Microbial community structure in an integrated A/O reactor treating dilutedlivestock wastewater during start-up period

In order to investigate the correlation between reactor performance and the microorganisms, an integrated A/O reactor was operatedfor 72 days to treat diluted livestock wastewater. Chemical oxygen demand (COD) removal e ciency increased from 79% to 94%,with total nitrogen (TN) removal e ciency from 37% to 50% (HRT 7.4 hr) when the influent COD and TN were ca. 1500 mg/L and 95mg/L, respectively, and the outlet COD concentration was less than 100 mg/L at the end. Microbial community was monitored duringstart-up period by denaturing gradient gel electrophoresis (DGGE) based on 16S rRNA gene. DGGE profiles showed that microbialcommunity had changed significantly during the start-up and these shifts were in accordance with the reactor performance. UPGMAclustering analysis showed that 14 anaerobic samples fell into five main groups and so did the aerobic ones, but the grouping patternswere di erent. Phylogenetic analysis indicated that microbial populations in the anaerobic compartment belonged to Firmicutes,Proteobacteria, Chloroflexi and Bacteroidetes, while Proteobacteria, Bacteroidetes, Firmicutes, Verrucomicrobiae and Nitrospira werepresent in the aerobic compartment. In the anaerobic compartment, more fermentative and acetogenic bacteria were detected during thestart-up while denitrifying bacteria faded away. Two functional populations such as Nitrospira defluvii and Dechloromonas denitrificanswere observed when nitrogen removal was high, indicating that simultaneous nitrification and denitrification occurred in the aerobiccompartment.