NASA scientists from the Moffet Field laboratory in California have proposed an ingenious process to grow algal biofuels in the ocean enclosed within large floating bags made of a special semi-permeable clear plastic membrane. Growing algae in floating bags in the sea solves several major problems that are faced by current land based methods of algal biofuel production in an elegant low energy, low impact manner. This is the kind of out of the box thinking that is needed in order to grow the green economy.
In a recent update to our original post on the NASA plan to produce biofuel in floating bags filled with sewage NASA engineers and seasoned biofuel industry veterans have launched a new biofuels company called Algae Systems to produce Carbon-Negative Diesel and Jet Fuel NASA-developed technology, called OMEGA (Offshore Membrane Enclosures for Growing Algae) that is covered in our original post from last May.
NASA’s, Lisa Lockyer, Deputy Director of New Ventures and Communications for the Ames Research Center, has echoed Algae Systems’ determination and confidence by announcing the center’s support for the commercialization of the technology.
The Problems Facing Current Land Based Algal Biofuel Systems
Although algae live in water current research has been focused on land based systems for producing algal biofuels from these one celled work horses. The two land-based methods being researched today are manmade open ponds and closed bioreactors. Open ponds are shallow channels filled with freshwater or seawater, depending on the kind of algae that is grown. Closed bioreactors instead are closed systems. Both land based methods require often scarce land resources of course and also each present their own unique set of problems.
In open pond systems the water must be continuously re-circulated in order to achieve high yields and efficient production of algae. In fact, if not circulated a layer of algae – i.e. pond scum — tends to form on the water surface preventing most light and oxygen from reaching the water volumes below this surface mat of tightly packed algae mass.
In order to keep the algae suspended and the pond aerated paddle wheels need to continuously re-circulate the water mass. These manmade ponds also have the problem of water evaporation, which is a limiting factor in dry water poor areas. As water evaporates out of these shallow warm re-circulated artificial ponds a continuous supply of new freshwater (or new ocean water for salt water systems) is needed to replenish the water that has been lost to evaporation. The salinity of the water needs to be kept within operational parameters; if it gets too salty the algae in the pond will be killed.
Bioreactors, which are enclosed systems constructed using clear plastic or glass, have their own set of problems. While water evaporation is minimal because they are closed systems keeping the water from getting too hot or cold is a big problem for these types of installations.
Algal Has the Potential to Produce Large Quantities of Plant Derived Oil
“The reason why algae are so interesting is because some of them produce lots of oil,” said Jonathan Trent, the lead research scientist on the Spaceship Earth project at NASA Ames Research Center, Moffett Field, Calif. “In fact, most of the oil we are now getting out of the ground comes from algae that lived millions of years ago. Algae are still the best source of oil we know.”
Biodiesel is currently mainly produced from soy, canola, and palm trees. The biofuel yields of these crops ranges from around 500 liters per hectare per year (or 50 gallons per acre per year) for soy beans; to around three times that figure for canola and 6,000 liters per hectare per year (or 600 gallons of oil per acre per year) for oil palm.
By comparison some species of algae can produce as much as 20,000 liters per hectare per year (or 2,000 gallons of oil per acre per year) of biofuel. This is 40 times the yield of soy beans!
How NASA Proposes to Produce Fuel From Sewage Using Floating Bags
“The inspiration I had was to use offshore membrane enclosures to grow algae”, said Trent “We’re going to deploy a large plastic bag in the ocean, and fill it with sewage. The algae use sewage to grow, and in the process of growing they clean up the sewage.”
The concept is simple and elegant. Large floating plastic bags are filled with sewage and floated in open ocean water. The sewage filled bags are inoculated or seeded with the desired carefully selected strains of oil producing algae that will feed on the nutrients in the sewage, growing rich, fatty cells. The bag is made with a semi-permeable membrane material that allows fresh water to flow out into the ocean, while retaining the algae and nutrients and that is also gas permeable enabling carbon dioxide to be consumed and oxygen to be released. These special types of membranes are called “forward-osmosis membranes”, essentially they allow fresh water to run in one direction while preventing salt water intrusion from the surrounding sea water.
The continuous mechanical action of ocean swells will keep the water within the bag well mixed and promote the exchange of gases through the membrane’s surface. It will do this for free. The internal temperature of the floating bag bioreactors will be moderated by the thermal mass of the surrounding ocean water.
Think how much semi-treated or raw sewage is currently just dumped into the ocean. This process promises to turn this harmful polluting waste into valuable products in a way that uses the ocean itself to help promote its productivity. The bags are expected to last two years, and can be recycled afterwards.
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