Aerobic biological treatment of landfill leachate

There is an ongoing need to treat leachates from landfills using approaches that avoid expensive installation and operating costs. Faced with such a problem, Powys County Council (Wales, UK) developed a treatment system based on practical experience. Leachate was re-circulated through aeration towers containing a biofilm supported on plastic media before being polished in reed/filter beds. Investigations were undertaken to evaluate the performance of these processes. Replicated model aeration towers (1/300 site scale) were used to establish treatment rates for pollutants in leachates of varying strengths; the effects of temperature and variations in pollutant concentrations were also evaluated. Data from these model experiments were corroborated with findings from pilot-scale plants (1/10 site scale) operating on landfill sites. Assessment of treatment performance was based on the degree of amelioration of standard chemical (ammoniacal-N and total organic carbon) parameters. A range of related parameters including nitrate, pH and redox potential were measured in support of these assessments. Model system experiments indicated treatment rates at 15 C (883-1895 mg NH3-N m h; 347-1600 mg TOC m h) that were similar across a wide range of leachate concentrations (37-1880 mgl ammoniacal-N; 130-5315 mgl COD). Marked changes in the concentration of leachates did not affect treatment efficiency following a short lag effect. Process rates roughly halved with each 5C decrease in temperature below 15C, significant nitrification was maintained at temperatures of 0.5-1 C. High variability in treatment capacity was observed for individual plastic media. Treatment rates in pilot scale plants were slightly higher but broadly consistent with those obtained in model systems.