Sulfur-mediated bacteria outperform glycogen-accumulating organisms in carbon-deficient wastewater: Key role of...

Biological nutrient (including nitrogen and phosphorus) removal is often hindered by the lack of organic carbon (C) sources, which can result in the excessive growth of glycogen-accumulating organisms (GAOs), even in sulfate-containing wastewater. Elemental sulfur (S⁰) has been considered as an economical and energy-efficient electron donor to achieve biological nutrient removal from wastewater. In this study, the long-term effects of C/S⁰ ratios on the competition between sulfur-mediated bacteria (SMB) and GAOs was investigated to explore the feasibility of using S⁰ to partially replace carbon and suppress the proliferation of GAOs in biological treatment systems. Four parallel bioreactors were continuously operated for approximately 100 days and fed a substrate consisting of 400, 200, 100, and 0 mg acetate-COD/L, in addition to 0.53 g S⁰/cycle (equal to 400 mg COD/L); the acetate-COD concentrations corresponded to C/S⁰ ratios of 0.28 (R1), 0.14 (R2), 0.07 (R3), and 0 (R4), respectively. The results showed that a relatively high C/S⁰ ratio of 0.28 (in R1) and low C/S⁰ ratios of 0.07 (in R3) and 0 (in R4) enhanced 1) S metabolism, especially anaerobic S⁰ reduction to form S^2-, which was mediated by sulfate/sulfur-reducing bacteria (SRB/S⁰RB, e.g., Desulfobacter and Desulfuromonas), or 2) S⁰ oxidation to form sulfate, which was mediated by sulfur-oxidizing bacteria (SOB, e.g., Thiobacillus) to promote their growth over GAOs (e.g., Candidatus_Competibacter). However, when the C/S⁰ ratio was 0.14 in R2, this reactor displayed a GAO phenotype rather than a SMB phenotype since GAO communities have a higher acetate uptake rate than SMB. Thus, an appropriate amount of S⁰ addition supported the competitiveness of SMB over GAOs. Finally, the potential mechanism about competition between the two communities (SMB and GAOs) was revealed. This study provides a new mechanistic strategy to promote the proliferation of SMB over GAOs in carbon-deficient wastewater.