Algal–Bacterial Granular Sludge Development from a Pond Microbiome: Rapid Granulation, Treatment Performance, and Nutrient Removal Pathways

Algal–bacterial granules (ABG) are attractive for mitigating greenhouse gas emissions, reducing aeration energy demand, and adopting circular economy in wastewater treatment plants. This study investigated ABG development from a pond-microbiome, nutrient removal capabilities, and microbial community succession in a photosequencing batch reactor (photo-SBR). The formation of compact, green-colored, and fast-settling granules was rapid and evident within 10 photo-SBR cycles. rRNA amplicon sequencing showed moderation of the microbial diversity during granulation and the presence of diverse communities including proteobacteria, cyanobacteria, and green algae in mature granules. Granulation was corroborated with the establishment of ammonium and phosphate removal pathways. ABG and photo-SBR conditions enabled the effective and simultaneous removal of chemical oxygen demand (COD; 89%), biochemical oxygen demand (BOD; 96%), NH 4 + -N (96%), and PO 4 3– -P (90%). The effective removal led to lower COD (