Coupling Microalgae-based Biochar with MBGS Enhances Microbial Synergy and Multi-Pollutant Removal from Saline...

The microalgal-bacterial granular sludge (MBGS) system has gained attention as an energy-efficient, multifunctional approach for wastewater treatment, yet its stability and pollutant removal under combined salinity and antibiotic stress remain unclear. In this study, we developed an MBGS system integrated with nitrogen-rich microalgae-derived biochar to enhance removal of organic matter, nutrients, and enrofloxacin (ENR) from saline aquaculture wastewater. The biochar-coupled MBGS achieved high removal efficiencies: 94.2±4.8% COD, 87.1±3.6% NH₄⁺-N, 60.3±4.6% PO₄^3--P, and 60.1±3.5% ENR. Microbial community analysis revealed enrichment of ammonia-oxidizing bacteria (Nitrosomonas, 3.3-9.7%), nitrite-oxidizing bacteria (Nitrospira, 2.3-6.4%), denitrifiers (Thauera, 14.9-27.6%), phosphate-accumulating organisms (Acinetobacter, 0.8-7.7%), and photosynthetic microalgae (Chlorophyceae, 1.4-23.6%). Fluorescence in situ hybridization (FISH) confirmed that biochar enhanced the spatial organization of these functional microbes within MBGS. Metagenomics revealed increased abundance of genes associated with carbon (porCD, CS, korD), nitrogen (amoAB, narGHI, norBC), phosphorus (ppk, phaA, acs), and photosynthesis-related (petABCD, psaA) genes, indicating improved metabolic capacity and synergy. Genome-resolved metagenomics further identified Nitrosomonas europaea, Acinetobacter sp002296655, Thauera aminoaromatica, and Chlorobium sp013334435 as core taxa driving carbon, nitrogen, and phosphorus cycling and energy flow, promoting synergistic interactions and enhancing pollutant removal under stress. Coupling MBGS with microalgae-based biochar improves resilience and multi-pollutant removal, offering a robust, sustainable strategy for advanced aquaculture wastewater treatment.