A techno-economical assessment of treatment by coagulation-flocculation with aluminum and iron-bases coagulants of landfill leachate membrane concentrates.

Landfill leachate treatment involved with the membrane bioreactor (MBR) combined with membrane treatment via nanofiltration (NF) and/or reverse osmosis (RO) is widely used in Turkey. This treatment produces landfill leachate membrane concentrates (LLMCs) with an undesirably high concentration of contaminants. In the study, two different nanofiltration concentrates of leachate were coagulated. Coagulant dosages from 0.10 to 5.0 g of Me3+/L (Me3+: Al3+ or Fe3+), and the pH values ranged from 4.0 to 8.0 and 3.0-9.0 for Al-based and Fe-based coagulants, respectively. The most efficient pH values were 5.0 and 4.0 for Al3+ and Fe3+, respectively. These pH values are lower than those known to be effective in coagulants. The reason for this is the presence of humic substances in the wastewater. The cost of Fe2(SO4)3.xH2O was the lowest than other coagulants at the end of the cost analyses obtained from Istanbul region landfill leachate NF concentrate (NFCL-1) and Kocaeli region landfill leachate NF concentrate (NFCL-2). Under optimum conditions, the costs for NFCL-1 and NFCL-2 were calculated as 0.55 and 0.46 $/removed kg COD, respectively.

Electrochemical oxidation of pretreated landfill leachate nanofiltration concentrate in terms of pollutants removal and formation of by-products.

This study compares the efficiencies of active (Ti/TiO2-RuO2-IrO2 (TIR)) and inactive (Ni/Boron Doped Diamond (BDD)) anodes in terms of pollutant treatment and by-product formation in pretreated (chemical coagulation) landfill leachate nanofiltration membrane concentrate (PLNC). PLNC has high chemical oxygen demand (COD:4900 mg/L), total organic carbon (TOC: 1874 mg/L), total Kjeldahl nitrogen (TKN: 520 mg/L), ammonium nitrogen (NH3-N: 21.35 mg/L), chloride (5700 mg/L) and sulfate (9000 mg/L - due to coagulant type). The parameters of COD, TOC, NH3-N, TKN, free and combined chlorine species, halogenated organic compounds (HOCs), adsorbable organic halogens (AOX), and nitrate at different current density (J: 111-555 A/m2) and initial pH (pHi:3.5-7) were compared for both anodes. The removal efficiencies at the optimum conditions (pHi 5.5, 333 A/m2 and 8 h) were obtained as 86.4% COD, 77.4% TOC, 93.4% TKN, 94.4% NH3-N with BDD and 34.3% COD, 27.3% TOC, 93.7% TKN, 97.4% NH3-N with TIR. According to gas chromatography-mass spectrometry (GC-MS) results obtained under optimum conditions, haloalkane/alkene, halonitroalkane, halonitrile, haloketone, haloalcohols, haloacids, haloaldehydes, haloamines/amides on both electrodes were detected as species of HOCs. In addition, the highest nitrate concentration was observed at the TIR anode, while the highest AOX concentration was observed at the BDD anode.