Anaerobic digestion of pressed off leachate from the organic fraction of municipal solid waste.

A highly polluted liquid ("press water") was obtained from the pressing facility for the organic fraction of municipal solid waste in a composting plant. Methane productivity of the squeezed-off leachate was investigated in batch assays. To assess the technical feasibility of "press water" as a substrate for anaerobic digestion, a laboratory-scale glass column reactor was operated semi-continuously at 37 degrees C. A high methane productivity of 270 m(-3) CH(4)ton(-1) COD(added) or 490 m(-3) CH(4)ton(-1) VS(added) was achieved in the batch experiment. The semi-continuously run laboratory-scale reactor was initially operated at an organic loading rate of 10.7 kg COD m(-3)d(-1). The loading was increased to finally 27.7 kg COD m(-3)d(-1), corresponding to a reduction of the hydraulic retention time from initially 20 to finally 7.7 days. During the digestion, a stable elimination of organic material (measured as COD elimination) of approximately 60% was achieved. Linearly with the increment of the OLR, the volumetric methane production of the reactor increased from 2.6m(3)m(reactor)(-3)d(-1) to 7.1 m(3)m(reactor)(-3)d(-1). The results indicated that "press water" from the organic fraction of municipal solid waste was a suitable substrate for anaerobic digestion which gave a high biogas yield even at very high loading rates.