Attached growth microalgae-bacteria consortia: A sustainable option for in-situ remediation of contaminated open drains

Rapid population growth and urbanization in developing countries challenge wastewater management due to limited resources. Affordable and innovative solutions are hence crucial. This study introduces a novel attached growth system using microalgae-bacteria consortia (MABC) on coir for in-stream remediation of polluted drains. Using a simple co-cultivation method with natural xenic cultures, we compared the consortia's efficacy to individual bacterial and microalgal cultures. Results from suspended growth studies revealed that the MABC system achieved higher removal rates, with 81 % removal of chemical oxygen demand (COD) and 71 % removal of ammonia-N in 24 h of batch study. Owing to the symbiotic interactions and enhanced extracellular polymeric substance (EPS) production (268 mg/g TSS), the MABC system exhibited superior biomass productivity (2.75 g/ m2/day) and settleability (Sludge volume index (SVI) = 38.3 mL/g) after 30 days of co-cultivation, outperforming stand-alone bacterial and algal systems. In the continuous flow study, the MABC biofilm system performed comparably to an aerated bacterial system at a low HRT of 1 h, eliminating the need for energyintensive aeration and indicating its cost-effective potential. The comparative life cycle assessment (LCA) shows that MABC in attached growth mode (MABC-A) has significantly lower environmental impacts across 18 categories compared to the conventional activated sludge process (ASP) and MABC in suspended growth mode (MABC-S), mainly due to its energy-free operation. Additionally, the substantial reduction in global warming potential observed in MABC systems underscores its potential as a low-energy method for improving water quality and mitigating climate change impacts.