The process parameters and sludge properties of an in-situ sludge ozone-reduction system were investigated under different ozone dosages and sludge ages. Subsequently, 75 mg·g-1 (as O3/MLVSS) was selected as the appropriate ozone dosage to satisfy the wastewater treatment capacity and in-situ sludge ozone-reduction. The calibration coefficient results of the sludge yield formula indicated that Yh was reduced from 0.331 g·g-1 to 0.326 g·g-1 (to MLVSS/COD m) by ozone treatment and Kd was increased from 0.046 d-1 to 0.050 d-1 at 75 mg·g-1. The effluent quality of the SBR system was satisfactory when the sludge age was 10 d. The ozone dosage of 75 mg·g-1 and sludge age of 10 d were selected as the appropriate process conditions, at which the excess sludge was reduced by 12%. The high-throughput sequencing results concluded that the microorganisms in the excess sludge after ozonation were different in phylum and genus. After ozone treatment, the abundance of Bacteroidetes increased by 1.2 times and the relative abundance of Proteobacteria with nitrification and denitrification ability decreased from 24% to 18%. The reduction in the abundance of nitrobacteria affected the denitrification capacity of the sewage treatment system, but the total effluent nitrogen still met the I B discharge standard of pollutants for municipal wastewater treatment plants. The relative abundance of Lactococcus increased from 0.4% to 21.6%. Simultaneously, the concentration of macromolecular organic substances in the EPS of the excess sludge increased from 40.6 mg·g-1 to 54.6 mg·g-1, while the CST increased from 15 s to 17 s after ozone treatment. The zeta potential decreased from -10.04 mV to -15.20 mV and the SVI of the excess sludge increased from 54 mL·g-1 to 62 mL·g-1, thereby indicating that the sedimentation performance and dewaterability were affected to some extent. However, the SS of the effluent and the solids content of the sludge cake after extraction did not change significantly, the system could still operate stably, and the subsequent dewaterability of the excess sludge was not significantly affected.
Keywords: dewaterability; microbial community; ozone; parameter; sedimentation performance; sludge.