Algae Photobioreactor Using Floating Enclosures With Semi-Permeable Membranes

The Surface-Adhering BioReactor (SABR) is a novel microbial cell cultivation platform that mimics the way vascular plants use transpiration to deliver nutrients to their cells. In this biomimetic platform, microbial cells are cultivated as immobilized cells on a porous substrate where transpiration is used to passively deliver water and nutrients as well as harvest and concentrate secreted biomolecules by the microbial cells. The SABR transports nutrients to microorganisms without using a pump. Instead, evaporation and the cohesive property of water are exploited to pull the nutrient medium through the device, with a high degree of control, on an as needed basis. It eliminates the hydrodynamic shear stress on the cells and decreases the working volume of water needed for cultivation by a factor of 25 compared to planktonic bioreactors. Furthermore, the transpiration mechanism allows for the concentration of secreted products in areas of relatively fast evaporation, thus providing a passive means of secreted product harvesting. By matching the time scales of nutrient medium delivery and product harvesting with the time scales of growth and product formation, minimal energy is wasted in bioreactor operation. Transpiration enables a passive cooling system for the cells where either externally imposed or internally generated heat due to cellular activity is mitigated, thus preventing overheating that can lead to decreased productivity or even cell death. This technology enables significant reductions in energy input for cultivating microorganisms.

Because resupply of commodities for long duration space missions would be prohibitively expensive and could take an extensive length of time to reach habitats in orbit around or on other planetary bodies, it is critical that astronauts have the ability to recycle and reuse local waste streams to provide resources such as clean water, fuel, and nutrients for growing plants. Scientists at Kennedy Space Center and the University of South Florida have developed a technology that addresses this critical mission need. The modular system design incorporates all wastewater streams and some food waste including urine water, hygiene water, humidity condensate, Sabatier water, fecal waste, laundry water, and organic food waste. These sources are fed simultaneously into the system, and a function-driven, sequential purification process occurs. The primary processes include carbon conversion, phase separation (solid/liquid/gas), disinfection, nutrient/salts management, and salts balancing to generate a clean water stream. The heart of the closed-loop bio-regenerative system is an anaerobic membrane bioreactor (AnMBR), which takes raw wastewater streams and utilizes an anaerobic microbial consortium to carry out the breakdown of the organic matter. An ultrafiltration membrane captures and destroys pathogenic bacteria and viruses. The AnMBR system generates a clean water stream containing fertilizer constituents which can be used to cultivate either microalgae (for food, pharma/nutraceuticals, fuel or bioplastics) in photobioreactors or crops in hydroponic systems. The system also generates methane and hydrogen gas which can be used for fuel (or conversion to bioplastics), and CO2 which can be used to support plant growth.

Bacterial contamination of water systems used in microgravity is a major issue for NASA because biofilms can clog or interfere with water system functions and bacterial ingestion can be harmful to astronaut health. To address this problem, NASA innovators developed a microwave based technology to purify contaminated water by eradicating and eliminating bacteria that grows in systems that generate potable water, in equipment utilizing cooling loops and heat exchangers, and removing bacterial contamination that is present on a variety of surfaces. This decontamination system is chemical free and requires minimal to no consumables. Initial testing identified a specific microwave frequency band and exposure times for killing bacteria (Burkholderia cepacia) and biofilm. Test results show that exposing static water to microwave energy for 90 seconds can effectively kill waterborne bacteria and biofilm within a water filtration system. Additional testing, using a circulating water test bed, demonstrated that microwave energy at the selected frequency can effectively eradicate waterborne bacteria within 30 seconds. This technology could be further developed into a portable, lightweight system for use in remote locations as well as commercial space applications. The microwave decontamination system could also be added to existing water systems to extend the life of the system.

PONDS was developed as a water/nutrient delivery system for the Vegetable Production System, called VEGGIE, on the International Space Station (ISS). PONDS uses an innovative wicking material to passively link a water/nutrient reservoir to a plant cylinder. The system enables higher germination rates and improved growth conditions compared to the VEGGIE water/nutrient delivery system currently used on the ISS. PONDs consists of two primary components: a water/nutrient reservoir (Figure 1), and a detachable plant cylinder containing growth substrate and wicking material (Figure 2). The reservoir includes a viewing window that allows the user to observe and record water-use data. The plant cylinder, which screws into the reservoir system, is made from commercial-off-the-shelf materials and fittings. Both the reservoir and plant cylinder include oxygen-permeable windows to enhance aeration to the root zone. Water is delivered from the reservoir to the substrate contained within the plant cylinder via the wicking material inserted into the growth substrate. The wicking material is intrinsically hydrophilic, providing improved capacity compared to the system previously used with VEGGIE. As a result, PONDS can continuously supply water to the root zone within the plant cylinder on demand.

This water filtration innovation is an acoustically driven molecular sieve embedded with small-diameter carbon nanotubes. First, water enters the device and contacts the filter matrix, which can be made of polymer, ceramic, or metallic compounds. Carbon nanotubes within the matrix allow only water molecules to pass through, leaving behind any larger molecules and contaminants. The unique aspect of the technology is its use of acoustics to help drive water through the filter. An oscillator circuit attached to the filter matrix propagates acoustic vibration, further causing water molecules to de-bond and move through the filter. This use of acoustics also eliminates dependence on gravity (and thus filter orientation) to move water through the device. When water exiting the system diminishes to a pre-determined set point, a cleaning cycle is triggered to clear the sediment from the inlet of the filter, reestablishing the standard system flow rate. Unlike other filtration systems, flushing of the filter system is not required. The combination of acoustics and small-diameter carbon nanotubes in this innovation make it an effective and efficient means of producing contaminant-free, clean water.