Biodegradability and methane productivity during anaerobic co-digestion of refractory leachate

Mature landfill leachate was anaerobically co-digested with synthetic wastewater to evaluate the degradability and methane productivity in various mixing ratios. The proportion of leachate was increased in three equal steps from 0% to 100%, and then decreased again through the same steps back to 0%. Both COD removal efficiency and methane production decreased as the leachate proportion in the influent was increased. When the influent contained 100% leachate, and when 33% synthetic wastewater was reintroduced, methane production was suppressed relative to COD removal. During the same phases, NH4+ accumulated, suggesting an excess of NH4+ mineralization versus uptake. After 100% leachate was supplied, methane yield decreased to near zero, and the production of methane remained suppressed relative to COD reduction even as more synthetic wastewater was reintroduced, until 100% synthetic wastewater was resupplied. This decline in methane yield might be caused by deterioration of methanogenic bacterial activity following treatment of 100% leachate. (C) 2012 Elsevier Ltd. All rights reserved.