To reduce the relatively high energy consumption in conventional membrane bioreactor (MBR), recent research effort has been dedicated to the development of osmotic membrane bioreactor (OsMBR) by replacing ultrafiltration (UF) and microfiltration (MF) membrane with FO membrane in a single biological tank. Similar to FO process, the OsMBR utilizes the osmotic pressure gradient across the semipermeable membrane to continuously harvest high-quality water from treated wastewater by high-rentention biomass in the feed tank. Depending on the biological process, OsMBR can be aerobic or anaerobic, and the typical configurations are presented in Fig.1.
Figure 1. Schematic digram of OsMBR systems. (a) Submerged OsMBR for wastewater reclamation, aerobic condition; (b) Submerged OMBR for wastewater treatment, aerobic condition; (c) Submerged OMBR for biogas recovery, anaerobic condition; (d) Side-stream OMBR, aerobic condition; (e) Combined OMBR, aerobic condition. Adapted from Wang X. et at., 2016. Click on the figure to see the originial paper.
Similar to FO process, the OsMBR suffers from continueous loss of draw solutes due to reverse solute flux, and as a result, gradual salinity build-up at feed side may inhibit microbial growth and nutrient removal performance. Another notable issue is separation and regeneration of draw solutes in final diluted draw solution to render clean and fresh water, though this process may be energy-intensive and a detailed cost-benefit analysis should be conducted compared to conventional MBR.