Algal-Bacterial Symbiotic Granular Sludge Technology in Wastewater Treatment: A Review on Advances and Future Prospects

This review systematically examines the critical mechanisms and process optimization strategies of algal-bacterial granular sludge (ABGS) technology in wastewater treatment. The key findings highlight the following: (1) enhanced pollutant removal-ABGS achieves >90% COD removal, >80% total nitrogen elimination via nitrification-denitrification coupling, and 70-95% phosphorus uptake through polyphosphate-accumulating organisms (PAOs), with simultaneous adsorption of heavy metals (e.g., Cu2+, Pb2+) via EPS binding; (2) energy-saving advantages-microalgal oxygen production reduces aeration energy consumption by 30-50% compared to conventional activated sludge, while the granular stability maintains >85% biomass retention under hydraulic shocks; (3) AI-driven optimization-machine learning models enable real-time prediction of nutrient removal efficiency (+/- 5% error) by correlating microbial composition (e.g., Nitrosomonas abundance) with operational parameters (DO: 2-4 mg/L, pH: 7.5-8.5). This review further identifies EPS-mediated microbial co-aggregation and Chlorella-Pseudomonas cross-feeding as pivotal for system resilience. These advances position ABGS as a sustainable solution for low-carbon wastewater treatment, although challenges persist in scaling photobioreactors and maintaining symbiosis under fluctuating industrial loads.