbon source competition by denitrificans. The estimated COD consumption and methane reduction were 55.0kg d-1 by TON reduction, and 20m3 d-1, respectively. Hence, this study served a potential strategy for postclosure care of landfills under low temperature variation.

Metagenomic analysis of antibiotic resistance genes (ARGs) during refuse decomposition

Landfill is important reservoirs of residual antibiotics and antibiotic resistance genes (ARGs), but the mechanism of landfill application influence on antibiotic resistance remains unclear. Although refuse decomposition plays a crucial role in landfill stabilization, its impact on the antibiotic resistance has not been well characterized. To better understand the impact, we studied the dynamics of ARGs and the bacterial community composition during refuse decomposition in a bench-scale bioreactor after long term operation (265d) based on metagenomics analysis. The total abundances of ARGs increased from 431.0ppm in the initial aerobic phase (AP) to 643.9ppm in the later methanogenic phase (MP) during refuse decomposition, suggesting that application of landfill for municipal solid waste (MSW) treatment may elevate the level of ARGs. A shift from drug-specific (bacitracin, tetracycline and sulfonamide) resistance to multidrug resistance was observed during the refuse decomposition and was driven by a shift of potential bacteria hosts. The elevated abundance of Pseudomonas mainly contributed to the increasing abundance of multidrug ARGs (mexF and mexW). Accordingly, the percentage of ARGs encoding an efflux pump increased during refuse decomposition, suggesting that potential bacteria hosts developed this mechanism to adapt to the carbon and energy shortage when biodegradable substances were depleted. Overall, our findings indicate that the use of landfill for MSW treatment increased antibiotic resistance, and demonstrate the need for a comprehensive investigation of antibiotic resistance in landfill.

Leachate recirculation between alternating aged refuse bioreactors and its effect on refuse decomposition

In a sequencing batch bioreactor landfill system which combined a fresh and an aged refuse bioreactor, blockage occurred frequently in the aged refuse bioreactor during the treatment of leachate from the fresh refuse bioreactor. To overcome this problem, another aged refuse bioreactor was added, when blockage occurred, the two aged refuse bioreactor operated alternatively. A fresh refuse bioreactor F combined with two alternating aged refuse bioreactors A1 and A2 was called alternate recirculation process (ARP) in this study. The bioreactor system was operated in three stages, and the three bioreactors were exposed to air to facilitate surface re-aeration. The effect of the ARP on the accelerated degradation of fresh refuse was compared before and after blockage occurs in A1. The results indicated that ARP can improve the leachate production rate. The average daily net production rates of leachate in Stages 2 and 3 were approximately 2.1 and 1.6 mL (kg refuse d)−1, respectively, which exceeded that of Stage 1 (1.3 mL (kg refuse d)−1). The chemical oxygen demand and NH3–N concentrations of the leachate from Stage 1 are 1000 and 25 mg L−1 after 2.1 and 2.7 y, respectively. For Stages 2 and 3, these concentrations reach approximately after 0.877 and 1.3 y. Faster refuse settlement was observed in Stages 2 and 3, with an average daily settlement of ∼0.11%, as compared with Stage 1 (∼0.099%). ARP can accelerate the biodegradation of the fresh refuse and overcome the problem of the blockage in the aged refuse reactor.

Comparison of Bacteria and Archaea communities in municipal solid waste, individual refuse components, and leachate

Refuse decomposition in landfills is a microbially mediated process that occurs primarily under anaerobic conditions. Because of limited moisture conditions, hydraulic transport as a means of cellular translocation within the landfill appears limited, especially during the initial stages of decomposition. Thus, microbial communities within the incoming refuse serve as a primary source of facultative and obligate anaerobic microorganisms that initiate refuse decomposition. Fresh residential refuse was collected five times over 26 months, and microbial communities in these samples were compared with those in individual refuse components and decomposed refuse. Bacterial and archaeal community structures were determined using T-RFLP. The Bacterial microbial community richness was correlated (r(2) = 0.91) with seasonal differences in ambient air temperature. Analysis of the results shows that fresh refuse is most likely not the source of methanogens in landfills. Microbial communities in the solid and leachate phases were different, indicating that both matrices must be considered when characterizing microbial diversity within a landfill.

Effect of Spatial Differences in Microbial Activity, pH, and Substrate Levels on Methanogenesis Initiation in Refuse

The initiation of methanogenesis in refuse occurs under high volatile fatty acid (VFA) concentration and low pH (5.5 to 6.25), which generally are reported to inhibit methanogenic Archaea. One hypothesized mechanism for the initiation of methanogenesis in refuse decomposition is the presence of pH-neutral niches within the refuse that act as methanogenesis initiation centers. To provide experimental support for this mechanism, laboratory-scale landfill reactors were operated and destructively sampled when methanogenesis initiation was observed. The active bacterial and archaeal populations were evaluated using RNA clone libraries, RNA terminal restriction fragment length polymorphism (T-RFLP), and reverse transcription-quantitative PCR (RT-qPCR). Measurements from 81 core samples from vertical and horizontal sections of each reactor showed large spatial differences in refuse pH, moisture content, and VFA concentrations. No pH-neutral niches were observed prior to methanogenesis. RNA clone library results showed that active bacterial populations belonged mostly to Clostridiales, and that methanogenic Archaea activity at low pH was attributable to Methanosarcina barkeri. After methanogenesis began, pH-neutral conditions developed in high-moisture-content areas containing substantial populations of M. barkeri. These areas expanded with increasing methane production, forming a reaction front that advanced to low-pH areas. Despite low-pH conditions in >50% of the samples within the reactors, the leachate pH was neutral, indicating that it is not an accurate indicator of landfill microbial conditions. In the absence of pH-neutral niches, this study suggests that methanogens tolerant to low pH, such as M. barkeri, are required to overcome the low-pH, high-VFA conditions present during the anaerobic acid phase of refuse decomposition.

Dynamic Properties of Municipal Solid Waste in Bioreactor Landfills with Degradation

Bioreactor landfills are operated to enhance refuse decomposition, gas production, and waste stabilization. The major aspect of bioreactor landfill operation is the recirculation of collected leachate back through the refuse mass. Due to the presence of additional leachate and accelerated decomposition, the characteristics of Municipal Solid Waste (MSW) in bioreactor landfills are expected to change. About 50% of the continental United States comes under the designated seismic impact zone. The federal regulations have focused increase attention on seismic design of solid waste fills, and have mandated that the solid waste landfills located in the seismic impact zones should be designed to resist the earthquake. Accordingly, assessment of dynamic properties of landfills is one of the major geotechnical tasks in landfill engineering. In order to understand the changes in dynamic properties of bioreactor waste mass with time and decomposition, four small scale bioreactor landfills were simulated in laboratory and samples were prepared to represent each phase of decomposition. The state of decomposition was quantified by methane yield, pH, and volatile organic content (VOC). A number of Resonant Column (RC) tests were performed to evaluate the dynamic properties (stiffness and damping) of MSW. The test results indicated that the normalized shear modulus reduction and damping curves are significantly affected by the degree of decomposition. The shear modulus increased from 2.11 MPa in Phase I to 12.56 MPa in Phase IV. The increase was attributed to the breakdown of fibrous nature of solid waste particles as it degrades. Therefore, considering MSW properties to be uniform throughout the bioreactor landfill is not a reasonable assumption and the shear modulus reduction curves should be evaluated based on the degree of MSW decomposition, rather than the sample composition itself.

Effect of an acidic and readily-biodegradable non-hazardous industrial process waste on refuse decomposition

Non-hazardous industrial process wastes are receiving increased interest from landfill owners, especially with respect to bioreactor operation. These wastes could benefit bioreactors as they represent sources of liquid, nutrients, and/or substrate as well as revenue. However, landfill operators should exercise caution in accepting these wastes, as some could have detrimental effects on refuse decomposition. In this research, the use of laboratory-scale tests to evaluate the effect of one such waste on refuse decomposition is demonstrated. The waste evaluated, referred to as burnt sugar, is an acidic byproduct of corn-based polylactic acid production and represents a source of readily-biodegradable carbon. Lactic acid was the primary constituent of the BS at 0.73 g/g and the COD was measured at 1230 mg COD/g. Testing protocols were adapted to address the specific concerns surrounding the material. Abiotic dissolution tests conducted at mesophilic temperatures indicated that the majority of the waste dissolved into leachate recirculated over a layer of the waste within several days. Abiotic mixing tests suggested that the waste would acidify refuse to pH 6.41 at a loading of 21.9 g/dry kg refuse. However, in biologically active tests, the refuse was able to convert loadings as high as 196.7 g/dry kg refuse to methane. As the loadings increased toward and beyond this level, pronounced detrimental effects to the refuse ecosystem were observed, including a decrease in pH, accumulation of volatile fatty acids and COD, and lag in methane production. The results suggested that actively decomposing refuse has the potential to attenuate relatively high loading of a rapidly degradable but acidic substrate. Nonetheless, caution in the implementation of a field program to accept rapidly biodegradable acidic wastes is critical.

Effect of biosolids on refuse decomposition and phosphorus cycling

Laboratory-scale reactors containing mixtures of municipal solid waste and wastewater treatment biosolids were monitored to assess the effect of biosolids on refuse decomposition and on phosphorus (P) cycling and speciation among orthophosphate, acid-hydrolysable P, and organic P. The co-disposal of 10 to 20% (by wet weight) aerobically-digested biosolids with residential refuse was compatible with refuse decomposition although the biosolids did not increase either the maximum methane production rate or the cumulative yield, and did not reduce lag times to the onset of methane production. The results of this study indicated that dissolved reactive phosphorus (DRP) was the dominant dissolved P fraction throughout refuse decomposition and that it was negatively correlated with the methane production rate and pH (r² = 0.35 for both). P was not found to limit methane production. Biosolids increased dissolved P as well as ammonia-N in some reactors, but this did not have a significant impact on maximum methane production rates. The maximum tolerated Na+ and K+ concentrations during active methane production were at least 4100 mg Na+ L⁻¹ and 800 mg K+ L⁻¹, respectively.

Stability Analyses of Municipal Solid Waste Landfills with Decomposition

A bioreactor landfill is operated to enhance refuse decomposition, gas production, and waste stabilization. Some of the potential advantages of bioreactor include rapid stabilization of waste, increased landfill gas generation, gain in landfill space, enhanced leachate treatment, and reduced post closure maintenance period. Due to the accelerated decomposition and settlement of solid waste, bioreactor landfills are gaining popularity as an alternative to the conventional Subtitle D landfills. However, the addition of leachate to accelerate the decomposition changes the physical and engineering characteristic of waste and therefore affects the geotechnical characteristics of waste mass. The changes in the physical and mechanical characteristics of solid waste with time and decomposition are expected to affect the shear strength of waste mass. The objective of this paper is to analyze the stability of solid waste slopes within the bioreactor landfills, as a function of time and decomposition. The finite element program PLAXIS is used for numerical modeling of bioreactor landfills. Stability analysis of bioreactor landfills was also performed using limit equilibrium program STABL. Finally the results from finite element program PLAXIS and limit equilibrium program STABL are compared. GSTABL predicted a factor of safety of more than 1 in all the cases analyzed, whereas PLAXIS predicted a factor of safety of less than 1 at advanced stages for a slope of 2:1. However, the interface failures between solid waste and landfill liners have not been considered in this paper.

Degradation of Refuse in Hybrid Bioreactor Landfill

To explore the process of refuse decomposition in hybrid bioreactor landfill. The bioreactor landfill was operated in sequencing of facultative-anaerobic and aerobic conditions with leachate recirculation, pH, COD, and ammonia in the leachate and pH, biodegradable organic matter (BDM), and cation exchange capacity (CEC) in refuse were detected. CEC increased gradually with the degradation of refuse, which was negatively correlated with BDM. COD and ammonia in the leachate was declined to 399.2 mg L(-1) and 20.6 mg N L(-1), respectively, during the 357-day operation. The respective concentrations of ammonia and COD were below the second and the third levels of current discharge standards in China. The refuse is relatively stable at the end of hybrid bioreactor landfill operation. Most of the readily biodegradable organic matter is mineralized in the initial phase of refuse degradation, whereas the hard-biodegradable organic matter is mainly humidified in the maturity phase of refuse degradation.

The effects of daily cover soils on shear strength of municipal solid waste in bioreactor landfills

Bioreactor landfills are operated to enhance refuse decomposition, gas production, and waste stabilization. The major aspect of bioreactor landfill operation is the recirculation of collected leachate back through the refuse mass. Due to the accelerated decomposition and settlement of solid waste, bioreactor landfills are gaining popularity as an alternative to the conventional landfill. The addition or recirculation of leachate to accelerate the waste decomposition changes the geotechnical characteristics of waste mass. The daily cover soils, usually up to 20-30% of total MSW volumes in the landfill, may also influence the decomposition and shear strength behavior of MSW. The objective of this paper is to study the effects of daily covers soils on the shear strength properties of municipal solid waste (MSW) in bioreactor landfills with time and decomposition. Two sets of laboratory-scale bioreactor landfills were simulated in a laboratory, and samples were prepared to represent different phases of decomposition. The state of decomposition was quantified by methane yield, pH, and volatile organic content (VOC). Due to decomposition, the matrix structure of the degradable solid waste component was broken down and contributed to a significant decrease in the reinforcing effect of MSW. However, the daily cover soil, a non-degradable constituent of MSW, remains constant. Therefore, the interaction between daily cover soil particles and MSW particles will affect shear strength behavior. A number of triaxial tests were performed to evaluate the shear strength of MSW. The test results indicated that the shear strength of MSW was affected by the presence of cover soils. The friction angle of MSW with the presence of cover soil is higher than the friction angle of MSW without any cover soils. The friction angle of MSW increased from 27 degrees to 30 degrees due to the presence of cover soils for Phase 1 samples. The increased strength was attributed to the friction nature of sandy soil that was used as daily covers soils. Therefore, the effects of cover soils on the shear strength properties of MSW should be evaluated and taken into consideration during stability analyses and design.

Shear Strength Parameters of Municipal Solid Waste with Leachate Recirculation

The objective of this study was to characterize relative changes in waste shear strength parameters during waste decomposition. Twelve direct shear tests ( 100 mm diameter by 50 mm thickness) were performed on waste specimens ranging from fresh to well-decomposed residential refuse. In addition, nine direct shear tests were performed on selected waste components including fresh paper, partially decomposed refuse, and plastics. Results indicate that the friction angle of refuse decreased with decomposition. As refuse decomposed, the plastic content increased, which contributed to a decrease in friction angle as the friction angle of plastics is 18– 19∘ as compared to 33° for fresh shredded waste. The extent of refuse decomposition was characterized by the cellulose plus hemicellulose to lignin ratio [(C+H)∕L] . The measured friction angle decreased from 32 to 24° as (C+H)∕L decreased from 1.29 to 0.25. The shearing pattern for decomposed refuse showed a peak, followed by residual, which was then followed b...

Biodegradation of Chlorinated Solvents in Bioreactor Landfills

The objective of this research is to investigate the intrinsic biodegradation potential of the municipal solid waste (MSW) landfill ecosystem for chlorinated aliphatic hydrocarbons (CAHs). The research was conducted in two complementary systems: simulated landfill bioreactors and batch degradation experiment in serum bottles. Refuse samples excavated from a MSW landfill were tested in laboratory bioreactors operated with leachate recirculation and gas collection. Tetrachloroethene (PCE) and trichloroethene (TCE) were added to reactors and maintained at 20 μM each in leachate to simulate the long-term exposure of refuse microorganisms to CAHs in landfills. Anaerobic microbial cultures were derived from reactors at two different stages of refuse decomposition: active refuse decomposition stage representing young landfills and maturation phase representing aged landfills. These cultures were tested in serum bottles for their abilities to biodegrade target CAHs. Results of this study show that MSW landfills have an intrinsic reductive dechlorination capacity for PCE and TCE. The decomposition of refuse also enhanced reductive dechlorination in this study. This research suggests the potential to develop engineering strategies to promote chlorinated solvent degradation concurrently with refuse decomposition in MSW landfills.

Effect of leachate recirculation on refuse decomposition rates at landfill site: a case study

In this study, a comparison of methane (CH4) generation rates for two test cells, one operated with (enhanced) and another without leachate recirculation at Odayeri Sanitary Landfill were compared using their bio-chemical methane potentials (BMP). Initial methane potential is approximately 34.5 m³ CH4/wet ton of solid waste. The remaining methane potential for the control (C1) and the enhanced (C2) cells are 32.6 m³ CH4/wet ton and 31.1 m³ CH4/wet ton of refuse after eight months of operation, respectively. The produced CH4 quantities for C1 and C2 after eight months of operation are 1.9 m³ CH4/wet ton and 3.4 m³ CH4/wet ton, respectively. On the other hand, 5.5% and 9.9% of the total potential are generated in eight months. However, the CH4 generation rates for the first year are determined as 2.85 and 5.10 m³/ton/year for C1 and C2 test cells, respectively. Due to the appropriate conditions such as moisture content, solid waste decomposition rate is enhanced at a rate of 79% at C2 test cell relative to C1 test cell. Hence, C2 test cell shows more decomposition relative to the C1 test cell.

Relationship of Compressibility Parameters to Municipal Solid Waste Decomposition

Recently, there has been substantial interest in the enhancement of refuse decomposition in landfills, which results in increased settlement. In this paper, changes in waste compressibility as a function of the state of decomposition are reported. Samples representative of residential refuse were decomposed under conditions designed to simulate decomposition in both control and bioreactor landfills. Twenty four one-dimensional oedometer tests (63.5 mm cell) were performed on refuse prepared in laboratory-scale reactors for measurement of primary (Cc) and secondary (Cαi, representing creep, and Cβi, representing biological) compression indices. The state of decomposition was quantified by the methane yield and the cellulose (C) plus hemicellulose (H) to lignin (L) ratio. The magnitude of compressibility was shown to increase as refuse decomposed and compressibility parameters were correlated with the state of decomposition. Initial settlement increased with decreasing (C+H)/L ratio while the creep index was fairly independent of the state of decomposition. The coefficients of primary compression (Cc) for bioreactor samples showed an increasing trend with decreasing (C+H)/L ratios. Cc increased from 0.16 to 0.36 as (C+H)/L decreased from 1.29 to 0.25, and similar values of Cc were obtained with control samples at similar (C+H)/L ratios. The creep index range was estimated at 0.02–0.03 for control and bioreactor samples in various states of decomposition. The magnitude of the biological degradation index (Cβi) depended on the degradation phase with the highest value of 0.19 obtained during the phase of accelerated methane production. Proposing a single Cc for landfill settlement calculations may lead to inaccurate predictions. Properties of each waste sublayer will change as a function of the decomposition stage, and dominating processes with appropriate compressibility parameters should be applied to individual sublayers.

Nitrogen management in bioreactor landfills

One scenario for long-term nitrogen management in landfills is ex situ nitrification followed by denitrification in the landfill. The objective of this research was to measure the denitrification potential of actively decomposing and well decomposed refuse. A series of 10-l reactors that were actively producing methane were fed 400 mg NO 3-N /l every 48 h for periods of 19–59 days. Up to 29 nitrate additions were either completely or largely depleted within 48 h of addition and the denitrification reactions did not adversely affect the leachate pH. Nitrate did inhibit methane production, but the reactors recovered their methane-producing activity with the termination of nitrate addition. In well decomposed refuse, the nitrate consumption rate was reduced but was easily stimulated by the addition of either acetate or an overlayer of fresh refuse. Addition of acetate at five times the amount required to reduce nitrate did not lead to the production of NH 4 + by dissimilatory nitrate reduction. The most probable number of denitrifying bacteria decreased by about five orders of magnitude during refuse decomposition in a reactor that did not receive nitrate. However, rapid denitrification commenced immediately with nitrate addition. This study shows that the use of a landfill as a bioreactor for the conversion of nitrate to a harmless byproduct, nitrogen gas, is technically viable.

Refuse Decomposition in the Presence and Absence of Leachate Recirculation

A side by side comparison of two 8,000 metric ton test cells was performed to evaluate the effects of leachate recirculation on refuse decomposition at Yolo County, CA. After about 3 years of operation, refuse was excavated in three borings from the enhanced cell (E1, E2, and E3) and two borings from the control cell (C1 and C2). Refuse moisture content data show that leachate recirculation resulted in an increase in refuse moisture content, but also show that the refuse in the enhanced cell was not uniformly wet. The average moisture content in E1, E2, and E3 was 38.8, 31.7, and 34.8%, respectively, while the average moisture content in C1 and C2 was 14.6 and 19.2%, respectively. Leachate recirculation resulted in both higher methane yields, (63.1 versus 27.9 L CH4/wet-kg over 1231 days) and increased settlement (15.5% versus 3% of the waste thickness). The extent of decomposition of excavated refuse samples was determined by the biochemical methane potential (BMP) and the ratio of cellulose plus hemicel...

Temporal variation of leachate quality in seawater saturated fills

Many waste fills are located along the coast, often encroaching into the sea, and are consequently subjected to seawater intrusion. Although previous investigations have demonstrated the beneficial effects of moisture addition on biodegradation processes, these studies have not considered the potential effects of seawater intrusion into a sea fill. In this study, a preliminary laboratory-scale experiment was conducted to evaluate the potential effects of seawater intrusion on biodegradation processes and leachate quality. Chemical analysis was performed on leachate samples for a period of 230 days to study the temporal variation of leachate quality in the early stages of refuse decomposition. Leachate samples were collected weekly and several parameters were monitored including pH, COD, TOC, TDS, EC, chlorides, sulfates, orthophosphates, nitrates, ammoniacal nitrogen, hardness, and heavy metals. Chemical concentration levels were related to biological activity within the test cells, and the results indicate that salt water could delay MSW biodegradation.

Production of non-methane organic compounds during refuse decomposition in a laboratory-scale landfill

The presence of non-methane organic compounds (NMOCs) in landfill gas is well documented. However, there is little understanding of the degree to which the production of NMOCs should be attributed to the volatilization of household hazardous waste as opposed to intermediates of the anaerobic decomposition of the major cellulosic components of municipal solid waste. The objectives of this study were: (1) to compare the NMOC yields for decomposed refuse, fresh residential refuse, and a synthetic refuse; and (2) to evaluate the source of NMOCs emitted during refuse decomposition. Replicate 2-1 reactors were filled with shredded residential refuse expected to contain household hazardous waste, synthetic refuse containing no hazardous constituents, and control reactors with decomposed refuse only. Anaerobic decomposition of each refuse was initiated with a seed of decomposed refuse, and the reported methane and NMOC yields were corrected for that attributable to the seed. The NMOC yields from the seed, synthetic refuse, and residential refuse were comparable (0.62 to 1.01 X 10-4 g NMOC (dry g)-1, suggesting that the volatilization of hazardous organic compounds is not the sole source of NMOCs in landfill gas and that anaerobic biodegradation intermediates also contribute to NMOCs.

Production of non-methane organic compounds during refuse decomposition in a laboratory-scale landfill

The presence of non-methane organic compounds (NMOCs) in landfill gas is well documented. However, there is little understanding of the degree to which the production of NMOCs should be attributed ...