Residual ozone in microorganisms enhanced organics removal and shaped microbial community

The residual ozone played an important role in enhancing the organics removal by stimulate subsequent biological processes. However, how the residual ozone affects the biological process is not well studied. In this work, a pilot scale integrated O₃-BAF, ordinary BAF and separated O₃-BAF were compared in advanced treatment of real bio-treated petrochemical wastewater. Results showed that residual ozone with 0.05-0.10 mg L^-1 in the BAF demonstrated relatively high chemical oxygen demand (COD) removal efficiency of 48.4%, which was 1.5-fold higher than that obtained by separated O₃-BAF and 3-fold higher than that obtained by ordinary BAF. The stimulative effect of low dosage of O₃ on biological treatment additionally donated 33.9% of the COD removal in the BAF. The COD removal amount per dosage of ozone reached 5.30 mg-COD/mg-O₃. The biofilm thickness in the integrated O₃-BAF was reduced by 30-50% while the dehydrogenase activity (DHA) was improved by 500%, indicating the stimulate effect on the bioactivity. Additionally, Illumina HiSeq sequencing of 16S rRNA gene amplicons demonstrated significant microbial diversity decreasing. Specially, Gemmatimonadetes and Bacteroidetes are the dominate microorganism in the integrated O₃-BAF, having a positive correlation with the proper residual ozone, and increased by 5.4% and 4.2% in comparison with the separated O₃-BAF, respectively. The residual ozone higher than 0.22 mg L^-1 showed inhibition effect on the bioactivity. In summary, the control of residual ozone introduced to BAF was crucial for stimulative effects and manager the microbial community in the integrated O₃-BAF, which still need further detail research.