Partial nitrification achieved by pulse sulfide doses in a sequential batch reactor.

A nitrifying sequential batch reactor operated under 2-day cyclic aerobic and anoxic conditions was pulse dosed with incremental sulfide concentrations during anoxic conditions. The nitrite-oxidizing bacteria were found to be more sensitive to sulfide than the ammonia oxidizers. A maximum of nitrite-N to (nitrite-N + nitrate-N) accumulation ratio of 0.75 was obtained at an initial pulse sulfide-S concentration of 45 mg/L under pH control at 7.5 +/- 0.2 and fully mixing conditions. Total ammonium nitrogen was removed almost 100% at a removal rate of 0.73 +/- 0.05 g/L x day, achieved during the aerobic days of the cycles. Denaturing gradientgel electrophoresis (DGGE) and fluorescence in situ hybridization (FISH) analyses indicated the shift in the ammonia- and nitrite-oxidizing populations triggered by sulfide addition, partial nitrification, and subsequent recovery to complete nitrification. Interestingly, archaeal amoA genes were retrieved under the conditions of sulfide addition. These results indicate that the pulse sulfide application can be used as a tool to accumulate nitrite, which is of importance for the subsequent anaerobic ammonium oxidation (anammox) process in the achievement of complete nitrogen removal.