The Effects of Alternative Biological Primary Processing Approaches on the Efficiency of an Integrated Water Processing System

Biological processes represent a potential primary treatment approach as part of an integrated system for recycling wastewater during long term space missions. The rationale for biological processing lies in the removal of organic and nitrogen contaminants within the wastewater, leading to concomitant reductions in the costs of downstream P/C systems used for production of potable water. Several different general approaches for biological processing are under evaluation; 1) separate versus single reactors for conducting nitrification and denitrification, 2) rotating the membrane unit to enhance the rate of nitrification, 3) integration of alternative electron acceptors (H₂ or CH₄) for more complete volatilization of nitrogen. Equivalent system mass (ESM analysis) of the different biological reactor configurations was performed to assess design alternatives for both the transit mission and early planetary base (EPB). Consolidating nitrification and denitrification into a single reactor or rotating the membrane units decreased ESM costs by 4–10% depending on the mission scenario. Adding a reactor to provide H₂ and enhanced denitrification led to the largest increases in ESM (13–20% in transit, 7–9% for the EPB). The majority of the costs associated with the biological processing (~70%) was associated with pumps and manpower. Preliminary evaluation of the effects of bioreactor effluent on downstream processing systems indicates that optimizing the extent of primary NH₄⁺ conversion (i.e., ammonia oxidation) is of primary importance in biological reactor design. Better data on the impacts of residual organics and non-volatile N (i.e., NO₃⁻, NO₂⁻) on biofouling of physicochemical systems is needed before the treatment standards for these effluent components can be established. This work serves as a basis for further ESM analysis of biological processing approaches using further refinements in assumptions, additional test data, and alternative reactor designs.