Biochar-calcium alginate composite immobilizing Pseudomonas sp. H6 for phosphate and ammonium recovery: Multi-omics insights and practical application evaluation.

Water eutrophication has emerged as a pervasive ecological challenge worldwide. To realize the resource utilization of waste and nutrients, a novel rape straw-derived biochar-calcium alginate composite (M-CA-RBC) immobilized Pseudomonas sp. H6 was synthesized to simultaneously remove phosphate (PO) and ammonium (NH) from distillery wastewater. The removal performance of PO and NH by M-CA-RBC were investigated. The removal mechanisms were explored by using different adsorption models combined with microbial degradation kinetics, analysis of dissolved organic matter components, electrochemical analysis, metagenomics, and metabolomics. The resource application potential of M-CA-RBC was evaluated. The results showed that M-CA-RBC had good removal performance for PO (17.81 mg/g) and NH (25.78 mg/g). Surface precipitation, electrostatic attraction, Poly-P accumulation, microbial-induced calcium precipitation, and microbial assimilation were the main removal mechanisms of PO by M-CA-RBC. The removal mechanisms of NH were micropore filling, ion exchange, electrostatic attraction, and heterotrophic nitrification-aerobic denitrification (HN-AD). M-CA-RBC had a good application potential in the practical distillery wastewater, with removal rates of PO and NH reaching 88% and 65%, respectively. After adsorption saturation, M-CA-RBC exhibited good stability, which could be used as a slow-release fertilizer to promote the growth of mung beans. This study provides practical significance for the efficient removal and recovery of nitrogen and phosphorus in wastewater.