Tertiary wastewater treatment in membrane photobioreactor using microalgae: Comparison of forward osmosis & microfiltration.

Discharge of wastewater with high nitrogen and phosphorus content is a major cause of eutrophication. In this study, a microfiltration-based membrane photobioreactor (MPBR) and forward osmosis-based osmotic membrane photobioreactor (OMPBR) have been operated with Chlorella vulgaris for continuous tertiary wastewater treatment. Both the bioreactors exhibited good biomass accumulation (over 2g/L), although the OMPBR achieved better nutrients removal due to high rejection properties of the membranes. At 2days HRT, the OMPBR achieved nitrogen and phosphorus removal efficiencies of 86-99% and 100%, respectively, whereas the corresponding values in the MPBR were 48-97% and 46%, respectively. Based on the energy input, the total operating costs for OMPBR were 32-45% higher than that of the MPBR, and filtration cost for OMPBR was 3.5-4.5 folds higher than that of the MPBR. These results indicate that the integration of membrane filtration with photobioreactors is promising in microalgae-based tertiary wastewater treatment.