Mass balance and bacterial characteristics in an in-situ full-scale swine wastewater treatment system occurring anammox process

[Display omitted] •A spontaneous anammox process in full-scale swine wastewater system was studied.•Anammox contributed 40% and 78% to N-loss in aerobic and anoxic tanks, respectively.•Mass balance showed that anammox rate was 1.6 times higher than denitrification.•Granular sludge had a high purity, with anammox relative abundance as much as 92.2%.•Mixing sludge had a higher oxygen tolerance compared with granules based on SAA test. A spontaneous development of full-scale anaerobic ammonium oxidation (anammox) process was seldom reported, and its operational parameters could supply references in actual applications. This engineered case indicated that anammox process was suitable for treating relatively high-strength ammonium and organics wastewater due to niche differentiation of biofilm. Results of isotope labelling showed that anammox contributed approximately 40% to N-loss in aerobic unit, but this value increased to 78.3% in anoxic tank. Mass balance showed that N-removal via anammox and denitrification pathways were 38.1 and 23.9 g m−3 d−1, and anammox rate was 1.6 times higher than denitrifiaction. The wild-type anammox granules had a high purity, with anammox accounting for 92.2%. Candidatus Brocadia was the predominant species. Mixing sludge had a higher oxygen tolerance compared with granules, although the latter had a higher anammox activity under anaerobic conditions. Moreover, physicochemical precipitation on the surface of granules may be related to granulation mechanism.