Integrated single-reactor system merging biological phosphate removal, semi-nitritation, anammox and in-situ sludge fermentation (PR-SNA-SF) to treat actual domestic wastewater

Abstract

This study is the first to integrate Tetrasphaera transcriptionally dominated biological phosphate removal, semi-nitritation, anammox and in-situ sludge fermentation (PR-SNA-SF) into a single reactor to treat actual domestic wastewater. The phosphorus release and sludge fermentation by Tetrasphaera occurred in anaerobic stage, followed by aerobic semi-nitritation coupled with anammox and aerobic phosphate uptake, and ultimately anoxic endogenous denitrification integrated with denitrifying phosphate removal. This integrated process concurrently realized effective nitrogen and phosphate removal, along with a decrease in residual sludge. Following 220 days of continuous operation, effluent ammonium concentration was approximately 0.4 mg/L. Meanwhile, the concentrations of phosphate, nitrate and nitrite in the effluent all stabilized at around 0.1 mg/L. Moreover, PR-SNA-SF process demonstrated significant efficiency in reducing residual sludge, achieving a reduction rate of 78.9 %. Flow cytometry analysis revealed a 3.5-fold increase in compromised cellular integrity, accompanied by 31.9-times elevation in extracellular DNA concentration and 59.5 % particle size reduction, collectively indicating structural disintegration of sludge and subsequent organic matter release, which accounted for the reduction in residual sludge. The analysis of transcriptional community revealed that Tetrasphaera was the predominant fermentative phosphate-accumulating organism, with a relative abundance as high as 71.4 %. Meanwhile, Nitrosomonas (AOB), Candidatus Brocadia and Candidatus Kuenenia (anammox), and Candidatus Competibacter (GAOs) accounted for 5.08 %, 8.11 %, 3.59 % and 8.02 %, respectively, indicating their significant role. The implementation of novel PSNAF process has effectively reduced operational expenses and costs associated with residual sludge disposal, without need for exogenous carbon supplementation. This advancement holds considerable importance for the field of wastewater treatment.