Effects of an organic carbon source on the coupling of sulfur(thiosulfate)-driven denitration with Anammox process

[Display omitted] •Appropriate organics (＜140 mg/L) positively affected the long-term SDDA system.•High TN removal (92.8 ± 0.3%) achieved at the NLR of 1.34 kg-N/(m3·d) in SDDA.•Organics accelerated SADN rates via the formation of dissolved polysulfide.•Potential conversion pathway in SDDA system with organics addition was proposed.•Anammox and SOB can coexist and remain active despite exogenous COD addition. The sulfur(thiosulfate)-driven autotrophic denitrification coupled with Anammox (SDDA) process is proposed as an emerging technology for wastewater containing NH4+-N and NO3−-N. However, the influence of organic matter on the SDDA process is not fully understood. A long-term experiment has shown that a moderate organic (acetate) (＜140 mg/L COD) can accelerate the heterotrophic/autotrophic denitrification and Anammox activity, to reach as high as 92.8% ± 0.3% total nitrogen at a loading rate of 1.34 kg-N/(m3·d). Batch test results showed that Anammox made the largest contribution to the removal of nitrogen, even in an SDDA system with COD addition. Additionally, organics can promote the bioavailability of solid sulfur through reaction with sulfide to form polysulfides, which increased nitrite accumulation to forward Anammox process. Sulfur-oxidizing bacteria (e.g., Thiobacillus and Denitratisoma) coexisted with Anammox bacteria (e.g., Ca. Brocadia and Ca. Kuenenia) in the SDDA system despite the addition of exogenous COD.