In the last blog post on EPA’s changes to cellulosic biofuel goal under the Renewable Fuel Standard (RFS) I touched on one of the challenges of growing feedstock for ethanol production – the land use conflict of food vs. fuel. Cellulosic ethanol helps to address this question by using byproducts such as corn stover and wood waste as inputs to the ethanol production process; but, progress on advancing this technology to commercial scale has been slow. For this Future Friday post we’ll look at research on seaweed-based biofuels that holds promise for addressing these problems while increasing the efficiency of biofuel production.
There are many advantages to using seaweed as the feedstock for biofuel production. With 71% of the earth’s surface covered in saltwater biofuel production from seaweed does not run into the same constraints and conflicts as terrestrial-based biofuels. Seaweed is up to five times more efficient at storing the suns energy in biomass, and it grows much faster than land-based plants. Another advantage is that seaweed farming is already a multibillion dollar global industry; though production to date is focused on producing alginate (a food thickener), vitamin supplements, inputs to the cosmetics and plastics industries and animal feed.
Though seaweed appears to be an ideal feedstock there are obstacles that must be overcome for it to be used for large-scale biofuel production. As with cellulosic ethanol the primary challenge is finding or engineering bacteria that can break down the carbohydrates in seaweed into fermentable sugars. One avenue being pursued is the collection of bacteria from the droppings of Scottish sheep that subsist on a diet largely of seaweed (Seaweed biofuels: a green alternative that might just save the planet). In 2012 the Bio Architecture Lab (BAL) in Berkeley, CA patented a genetically modified bacterium that can break down the carbohydrates in brown seaweed. Research shows that the bacterium is highly efficient, making 80% of the maximum sugar yield from seaweed available. With this technology seaweed has the potential to produce 1,500 gallons of ethanol per acre, which is 50% more than sugar cane and three times as much as corn-based ethanol (Unlocking Seaweed’s Next-Gen Crude: Sugar).
Seaweed’s fast growing, carbohydrate dense characteristics confer many advantages, but economic viability of seaweed-based biofuels will likely depend on it being part of a larger interconnected value chain. For example, seaweed is being integrated into aquaculture operations (e.g., fish, shrimp, oysters) because of seaweeds ability to clean the water and maximize nutrient use. The ability to extract a high value product to serve an existing market, and then produce biofuel could make the economics more favorable and increase the likelihood of a future with seaweed-based biofuels.