Abstract
Nitrous oxide (N 2O) can be emitted as a by-product of the process of nitrogen removal from wastewater. Two methods of complete denitrification and media application were studied in lab-scale intermittent aeration reactors fed with domestic wastewater to refine methods of controlling the N 2O emission rate. A study on cyclic patterns showed that the highest N 2O emission rate was at the beginning of the aerobic phase rather than the anoxic phase. This was probably because the nitrifying bacteria had accumulated nitrite nitrogen (NO 2 −) under low DO conditions. Methanol as an external carbon source was added during the anoxic phase to reduce nitrate nitrogen (NO 3 −) when denitrification was completed. The N 2O emission rates in both the aerobic and anoxic phases were significantly influenced by residual NO 3 −, increasing monotonically as the concentration of NO 3 − in the reactor increased. Over 95% of average N 2O emissions in both the aerobic and anoxic phases were prevented when methanol was added. The biofilm reactor showed similar patterns to those of the non-biofilm reactor in track behavior, but the former was more effective in the reduction of N 2O emissions.
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