Evaluating the Performance of a Microalgal-Bacterial Nexus for Sustainable Wastewater Treatment

The rising need for sustainable wastewater treatment has prompted the exploration of microalgal-bacterial integrated systems. This study evaluates the treatment efficiency of a treatment system for municipal wastewater collected from Zenin Wastewater Treatment Plant, Giza, Egypt. Experiments were conducted at a range of hydraulic retention time (HRT) from 1.0 d to 2.4 d, to determine the maximum efficiency of the treatment system. The raw wastewater was characterized by total suspended solids (TSS) of 61 mg/L, turbidity of 24 NTU, biochemical oxygen demand (BOD) of 21 mgO₂/L, and a high bacterial load of total coliforms of 9.4×10⁶ MPN/100 mL and E. coli of 5.4×10⁴ MPN/100 mL. Results revealed remarkable pollutant reduction with maximum removal rates of 91.1% for TSS and 94.2% for turbidity at an HRT of 1.7 days. BOD was reduced to 3.2 mgO₂/L, achieving an 85% removal efficiency. Total and fecal coliforms showed reductions of 5.2 and 4 log units, respectively, while E. coli was completely removed, meeting Egyptian irrigation water standards. The synergistic interactions between microalgal and bacterial biofilms contributed significantly to pollutant removal, with algal species such as Chlorella vulgaris and Nitzschia linearis forming dominant biofilms on rotating surfaces, and underscore the potentiality of this system.