Biofuel from Seaweed

A relatively new contender for a source for biofuels, ethanol from seaweed, has come to the fore. Ethanol is blended with gasoline, commonly a ten percent blend in gasoline or less frequently E-85, a blend of eighty-five percent ethanol with fifteen percent gasoline. The latter is used extensively in Brazil. First a little background on making ethanol by traditional means.

The most common method for making fuel ethanol is fermentation of sugar with yeast. The sugar itself can be had directly from sugar cane, sugar beets or various fruit juices or indirectly from any source of starch such as grains or potatoes. Enzymes obtained from malted barley convert the large polymeric starch into small molecules which the yeast can use as a substrate for fermentation. The process has been known for over five thousand years. The oldest evidence of writing is cuneiform tablets found in modern day Iraq, then known as Sumeria. Some of these ancient tablets have records for beer production and distribution.

Virtually all ethanol produced in the United States is derived from corn and that is a problem on several levels. First and foremost is the fact that the process of capturing energy from sunlight is very inefficient compared to solar panels or wind turbines. Large swathes of land must be dedicated to energy production which otherwise would be suitable for food production. Ethanol from corn also consumes large amounts of fresh water and degrades the soil over time.

Ethanol can hypothetically be produced from plant fiber (cellulose) rather than starch, hence waste plant matter such as grass clippings and leaves could be turned into fuel. Although cellulosic ethanol has been studied intensely for decades, no commercial production has yet been achieved.

Now back to ethanol from seaweed. It’s recently been reported that ethanol can be made from seaweed using a genetically engineered bacteria. This is possible because the chemistry of seaweed is fundamentally different from land plants. Seaweed is comprised of large alginate molecules rather than cellulose or starch.

E. Coli, a bacteria common in the intestines of mammals and birds has been modified so that it has the enzymes necessary to disassemble the seaweed. This releases small molecules similar to sugar just as barley malt releases sugar from starch. A second modification of the genes in the bacteria allow metabolic processes that convert the sugar equivalent to ethanol, hence acting like yeast.

There are a number of advantages to the use of seaweed for fuel production. There is no diversion of food crops to fuel production. Seaweed can be harvested as a perennial crop from coastal areas or salt marshes so there is no impact on freshwater or land erosion. Seaweed production could even have a positive effect in certain coastal areas. Fertilizer runoff from the grain belt ends up in the Mississippi and ultimately the Gulf of Mexico. This nutrient-laden water causes unwanted algae blooms which consume oxygen and create a “dead zone.” If seaweed were farmed in this location it could absorb the nutrients for its growth and then be harvested for fuel production- a win-win situation.

Next time you have a little sake (the ethanol portion ) with your sushi (the wrapper part) consider that it could be coming from the same seaweed, all the while cleaning the environment.

Dr. Bob Allen, Ph.D., is Emeritus Professor of Chemistry at Arkansas Tech University

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