Heterotrophic nitrification and aerobic denitrification of high-strength ammonium in anaerobically digested sludge by Alcaligenes faecalis strain No. 4

Alcaligenes faecalis   strain No. 4 which is capable of heterogeneous nitrification and aerobic denitrification, was used to remove high-strength ammonium (approximately 1 g NH4+-N/l) from digested sludge, the product of an anaerobic digestion reactor, in which methane was produced from excess municipal sewage sludge. Repeated batch operations were conducted at 20°C and 30°C for 550 h, using a jar fermentor. The removal ratios of high-strength ammonium reached 90–100% within 24 h, and the average ammonium removal rate was 2.9 kg-N/m3/day, more than 200 times higher than that in conventional nitrification–denitrification processes. During these operations, the cell density was maintained at 108–109 cells of A. faecalis strain No. 4/ml. At 3% NaCl in the digested sludge, strain No. 4 exhibited an ammonium removal rate of 3 kg-N/m3/day.