andfi ll leachate (LFL), especially old LFL, is very diffi cult to treat using convent ional 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 main tain a high biomass concentration, resulting in an effi cient biological digestion system. As a result, excellent biological oxyge n demand (BOD) and ammonia removals of 90% or higher are achievable with a much sho rter 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) remov al (75% or higher), even with
old LFL under optimized conditions. MBRs have also been demonstrated to be effective in the removal of
micropollu tants. Furthermore, recent developmen ts such as anaerobic MBR and PAC (powdered activated
carbon)-amended MBR have shown great potent ials in LFL treatment. MBRs can provide stable performance
while accommodating large varia tions in composition of infl uents and other operation conditions. However,
short HRT and high ammonia concentratio n were found to have adverse effects. Extremely long solids residence time was also found to lower MBR performance.
© 2011 Elsevier B.V. All ri