Feasibility of biological aerated filters (BAFs) for treating landfill leachate

Ammonia can be removed from landfill leachate using aerobic biological treatment processes. The biological aerated filter (BAF) combines biological treatment and subsequent biomass separation in one reactor providing a small footprint alternative to conventional systems. Leachate from an operational landfill was found to be aerobically treatable using the OECD recommended Modified Zahn-Wellens test. This leachate was used as feed to a pilot-scale BAF at influent chemical oxygen demand (COD) and ammoniacal-nitrogen concentrations of 765 mg l(-1) and 568 mg l(-1) respectively. During an initial period of stable operation without pH control, 33 %w/w of influent ammonia was removed. The reactor pH was 9.2 with little conversion to total oxidized nitrogen (< 45 mg l(-1)), this removal was accounted for primarily by air stripping. In a second period of stable operation, the reactor pH was reduced to pH 7.2 and ammonia removal increased to 97 %w/w with a concomitant increase in effluent nitrite concentration to an average of 524 mg l(-1). Biological aerated filters (BAFs) can be used to nitrify landfill leachates though onward denitrification of nitrite-nitrogen and COD polishing is required to reach typical discharge consent standards.