Microalgal-bacterial granular sludge can remove complex organics from municipal wastewater with algae-bacteria interactions

Abstract Interactions between algae and bacteria are pivotal in transforming complex organics for microalgal-bacterial granular sludge process, but the intrinsic removal mechanisms have not been well understood. Here, we investigate the mechanisms by which complex organics are removed from municipal wastewater. Complex organics can be disposed during day-night cycles, significantly impacted by the carbon-to-nitrogen ratio in the influent. Upregulated gap2 and gpmA genes enhanced the conversion of complex organics into CO 2 , mediated by the interactions of Chlorophyceae with Acidobacteriae / Sumerlaeia / Fimbriimonadia , and the upregulated petH gene in Cyanobacteria strengthened the fixation of CO 2 into biomass. The breakdown of starch, glycerol, and fatty acid were depended on Actinobacteriota , Chlorophyceae with Chloroflexia / Verrucomicrobiae , and Cyanobacteria with Desulfobacterota I , respectively. These findings provide new insights into the removal mechanisms of complex organics through microalgal-bacterial symbiosis and contribute to our understanding of the carbon cycle by microalgal-bacterial symbiosis in natural aquatic ecosystems.