Simulated Bioreactor Landfills Research Articles

Enhancing biogas production from municipal solid waste through recirculation of blended leachate in simulated bioreactor landfills

This study is an attempt to assess biogas production improvement from organic fraction of municipal solid waste in simulated bioreactor landfills through recirculation of blended landfill leachate. In this study, various old and new leachate blends (66.6%New/33.3%Old, 33.3%New/66.6%Old, 100%New and 100%Old) were recirculated through 6 laboratory-scale bioreactors using open-loop and closed-loops modes. Compared with the control bioreactor where 100% new leachate was recirculated and operated as a closed-loop, cumulative biogas production was improved by as much as 77.2 to 193.2% when a leachate blend of 33.3%New/66.6%Old was recirculated. Furthermore, comparison of the results from open-loop and closed-loop operated bioreactors indicated that there was approximately 28.3 to 65.4% more biogas in open-loop bioreactors. The Gompertz model produced a better fit (R2 > 0.99) than first-order and logistic function models. Leachate blending reduced the lag phase by almost half and thus helps in alleviating the ensiling during the start-up phase.

Development of Fuzzylogic model to predict the effects of ZnO nanoparticles on methane production from simulated landfill

Nano-ZnO enters landfills mostly through disposal of cosmetics, sunscreens and catalysts. However, its effects on waste degradation are still unclear. In this paper, a fuzzy-based model is proposed to predict biogas and methane production from simulated bioreactor landfill with and without ZnO nanomaterials. Eight deterministic inputs (pH, RedOx potential, chemical oxygen demand, volatile fatty acids, alkalinity, Zn concentration, Zn background and leachate recirculation flow rate) were identified as antecedent variables. Two outputs, or consequents, were chosen: biogas production rate and methane fraction. Antecedents and consequents were linked by 66 IF-THEN rules, which stated the effects of the input parameters in a linguistic form. The fuzzy model was tested on the data of a lab-scale study simulating a bioreactor landfill with 100mg of added nano-ZnO per kg of dry waste. Experimental results indicated that the addition of nano-ZnO resulted in a reduction of methane generation by about 30%.The fuzzy model showed good performance in the prediction of methane generation; in addition, the comparison with the commonly used Gompertz equation showed that the fuzzy model is more consistent with the data. Fuzzy modelling could easily handle the Zn concentration together with other parameters and it highlighted the importance of including this input in the model. The modelling results confirmed the high potential of fuzzy macro-approach in the modelling of very complex processes taking place in landfill environments under different operating conditions.

Leachate purification of mechanically sorted organic waste in a simulated bioreactor landfill

The bioreactor environment for the mechanically sorted organic fraction (MSOF) of residual municipal solid waste was simulated for a period of 300 days. A closed-loop system was implemented for analysing the leachate purification process due to its recirculation through MSOF. Maximum concentrations of Cu, Zn and Ni in the leachate were about 60, 20 and 15 mg L(-1), whereas Pb and Cr were about 5.5 and 7 mg L(-1). About 60 days from the start of recirculation these concentrations dropped to < 1 mg L(-1). Chemical (COD) and biological oxygen demand (BOD5) dropped, respectively, by about 50 and 80%, achieving a COD-to-BOD5 ratio > 7. Volatile fatty acids, which were about 10 g L(-1), fell to about 3.5 g L(-1) whereas biomethane production was about 34 NL kg TS(-1). As expected, recirculation under strictly anaerobic conditions gave minor benefits in reducing nitrogen and ammonium which reached final concentrations of about 4 and 3.8 g L(-1), respectively.

The behavior and long-term fate of metals in simulated landfill bioreactors under aerobic and anaerobic conditions

The long-term behavior and fate of metals in leachate from four simulated bioreactor landfills were explored using lysimeters under both aerobic and anaerobic conditions for a maximum of 1650 days. Metal concentrations varied with time and stage of landfill activity. The behavior of selected metals (Al, As, Cr, Cu, Fe, Pb, and Zn) significantly differed between aerobic and anaerobic conditions. Leachate from the aerobic lysimeters contained greater concentrations of Al, Cu, and Pb compared to leachate derived from the anaerobic lysimeters (average concentrations of Al, Cu and Pb in the aerobic/anaerobic lysimeters were 8.47/0.78 mg/L, 1.61/0.04 mg/L and 0.10/0.03 mg/L, respectively). In the anaerobic lysimeters, As, Fe and Zn leached at greater concentrations (average concentrations of As, Fe and Zn in the aerobic/anaerobic lysimeters were 0.40/1.14 mg/L, 13.5/136 mg/L and 15.3/168 mg/L, respectively). Though no significant difference in overall Cr concentrations was observed in leachate samples from aerobic and anaerobic lysimeters, during the alkali and methane phases approximately 45% of Cr was presented as Cr(VI) under aerobic conditions, whereas no Cr(VI) was detected under anaerobic conditions.

An innovative combined on-site process for the remote rural solid waste treatment – A pilot scale case study in China

The aim of this study was to find a feasible method for the treatment of solid waste generated in the remote rural, where the transportation costs are prohibitive and the resources to construct and maintain conventional treatment plants are not available. This process, consisted of two types of simulated bioreactor landfill (one was recirculated bioreactor landfill, and the other was comprised of fresh and aged refuse reactor) and a soil infiltration system, was operated in ambient temperature for 180days all together. After treated by the system of fresh and aged refuse reactor, the refuse and leachate reached a strongly degraded and stable state. The remaining leachate can be treated by the soil infiltration system, and 87.5±2.1%, 98.6±1.0% and 95.7±1.7% were achieved by 60cm soil depths for organic matter, ammonium nitrogen and total nitrogen removal, respectively.

Bio-immobilization of Cu and Zn in recirculated bioreactor landfill

To protect the environmental quality of soil, groundwater, and surface water near the landfill site, it is necessary to make an accurate assessment of the heavy metal mobility. This study aims to present the bio-immobilization behavior of heavy metals in landfill and provide some reference suggestion for the manipulation of heavy metal pollution control after closure. Two simulated bioreactor landfill system loaded with real municipal solid waste (MSW), namely, conventional bioreactor landfill (CL) and leachate recirculated bioreactor landfill (RL), were operated. Cu and Zn, the two conventional heavy metals with the highest contents in MSW, were chosen to track the heavy metal bio-immobilization behavior in landfill. The MSW in landfill is a great threat to environment because much of the heavy metal is "hidden" in different components. The weight ratio of Cu and Zn in landfill amounts to 0.00427% and 0.00437%, respectively. The accumulated effluent masses of Cu and Zn in CL increased all along, while they still kept at a stable level after day105 in RL. The microbes like sulfate-reducing bacteria mediate the behavior of Cu and Zn in bioreactor landfill system. Cu and Zn can be bio-immobilized in bioreactor landfill system with leachate recirculation like RL.

Releasing behavior of zinc in recirculated bioreactor landfill

The purpose of this research was to determine the releasing behavior of zinc in municipal solid waste (MSW) in landfill site with respect to refuse and leachate as an inseparable system. Two simulated bioreactor landfills, one with leachate recirculation and the other without, were operated in room temperature for 320 days. Results showed that the content of zinc in MSW could amount to 591.29 ± 31.33-632.14 ± 18.98 µg g − 1 dry weight − 1 (DW − 1 ). It exceeded the set standard for “Environmental quality standard for soil” (≤ 500 µg g − 1 DW − 1 ) and had high potential environmental risk. The releasing behavior of zinc in refuse mainly experienced speciation of solid-Zn, Zn 2+, ZnHCO 3 +, ZnCO 3, Zn(OH) +, Zn(OH) 2, Zn(NH 3) 4 2+, ZnS, etc. Zinc in refuse showed behaviors of staggered migration and retention, which corresponded with the degradation process of refuse in bioreactor landfill. The Zn 2+ concentration in leachate, which varied correspondingly with releasing behavior of zinc in refuse, were 0.75 mg L − 1 to 3.13 mg L − 1 and had no great difference in landfill with different operation modes (CL and RL). However, the amount of Zn 2+ leached out from refuse, which accounted for 28.70 mg and 130.67 mg after 320 day's operation, respectively. More attention should be paid to the inseparable system including refuse and leachate together.

Releasing behavior of copper in recirculated bioreactor landfill

The purpose of this study was to determine the releasing behavior of copper in municipal solid waste (MSW) in landfill with respect to refuse and leachate as an inseparable system. Two simulated bioreactor landfills, one with leachate recirculation and the other without, were operated in room temperature for 320 days. Copper in refuse showed behaviors of staggered migration and retention, which corresponded with the degradation process of landfill obviously. The significant different amounts of Cu 2+ leached out from refuse into leachate of two landfills were 24.74 mg and 118.53 mg after 320 days’ operation, respectively. It also reflected the releasing behavior of copper in landfill refuse at different stage accordingly. The results confirmed that the refuse in landfill had high potential of secondary pollution after closure.

Settlement analysis of fresh and partially stabilised municipal solid waste in simulated controlled dumps and bioreactor landfills

The patterns of settlement of fresh as well as partially stabilised municipal solid waste (MSW), undergoing degradation in five different landfill lysimeters, were studied elaborately. The first two lysimeters, R1 and R2, contained fresh MSW while the other three lysimeters, R3, R4 and R5, contained partially stabilised MSW. R1 and R3 simulated conventional controlled dumps with fortnightly disposal of drained leachate. R2 and R4 simulated bioreactor landfills with leachate recirculation. Fortnightly water flushing was done in R5. Settlement of MSW, monitored over a period of 58 weeks, was correlated with the organic carbon content of leachate and residual volatile matter in the MSW to establish the relationship between settlement and organic destruction. Compressibility parameters such as modulus of elasticity and compression indices were determined and empirical equations were applied for the settlement data. Overall settlements up to 49% were observed in the case of landfill lysimeters, filled with fresh MSW. Landfill lysimeters with liquid addition, in the form of leachate or water, experienced lower primary settlements and higher secondary settlements than conventional fills, where no liquid addition was practised. Modified secondary compression indices for MSW in lysimeters with leachate recirculation and flushing were 30%-44% higher than that for lysimeters where no liquid addition was done. Secondary settlements in bioreactor landfills were found to vary exponentially with time.

Performance and Cost Comparison of a FWS and a VSF Constructed Wetland System

The biodegradation of municipal solid waste (MSW) was investigated in simulated bioreactor landfills under aerobic conditions. The bioreactors were operated to determine Two constructed wetland systems, treating domestic wastewater, are compared in terms of performance and costs. One is a free water surface (FWS) wetland system located in Pompia, Crete, south Greece, and the other one is a vertical subsurface flow (VSF) wetland system located in Gomati, Chalkidiki, north Greece. The FWS system is designed for 1200 p.e. Its construction cost was €305,000, and the capital, operation and maintenance cost was €22.07 p.e.−1 yr−1 or €0.50 m−3 of influent. The VSF system is designed for 1000 p.e. Its construction cost was €410,850, and the capital, operation and maintenance cost was €36.81 p.e.−1 yr−1 or €0.56 m−3 of influent. Both systems achieved high removal rates for BOD5, COD, TSS, TKN, phosphorus, TC, and FC, which makes them ideal for small communities in the Mediterranean region.

Degradation of Municipal Solid Waste in Aerobic Bioreactor Landfills

The biodegradation of municipal solid waste (MSW) was investigated in simulated bioreactor landfills under aerobic conditions. The bioreactors were operated to determine the amount of leachate recirculation and municipal wastewater sludge addition required to optimize waste degradation. The leachate generated was recycled over 47 weeks, leachate samples were collected on a weekly basis and analyzed for pH, biochemical oxygen demand (BOD), chemical oxygen demand (COD), Total Kjeldahl Nitrogen (TKN), and ammonia nitrogen (NH3-N). The temperature of the MSW in the bioreactors was measured on a daily basis. Leachate and sludge were added at the rates of 5 l wk−1 to 15 l wk−1 and 0.5 l wk−1 to 1.5 l wk−1, respectively. Within 27 weeks enhanced MSW degradation was observed at a leachate recirculation rate of 15 l wk−1 (855 mg l−1 of MSW d−1) and sludge addition rate of 1.5 l wk−1 (85 mg l−1 of MSW d−1). During this period, the COD concentration in the leachate dropped significantly. A reduction in the leachate recirculation and sludge addition rate increased the waste stabilization period up to 45 weeks.

Enhancing waste decomposition and methane production in simulated landfill using combined anaerobic reactors

The design of leachate recirculation to enhance municipal solid waste decomposition, methane production and microbial activities was taken into account in this study by using the combined anaerobic reactors of a simulated high organic content landfill reactor and a stabilized fixed film anaerobic reactor. The latter aimed to treat high strength leachate from the simulated landfill reactor before recirculation back to the former reactor. The results showed the possibility to apply this technique to high organic waste landfill where rapid and accumulative acids formed in the leachate were removed and treated by a fixed film anaerobic reactor. In addition, the treated leachate when circulated back to the simulated bioreactor landfill helps accelerate waste decomposition and methane production by providing buffer capacity as well as diluting organic content in the leachate to achieve the favourable conditions for acidogen and methanogen, respectively, to rapidly enter into the methanogenesis phase.

Dissolved organic matter (DOM) in recycled leachate of bioreactor landfill

Landfill leachate needs sufficient treatment before safe disposal. Bioreactor landfill technology could effectively degrade the organic matters in recirculated leachate, hence leaving a leachate stream of low biodegradability. This study characterized the dissolved organic matter (DOM) in the leachate from simulated bioreactor landfill columns with or without presence of trace oxygen. The removal efficiencies of this DOM using coagulation–sedimentation or electrolysis processes were demonstrated. Recirculated leachates were sampled from the simulated landfill columns applying conventional mode, intermittent-aeration mode, and natural aeration mode, whose DOM was fractionated into humic acids (HA), fulvic acids (FA) and hydrophilic fractions (HyI) by the XAD-8 resin combined with the cation exchange resin method. The recirculated leachate had low BOD/COD ratio, high humic substances contents, and high aromatic content. Their HA fraction comprised mainly large molecules (>10 k Da), while the FA and HyI were composed of smaller molecules (<50 k and <4 k Da, respectively). With the presence of oxygen, the TOC contents and the contents of HA, FA and HyI in leachate reduced, with FA and HyI fractions of molecular weight (MW) lower than 4 k Da more readily degraded. The organic matters left in leachates from intermittent-aeration mode and natural aeration mode were of low biodegradability. It was tested in the following sections the effects of coagulation–sedimentation process and of electrolysis process on the removal of residual DOM in recirculated leachate. Coagulation–sedimentation tests revealed that poly ferric sulphate (PFS) could remove more COD (58.1%) from leachate than polyaluminum chloride (PACl) (22.9%), particularly on the HA fraction with MW>10 k Da. Coagulation–sedimentation could not remove most of HyI in leachate. Furthermore, the corresponding BOD/COD ratio was not improved through coagulation. Electrolysis test could also effectively removed HA of MW>10 k Da. However, the biodegradability of treated effluent considerably was improved. The electrolysis could decompose high MW substances and increase biodegradability of recirculated leachate from bioreactor landfill.