Sludge reduction and pollutants removal in anaerobic-anoxic-oxic reactor with 2450 MHz electromagnetic wave loading on returned sludge: Performance and mechanism

Abstract To comprehensively evaluate the impact of 2450 MHz electromagnetic wave (EW) loading on returned sludge (RS) for sludge reduction and pollutants removal in anaerobic/anoxic/oxic (A2O) process, the performance of the coupled process (EWRS-A2O) was investigated in current study. 250 W was the appropriate loading power when considering both biological effect and dissolution effect of electromagnetic wave on the returned sludge. After being loaded, floc structure of the returned sludge became looser, and the microbial composition changed. The continuous operation indicated that an 8.3 % improvement in total nitrogen removal and a 33.1 % of sludge reduction were achieved in EWRS-A2O, accompanied by an observed yield coefficient of 0.35 kg SS/kg COD. Although an increase in the total phosphorus concentration of the effluent was found, the impacts on the chemical oxygen demand and ammonia nitrogen of the effluent were minimal. When contrasted to conventional A2O, EWRS-A2O process exhibited higher microbial metabolic activity. Miseq sequencing results showed that the microbial richness increased in EWRS-A2O system with changing of the microbial community structure. Additionally, functional microorganism analysis revealed the enrichment of slow-growing bacteria (Dechloromonas), fermenting bacteria (Clostridium sensu stricto and Tolumonas), and heterotrophic denitrifying bacteria (Thermomonas).