Characteristics of the pH‐influenced adaptation of methanogenic sludge to ammonium toxicity

Abstract

AbstractIncreasing ammonium‐nitrogen concentrations caused failure of methanogenesis at 1900‐2000 mg dm−3. After an adaptation period characterised by an almost nil methane production, methanogenesis appeared to be possible at even higher concentrations. A kinetic analysis of methane production during the adaptation process indicated that the adaptation was the result of a metabolic change in the methanogenic bacteria already present, rather than of growth of new bacteria. A high pH value causing toxic concentrations of un‐ionised ammonia during the adaptation period appeared to result in a decreased maximum specific methanogenic activity of the adapted sludge. A low pH value during the adaptation period resulted in a retarded degradation of propionic acid, probably due to inhibition of the hydrogen consuming methanogenic bacteria by undissociated volatile fatty acids, but this did not result in a decreased maximum specific methanogenic activity in the adapted sludge. The maximum specific methanogenic activity at an ammonium‐nitrogen concentration of 2315 mg dm−3 after adaptation as a percentage of that at 1000 mg dm−3 before adaptation was 31, 65 and 61% for a pH during the adaptation period of 7.6, 7.25 and 7.0 respectively. Except for the sludge which was maintained at pH 7.6 during the adaptation period, after adaptation the maximum specific methanogenic activity at an ammonium‐nitrogen concentration of 2315 mg dm−3 was higher than the maximum specific methanogenic activity at an ammonium nitrogen concentration of 1900 mg dm−3 before adaptation.