Impact of carbon sources on nitrous oxide emission and microbial community structure in an anoxic/oxic activated sludge system

Abstract

The carbon source used for denitrification is a key factor in the reduction of nitrous oxide (N2O) produced from wastewater treatment plants because it affects denitrification activity. In this study, two laboratory-scale Modified Ludzak Ettinger (MLE) processes were operated with methanol and sodium acetate as the sole carbon sources. Removal efficiency of soluble nitrogen was not affected by carbon source, but the N2O emission rate from the acetate-fed MLE process (1.6 ± 0.6 lg N–N2O/min) was lower than that from the methanol-fed process (3.0 ± 0.7 lg N–N2O/min). This is supported by the batch experiment data showing the acetate-fed biomass had a higher N2O reduction rate of 10.3 mg/gVSS/h than that of the methanol-fed biomass (3.3 mg/gVSS/h). In the methanol-fed process, 34.9% of the total bacteria was the genus Methylotenera, which is reportedly incapable of N2O reduction. The acetate-fed process enriched the genera Dechloromonas and Rubrivivax, potential N2O reducers, accounting for 12.2 and 15.9% of the total bacteria, respectively. The results indicated that acetate is a suitable replacement for methanol for wastewater treatment plants interested in mitigating N2O emission from the MLE process.