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Copyright of Sigma: Journal of Engineering & Natural Sciences / Mühendislik ve Fen Bilimleri Dergisi is the property of Sigma: Journal of Engineering & Natural Sciences / Mühendislik ve Fen Bilimleri Dergisi and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Sigma: Journal of Engineering & Natural Sciences / Mühendislik ve Fen Bilimleri Dergisi is the property of Sigma: Journal of Engineering & Natural Sciences / Mühendislik ve Fen Bilimleri Dergisi and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The main aim of this study was to investigate the effect of leachate recirculation and aeration on volatile fatty acid (VFA) concentrations in aerobic and anaerobic landfill leachate samples. In this study, two aerobic (A1, A2) and two anaerobic (AN1, AN2) reactors with (A1, AN1) and without (A2, AN2) leachate recirculation were used in order to determine the change of volatile fatty acids components in landfill leachate. VFA degradation rate was almost 100% in each reactor but the degradation rate show notable differences. In aerobic landfill reactors, total VFA concentrations decreased below 1000 mg L−1 after 120 days of operation and only caproic and acetic acids were determined at this time. The stabilization of the VFA concentrations takes about 350 and 450 days for AN1 and AN2 reactors, respectively. VFA concentrations were higher than that of aerobic reactors because of the acidogenic phase occurred in anaerobic environment. According to the results of VFA components, the stabilization of the waste was achieved after 120 days of operation in aerobic landfills. At this time, anaerobic reactors were in the acidogenic phase which results with the high concentrations of VFA. The results also indicated that leachate recirculation does not affect the degradation rate in aerobic landfills as much as it does in anaerobic landfills [ABSTRACT FROM PUBLISHER]

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]

Abstract: 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 1250m2 (25m×50m), 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. [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]