OMEGA is a system for cultivating microalgae using wastewater contained in floating photobioreactors (PBRs) deployed in marine environments and thereby eliminating competition with agriculture for water, fertilizer, and land. The offshore placement in protected bays near coastal cities co-locates OMEGA with wastewater outfalls and sources of CO 2-rich flue gas on shore. To evaluate the feasibility of OMEGA, microalgae were grown on secondary-treated wastewater supplemented with simulated flue gas (8.5% CO 2 V/V) in a 110-liter prototype system tested using a seawater tank. The flow-through system consisted of tubular PBRs made of transparent linear low-density polyethylene, a gas exchange and harvesting column (GEHC), two pumps, and an instrumentation and control (I&C) system. The PBRs contained regularly spaced swirl vanes to create helical flow and mixing for the circulating culture. About 5% of the culture volume was continuously diverted through the GEHC to manage dissolved oxygen concentrations, provide supplemental CO 2 , harvest microalgae from a settling chamber, and add fresh wastewater to replenish nutrients. The I&C system controlled CO 2 injection and recorded dissolved oxygen levels, totalized CO 2 flow, temperature, circulation rates, photosynthetic active radiation (PAR), and the photosynthetic efficiency as determined by fast repetition rate fluorometry. In two experimental trials, totaling 23 days in April and May 2012, microalgae productivity averaged 14.1 ± 1.3 grams of dry biomass per square meter of PBR surface area per day (n = 16), supplemental CO 2 was converted to biomass with >50% efficiency, and >90% of the ammonia-nitrogen was recovered from secondary effluent. If OMEGA can be optimized for energy efficiency and scaled up economically, it has the potential to contribute significantly to biofuels production and wastewater treatment.

The influence of PBR composition [clear polyurethane (PolyU) vs. clear linear low-density polyethylene (LLDPE) (top) and black opaque high-density polyethylene (bottom)] and shape (rectangular vs. tubular) on biofouling and the influence of biofouling on algae productivity were investigated. In 9-week experiments, PBR biofouling was dominated by pennate diatoms and clear plastics developed macroalgae. LLDPE exhibited lower photosynthetic-active-radiation (PAR) light transmittance than PolyU before biofouling, but higher transmittance afterwards. Both rectangular and tubular LLDPE PBRs accumulated biofouling predominantly along their wetted edges. For a tubular LLDPE PBR after 12 weeks of biofouling, the correlation between biomass, percent surface coverage, and PAR transmittance was complex, but in general biomass inversely correlated with transmittance. Wrapping segments of this biofouled LLDPE around an algae culture reduced CO2 and NH3-N utilization, indicating that external biofouling must be controlled.

Adsorption isotherms are reported for pure water vapor on zeolite 13X (also called zeolite NaX) pellets. Data were obtained using a gravimetric method over a temperature range of 25 to 100 °C and a pressure range of 0.006 to 25 kPa. These pure-component equilibria are fit with the Sips, Toth, and multisite Langmuir models, all modified with the Aranovich–Donohue (A–D) model. The A–D Sips isotherm is recommended for modeling water adsorption on zeolite 13X because it provides the best agreement with the measured isotherm data.

Due to the high cost of delivering supplies to space, the recovery of potable water from spacecraft wastewater is critical for life support of crewmembers in short-and long-term missions. It is estimated that in future long-term space missions, human wastes such as urine will contribute more than 50% of the total waste. Thus, we will demonstrate how unused components, such as urea, can be recovered and reused in wastewater recycling processes. In this system, a urea bioreactor (GAC-urease) converts urea to ammonia. Then, an electrochemical cell converts the ammonia to power. The combined system is referred to as the Urea Bioreactor Electrochemical (UBE) unit. The results of this research showed the feasibility of interfacing wastewater-recycling processes with bioelectrochemical systems to achieve water recycling while reusing useful resources. The UBE systems removed >80% of organic carbons and converted approximately 86% of the urea to ammonia. Therefore, the concept herein proposed has the potential to be used in water recycling applications with emphasis in contaminant recovery from wastewater for useful resources and energy.

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