Simultaneous microalgae cultivation and wastewater treatment in submerged membrane photobioreactors: A review

This review focuses on the potential advantages and challenges of submerged membrane photobioreactors (MPBRs) for microalgae cultivation and wastewater treatment. MPBR technology combines a conventional photobioreactor (PBR) with a membrane process to grow microalgae, enabling complete retention of algal biomass. Microalgae populations in MPBRs are affected by a number of factors, including wastewater characteristics and operational conditions. Although the wastewater types used in previous MPBR studies varied significantly in terms of composition, especially nitrogen (7.5 to 25 mg/L) and phosphorus (0.15 to 20 mg/L) concentrations, general trends and some optimised operating conditions can now be defined. Individual parameters, including hydraulic retention time (HRT), solids retention time (SRT), lighting, aeration, temperature, and pH were all found to be important factors affecting process efficiency; furthermore, there is evidently complex inter-relationships between these parameters, which should not be overlooked during MPBR design. Membrane fouling is still considered an operational challenge, with previous studies focusing on the relationship between membrane performances and algal organic matter. Applying immobilised microalgal technology to MPBRs has the potential to enhance productivity and mitigate fouling.