Aerobic biological treatability studies on landfill leachate with nitrification and denitrification

Abstract

Large pilot-scale treatment trials have examined the treatment of a leachate typical of those found at many closed landfill sites, containing approximately 200mg/l of ammoniacal-N. At such sites, treatment of these leachates with nitrification of am-moniacal-N alone, will not allow discharges of treated leachate to be made into sensi-tive surface watercourses, because of concerns about nitrate-N. The trials therefore included denitrification processes, by modification of an SBR process configuration, using the waste product glycerol, widely available as a by-product from the production of biodiesel, as the carbon source for denitrification. Initially a nitrification-only Stage 1 treatment trial treated strong, methanogenic leachate containing 2000mg/l of ammoniacal-N and 4000mg/l COD, completely nitrifying all ammoniacal-N to ni-trate-N. Following the successful treatment of strong leachate through nitrification, the innovative combined nitrification and denitrification treatment system was con-structed. Stage 2 of the treatability trial used this newly designed system to incorpo-rate both aeration and anoxic phases within a single reactor; enabling full nitrification and denitrification of weaker leachate from a closed landfill, containing 150mg/l am-moniacal-N and 200mg/l COD. In particular, the development of an innovative, stable, robust and relatively simple combined nitrification and denitrification process will have wide application at many closed landfill sites, where a reliable and robust treatment process is required, whilst full denitrification of nitrate-N is essential if treated leachate is to be discharged locally into small watercourses. The relative simplicity of the new process, in a single tank, with readily-automated operation and few chemical additions, means that it can be used at remote closed landfills, to produce high quality effluents suitable for discharge into many surface watercourses.