Start-up of the combined anaerobic ammonium oxidation and solid phase denitrification process and microbial characterization analysis

To improve the nitrogen removal performance of anaerobic ammonia oxidation (anammox)-based processes, a modified anaerobic baffled reactor (ABR) equipped with a packed bed of poly-3-hydroxybutyrate-cohyroxyvelate (PHBV) was employed to start up the combined anammox and solid phase denitrification (SPD) process for the treatment of nitrogen-rich wastewater. Results showed that a stable removal of total inorganic nitrogen (TIN) of 98.5 % was achieved with a nitrogen loading rate of 0.46 kg center dot(m(3)center dot d)(-1), decreasing the effluent TIN concentration to <2 mg center dot L-1. Throughout the operation period of 180 days, sludge granulation in three compartments of the ABR was promoted by a stepwise decrease in the hydraulic retention time. The anammox reaction and endogenous denitrification mainly occurred in the first two compartments with inorganic feeding and contributed >86 % of TIN removal. 16S rRNA gene amplicon sequencing showed that anammox communities, dominated by genera Candidatus Kuenenia and Candidatus Brocadiaceae, were enriched in granular sludges with symbiotic heterotrophic bacteria. Co-cultures of hydrolytic bacteria (Burkholderiales, Kapabacteriales, and Clostridium-sensustricto-7) and denitrifying bacteria (Comamonadaceae, Rhodocyclaceae, and Denitratisoma) were detected within the biofilm on the surface of PHBV particles. PHBV hydrolysate input effectively drove heterotrophic denitrification in the successive compartment and increased the complexity of microbial co-occurrence networks. These findings provide insight into the synergistic mechanisms between anammox and SPD and present a feasible combined process application for advanced biological nitrogen removal.