Algal-bacterial symbiotic system for treatment of heavy metal containing wastewater: performance, mechanisms and applications

In algal symbiotic systems (ABSS), bacteria and algae establish mutualistic, commensal, or parasitic relationships, leveraging their respective biosorption and bioaccumulation mechanisms, along with symbiotic effects, to effectively treat heavy metal (HM)-containing wastewater. The HM removal mechanisms by ABSS are modulated by multiple factors, including light intensity, pH, temperature, algal-bacterial ratio, and exhibit distinct patterns for different HMs. Based on a comprehensive literature review, the optimal conditions for ABSS are a light intensity of 60–300 μmol/m2/s, a slightly acidic to neutral pH, a temperature of 23–30 °C, and brown algae being the most effective. Furthermore, the practical applications and limitations of ABSS in different industries producing HM-containing wastewater (such as mining, animal agriculture, urban discharges, and textiles) were discussed, and analyzes its sustainability. This review establishes a robust theoretical framework for ABSS treatment mechanism of HM-containing wastewater, offers practical engineering guidelines, and promotes ABSS research and application.