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The aim of this study was to investigate the aerobic and anaerobic degradation of phenol and its derivatives in aerobic and anaerobic landfills. Phenolic compounds were extracted from leachate samples using the solid phase micro-extraction method. In this study, analysis of the 24 phenolic compounds included in the standard mixture and the change in the concentrations over time of 23 of the 24 compounds found in the calibration mix standard were determined in both aerobic and anaerobic landfill reactors. It can be concluded that faster and complete removal of phenol, chlorophenol, dichlorophenols, and trichlorophenol were achieved in the aerobic landfill while aerobic treatment was less effective on tetrachlorophenol and pentachlorophenol. In the anaerobic landfill, anaerobic reductive dechlorination probably occurred from all the highly chlorinated phenols and resulted in the accumulation of phenol and chlorophenol. The phenol could not be further degraded because the anaerobic methanogenic phase did not start during the 150 days of operation in an anaerobic landfill reactor. Nitrophenols can be degraded rapidly under aerobic conditions. These compounds are degraded to amino groups in the first step and then these amino groups are degraded to methane and CO(2) under anaerobic conditions. Although the degradation could not reach the methanogenic phase in anaerobic landfill reactor during the operational period, it is indicated that nitrophenol concentrations decreased in the anaerobic reactor. This is revealed as a result of the formation of the amino groups.

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 (0.25 m3) with different composite liners (R1: 0.10+0.10 m of compacted clay liner (CCL), L(e) = 0.20 m, k(e) = 1 × 10(-8) m/s, R2: 0.002-m-thick damaged high-density polyethylene (HDPE) geomembrane overlying 0.10+0.10 m of CCL, L(e) = 0.20 m, k(e) = 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+0.10 m CCL, L(e) = 0.22 m, k(e) = 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+0.10 m CCL, L(e) = 0.22 m, k(e) = 4.24 × 10(-7) m/s) were simultaneously run for a period of about 540 days 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) m(2)/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 © 2011 Elsevier Ltd. All rights reserved.)

Four identical pilot-scale landfill reactors with different alternative composite liners were simultaneously operated for a period of about 540 days 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 (10 cm+10 cm, k=10(-8)m/sn), R2: Geomembrane (2 mm HDPE)+compacted clay liner (10 cm+10 cm, k=10⁻⁸ m/sn), R3: Geomembrane (2 mm HDPE)+compacted clay liner (10 cm, k=10⁻⁸ m/sn)+bentonite liner (2 cm)+compacted clay liner (10 cm, k=10⁻⁸ m/sn), and R4: Geomembrane (2 mm HDPE)+compacted clay liner (10 cm, k=10⁻⁸ m/sn)+zeolite liner (2 cm)+compacted clay liner (10 cm, 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 © 2011 Elsevier B.V. All rights reserved.)

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 CH(4) potentials of solid wastes during 27 months of landfilling operation in two pilot scale landfill reactors. The initial methane potential of solid wastes filled to the reactors was around 0.347 L/CH(4)/g dry waste, which decreased with operational time of landfill reactors to values of 0.117 and 0.154 L/CH(4)/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 0.01195 1/d, respectively. The correlation between the model and the experimental parameters was more than 95%, showing the good fit of the model.

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.

Leachate and solid waste samples from aerobic and anaerobic simulated landfill reactors operated with and without leachate recirculation were characterized in terms of metals such as Fe, Ca, K, Na, Cd, Cr, Cu, Pb, Ni, and Zn. Metal concentrations of aerobic landfill reactor leachate samples are always below the regulation limits. The higher concentrations in anaerobic landfill leachate samples decreased to regulation limits after the landfill becomes methanogenic. The effect of leachate recirculation is determined in anaerobic landfills more clearly than aerobic landfills. Metal precipitation resulted in a decrease in leachate metal content and an increase in solid waste metal content as expected. Result of the study show that the metal content of landfill leachate samples is not a major concern for both aerobic and anaerobic landfills.

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.

We have monitored non-biodegradable soluble COD of leachates derived from two different landfill test cells, which were constructed at Odayeri Sanitary Landfill and operated with (C2) and without (C1) leachate recirculation for 1080 days. Refuse height and the placement area of test cells were 5m and 1250m(2) (25mx50m), respectively. For leachates of both cells, initial inert soluble COD fraction (f(non)) increased from it is initial value of 0.01 to around 0.1 after 300 days of operation. Due to the development of anaerobic conditions, the value showed an increasing trend and the maximum value of 0.4 was reached on day 600. Several suitable models were also fitted to the experimental data on the basis of statistical reasoning. So as to evaluate the goodness of obtained fits, the calculated values of the sum of squares due to error (SSE), R-square, the residual degrees of freedom (DFE), adjusted R-square, and root mean square errors (RMSE) associated with the model results were compared. Logistic model for C1 test cell and Gompertz model for C2 test cell gave the best fits to the experimental data. Moreover, using the fitted model parameters, pollution loads, and BOD/COD ratios in leachates from C1 (control) and C2 (recirculation) cells were estimated and deeply discussed. The results of the study can be satisfactorily used to predict change in the composition of leachate over time, which may help to obtain better effluent quality in biological treatment of leachate.

Each day approximately 10,000 t of municipal solid wastes (MSW) are being produced in Metropolitan Municipality Area of Istanbul. These wastes are disposed at convenient sanitary landfills. MSWs on the European side are being disposed at Odayeri Sanitary Landfill and this study is carried out at this landfill. Approximately 1.5 ha of landfill area is selected as test area for leachate recirculation and the leachate is recirculated to the wells, which are opened at 14 points, and have 18 m depth, 0.4 m diameter. This research presents a summary of findings from a full-scale sanitary landfill study conducted for the first time in Turkey. It also presents the results of the monitoring data obtained from the test area in Odayeri Sanitary Landfill. It attempts to quantify the effects of leachate recirculation in terms of various stabilization indicators, landfill gas (LFG) composition, leachate analysis, and landfill settlement.