Effect of adding exogenous nutrients on refractory wastewater treatment and bacterial community in activated sludge

Conventional biochemical processes have unsatisfactory effects on refractory wastewater treatment. Thus, a technically feasible and economical treatment should be established. In the conventional culture of microorganisms, adding exogenous nutrients to a medium can effectively promote micro-organism growth. Therefore, using exogenous nutrients in wastewater treatment may enhance microbial activity, subsequently speeding up the removal of contaminants. In this study, nutrients with different carbon and nitrogen (C/N) ratios were added to activated sludge and a chemical oxygen demand (COD) of 1000 mg/L was considered the benchmark for carbon source in the activated sludge process. Results showed that wastewater COD was reduced below 130 mg/L, and the removal rate reached 90% when the C/N ratio was 5:1. Along with the results from the study on F/M, dehydrogenase activity, content of extracellular polymeric substances, and microbial community in the wastewater treatment process, our findings indicated that adding exogenous nutrients increase microbial community diversity and promote the activity of microorganisms, thereby wastewater COD was reduced to 130 mg/L after 12 h and the removal rate reached approximately 90%. Simultaneously, analysis results on microbial community structure indicated that Proteobacteria, Firmicutes, and Bacteroidetes were the dominant species of bacteria. The addition of exogenous nutrients may increase the abundances of Pseudomonas and Bacillus species, which were essential in COD removal.