Degradation of organic compounds in a municipal landfill leachate treated in a suspended-carrier biofilm process

Leachate from a Swedish municipal landfill was analyzed for organic compounds before and after biological treatment in a pilot plant. The treatment consisted of two stages: one aerobic (nitrification) and one anoxic (denitrification), both working as suspended-carrier biofilm processes. The chemical oxygen demand reduction in the aerobic stage was 15 to 30% during the study. Ultrafiltration and gel filtration chromatography studies showed that mainly organic compounds with a low molecular weight were degraded during treatment; however, a fraction of these low-molecular-weight compounds was still left after treatment. Furthermore, reversed-phase chromatography analyses indicated that a large part of the hydrophilic fractions of the organic compounds were unaffected by the treatment. Gas chromatography-mass spectrometry analyses showed that the leachate contained low concentrations of plasticizer; and polycyclic aromatic hydrocarbons. Toxicity tests indicated that much, but not all, of the toxicity depended on the high ammonium ion concentration in the untreated leachate.