Towards simultaneously removing nitrogen and sulfur by a novel process: Anammox and autotrophic desulfurization–denitrification (AADD)

The combined anammox (anaerobic ammonium oxidation) and autotrophic desulfurization–denitrification (AADD) process represents a promising innovative technology for biological nitrogen and sulfur removal. In this study, an up-flow anaerobic sludge blanket reactor, which was started with anammox and methanogenic granules, was operated for 245 days to evaluate the co-treatment of wastewater containing nitrogen and sulfur. The reactor demonstrated good performance in terms of nitrogen and sulfide removal and exhibited excellent behavior for removal of NH4+-N, NO2−-N and S2−-S exceeding 252, 333 and 330 mg L−1, respectively. The highest nitrogen removal rate and sulfide removal rate attained were 4.00 kgN m−3 d−1 and 2.39 kgS m−3 d−1, respectively, which were also the highest reported values for a coupling-system. The influent NH4+-N:S2−-S and NO2−-N:S2−-S ratios set at 1.74 and 2.20–2.27 are suitable for maintaining system stability. The specific activities of anammox and autotrophic desulfurization–denitrification (SAA and SADD), extracellular polymeric substance (EPS), heme c (an important cofactor of some anammox bacterial enzymes) and the diversity of anammox and autotrophic desulfurization–denitrification (ADD) bacteria were investigated during the operation. The SAA and SADD are regarded as key factors for high efficiency. The granules contained many EPS (128.4–204.5 mg g−1 VSS) and minor heme c content (1.17 μmol g−1 VSS). The dominant bacteria belonged to members of Brocadiaceae and Hydrogenophilaceae, a majority of which were anammox bacteria and ADD bacteria, respectively. These observations suggest a new removal process for ammonia, nitrite and sulfide utilizing an uncommon mechanism involving simultaneous anammox and ADD.