A novel process based on marine heterotrophic nitrification and aerobic denitrification bacteria for treating mariculture wastewater: Performance, biofilm characteristics and microbiome responses to dissolved oxygen

A novel reactor utilizing marine heterotrophic nitrification and aerobic denitrification (MHNAD) bacteria offers an effective approach for treating mariculture wastewater. However, the impact of dissolved oxygen (DO) concentration on its performance has been understudied. This research investigated how varying DO concentrations influence the performance, biofilm characteristics, and microbiome of the reactor when inoculated with MHNAD bacteria. The results demonstrated that reducing the DO concentration from 6 mg/L to 2 mg/L decreased the removal efficiency of chemical oxygen demand (COD) and ammonia nitrogen (NH4+-N) but significantly improved nitrate nitrogen (NO3--N) removal. Higher DO concentrations (6 mg/L) promoted the production of extracellular polymeric substances (EPS), particularly proteins. Microbial analysis revealed that MHNAD bacteria, particularly the genus Zobellella, consistently dominated the bioreactor, though their abundance decreased at lower DO concentrations. Bugbase analysis indicated that biofilm formation and aerobic bacterial abundance decreased as DO concentration declined. Additionally, metabolic pathway analysis suggested that lower DO levels might inhibit glycolysis and TCA cycle processes, while also altering the primary nitrogen removal pathways.