The impact of biological pretreatment on reverse osmosis performance in space flight applications

RO is a treatment technology likely to be used for the recovery of wastewater on board long duration, manned space flights. As with terrestrial RO applications, concentration polarization and fouling lead to decreasing productivity and increasing energy demands with time. These problems are further complicated in a closed loop environment that demands a high level of recovery and quality.

Physiochemical and biological pretreatment options can enhance the performance of the RO system. Physiochemical pretreatment is not always desirable in the application of long duration space flight because the transport and stowage of consumables can be cost prohibitive. Also, the transport and stowage of hazardous materials such as strong acids and bases is not desirable. Biological pretreatment is a low energy option that requires only a limited supply of consumables. Additionally, biological pretreatment is a proven terrestrial technology that is well understood.

To determine the degree to which the incorporation of biological treatment enhances RO performance, a series of bench scale experiments were performed. The RO performance was measured in terms of permeate flux decline, solute rejection, and flow resistances. A mass balance and observed solute concentrations also helped to determine the fate of selected solutes. The gel layer model was used to evaluate the permeate flux for each of the experiments. Observed resistances also indicate that biological pretreatment alleviates the degree of fouling. Results indicate that enhanced urea hydrolysis, pH decrease, and carbon oxidation serve as the primary benefits of biological pretreatment.