Biological processes for treatment of landfill leachate

This review presents an overview with critical analysis of the technical applicability of biological treatments for landfill leachate. A particular focus is given to activated sludge (AS), sequencing batch reactors (SBR), aerated lagoons (AL), and upflow anaerobic sludge blankets (UASB). Their advantages and limitations in application are evaluated. Selected information is presented such as pH, hydraulic retention time (HRT), organic loading rate (OLR), characteristics of leachate and treatment performance. It is evident from the literature survey of 188 papers (1976-2010) that none of the individual biological treatments presented is universally applicable for removing recalcitrant contaminants from leachate. Among the biological treatments reviewed, AS, SBR and UASB are the most frequently applied. These treatments are effective not only to remove over 90% of COD with a concentration ranging from 3500-26000 mg L^-1, but also to achieve 80% of NH₃-N removal with a concentration ranging from 100-1000 mg L^-1. A combination of physico-chemical and biological treatment into an integrated process is effective for leachate treatment. Almost complete removal of COD and NH₃-N was reported for combined reverse osmosis (RO) and UASB with an initial COD concentration of 35000 mg L^-1 and NH₃-N concentration of 1600 mg L^-1. Integrated Fenton's oxidation and AS could achieve about 98% and 99% of COD and NH₃-N removal, respectively, with initial COD and NH₃-N concentrations of 7000 mg L^-1 and 1800 mg L^-1. Overall, the selection of the most suitable treatment for leachate depends on its characteristics, technical applicability and potential constraints, effluent limit required, cost-effectiveness, regulatory requirements and long-term environmental impacts.