Abstract

Ammonia is a metabolic product in the decomposition of protein wastes, and has a recognized inhibitory effect on methanogenesis; this effect has been slightly quantified on methanogenic biofilms and particularly those populated by methanogenic Archaea which produce ammonia as a catabolic product from methylated amines. This paper presents studies on the effect of ammonia on maximum methanogenic activity of anaerobic biofilms enriched by methylaminotrophic methane producing Archaea (mMPA). The effect of unionized free ammonia on the specific maximum methanogenic activity of a mMPA enriched biofilm was studied, using 250mL flasks containing ceramic rings colonized by 30 day-old experimental biofilm and adding 48.8 (control system), 73.8, 98.8, 148.8, 248.8, 448.8 and 848.8mg NH3-N/L. The systems were maintained for ten days at a pH of 7.5 and temperature of 37°C. The results showed that at 848.8mg NH3-N/L, biofilm methane production required 36h adaptation period, prior to entering into maximum production phase. The highest maximum methanogenic activity reached a value of 2.337±0.213g COD methane/g VSS*day when 48.8mg NH3-N/L was added, and inhibition was clearly observed in those systems above 148.8mg NH 3-N/L, producing under 1.658±0.185g COD methane/g VSS*day. The lowest methanogenic activity reached was 0.639±0.162g COD methane/g VSS*day at the system added with 848.8mg NH3-N/L. When applying the Luong and non-competitive inhibition models, the best fit was obtained with the non-competitive model, which predicted 50% inhibition of methanogenic activity at 365.288mg NH3-N/L. © 2003 Elsevier Ltd. All rights reserved.