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OMEGA Global Initiative (OGI)
- Jonathan Daniel Trent
- Tom Miller
- Peter Becker
Microalgae technology continues to show tremendous promise for becoming a major source of renewable transportation fuel in the coming decades. However, for microalgae to provide a significant fraction of the current US demand for fuel, their cultivation will be required on an enormous scale. One of the many formidable challenges that must be met to achieve this scale is the development of appropriate sensor networks to provide information about the growth conditions and the algae themselves. These sensors would monitor the heterogeneity of a) environmental parameters, such as pH, oxygen, and nutrient levels and b) algal characteristics such as size, oil content, and viability. Here we present a wireless sensor network to measure the local pH in NASA OMEGA project (Offshore Membrane Enclosures for Growing Algae). The pH is measured using Ion Sensitive Field Effect Transistor (ISFET) technology, which is more robust and has a faster response than traditional glass pH electrodes. A custom circuit drives the ISFET sensor and interfaces with an ANT wireless network system. The wireless network consists of a network hub which can service up to 8 sensor nodes and a series of relays to transmit the data to a PC. The data is logged with a custom LabVIEW program. In this work, we demonstrate operation of this network using a single ISFET pH sensor, one hub, and two relay units. The performance of the pH sensor network is evaluated and compared in parallel with an existing wired glass electrode based pH monitoring system at the NASA OMEGA project.
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 CO2-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% CO2 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 CO2, harvest microalgae from a settling chamber, and add fresh wastewater to replenish nutrients. The I&C system controlled CO2 injection and recorded dissolved oxygen levels, totalized CO2 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 CO2 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 12weeks 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.
Background OMEGA is an integrated aquatic system to produce biofuels, treat and recycle wastewater, capture CO2, and expand aquaculture production. This system includes floating photobioreactors (PBRs) that will cover hundreds of hectares in marine bays. To assess the interactions of marine mammals and birds with PBRs, 9 × 1.3 m flat panel and 9.5 × 0.2 m tubular PBRs were deployed in a harbor and monitored day and night from October 10, 2011 to Janurary 22, 2012 using infrared video. To observe interactions with pinnipeds, two trained sea lions (Zalophus californianus) and one trained harbor seal (Phoca vitulina richardii) were observed and directed to interact with PBRs in tanks. To determine the forces required to puncture PBR plastic and the effects of weathering, Instron measurements were made with a sea otter (Enhydra lutris) tooth and bird beaks. Results A total of 1,445 interactions of marine mammals and birds with PBRs were observed in the 2,424 hours of video recorded. The 95 marine mammal interactions, 94 by sea otters and one by a sea lion had average durations of three minutes (max 44 min) and represented about 1% of total recording time. The 1,350 bird interactions, primarily coots (Fulica americana) and gulls (Larus occidentalis and L. californicus) had average durations of six minutes (max. 170) and represented 5% of recording time. Interactive behaviors were characterized as passive (feeding, walking, resting, grooming, and social activity) or proactive (biting, pecking, investigating, and unspecified manipulating). Mammal interactions were predominantly proactive, whereas birds were passive. All interactions occurred primarily during the day. Ninety-six percent of otter interactions occurred in winter, whereas 73% of bird interactions in fall, correlating to their abundance in the harbor. Trained pinnipeds followed most commands to bite, drag, and haul-out onto PBRs, made no overt undirected interactions with the PBRs, but showed avoidance behavior to PBR tethers. Instron measurements indicated that sea-otter teeth and gull beaks can penetrate weathered plastic more easily than new plastic. Conclusions Otter and bird interactions with experimental PBRs were benign. Large-scale OMEGA systems are predicted to have both positive and negative environmental consequences.
The goal of the workshop was to design an offshore algae cultivation system to economically grow copious amounts of algae in a way that improves the environment. Our focus was on the merits and drawbacks of the OMEGA system. The basic idea of OMEGA is to grow freshwater algae in plastic enclosures, filled with municipal wastewater, and in effect grow contained algal blooms, while tertiary treating the sewage released into the ocean.
IN FEBRUARY 2011, the National Aeronautics and Space Administration (NASA) signed a Memorandum of Agreement (MOA) with the Navy to test a system for producing what many believe to be the fuel of the future, using algae grown in the ocean. “Changing the way energy is used and produced in our country is the right thing to do,” said Navy Secretary Ray Mabus, upon signing the agreement. “It’s the right thing to do for our security, it’s the right thing to do for our economy, and it’s the right thing to do for our environment.”
How and where it will be possible to produce biofuels at a scale that can compete with fossil fuels, without competing with agriculture for water, fertilizer and land, is a fundamental unanswered question. We propose that the answer could be offshore membrane enclosures for growing algae. Microalgae are the fastest growing biomass and best oil producers known; by cultivating microalgae offshore using wastewater as a source of water and nutrients in floating photobioreactors (PBRs), the system would not compete with agriculture. Furthermore, freshwater microalgae clean the wastewater, capture CO2 and, if they accidentally escape, they cannot become invasive species because they cannot thrive in seawater. The seawater supports the PBRs, controls temperature and can be used for forward osmosis to concentrate nutrients and facilitate harvesting. Algae products, wastewater treatment, carbon sequestration and compatible aquaculture support the economics of the system as a whole. The completion of a 2-year feasibility study on prototype PBRs, control systems, biofouling, wastewater treatment, life cycle analysis and energy return on investment sets the stage for future offshore studies.
The biofuels community has shown considerable interest in the possibility that microalgae could contribute significantly to providing a sustainable alternative to fossil fuels. Microalgae species with high growth rates and high yields of oil that can be grown on domestic wastewater using nonarable land could produce biofuel without competing with agriculture. It is difficult to envision where the cultivation facilities would be located to produce the quantity of algae needed for fuels, given that these facilities must be close to wastewater treatment plants to save energy. Researchers investigated a possible solution called Offshore Membrane Enclosures for Growing Algae for coastal cities. This system involved growing fast-growing, oil-producing freshwater algae in flexible, inexpensive clear plastic photobioreactors attached to floating docks anchored offshore in naturally or artificially protected bays. Wastewater and carbon dioxide from coastal facilities provided water, nutrients, and carbon. The surrounding seawater controlled the temperature inside the photobioreactors and killed any algae that might escape. The salt gradient between seawater and wastewater created forward osmosis to concentrate nutrients and to facilitate algae harvesting. Both the algae and forward osmosis cleaned the wastewater, removing nutrients as well as pharmaceuticals and personal care products, so-called compounds of emerging concern. This report provided the results of two years of research into the feasibility of the Offshore Membrane Enclosures for Growing Algae system in which prototype systems were studied, built, and tested in seawater tanks. A 110-liter floating system was developed and scaled up to 1,600 liters. Algae’s ability to grow on and treat wastewater was described. The impact of biofouling on photobioreactors and forward osmosis membranes floating in the marine environment was considered. Life-cycle and technoeconomic analyses provided a perspective on what must be done to make this system commercially viable. Outreach efforts have carried the concept worldwide. Keywords: biofuels, microalgae, algae, OMEGA, offshore systems, carbon sequestration, aquaculture, wastewater treatment, biofouling, life cycle analysis, technoeconomic analysis Please use the following citation for this report: Trent, Jonathon. (NASA Ames Research Center). 2012. OMEGA (Offshore Membrane Enclosures for Growing Algae) - A Feasibility Study for Wastewater to Biofuels. California Energy Commission. Publication number: CEC-500-2013-143.