METHANE PRODUCTION FROM ACETAMIDE IN AN UPFLOW ANAEROBIC SLUDGE-BLANKET REACTOR BASED AN A SYNERGISTIC ASSOCIATION BETWEEN AN AEROBIC ROD AND METHANOGENS

Acetamide degradation was investigated in a bench-scale upflow anaerob ic sludge-blanket (UASB) reactor, successively fed with acetamide, ace tate and acetamide, over a period of 343 days, at different hydraulic retention times (t(HR)) The reactor was seeded with the sludge previou sly described [Guyot et al. (1994) Appl Microbiol Biotechnol, 42:452-4 56], in which methanogenesis from acetamide was performed through a sy nergistic relationship between an acetamide-degrading, aerobic rod and methanogens. When the reactor was fed acetamide, the chemical oxygen demand (GOD) removal efficiency was 86% at volumetric loads less than 1.18 kg COD m(-3) day(-1). At higher volumetric loads, the efficiency decreased markedly, e.g. 50.9% at a volumetric organic load of 3.39 kg COD m(-3) day(-1) (1 day t(HR)) with an accumulation of both acetamid e and acetate. The same reactor, when fed with acetate at t(HR) 1 day, reached a high COD removal (99%). Evidence of the inhibition of aceta te degradation by acetamide is presented. After a long period (135 day s) without feeding the reactor with: acetamide, the sludge reactor was still capable of degrading acetamide when this substrate was supplied again. It seems that the synergistic degradation of acetamide by aero bes and methanogens present in the UASB reactor sludge is stable over a long period (343 days), in spite of limiting concentrations of disso lved oxygen in the feed.