"Clean Energy" From Algae Grown in Waste Water
NASA scientists have proposed an ingenious and remarkably resourcefulprocess to produce "clean energy" biofuels, that cleans waste water,removes carbon dioxide from the air, retains important nutrients, anddoes not compete with agriculture for land or freshwater.
Algae are similar to other plants in that they remove carbondioxide from the atmosphere, produce oxygen as a by-product ofphotosynthesis, and use phosphates, nitrogen, and trace elements togrow and flourish. Unlike many plants, they produce fatty, lipid cellsloaded with oil that can be used as fuel.
"The inspiration I had was to use offshore membrane enclosures to growalgae. We're going to deploy a large plastic bag in the ocean, and fillit with sewage. The algae use sewage to grow, and in the process ofgrowing they clean up the sewage," said Jonathan Trent, the lead research scientiston the Spaceship Earth project at NASA Ames Research Center, MoffettField, Cali.
It is a simple, but elegant concept. The bag will be made ofsemi-permeable membranes that allow fresh water to flow out into theocean, while retaining the algae and nutrients. The membranes arecalled "forward-osmosis membranes." NASA is testing these membranes forrecycling dirty water on future long-duration space missions. They arenormal membranes that allow the water to run one way. With salt wateron the outside and fresh water on the inside, the membrane prevents thesalt from diluting the fresh water. It's a natural process, where largeamounts of fresh water flow into the sea.
Floating on the ocean's surface, the inexpensive plastic bagswill be collecting solar energy as the algae inside produce oxygen byphotosynthesis. The algae will feed on the nutrients in the sewage,growing rich, fatty cells. Through osmosis, the bag will absorb carbondioxide from the air, and release oxygen and fresh water. Thetemperature will be controlled by the heat capacity of the ocean, andthe ocean's waves will keep the system mixed and active.
When the process is completed, biofuels will be made and sewage will beprocessed. For the first time, harmful sewage will no longer be dumpedinto the ocean. The algae and nutrients will be contained and collectedin a bag. Not only will oil be produced, but nutrients will no longerbe lost to the sea. According to Trent, the system ideally is failproof. Even if the bag leaks, it won't contaminate the localenvironment. The enclosed fresh water algae will die in the ocean.
The bags are expected to last two years, and will be recycledafterwards. The plastic material may be used as plastic mulch, orpossibly as a solid amendment in fields to retain moisture.
Source: nasa.govAdded: 25 May 2009