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Abstract: The main goal of this study was to present a comparison of landfill performance with respect to solids decomposition. Biochemical methane potential (BMP) test was used to determine the initial and the remaining CH4 potentials of solid wastes during 27months of landfilling operation in two pilot scale landfill reactors. The initial methane potential of solid wastes filled to the reactors was around 0.347L/CH4/g dry waste, which decreased with operational time of landfill reactors to values of 0.117 and 0.154L/CH4/g dry waste for leachate recirculated (R1) and non-recirculated (R2) reactors, respectively. Results indicated that the average rate constant increased by 32% with leachate recirculation. Also, the performance of the system was modeled using the BMP data for the samples taken from reactors at varying operational times by MATLAB program. The first-order rate constants for R1 and R2 reactors were 0.01571 and 0.011951/d, respectively. The correlation between the model and the experimental parameters was more than 95%, showing the good fit of the model. [Copyright &y& Elsevier]

Abstract: One of the most important problems with designing and maintaining a landfill is managing leachate that generated when water passes through the waste. In this study, leachate samples taken from aerobic and anaerobic landfill reactors operated with and without leachate recirculation are investigated in terms of biodegradable and non-biodegradable fractions of COD. The operation time is 600 days for anaerobic reactors and 250 days for aerobic reactors. Results of this study show that while the values of soluble inert COD to total COD in the leachate of aerobic landfill with leachate recirculation and aerobic dry reactors are determined around 40%, this rate was found around 30% in the leachate of anaerobic landfill with leachate recirculation and traditional landfill reactors. The reason for this difference is that the aerobic reactors generated much more microbial products. Because of this condition, it can be concluded that total inert COD/total COD ratios of the aerobic reactors were 60%, whereas those of anaerobic reactors were 50%. This study is important for modeling, design, and operation of landfill leachate treatment systems and determination of discharge limits. [Copyright &y& Elsevier]

In this study, the effect of leachate recirculation on aerobic and anaerobic degradation of municipal solid wastes is determined by four laboratory-scale landfill reactors. The options studied and compared with the traditional anaerobic landfill are: leachate recirculation, landfill aeration, and aeration with leachate recirculation. Leachate quality is regularly monitored by the means of pH, alkalinity, total dissolved solids, conductivity, oxidation–reduction potential, chloride, chemical oxygen demand, ammonia, and total Kjeldahl nitrogen, in addition to generated leachate quantity. Aerobic leachate recirculated landfill appears to be the most effective option in the removal of organic matter and ammonia. The main difference between aerobic recirculated and non-recirculated landfill options is determined at leachate quantity. Recirculation is more effective on anaerobic degradation of solid waste than aerobic degradation. Further studies are going on to determine the optimum operational conditions for aeration and leachate recirculation rates, also with the operational costs of aeration and recirculation. [Copyright &y& Elsevier]

Abstract: In this study we present a neural network model for predicting the methane fraction in landfill gas originating from field-scale landfill bioreactors. Landfill bioreactors were constructed at the Odayeri Sanitary Landfill, Istanbul, Turkey, and operated with (C2) and without (C1) leachate recirculation. The refuse height of the test cell was 5m, with a placement area of 1250m2 (25m×50m). We monitored the leachate and landfill gas components for 34 months, after which we modeled the methane fraction in landfill gas from the bioreactors (C1 and C2) using artificial neural networks; leachate components were used as input parameters. To predict the methane fraction in landfill gas as a final product of anaerobic digestion, we used input parameters such as pH, alkalinity, Chemical Oxygen Demand, sulfate, conductivity, chloride and waste temperature. We evaluated the anaerobic conversion efficiencies based on leachate characteristics during different time periods. We determined the optimal architecture of the neural network, and advantages, disadvantages and further developments of the network are discussed. [Copyright &y& Elsevier]

Abstract: One-dimensional (1D) advection–dispersion transport modeling was conducted as a conceptual approach for the estimation of the transport parameters of fourteen different phenolic compounds (phenol, 2-CP, 2-MP, 3-MP, 4-MP, 2-NP, 4-NP, 2,4-DNP, 2,4-DCP, 2,6-DCP, 2,4,5-TCP, 2,4,6-TCP, 2,3,4,6-TeCP, PCP) and three different inorganic contaminants (Cu, Zn, Fe) migrating downward through the several liner systems. Four identical pilot-scale landfill reactors (0.25m3) with different composite liners (R1: 0.10+0.10m of compacted clay liner (CCL), Le =0.20m, ke =1×10−8 m/s, R2: 0.002-m-thick damaged high-density polyethylene (HDPE) geomembrane overlying 0.10+0.10m of CCL, Le =0.20m, ke =1×10−8 m/s, R3: 0.002-m-thick damaged HDPE geomembrane overlying a 0.02-m-thick bentonite layer encapsulated between 0.10+0.10m CCL, Le =0.22m, ke =1×10−8 m/s, R4: 0.002-m-thick damaged HDPE geomembrane overlying a 0.02-m-thick zeolite layer encapsulated between 0.10+0.10m CCL, Le =0.22m, ke =4.24×10−7 m/s) were simultaneously run for a period of about 540days to investigate the nature of diffusive and advective transport of the selected organic and inorganic contaminants. The results of 1D transport model showed that the highest molecular diffusion coefficients, ranging from 4.77×10−10 to 10.67×10−10 m2/s, were estimated for phenol (R4), 2-MP (R1), 2,4-DNP (R2), 2,4-DCP (R1), 2,6-DCP (R2), 2,4,5-TCP (R2) and 2,3,4,6-TeCP (R1). For all reactors, dispersion coefficients of Cu, ranging from 3.47×10−6 m2/s to 5.37×10−2 m2/s, was determined to be higher than others obtained for Zn and Fe. Average molecular diffusion coefficients of phenolic compounds were estimated to be about 5.64×10−10 m2/s, 5.37×10−10 m2/s, 2.69×10−10 m2/s and 3.29×10−10 m2/s for R1, R2, R3 and R4 systems, respectively. The findings of this study clearly indicated that about 35–50% of transport of phenolic compounds to the groundwater is believed to be prevented with the use of zeolite and bentonite materials in landfill liner systems. [Copyright &y& Elsevier]

Abstract: Four identical pilot-scale landfill reactors with different alternative composite liners were simultaneously operated for a period of about 540days to investigate and to simulate the migration behaviors of phenolic compounds (phenol, 2-CP, 2-MP, 3-MP, 4-MP, 2-NP, 4-NP, 2,4-DNP, 2,4-DCP, 2,6-DCP, 2,4,5-TCP, 2,4,6-TCP, 2,3,4,6-TeCP, PCP) and heavy metals (Pb, Cu, Zn, Cr, Cd, Ni) from landfill leachate to the groundwater. Alternative landfill liners of four reactors consist of R1: Compacted clay liner (10cm+10cm, k=10−8 m/sn), R2: Geomembrane (2mm HDPE)+compacted clay liner (10cm+10cm, k=10−8 m/sn), R3: Geomembrane (2mm HDPE)+compacted clay liner (10cm, k=10−8 m/sn)+bentonite liner (2cm)+compacted clay liner (10cm, k=10−8 m/sn), and R4: Geomembrane (2mm HDPE)+compacted clay liner (10cm, k=10−8 m/sn)+zeolite liner (2cm)+compacted clay liner (10cm, k=10−8 m/sn). Wastes representing Istanbul municipal solid wastes were disposed in the reactors. To represent bioreactor landfills, reactors were operated by leachate recirculation. To monitor and control anaerobic degradation in the reactors, variations of conventional parameters (pH, alkalinity, chloride, conductivity, COD, TOC, TKN, ammonia and alcaly metals) were also investigated in landfill leachate samples. The results of this study showed that about 35–50% of migration of organic contaminants (phenolic compounds) and 55–100% of migration of inorganic contaminants (heavy metals) to the model groundwater could be effectively reduced with the use of bentonite and zeolite materials in landfill liner systems. Although leachate contaminants can reach to the groundwater in trace concentrations, findings of this study concluded that the release of these compounds from landfill leachate to the groundwater may potentially be of an important environmental concern based on the experimental findings. [Copyright &y& Elsevier]

Abstract: In this study, characterization and electrocoagulative treatability of nanofiltration concentrate from a full-scale landfill leachate treatment plant (Istanbul, Turkey) were investigated. The average concentrations of COD, TKN and ammonia were determined as 6200, 587.5, and 110mg/L, respectively. Membrane concentrate also have almost neutral pH, high conductivity and color. Besides, nanofiltration concentrate contains low metal concentrations. After the characterization of the concentrate, treatment of the concentrate by electrocoagulation method with aluminum plate electrodes was investigated. The effects of electrode type, current intensity and treatment time on the treatment of nanofiltration concentrate by EC process were investigated. According to the results, the most acceptable current intensity for COD, color, and phosphorus removal was determined to be 15.9mA/cm2 and the most acceptable treatment time was determined to be 30min. The treatment efficiencies for COD, color, and phosphorus at 15.9mA/cm2 and 30min were determined as 45%, 60%, and 91.8%, respectively. According to the results of this study, EC process may be an acceptable solution for the treatment of leachate nanofiltration concentrate. More detailed studies however need to be done for the determination of the optimum operational parameters of the electrocoagulative treatment of membrane concentrate. [ABSTRACT FROM AUTHOR]