Effects of hydraulic retention time on nitrous oxide production rates during nitrification in a laboratory-scale biological aerated filter reactor

Abstract

This study investigated the effects of hydraulic retention time (HRT) on nitrous oxide (N2O) production during nitrification in a laboratory-scale biological aerated filter (BAF) reactor. Furthermore, its underlying mechanisms were explored by microelectrode technology and PCR-denaturing gradient gel electrophoresis (PCR-DGGE). The results showed that the N2O production rate was at its maximum at HRT of 4 h and at its minimum at HRT of 6 h. And there was only a little increase in N2O production rate at HRT of 8 h compared to HRT of 6 h. The average N2O production rates were 0.2258, 0.0872, and 0.1015 mg/h for HRT of 4, 6, and 8 h, respectively. Results of analysis of the internal biofilm microenvironment were consistent with the results of the N2O production rate. Production of N2O decreased sharply when HRT was increased from 4 to 6 h, whereas a slight increase in N2O production was observed when HRT was further increased from 6 to 8 h. Determination of DO, ORP, and nitrogen by microelectrode also demonstrated that the internal microenvironment of the biofilm was responsible for N2O generation. DNA analysis showed that Proteobacteria and Bacteroidetes might be responsible for N2O emission in the biofilm. These results indicate that HRT significantly affects the microbial community structures between the seed sludge and BAF biofilm, thereby affecting N2O production ability and rates, and hence, should be taken into consideration during BAF application.