[Treatment of domestic wastewater using sequence batch reactor enhanced by low intensity ultrasound]

Enhancement effect of ultrasound (US) on the bio-treatment of domestic wastewater was studied through contrast experiments between two sequence batch reactors (SBR) with and without US. The results showed that when US with intensity of 0.3 W x cm(-2) was employed to irradiate 10% of the activated sludge in the SBR for 10 minutes every 8 hours, the removal rate of COD was improved by 3% - 6%, and the effluent COD of US-SBR was lower than that of the control SBR by 40% - 53%. Moreover, the tolerance of SBR to high concentration and toxicity impact was improved effectively. For the practical domestic wastewater, the sludge activity was 14% higher in the US-SBR than that in the control SBR, increasing the capacity of microorganism to degrade the refractory compounds. The settleability of activated sludge in the US-SBR descended slightly and 5% increase of SVI (sludge volume index) was observed during the experiment, but it had little influence on the system since the increment was very small. According to the results of scan electro-microscope (SEM) and microbial community structures analysis, the microorganism in the US-SBR was damaged by US and compared with the control, the cell wall was ruffled obviously, but it didn't change the community structures of activated sludge. Kinetics analysis of microbial respiration in the two SBRs showed that the activated sludge in the US-assisted SBR could make better use of substrate.