Exploring the feasibility of sewage treatment by algal–bacterial consortia

Current biological wastewater treatment is energy intensive. The application of algal–bacterial consortia to treat wastewater has recently attracted considerable attention because mechanical aeration is unnecessary. Therefore, algal–bacterial bioreactors are emerging as alternatives to activated sludge-based bioprocesses. Most studies have used a plate substratum to support the growth of algal–bacterial biofilms, which results in low reactor efficiencies. Usually, 2–10 days are required for targeted pollutant removal effects. Substratum structures can significantly influence reactor efficiencies. Indeed, substratum-free biofilms (granules) generally achieve high reactor efficiencies that rapidly form. 7–12 h are sufficient for a high-level pollutant removal efficiency. However, granule stability must be validated during long-term experiments (>1 year) involving real wastewater. In addition, the application of algal–bacterial membrane bioreactors represents a novel treatment approach. In membrane bioreactors, good reactor efficiencies and stabilities can be achieved. However, the maximum capacity of algal–bacterial membrane bioreactors requires further investigation. In addition, an accurate model for pollutant removal kinetics in algal–bacterial reactors is not yet available but is necessary for reactor control and up-scaling. The microbial and physical structures of algal–bacterial biofilms require more studies to clarify the system. Finally, the operational costs of algal–bacterial systems must be kept low in order to enhance their potential for sewage treatment at large scales. Good illumination control and recycling biomass for biodiesel or methane production could be applied to reducing the operation cost.