Construction and optimization of low C/N-adapted Chlorococcum-Bacteria symbiosis for energy-efficient wastewater remediation

This study developed a microalgal-bacterial symbiosis (MBS) system using Chlorococcum robustum AY122332.1 isolated from rare earth tailings wastewater to treat synthetic municipal wastewater. Systematic optimization identified a 1:1 bacteria-microalgae ratio (MBS 1) as optimal, achieving nearly 100% for ammonia and 92.2% for COD removal. Mechanistic analysis revealed enriched nitrogen-transforming consortia in MBS 1, particularly Thauera, whose nitrite reductase and polyhydroxyalkanoate synthesis capabilities enhanced simultaneous nitrification-denitrification. MBS 1 showed superior system stability via elevated zeta potential , driven by protein-rich extracellular polymeric substances (EPS) production and humic acid accumulation. These biopolymers facilitated microaggregate formation through ligand bridging and hydrophobic interactions, establishing redox-stratified micro-niches that sustained functional microorganisms. The synergistic interactions in MBS system enable efficient nutrient recovery while maintaining ecological resilience under low C/N conditions, providing new insights into sustainable wastewater bioremediation.