LAUSR

Autotrophic ammonium removal by sulfate-dependent anaerobic ammonium oxidation (S-Anammox) process was studied in an upflow anaerobic sludge bed reactor inoculated with Anammox sludge. Over an operation period of 371 days, the reactor with a hydraulic retention time of 16 h was fed with influent in which NH4+ concentration was fixed at 70 mg N L−1, and the molar ratio of NO2−:NO3−:SO42− was 1:0.2:0.2, 0.5:0.1:0.3 and 0:0:0.5 in stages I, II and III, respectively. As the NO2− in influent was entirely replaced by SO42−, the NH4+ removal rate was 31.02 mg N L−1 d−1, and the conversion rate of SO42− was 8.18 mg S L−1 d−1. On grounds of the high NH4+:SO42− removal ratio (8.67:1), the S2− accumulation and pH drop in effluent, as well as the analysis results of microbial community structure, the S-Anammox process was speculated to play a dominant role in stage III. The NH4+ over-transformation was presumably as a consequence of the cyclic regeneration of SO42−. Concerning the microbial characteristics in the system, the Anammox bacteria (Candidatus Brocadia), sulfate-reducing bacteria (SRB) (Desulfatiglans and Desulfurivibrio) and sulfur-oxidizing bacteria (SOB) (Thiobacillus) in biomass was enriched in the case of without addition of NO2− in influent. Sulfate reduction driven ammonium anaerobic oxidation was probably attributed to the coordinated metabolism of nitrogen- and sulfur-utilizing bacteria consortium, in which Anammox bacteria dominates the nitrogen removal, and the SRB and SOB participates in the sulfur cycle as well as accepts required electrons from Anammox bacteria through a direct inter-species electron transfer (DIET) pathway.