Interplay role of microalgae and bio-carriers in hybrid membrane bioreactors on wastewater treatment, membrane fouling, and microbial communities

Algal membrane bioreactors (algae-MBRs) and advanced hybrid biocarrier algal membrane bioreactors (hybrid algae-MBRs) have been investigated to improve the performance of conventional MBRs (C-MBRs). Maximum chemical oxygen demand and nutrient removal efficiencies, similar to the maximum biomass growth rate, chlorophyll-a concentration, and balanced microbial growth, were achieved in the hybrid algae-MBR inoculated with polyethylene biocarriers and algal cells. During the 90 days of operation, the hybrid algae-MBR demonstrated lower membrane fouling without membrane washing, whereas the C-MBR and algae-MBR were washed seven and four times, respectively. Compared to the C-MBR, both the algal MBR and hybrid algal MBR exhibited higher levels of nitrification, with 6 and 10 % greater rates, respectively. In addition, they displayed significant improvements in ammonium biomass uptake compared to the C-MBR, with increases of 30 and 37 %, respectively. In the algae-MBR, the chlorophyll-a results showed proliferation of algae over time. However, biocarriers that provide an additional surface for microbial growth, particularly algal strains, inhibit algal proliferation and result in balanced microbial growth (based on chlorophyll-a/MLVSS) in the bulk solution of the hybrid algae-MBR. In addition, the oxygen mass balance estimated that photosynthesis provided 45 % of the dissolved oxygen required in the studied algal reactors, whereas mixing provided the remainder. Additionally, microbial sequencing results indicated that the microbial communities (e.g., Candidatus, Cloacibacterium, and Falavobacterium) were altered by introducing microalgae and biocarriers that affected the activity of different microorganisms, changed the sludge and fouling layer properties, and improved the performance of the C-MBRs.