Integrated process of Tetrasphaera-dominated enhanced biological phosphorus removal and sulfur autotrophic denitrification in a single reactor to treat VFAs-free wastewater: Feasibility, performance and mechanism

Abstract

This study investigated the toxicity response in Tetrasphaera-dominated enhanced biological phosphorus removal (EBPR(T)) under different thiosulfate stress conditions and developed a one-stage process combining EBPR(T) and thiosulfate-driven sulfur autotrophic denitrification (SADN) in a single reactor to achieve advanced nutrient removal from low COD/N and VFAs-free wastewater. Batch experiments demonstrated that 120 mg/L thiosulfate was barely toxic to the EBPR(T) system, while more than 200 mg/L thiosulfate disrupted the physiological activities related to cell membrane integrity, esterase activity, early apoptosis, membrane potential, and metabolism in functioning microorganisms, leading to the deterioration of the EBPR(T) system. The one-stage EBPR(T) - SADN process was operated for 90 days under 120 mg/L thiosulfate, during which effluent total inorganic nitrogen (TIN) and PO₄^3–P were less than 4 mg/L and 0.42 mg/L, respectively. High transcriptional activity of clades 1 and 2 of Tetrasphaera ensured effective PO₄^3–P removal performance under 120 mg/L thiosulfate stimulation. As the dominant microorganisms, Tetrasphaera (14.35 %) and Thiobacillus (8.37 %) were assisted by conventional PAOs and heterotrophic denitrifying microorganisms to achieve efficient nutrient removal. The results indicate that the one-stage EBPR(T) - SADN process with 120 mg/L thiosulfate stress has significant potential for nutrient removal from low COD/N and VFAs-free wastewater.