Treatment of landfill leachate using membrane bioreactors: A review

Landfill leachate (LFL), especially old LFL, is very difficult to treat using conventional biological processes. To this end, membrane bioreactor (MBR) has proven to be a promising alternative. The membrane separation capacity of a MBR allows the retention of most microbial cells in the reactor to maintain a high biomass concentration, resulting in an efficient biological digestion system. As a result, excellent biological oxygen demand (BOD) and ammonia removals of 90% or higher are achievable with a much shorter hydraulic residence time (HRT) and much larger organic loading rate (OLR) in comparison to conventional biological systems. MBR also allows excellent chemical oxygen demand (COD) removal (75% or higher), even with old LFL under optimized conditions. MBRs have also been demonstrated to be effective in the removal of micropollutants. Furthermore, recent developments such as anaerobic MBR and PAC (powdered activated carbon)-amended MBR have shown great potentials in LFL treatment. MBRs can provide stable performance while accommodating large variations in composition of influents and other operation conditions. However, short HRT and high ammonia concentration were found to have adverse effects. Extremely long solids residence time was also found to lower MBR performance.