(159ar) How Low Can It Go?: Survivability of Aerobic Activated Sludge Fed Dilute-Strength Wastes for Space Applications

As the idea of human planetary camps develops, the question of long-term stability and success necessitates the capability of recovering life-support materials from waste streams produced by the inhabitants. Any valorization efforts on the expected waste vectors will help diminish the need for costly deliveries of items crucial for life. A comprehensive unit designed to treat these camp’s expected (relatively low) organic and inorganic loading should be able to handle fluctuations in both the feedstock flow rate and composition, and have no net energy or oxygen consumption for sustainability. Further, the unit’s size and mass must be minimized due to limited vacancy aboard space vehicles. Utilizing microbial consortia, algal cells, and adsorption media, the proposed Biochemical Conversion System [BIOSYS] will serve a dual purpose by not only treating the wastes to treatment levels standard for reuse, but also producing various value-added products.

Anaerobic digestion will act as the initial processing stage to truncate the system’s overall oxygen demand, while a secondary aerobic stage will be implemented to reduce contaminants to levels closer to the goal of potable water (< 10 mg/L chemical oxygen demand [COD]). Due to the diet and activities predicted to occur, a dilute-strength wastewater is expected to be received by the aerobic processing stage, and currently the literature lacks evidence of these aerobic microorganisms being pushed to survive on low-strength organics as their feed.

Focusing on the aerobic treatment step, a suspended growth, activated sludge setup will be initiated, seeded with waste activated sludge from a local wastewater treatment plant’s return sludge basin. The degradation of various substrate components into carbon dioxide and water requires oxygen to satisfy the stoichiometric demands of aerobic metabolism, but due to the scarcity of oxygen in foreign atmospheres the total oxygen flux requirement must be optimized. The oxygen uptake rate anticipated for this processing stage is significantly lower than those experienced by aerobic wastewater treatment facilities operated on Earth (< 0.05 mg/L O₂/g VSS-min). Although attention has already been brought towards high COD removal rates here on Earth, the juxtaposition with low strength wastes as a feedstock (< 200 mg/L COD) poses a new challenge. Modified chemostats (see Figure 1 below) will be used to simulate the reactor vessels, allowing the governing parameters (hydraulic and solids retention time/air flow rate) to be easily adjusted while monitoring the operating conditions (temperature/pH/DO/COD/mixed liquor suspended solids [MLSS]/etc.) continuously. A thorough understanding of the expected COD removal characteristics was developed using shake flask experiments where it was found that the ideal hydraulic residence time will likely fall between 8 and 16 hours, with an initial mixed liquor concentration of ~2000 mg/L MLSS following standard methods 2540D. These operating conditions resulted in a COD removal efficiency of about 65% COD, producing an effluent of ~50 mg/L COD following standard method 5220D. Experimentation will soon evolve into continuous culturing where steady state effluent values are expected to approach our goals.