Membrane photobioreactors for integrated microalgae cultivation and nutrient remediation of membrane bioreactors effluent

• Integrated microalgae cultivation and nutrient removal in wastewater stream using MPBR.
• MPBR effectively avoid wash-out and increase the optimum D of 0.2 day−1 in PBR to 0.5 day−1.
• 3.5× biomass concentrations and 2× volumetric productivities were achieved with MPBR.
• Possible drawback: lower nutrient removal with increasing D.

The feasibility of a new concept of wastewater treatment by combining a membrane bioreactor (MBR) and a microalgae membrane photobioreactor (MPBR) is assessed in this study. In this system, the organic carbon present in wastewater is expected to be fully oxidized in the MBR, while the nutrients are removed via the subsequent MPBR treatment. The effluent of a lab-scale MBR was fed into a PBR and a MPBR which served as growing medium for Chlorella vulgaris. The MPBRs demonstrated their superiority by limiting the algae wash-out, thus increasing the allowable optimum dilution rate (Dopt). At these corresponding Dopt values, 3.5 and 2 times higher biomass concentrations and volumetric productivities respectively were achieved by the MPBR. It is also possible to run the MPBR at still higher biomass concentration, thus enabling a smaller footprint and higher nutrient removal efficiency. However, reduced nutrient removal efficiencies were found to be one possible drawback.