Functional differentiation of size-fractionated biomass in the mixotrophic mainstream UASB-anammox process

Abstract

The soluble organic matter in sewage is one of the major obstacles to the stable operation of mainstream anammox, which would induce the excessive proliferation of heterotrophic bacteria. Given its excellent volumetric nitrogen removal rate (>2.0 kg N m−3 d−1) in mainstream treatment at 15 °C, the physicochemical properties and microbial ecology of size-fractionated aggregates in mixotrophic anammox-UASB system were investigated to develop strategies for population management. The presence of glucose or acetate (COD/N = 1.0) decreased the contribution of anammox by approximately 30 %, thereby causing the increase of effluent TN concentrations to over 12 mg N L−1, in which NH4+-N accounted for ∼85 %. Interestingly, the relative abundance of anammox bacteria were increased from 1.0 % in flocs (<0.2 mm) to 34.9 % in big granules (>0.8 mm) of the acetate-fed reactor, while the abundance of denitrifying bacteria was decreased from 74.0 % in flocs to 12.0 % in big granules. Similar trend was also observed for the glucose-fed reactor. As a result, the expressions of anammox functional genes, specific anammox activity, extracellular polymeric substances and heme c contents were all increased with the increase of particle sizes. Notably, in contrast to the glucose-fed biomass, the acetate-fed biomass showed significant potential of denitratation. Accordingly, the screen with a size of around 0.2 mm may be an effective tool to uncouple the retention times of denitrifying bacteria and anammox bacteria. These results provided direct evidences for functional differentiation of size-fractionated biomass and would guide us to balance their functions for a satisfactory effluent quality.