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Hollow fiber membrane reactors (HFMBRs) may be used for biological wastewater treatment, and may be integrated with NASA's current research developments. The goal of this paper is to (a) evaluate the effect of mass transfer and hydrodynamics in a microporous HFMBR and (b) appropriateness of HFMBRs for use in space applications. Even though bubble-less aeration was not achieved by the use of microporous membranes, mass transfer within the HFMBR was found to increase after biofilm formation. Conversely, convective flow dominated transport within the system. Despite the high treatment efficiency obtained by the HFMBR, due to the bioreactor size, configuration and membrane spacing within the HFMBR, the bioreactor was not a suitable option for application under microgravity conditions. Even though developing a system with more favorable system hydrodynamics would aid in treatment efficiency, the use of a microporous HFMBR is not a recommended option to meet NASA's needs.

Hollow fiber membranes aerate wastewater without bubble formation by separating the liquid and gases phases with a semi-permeable membrane. These membranes have shown to successfully create aerobic conditions within a biological reactor. This research investigated the effect of long term usage and biofilm growth on membrane's ability to transfer oxygen to solution. Results show that oxygen transfer across the membrane decreased significantly compared to unused membranes in areas of high biofilm growth while low biofilm growth showed only slight decreases.

Microbial control in closed environmental systems, such as those of spacecraft or proposed base missions is typically limited to disinfection in the potable water system by a strong chemical agent such as iodine or chlorine. However, biofilm growth in the environmental system tubing threatens both the sterility of the potable water distribution as well as operational problems with wastewater systems. In terrestrial systems, biofilm has been recognized for its difficulty to control and eliminate as well as resulting operational problems. In order to maintain a potable water source for crew members as well as preventing operational problems in non-sterile systems, biofilm needs to be considered during system design. While biofilm controls can limit biofilm buildup, they are typically disruptive and cannot completely eliminate biofilm. Selenium coatings have shown to prevent initial biofilm attachment as well as limit attached growth on a variety of materials.

Biological pre-treatment of early planetary/lunar base wastewater has been extensively studied because of its predicted ability to offer equivalent system mass (ESM) savings for long term space habitation. Numerous biological systems and reactor types have been developed and tested for treatment of the generally unique waste streams associated with space exploration. In general, all systems have been designed to reduce organic carbon (OC) and convert organic nitrogen (ON) to nitrate and/or nitrite (NOx -). Some systems have also included removal of the oxidized N in order to reduce overall oxygen consumption and produce additional N2 gas for cabin use. Removal of organic carbon will generally reduce biofouling as well as reduce energy and consumable cost for physiochemical processors.

When compared to physical and chemical processes for wastewater treatment in space, the benefits of biological systems include reduced storage and handling of waste material, lower energy requirements and plant growth system compatibility. An advanced membrane reactor (AMR) was constructed to treat ammonium-rich simulated wastewater. The effluent pH was approximately 6.3, and ammonium and TOC reduction rates were greater than 60 percent and 99 percent, respectively. The experimental results demonstrate that this technology may be suitable for space applications. However, the long-term performance of these systems should be investigated.

The objective of this study was to evaluate the treatment efficiency and reliability of a small-scale (1/20th) replica of the JSC biological treatment system over an extended period of time (18 months of operation). The two biological reactor components were an anaerobic packed bed for denitrification and an aerobic tubular reactor for nitrification. A recycle line (20X) linked the two biological reactors. Effectiveness of the biological system to treat a waste stream (1 L/day) containing water, urine, and soap (Igepon T42) was quantified by monitoring total nitrogen and organic carbon. Distribution of nitrogen in the effluent was measured and consisted of ammonium, nitrite, and nitrate. Daily concentrations of total nitrogen in the influent varied greatly. The system achieved 50% removal of total nitrogen and 80% removal of the influent organic carbon. The results indicate improved treatment effectiveness and resiliency with time.

This research compared the nutrient content of the Biological Water Processor (BWP) effluent at JSC with acceptable nutrient ranges for general hydroponic NFT-solutions. Evaluated nutrient-components were NO3-N, P, K, Ca, Mg, Fe, Mn, Zn, B, Cu and Mo. Compared to Cooper's and Molyneaux's solution (Jones, 1997) BWP-nutrient concentrations were low for Ca, Mg, Fe and B. Compared to the NFT-solution used at KSC (Wheeler et al., 1997), the BWP-effluent showed higher contents of P, K, Zn, Cu and Mo and lower contents of N, Ca, Mg, Fe and B. This indicates that the BWP-effluent could support NFT-plant production.

This research is based on the hypothesis that recycling biofilm can provide the required carbon to increase biological denitrification of the carbon limited early planetary base wastewater. Recycling biofilm may offer significant advantages including a reduction in solid waste from biological wastewater processors, increased N2 return to cabin air, a reduction in TDS loading to the RO system, and increased alkalinity to drive further nitrification. The results of the study indicate that denitrification rate did increase due to the addition of lysed biofilm derived from the nitrification reactor. However, there was a simultaneous large release of additional ammonium. Further work will be required to understand the magnitude of the ammonium release and overall benefits of the process.

Three replicate aerobic-heterotrophic biotrickling filters were designed to promote the simultaneous biodegradation of graywater and a waste gas containing NH3, H2S and CO2. Upon visual observation of discolored solids, it was originally hypothesized that gas-phase CO2 concentrations were excessive, causing regions of anoxic zones to form within the biotrickling filters. Observed discolored (black) biofilm of this nature is typically assumed to be either lysed bacterial cells or anaerobic regions, implying alteration of operational conditions. Solid (biofilm) samples were collected in the presence and absence of gas-phase wastestream(s) to determine if the gas-phase contaminants were contributing to the solid-phase discoloration. Two sets of experiments (shaker flask and solids characterization) were conduced to determine the nature of the discolored solids. Results indicated that the discolored solids were neither anaerobic bacteria nor lysed cells.

The purpose of this study was to evaluate the viability of treating wastewater through edible plant hydroponics. After the harvest in the hydroponic experiment (32 day study period), plant yield for edible biomass (corresponds to the harvested leaves) in wastewater and hydrosol (control) were 0.131 kg/m2 and 0.104 kg/m2, respectively. Potassium, TDS, and TN showed decreasing trends in hydrosol and wastewater during the experiment. Nitrification was observed in the wastewater unit with a significant increase (92.5%) in nitrate mass. Nitrite and ammonium mass in wastewater decreased with time, while hydrosol had negligible amounts of nitrite and ammonium during the study period. Calcium and magnesium masses decreased in the control and increased in wastewater. Wastewater showed a decrease in the mass of TOC (19.7%), while the hydrosol had negligible mass with respect to TOC.

The Bioregenerative Air Treatment for Health system has been proposed for Advanced Life Support (ALS) planetary base applications. The system will be operated as a biotrickling filter to simultaneously treat graywater and waste gas. Preliminary experiments have focused on carbon removal from a graywater simulant. Six bench scale biotrickling filter reactors were constructed and monitored continuously. After a reactor startup phase of 40 days, the average total organic carbon (TOC) removal for reactors packed with Tri-packs® packing material was 62%. A second set of experiments was designed to evaluate TOC removal using different packing materials (Bee-cell and Biobale). It was hypothesized that the alternative packing materials would reduce the effects of channeling in the reactors, thus improving TOC removal. However, TOC removal did not significantly improve during the second set of experiments.

Biological pre-treatment of liquid waste could potentially offer equivalent mass savings for long term space habitation. However, limited engineering studies have been performed to determine the optimum loading rates or to fully characterize (limiting reactants) the biochemical transformations occurring within the reactors. The objective of these studies was to provide loading rate data on a proposed and well studied reactor configuration. All studies were performed using a simulated early planetary base waste stream. Results indicate that the reactor’s efficiency is greater than typical terrestrial reactors and that transformation is limited by non-kinetic parameters.

The objective of this study was to investigate the potential of membrane-aerated bioreactors as long term microgravity compatible nitrifying biological water processors (BWP). A small-scale (1/20th) replica of the water recovery system (WRS) at JSC has been operated and extensively analyzed at Texas Tech University (TTU) for the last 3 years. The current nitrifying tubular reactor at JSC and TTU has experienced difficulty in maintaining efficiency and low maintenance. In an attempt to increase the efficiency of the biological portion of the WRS, a membrane-aerated bioreactor (MABR) was constructed and operated using the same parameters as the TTU-WRS in August 2003. The MABR is downstream of an anaerobic packed bed and is designed to promote nitrification (NH4 → NOx). The MABR achieved a percent nitrification of 61% and 55% for recycle ratios of 10 and 20, respectively.

Simulated wastewater, known as early surface mission wastewater, treated in previous experiments at JSC and TTU included urinal flush water, shower water, humidity condensate, oral hygiene water, and hand wash water. In reality, there is a difference between the early surface mission wastewater and the International Space Station wastewater. The ISS does not have a shower or hand wash, which contributes approximately 59 percent of the make-up water treated. The average influent ammonia concentration in the simulated wastewater treated by the TTU water reclamation system frequently exceeds 500 mg/L. Removal of the shower make-up water in simulated wastewater will result in a significant increase in the ammonia concentration, resulting in higher influent pH values and ammonia concentrations that may be inhibitory. Biological treatment technologies have suitably treated the diluted waste stream but a more concentrated waste stream may present a greater challenge.

Biological pre-treatment of liquid waste could potentially offer equivalent mass savings for long term space habitation. Previous work has demonstrated the technological feasibility. However, limited work has been conducted on optimizing the biological reactors or fully characterizing the biochemical transformations occurring within the reactors. The objective of these studies was to provide long-term operating data on a proposed and well studied reactor configuration, and explore the effects of RR on system performance. The water recovery system has been in successful operation for over 2 years. Data to be presented will include both typical removal efficiencies for nitrogen species, DOC as well as important water quality parameters. In addition the effect of recycle ratio (2X, 5X, 10X, and 20X) will be quantified.

For prolonged manned spaceflight, recycling of wastewater is critical to minimize payload costs. We have constructed a pilot-scale, closed-loop water recycling system (CLWRS). Due to slow process dynamics, evaluation of multiple experimental scenarios is very time-consuming. To accelerate evaluation, we have developed mathematical models of the individual reactors, as well as a process model of the pilot plant, which combines nitrification, denitrification, recycle, and degassing steps. The simulation accurately reproduces the 35% total nitrogen (TN) reduction observed experimentally at a 20/1 recycle ratio. Both experiments and simulations indicate that biological CLWRS have significant potential for long-duration manned space flight.

A modified membrane-aerated biofilm reactor (mMABR) was constructed by incorporating two distinct biofilm immobilization media: gas-permeable hollow fiber membranes and high surface area inert bio-media. In order to evaluate the mMABR for space flight applications, a synthetic ersatz early planetary base (EPB) waste stream was supplied as influent to the reactor, and a liquid loading study was conducted at three influent flow rates. On average, percent carbon removal ranged from 90.7% to 93.1% with volumetric conversion rates ranging from 25 ± 3.3 g / m3 d and 95 ± 13.4 g / m3 d. Simultaneous nitrification/denitrification (SND) was achieved in a single reactor. As the liquid loading rate increased from 0.15 mL/min to 0.45 mL/min, the volumetric denitrification rates elevated from 27 ± 3.3 g / m3 d to 65 ± 5.2 g / m3 d. Additionally, it was found that nitrification and denitrification were linearly related with respect to both percent efficiency and volumetric reaction rates.