Comparative performance of nanofiltration and forward osmosis membranes in a lab-scale forward osmosis membrane bioreactor

Nanofiltration (NF) and commercial HTI Forward Osmosis (FO) membranes were tested in a live membrane bioreactor (MBR) for performance comparison. Inorganic draws (NaCl, Na3PO4), surfactants (TEAB, SDS), and polyelectrolytes (PDAC, PGBE) were all tested as draw solutes; water flux, reverse solute transport (RST), toxicity and viscosity were observed and compared for each. Synthetic municipal wastewater was selected as a feed and Bacillus Subtilis species was inoculated in the solution and grown overnight for development of a monoculture bioreactor. Deionized (DI) water was also used as a feed for control. The results indicated that the NF membrane showed good promise in the FOMBR process when used with high molecular weight draw solutions. In comparison to the FO membrane, it showed a significantly higher water flux with only a slightly higher RST. The NF membrane is recommended for further investigation in the FOMBR, provided fouling control is in place. Although the observed reverse solute transport values were not toxic to the bacteria under observation, long-term accumulation of draw solute in the bioreactor of an FOMBR wastewater treatment plant is an issue which requires further investigation.