| Summary: | The treatment of sulfur-containing wastewater from industries such as petroleum refineries and tanneries can produce significant amounts of low-cost elemental sulfur (S0). In recent years, numerous studies have investigated the use of inexpensive sulfur sources to improve denitrification and nitrogen removal efficiencies in wastewater treatment. However, there has been relatively less research on enhancing phosphorus removal through sulfur sources. Therefore, when the influent carbon source concentration was 200 mg/L (in terms of COD), the anaerobic/aerobic operation mode was first used to acclimate traditional enhanced biological phosphorus removal sludge. Nitrate was then added at the end of each anaerobic period to establish a denitrifying phosphorus removal system. Finally, 67.5 mg/L of S0 was added to the reactor in each cycle to assess its impact on enhancing the denitrifying phosphorus removal performance. The results demonstrated that the addition of S0 enhanced the reductive environment during the anaerobic phase, facilitating anaerobic phosphorus release, and it served as an electron donor during the anoxic phase. Furthermore, the addition of S0 could reduce microbial richness and diversity, leading to decreased relative activities among glycogen-accumulating organisms, whereas there was an increase in the relative abundance of Thiothrix bacteria, increasing from 18.5% to 23.6%. Consequently, the phosphorus removal rate increased from 92.3% ± 9.7% to 97.2% ± 1.9%, with a higher average and reduced fluctuation; nitrate removal increased from 50 mg N/L to approximately 62 mg N/L. Sulfate production increased from 1.4 mg S/L to 13.6 mg S/L in the anoxic stage, which was significantly higher than the sulfate production in the anaerobic stage. Following the addition of S0 each cycle, only sulfate was detected, while no sulfide or thiosulfate was found, indicating sulfur oxidation occurred, with almost no sulfur reduction in the reactor. In the typical cycle experiments, acetate was completely consumed within 60 minutes, suggesting that the system had a good carbon removal effect; nitrate could be rapidly consumed to a low concentration within 30 minutes, revealing that the reactor had a high nitrate removal rate and stable denitrification effect; the addition of S0 could enhance anaerobic phosphorus release, and its contribution rate to anaerobic phosphorus release is approximately 26%; the phosphorus absorption per 1 mg N/L of nitrate increased from 0.895 mg P/L to 1.207 mg P/L, with S0 contributed 25.9% to denitrification and phosphorus removal.
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