Effects of solar radiation on the treatment of real domestic wastewater: pollutant removal efficiency, microbial structure, function, and metabolic pathways

Abstract

Municipal domestic wastewater often contains a variety of pollutants, such as phosphorus and organic matter. The activated sludge process is often affected by a variety of environmental factors, and it is not clear whether the intense solar radiation at high altitude affects its biodegradation process.In this study, a laboratory-scale A²O reactor was constructed and placed under solar irradiation, and the A²O process was applied to treat domestic wastewater under continuous solar irradiation. The experimental results showed that the average removal rate of COD reached 91.75% at 40 days; the increase in solar irradiation time helped the removal of organic pollutants, but the strong solar radiation would have an inhibiting effect on the removal of TP. 16S rRNA sequencing analysis showed that the dominant phyla that emerged in the system were Bacteroidota and Proteobacteria, and that the above bacteria contributed to organic matter degradation, but the abundance of the major PAOs,DPAOs, and Denitrifiers was suppressed by the accumulation of solar radiation, and the abundance of Nitrobacterias was promoted by the accumulation of solar radiation. The relative abundance of genes involved in central carbon metabolism, such as Glycolysis, Pentose phosphate pathway, and the TCA cycle, was predicted based on PICRUSt2. In addition, two key genes, PPK and PPX, which are involved in encoding hydrolytic and synthetic enzymes of Poly-P, were identified. The above findings may provide new insights into the nutrient removal mechanisms of the A²O process for the treatment of real domestic wastewater in areas of intense solar radiation.