Characteristics of N₂O generation within the internal micro-environment of activated sludge flocs under different...

Nitrous oxide (N₂O) is a strong greenhouse gas that is produced in significant quantities through biological nitrogen removal processes in wastewater treatment plants; however, N₂O generation within the internal micro-environment of activated sludge flocs (ASFs) is poorly understood. In this study, microelectrodes and molecular techniques were employed to investigate the concentrations of N₂O and other chemicals and the composition and distribution of microbes within ASFs, respectively. The results showed that N₂O generation was correlated with the ASF micro-environment, and was significantly influenced by the dissolved oxygen (DO) concentration of the bulk wastewater. Equal N₂O, DO, NH₄⁺-N, and NO₃^--N concentrations were found in small flocs (<100 μm). By contrast, higher N₂O generation rates and lower DO, NH₄⁺-N, and NO₃^--N concentrations were detected in the center of large flocs (>200 μm) compared with those at their surfaces. Microbial structures of varying particle sizes were distinct and depended on the micro-environmental characteristics.