Abstract
This paper reports on the use of forward osmosis (FO) with polyelectrolyte draw solutions to recover water from bioreactor mixed liquors. The work was motivated by the need for new regenerative water purification technologies to enable long-duration space missions. Osmotic membrane bioreactors may be an option for water and nutrient recovery in space if they can attain high water flux and reverse solute flux selectivity (RSFS), which quantifies the mass of permeated water per mass of draw solute that has diffused from the draw solution into a bioreactor. Water flux was measured in a direct flow system using wastewater from a municipal wastewater treatment plant and draw solutions prepared with two polyelectrolytes at different concentrations. The direct flow tests displayed a high initial flux (>10 L/m2/h) that decreased rapidly as solids accumulated on the feed side of the membrane. A test with deionized water as the feed revealed a small mass of polyelectrolyte crossover from the draw solution to the feed, yielding an RSFS of 80. Crossflow filtration experiments demonstrated that steady state flux above 2 L/m2·h could be maintained for 70 h following an initial flux decline due to the formation of a foulant cake layer. This study established that FO could be feasible for regenerative water purification from bioreactors. By utilizing a polyelectrolyte draw solute with high RSFS, we expect to overcome the need for draw solute replenishment. This would be a major step towards sustainable operation in long-duration space missions.
Highlights
Treating crew waste streams for long-duration (i.e., 30 months) space missions will require regenerative approaches to maximize water recovery and shift focus from waste removal to resource recovery [1]
Water recovery from bioreactor digester mixed liquors was achieved with adequate Water recovery from bioreactor digester mixed liquors was achieved with adequate flux over long periods of time using forward osmosis with polyelectrolyte draw solutions
Fouling was the largest contributor to flux decline in direct flow measurements
Summary
Treating crew waste streams for long-duration (i.e., 30 months) space missions will require regenerative approaches to maximize water (and nutrient) recovery and shift focus from waste removal to resource recovery [1]. Designs based on municipal wastewater treatments plants (WWTPs) are not feasible for ECLSS. Such facilities have large footprints encompassing many different processes designed to handle large intake volumes and complex feed compositions. WWTPs based on conventional activated sludge treatment include primary clarifiers, grit removers/filters, aeration tanks, digesters, and additional clarification steps. They require addition of chemicals to treat the wastewater. The resulting biosolids produced from activated sludge solids, once dewatered, may be converted into useful components such as fertilizer, biogas, and other fatty acids after digestion
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have