Performance Evaluation and Optimization of a Single-Tank Anaerobic/Anoxic/Oxic Membrane Bioreactor for Landfill Leachate Treatment

Abstract

Landfill leachate, characterised by high levels of COD, BOD₅, NH₃-N, TSS, and colour, poses significant environmental risks and requires stringent treatment to comply with discharge regulations. This study evaluates the performance of a prototype single-tank anaerobic/anoxic/oxic membrane bioreactor (A2O-MBR) for landfill leachate treatment, focusing on the effects of hydraulic retention time (HRT) and dissolved oxygen (DO) levels. The A2O-MBR, integrating biological and membrane filtration processes within a compact configuration, was assessed under varying HRTs (12, 15, 18 hours) and DO levels (2.6, 3.1, 3.5 mg/L). Effluent parameters were analysed for COD, BOD₅, NH₃-N, TSS, and colour, and compared against Malaysian regulatory standards. Results revealed that an HRT of 15 hours and a DO level of 3.1 mg/L provided optimum performance, achieving COD and BOD₅ removal efficiencies exceeding 90%, while TSS consistently met discharge standards. NH₃-N removal was moderate, with the lowest effluent concentration of 430 mg/L observed at DO 3.5 mg/L. However, colour removal remained limited, highlighting the persistence of refractory compounds. The findings underscore the critical role of optimising HRT and DO to balance microbial activity and pollutant removal efficiency. Notably, prolonged HRTs showed diminishing returns on performance improvement and increased operational costs. This study demonstrates the feasibility of a single-tank A2O-MBR for cost-effective leachate treatment, with potential enhancements through advanced oxidation or adsorption for improved ammonia and colour removal. The insights provided contribute to the design and optimisation of sustainable leachate management systems.