The evolution of bacterial community structure and function in microalgal-bacterial consortia with inorganic nitrogen fluctuations in piggery digestate

Abstract The inorganic nitrogen concentrations in full-scale anaerobic digestion plants always vary seasonally, challenging the removal stability of microalgal-bacterial consortia in treating piggery digestate. Using a continuous photobioreactor, this study revealed the evolution of bacterial community under inorganic nitrogen fluctuations with influent nitrate loading ranged from 11 to 90 mg-N L−1 and influent ammonium loading ranged from 130 to 550 mg-N L−1. The loading of gradient nitrogen concentrations demonstrated that the optimal removal rate of total inorganic nitrogen was 45.62 mg-N L−1 d−1 along with the total chlorophyll concertation of 19.27 mg L−1, when introducing 240 mg-N L−1 of ammonium and 11 mg-N L−1 of nitrate. High throughput sequencing indicated that the dominant community members for nitrogen removal were shifted from prokaryotic algae to nitrifying and denitrifying bacteria, with nitrate being changed to ammonium. With the increasing influent ammonium loading, the suspended microalgal bacterial consortia gradually changed to microalgal bacterial biofilm, which was attributed to the biofilm-producing prokaryotes Thauera Comamona and Arenimonas. Co-occurrence network analyses illustrated that more functional bacterial modules were formed under ammonium fluctuation. Further correlation test identified influent ammonium loading as the important functional parameter shaping the bacterial community. Overall, this study expands our understanding of the homeostasis in microalgal-bacterial system in the cleaner production of piggery digestate.