Date of Award
Master of Science (MS)
Chemical and Biomolecular Engineering
The objective of this research was to test the feasibility of using forward osmosis (FO) with polyelectrolyte draw solutions to recover water from bioreactor mixed liquors. When combined with an Anaerobic Osmotic Membrane Bioreactor (AnOMBR), such a system could process fecal and food waste from astronauts aboard the International Space Station (ISS) and reclaim important nutrients and water. This project focused on measuring the obtainable water recovery rates from bioreactor effluent, and the identifying challenges associated with the operation.
AnOMBRs feature several advantages over aerobic bioreactors, and non-osmotic anaerobic membrane bioreactors (AnMBR). Anaerobic bioreactors avoid the significant energy costs of aerobic bioreactors. Conventional AnMBRs use microfiltration or ultrafiltration with an applied pressure. AnOMBRs use FO membranes that do not allow low molecular weight organics to pass, and do not require an applied pressure. AnOMBRs 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 volume of permeated water per gram of draw solute that has diffused from the draw solution into the bioreactor. To obtain a high RSFS, poly(acrylic acid) and poly(acrylic acid-co-maleic acid) were evaluated as draw solutes. The large size of the polymer and the high osmotic pressure they can provide make them highly advantageous.
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 an exceedingly small mass of polyelectrolyte crossover from the draw solution to the feed; thus, RSFS was 80, which was higher than the target value of 20 for viable operation. 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 formation of a foulant cake layer. This study established that FO could be feasible for regenerative water purification from bioreactor digesters. By utilizing a polyelectrolyte draw solute with exceedingly 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 lasting 30 months or more.
Raulerson, Calen, "Water Recovery from Bioreactor Mixed Liquors Using Forward Osmosis with Polyelectrolyte Draw Solutions" (2021). All Theses. 3660.