Fouling potential and reclamation feasibility for a closed landfill leachate treated by various pretreatment processes on membrane system

Abstract: A closed sanitary landfill leachate with high recalcitrant organics (COD = 4,000 mg/L) in a full-scale plant was intended for reuse. Various methods including coagulation, enhanced coagulation, microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO) were conducted, and modified fouling index (MFI) was used to evaluate the membrane fouling potential. The results showed that the current biological treatment process (activated sludge and sedimentation) in the full-scale plant only achieved 20% of COD removal with MFI still higher than 550,000 s/L². After conventional coagulation (CC) process, the MFI reduced only to 22,497 s/L², and additional MF/UF processes can only lower the MFI value to 28.5 s/L², which is still higher than the recommended operational value of 10 s/L² for NF or 2 s/L² for RO. Consequently, enhanced coagulation was used to replace the current coagulation process before MF/UF processes, and the result shows the MFI value was capably lowered to 10.98 s/L² with COD removal efficiency of 50.7%. The correlation of MFI, COD, and SS of leachate was derived by linear regression as follows: log MFI = 2.70 × log COD + 1.72 × log SS − 7.11. The minus sign in the coefficient of “ − 7.11” indicates fouling would occur only at COD and SS were higher enough to surpass the negative values in this equation. This regression equation not only can predict the fouling potential, but also can evaluate the optimum operation parameters for the pretreatment before NF/RO membrane processes. Moreover, the NF and RO processes followed by these pretreatment procedures can reach COD removal efficiencies of 97.6 and 98.3%, and TN removal of 98.66 and 99.86%, respectively, indicating these treated effluents can be reused for the irrigation.