Enhanced the Treatment of Seafood Processing Wastewater Using the Anaerobic–Anoxic–Oxic (AAO) Process With Granular Sludge

Seafood processing wastewater contains high concentrations of organics and nutrients that need to have an effective solution. This study aims to explore the use of granular sludge in seafood wastewater treatment using anaerobic-anoxic-aerobic (AAO) process. The results showed that the granular sludges were successfully cultivated from the traditional activated sludge sources. The bioreactor demonstrated robust treatment performance, achieving a high chemical oxygen demand (COD) removal efficiency exceeding 93%, total nitrogen (TN) removal ranging from 56.6% to 68.6%, and ammonium removal (NH₄ ⁺-N) of 80% to 88.57%. However, total phosphorus (TP) removal efficiency was relatively moderate at 47.36% ± 10.33%. Metagenomic analysis (16S rRNA) revealed a diverse and evenly distributed microbial community within the granular sludge. In anaerobic granular sludge, the dominant phylum was Bacillota (45.3%), followed by Thermodesulfobacteriota (18.2%) and Synergistota (11.24%), with minor contributions from Campylobacterota (7.58%), Chloroflexota (3.98%), and Bacteroidota (3.6%), alongside other less abundant phyla (10.1%). Anoxic granular sludge exhibited a shift, with Pseudomonadota (32.87%) and Thermodesulfobacteriota (25.08%) dominating, while Bacillota (11.95%), Bacteroidota (7.9%), and Chloroflexota (4.1%) contributed less, and other phyla comprised 18.21%. For aerobic granular sludge, Pseudomonadota represented the most prevalent phylum (42.21%), followed by Thermodesulfobacteriota (14.94%) and Bacillota (14.87%), with lower abundances of Bacteroidota (7.74%) and Chloroflexota (4.91%), while other phyla accounted for 15.42%.