We are developing Offshore Membrane Enclosures for Growing Algae (OMEGA). OMEGAs are closed photo-bioreactors constructed of flexible, inexpensive, and durable plastic with small sections of semi-permeable membranes for gas exchange and forward osmosis (FO). Each OMEGA modules is filled with municipal wastewater and provided with CO2 from coastal CO2 sources. The OMEGA modules float just below the surface, and the surrounding seawater provides structural support, temperature control, and mixing for the freshwater algae cultures inside. The salinit7 gradient from inside to outside drives forward osmosis through the patches of FO membranes. This concentrates nutrients in the wastewater, which enhances algal growth, and slowly dewaters the algae, which facilitates harvesting. Thy concentrated algal biomass is harvested for producing biofuels and fertilizer. OMEGA system cleans the wastewater released into the surrounding coastal waters and functions as a carbon sequestration system

Buckwalter, Patrick

Embaye, Tsegereda

Kagawa, Hiromi

Martis, Mary

Reinsch, Sigrid

Richardson, Tra-My

Trent, Jonathan

NASA Technical Reports Server

Trent et al.  RE 2010 
 1 
OFFSHORE MEMBRANE ENCLOSURES FOR GROWING ALGAE (OMEGA): 
A SYSTEM FOR BIOFUEL PRODUCTION, WASTEWATER TREATMENT, AND 
CO2 SEQUESTRATION 
Jonathan Trent1*, Tsegereda Embaye2, Patrick Buckwalter3, Tra-My Richardson3, Hiromi Kagawa2, Sigrid 
Reinsch1, and Mary Martis4 
1NASA Ames Research Center, 2SETI Institute, 3Universities Space Research Association, 4URS Corp.  
*Corresponding author: jonathan.d.trent@nasa.gov 
 
OMEGA is a system of photo-bioreactors (PBRs) filled with municipal wastewater, floating in seawater. It is constructed of 
flexible plastic with internal gas-permeable membranes diffusing CO2 into the cultures and external forward osmosis (FO) 
membranes concentrating nutrients in wastewater and dewatering the algae for harvesting. The FO membranes also clean 
the water released into seawater. The OMEGA modules float at the sea surface. The surrounding seawater provides 
structural support, temperature control, and containment (the cultivated freshwater algae cannot survive in seawater).  
Waves and bubbling provide mixing.  OMEGA produces biomass for biofuel, food, and fertilizer, while treating wastewater 
and sequestering carbon.   
Keywords: microalgae, biofuel, wastewater treatment, photobioreactor, carbon sequestration 
 
CHALLENGES WITH CURRENT BIOFUEL 
PRODUCTION METHODS 
 
From Fossil Fuels to Biofuels 
There are many strong incentives to replace fossil fuels 
with biofuels, among them are national security issues, 
sustainability of limited resources, and avoiding 
environmental disasters—the gradual disaster of climate 
change and the more imminent disasters caused by 
offshore oil spills.[1]  While there are known species of 
plants that produce vegetable oil and well-established 
refining methods for transforming vegetable oils into 
biofuels, it is challenging to envision how adequate 
supplies of fuel can be produced from plants. The oil yield 
of soy plants, for example, is 50 gal/acre/year, Jatropha is 
approx. 200 gal/acre/yr, and some species of palm 
produce >600 gal/acre/yr.[2] The best oil producers are 
among the microalgae, which produce between 2,000 
and 5,000 gal/acre/yr.  In contrast, the 2008 average 
production from the 525,000 active oil wells in the USA 
was 144,102 gal/well/yr and all these wells provided only 
about 40% of the oil used domestically.[3] Thus it is clear 
that to replace a significant portion of fossil fuel with 
biofuels will require an enormous commitment of land—to 
replace production of a single average oil well requires 72 
acres of algae or 2,882 acres of soy.  This commitment of 
land, as well as water and fertilizer needed for growing 
biofuels crops, is the basis for the clash between biofuels 
and agriculture[4].  
 
To avoid the “fuels vs. food” clash, it has been suggested 
that biofuels should be made from plants grown in 
deserts or on other non-agricultural land, using salt-
tolerant or drought resistant plants, watered with 
seawater or municipal wastewater. Given the relatively 
high oil yields of algae, including marine algae that can 
grow in saltwater or freshwater strains that grow on 
municipal wastewater, it is generally agreed that 
microalgae are the most promising biofuels crop.  The 
question is whether existing or new algae cultivation 
methods can be scaled up to meet the needs for biofuels 
and if these methods can avoid competing with 
agriculture.[5] 
 
Raceways and Closed Photobioreactors 
Microalgae are currently grown commercially in shallow 
open ponds called “raceways” or in sealed enclosures 
known as photobioreactors (PBRs).[6]  These commercial 
systems grow algae that make high-value products, such 
as nutriceuticals, food additives, cosmetics, or 
pharmaceuticals, which means a small-scale algae 
cultivation system can be economically viable.  Biofuels 
however, are a low-value commodity and to reach the 
economies of scale that will meet the demand for 
biofuels, will require raceway or PBR installations orders 
of magnitude larger than those currently in use. With 
sufficient motivation, huge raceways can be excavated 
and large numbers of PBRs can be built and these 
enormous installations can be located so as not to 
compete with agriculture, but the costs of infrastructure 
and logistics of water and product transport have made 
such ventures into algae biofuels impractical to date.  
 
The Devil is in the Details  
Indeed, while huge areas of raceways and large numbers 
of PBRs can be installed in remote locations that would 
not compete with agriculture, the actual use of these sites 
have been shown to be logistically problematic and 
prohibitively expensive.[6] Considering the volumes of 
water required for producing the quantities of algae need 
for fuels, an enormous infrastructure of pipes or roads will 
be needed for transporting the volumes of water, 
wastewater, and CO2, as well as the harvested algae. 
Such an enormous algae cultivation system will require 
formidable amounts of energy for moving the large 
https://ntrs.nasa.gov/search.jsp?R=20100039342 2019-08-30T13:04:32+00:00Z
Trent et al.  RE 2010 
 2 
volumes of liquids and gas as well as for harvesting, 
processing, and transporting the tons of algae being 
processed. There is also the problem of water.   
 
Raceways are open to the air, which means the water 
can evaporate.  It is estimated that the replacement water 
required to grow freshwater algae and appropriate 
salinities for marine algae on a scale relevant to biofuels 
would be measured in the trillions of gallons of freshwater 
per year [7].  In addition, there are the energy 
requirements to move the volumes of water to deserts or 
remote cultivation sites and these consideration raise the 
question of whether fuel or food should be produced with 
this use of resources. 
 
While evaporation may not be a problem for PBRs, which 
can be closed and sealed chambers, freshwater may still 
be a problem because many PBR systems use water for 
cooling.  Why is it necessary to cool algae?  Algae 
require light and if the light comes from the sun, there is 
also heat.  Sealed PBRs are functionally solar-thermal 
collectors and to maintain temperatures suitable for 
growing algae, they need to be cooled and evaporative 
cooling using freshwater is a simple method.  Here again, 
the system requires energy and competes with 
agriculture.  Indeed, PBRs already use a lot of energy for 
mixing and circulating algae cultures. Even with the 
small-scale PBR systems used for making high-value 
products, it is the capital and operating costs that make 
them impractical.   
 
Therefore, although algae have great potential as a 
source of biofuels, growing algae in raceways or in 
standard PBRs on a large enough scale to produce 
biofuels at a cost that can compete with fossil fuels 
remains as daunting challenge.   
 
Is there another approach for growing oil-producing 
microalgae without competing with agriculture for land, 
freshwater, or fertilizer, without pumping water great 
distances, and in a way that benefits the environment? 
 
OMEGA (OFFSHORE MEMBRANE ENCLOSURES 
FOR GROWING ALGAE) 
 
Fig. 1: Schematic representation of OMEGA system 
 
The OMEGA System 
The OMEGA system consists of individual modules that 
are closed photo-bioreactors filled with domestic 
wastewater, floating offshore—just beneath the sea 
surface. Unlike PBRs on land, which have problems with 
heat and energy use, OMEGA modules transfer heat to 
the surrounding seawater, while mixing and circulating 
the algae is done using wave energy.  The OMEGA 
system also uses buoyancy, gravity, and osmosis.  Air 
and water filled bladders in the OMEGA structure provide 
buoyancy and structural integrity. Concentrated CO2 from 
remote sources (wastewater facilities or power plants) 
diffuses into the algae culture through gas-permeable 
membranes. Patches of forward osmosis (FO) 
membranes on the bottom of the plastic enclosures allow 
water to diffuse out into the surrounding saltwater.  This 
process is driven by the salt gradient and during an 
incubation period of 5-10 days, more than 65% of the 
bulk water can be removed from the culture.  The FO 
process stimulates algal growth by concentrating 
nutrients in the wastewater and assists in harvesting by 
initiating dewatering of the algae.  Furthermore, the water 
passing through the FO membrane is clean (bacteria, 
virus, and pollutants do not pass FO).  This will help 
remediate dead zones in polluted coastal areas.  The 
surrounding saltwater also prevents the freshwater 
growing inside the OMEGA system from becoming 
invasive species in the marine environment.  In other 
words, if the OMEGA system catastrophically fails, it 
releases wastewater that is certified for release, 
freshwater algae that cannot grow and are completely 
biodegradable, and plastic that can be readily recovered.  
 
OMEGA LOCATIONS AROUND THE WORLD 
It is proposed that OMEGA farms will be located in 
marine (salty) environment in the vicinity of a source of 
nutrient-rich freshwater and a source of CO2, such as a 
coastal power plant. Other conditions, including 
temperatures, light, water clarity, frequency and severity 
of storms, geography, boat traffic, wildlife conservation, 
will all influence how the OMEGA farm will be configured 
and what algae will be cultivated.  The plan is to only 
cultivate freshwater algae and to use wastewater that 
meets regulations for release into the marine 
environment.  
 
To accommodate sea birds and marine mammals, the 
OMEGA modules in a farm will be spaced to allow ample 
access.  This also allows light to penetrate into the water 
column between the modules.  The number of OMEGA 
modules in a farm will depend on the location, shipping 
lanes and the amount of wastewater to be processed in a 
given location. 
 
Obviously, OMEGA farms will be easier to build in 
protected bays, in areas surrounded by breakwaters, or in 
places with existing marine infrastructure such as 
offshore platforms or wind farms.  In the case of wind 
farms, OMEGA farms would use the infrastructure for 
anchorage and organization and could benefit from the 
source of local energy for pumping water, air, and CO2, 
and well as producing artificial light.  In turn, the wind-
Trent et al.  RE 2010 
 3 
farm benefits by using the algal biomass as a way to 
solve the problem of long-term storage of wind energy. 
 
As designs and methods for OMEGA farming develop, 
exposed open ocean locations may also be used.  These 
will require robotic systems for transporting wastewater 
from the major sewage outfalls and for return algae 
biomass to shore.  On the other hand, with global 
warming and rising sea levels, OMEGA farms may take 
advantage of flooded coastal zones, forming a new 
coastal infrastructure for algae production, wastewater 
treatment, and carbon sequestration. 
 
LABORATORY TESTING OF OMEGA COMPONENTS 
Algal Growth, Oil Production  
Chlorella vulgaris was grown in lab-scale OMEGA 
modules and the growth and biodiesel production were 
monitored (Fig. 2). The growth conditions included using 
primary or secondary wastewater from the Sunnyvale 
wastewater treatment facility or using a standard 
laboratory medium for growing algae (BG11).  We used 
constant light (177 ft candles), constant stirring, and 
added CO2.  The cultures grown in OMEGA modules 2 or 
3 cm deep did not exceed 2 g/L dry wt, indicating the 
cultures were light limited.  Cultures grown in 1 cm deep 
OMEGA modules achieved 6 g/L (data not shown), which 
is in agreement with previously published work on light 
limitation[4].   
 
 
Fig. 2: Algal growth and % lipid results in simulated ocean 
with both primary wastewater and laboratory media.  
Note: biomass concentration scaled up 10X to 
correspond to % biodiesel. 
 
Forward Osmosis and Biofouling  
Chlorella vulgaris was grown in the laboratory in small 
OMEGA modules  (20 cm x 20 cm x 1, 2, or 3 cm) made 
of clear polyurethane with or without forward osmosis 
(FO) membranes. Floating these modules in a seawater 
tank, the algal culture was dewatered up to 85% (range 
65-85%) over a 4-day period (Fig. 3). 
 
 
Fig. 3: Dewatering of algae culture in OMEGA module 
with FO membrane. 
 
FO has the potential to concentrate nutrients and 
facilitate harvesting, if it could work under marine 
conditions.  Nearly all surfaces in the marine environment 
are subject to biofouling and to determine the impact of 
biofouling on FO membranes, FO chambers were 
attached to a buoy in the ocean for 45 or 52 days (Fig 4). 
 
(a)  (b)  (c) 
  
Fig. 4: FO chambers after exposure to the marine environment 
without dewatering.  (a) FO chamber stored in artificial seawater 
in the laboratory for 45 days, (b) FO chamber off Capitola Pier, 
CA after 45 days, and (c) another FO chamber off Capitola Pier 
after 52 days. 
 
As expected, compared to laboratory controls (Fig. 4a), 
the ocean exposed FO chambers accumulated thick 
layers of biofouling (Fig. 4 b&c). Surprisingly, however, 
the heavily biofouled FO chambers showed similar 
dewatering rates to the unfouled chambers, provided their 
membranes were not damaged by the encrusting material 
or by the added flexing due to drag on their surfaces 
(Buckwalter et al. in preparation).  
 
OMEGA FEASIBILITY AND SCALABILITY 
With the limits of fossil fuels on the horizon and ample 
evidence that their continued use will have catastrophic 
environmental consequences, the OMEGA project is an 
opportunity to be part of an international team to co-
develop this alternative fuels technology.  OMEGA is a 
novel approach to growing oil-producing, freshwater 
algae in offshore enclosures, using municipal wastewater 
that is currently discharged into the ocean. The 
technology is meant to produce sufficient quantities of 
algae to significantly contribute to the production of 
sustainable and carbon-neutral biofuels without 
competing with agriculture for land, water, of fertilizer. 
The OMEGA system uses solar energy, wave energy, the 
Trent et al.  RE 2010 
 4 
heat capacity of water, and the salt gradient between 
seawater and wastewater for forward osmosis. FO 
concentrates nutrients and stimulate algal growth, while 
facilitating the harvesting of the microalgae.  OMEGA 
provides biofuels, as well as food, fertilizer, and other 
useful products, while processing wastewater released 
into the environment and removing carbon dioxide from 
the air.  OMEGA was inspired by NASA’s closed-loop life 
support systems and it represents an “ecology of 
technologies” in which waste products from one part of a 
system become resources for another.  Like natural 
ecosystems, technology ecology is efficient, effective, 
and sustainable.  
 
A team of scientists, engineers, ecologist, and 
economists supported by NASA ARMD and the California 
Energy Commission, are doing a demonstration project to 
determine if OMEGA is feasible and scalable.  This 
demonstration is meant to determine if OMEGA is 
feasible: technically, biologically, environmentally, and 
economically, and if it can be done at a scale that impacts 
the current use of fossil fuels. Algae products from 
OMEGA could include biomass, oil, fertilizer, animal 
fodder and high-value products such as dyes, 
nutraceuticals, cosmetics, and drugs.  Services could 
include wastewater treatment, dead-zone remediation, 
and CO2 sequestration.  The OMEGA system integrates 
solar, wave, and wind energy with gravity, buoyancy, heat 
capacity, and osmosis.  The viability of the OMEGA 
system will be determined by prototype and pilot testing 
as well as energy return on investment and a detailed life-
cycle analyses.  The economics of OMEGA will be 
determined based on products and services as well as 
considerations of the consequences of not doing 
OMEGA.   
 
OMEGA products and services do not compete with 
agriculture or damage marine ecosystems.  Indeed, 
OMEGA is meant to improve the marine environment by 
removing nutrients that are currently contributing to the 
formation of dead zones and by sequestering CO2 that is 
contributing to ocean acidification.  The hope is that 
based on the results on the demonstration, people 
around the world will be motivated to develop OMEGA 
systems for their locations.  Projects like OMEGA will 
require local experts supported by government agencies 
and private investors who all recognize the magnitude of 
global problems and the urgency of finding solutions.  If 
such experts can be mobilized and openly share 
information, it is estimated that OMEGA technology can 
be developed to significant scales within 10 years.  It is 
impossible to predict as yet if OMEGA is feasible and 
scalable, but having just emerged from the warmest 
decade on record, we enter a new era with the 
knowledge that it is imperative that civilization move 
without delay from hunting-and-gathering energy to 
sustainably and responsible cultivating and harvesting it.  
As we consider options for future energy “farms,” the 
oceans emerge as the world’s most promising energy 
frontier. 
 
 
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Offshore Membrane Enclosures for Growing Algae (OMEGA: A System for Biofuel Production, Wastewater Treatment, and CO2 Sequestration

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