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Algae Based Butanol Production Gains Working Processes
March 4, 2011 | 4 Comments
This week two new algae process paths made it out into view. One deals with algae directly producing butanol and the other is a growth process for algae that exploits an already concentrated algae growth medium with innovative processing.
First and simplest, and likely most easily adoptable is from a team of chemical engineers at the University of Arkansas led by Jamie Hestekin, assistant professor and leader of the project.
Fiber Membranes and Raceway for Algae Production. Click image for the largest view. Image Credit: University of Arkansas.
Hestekin and his research team of undergraduates from the Honors College and several graduate students, including a doctoral student who has discovered a more efficient and technologically superior fermentation method, grow algae on “raceways,” which are long troughs – usually 2 feet wide and ranging from 5-feet to 80-feet long, depending on the scale of the operation. The troughs are made with screens or carpet, although Hestekin said algae would grow on almost any surface.
The clever innovation is the raceways are fed runoff or wastewater rich in nitrogen and phosphorous the algae need to prosper. They enhance this growth by delivering high concentrations of carbon dioxide through hollow fiber membranes that look like long strands of spaghetti. With natural sunlight the algae in the nutrient rich water produce well. It also recovers the lost phosphorus and nitrogen cleaning up the water used and getting a second use from the nutrients.
Algae are harvested every five to eight days by vacuuming or scraping it off the screens. After drying, the algae are crushed and ground into a fine powder as the means to extract the sugar and starch carbohydrates from the plant cells. For this project, Hestekin’s team works with starches. The first stage is to treat the carbohydrates with acid and then heat them to break apart the starches and convert them into simple, natural sugars. They then begin a unique fermentation process in which organisms turn the sugars into organic acids – butyric, lactic and acetic.
The Arkansas team’s second stage of the fermentation process focuses on butyric acid and its conversion into butanol. The researchers use a unique process called electrodeionization, a technique developed by one of Hestekin’s doctoral students. This technique involves the use of a special membrane that rapidly and efficiently separates the acids during the application of electrical charges. By quickly isolating butyric acid, the process increases productivity, which makes the conversion process easier and less expensive.
The team is currently working with the New York City Department of Environmental Protection to create biofuel from algae grown at the Rockaway Wastewater Treatment Plant in Queens.
The Arkansas team’s research articles detailing findings from algae-to-fuel project have been submitted to Biotechnology and Bioengineering and Separation Science and Technology. This team is making algae much more practical.
At the University of California, Berkeley, a team led by Michelle C. Y. Chang, assistant professor of chemistry, has constructed a chimeric pathway assembled from three different organisms for the high-level production of normal butanol in E. coli bacteria. The pathway uses an enzymatic chemical reaction mechanism in place of a physical step as a kinetic control element to achieve high yields from the sugar glucose. It’s a straight to fuel product process from sugar.
Various species of the Clostridium bacteria naturally produce a chemical called n-butanol (normal butanol), which is often proposed as a substitute for diesel oil and gasoline. So far most researchers, including a few biofuel companies, have genetically altered Clostridium to boost its ability to produce n-butanol, others have plucked enzymes from the bacteria and inserted them into other microbes, such as yeast, to turn them into n-butanol factories because yeast and E. coli are considered to be easier to grow on an industrial scale.
The problem? The n-butanol production has been limited to little more than half a gram per liter, far below the amounts needed for affordable production and the process leaves most of the precious raw material – sugar, behind. Other researchers who have engineered yeast or E. coli to produce n-butanol have taken the entire enzyme pathway and transplanted it into these microbes. But n-butanol is not produced rapidly in these systems because the native enzymes also can work in reverse to convert butanol back into its starting precursors. Wouldn’t that drive a researcher a bit crazy?
N-Butanol Synthetic Pathway. Click image for more info.
Chang and her colleagues innovation is they’ve stuck the same enzyme pathway into E. coli, but replaced two of the five enzymes with look-alikes from other organisms that avoided the problems other researchers have had: n-butanol being converted back into its chemical precursors by the same enzymes that produce it.
The team’s new genetically altered nearly non reversing E. coli produced nearly five grams of n-butanol per liter, about the same as the native Clostridium and one-third the production of the best genetically altered Clostridium, but about 10 times better than current industrial microbe systems.
Chang is understandably a bit excited saying, “We are in a host that is easier to work with, and we have a chance to make it even better. We are reaching yields where, if we could make two to three times more, we could probably start to think about designing an industrial process around it. We were excited to break through the multi-gram barrier, which was challenging,”
The Berkley work isn’t so simple as it sounds. Chang found the two new enzyme versions in published sequences of microbial genomes, and based on her understanding of the enzyme pathway, substituted the new versions at critical points that would not interfere with the hundreds of other chemical reactions going on in a living E. coli cell. In all, she installed genes from three separate organisms – Clostridium acetobutylicum, Treponema denticola and Ralstonia eutrophus — into the E. coli.
Chang is optimistic that by improving enzyme activity at a few other bottlenecks in the n-butanol synthesis pathway, and by optimizing the host microbe for production of n-butanol, she can boost production two to three times more, that might justify considering scaling up to an industrial process. She also is at work adapting the new synthetic pathway to work in yeast, a workhorse for industrial production of many chemicals and pharmaceuticals.
These two paths, using the starch and the sugar components of algae offer great promise. Taken together butanol would be coming from a large share of the carbohydrates. What proportion or percentage isn’t stated, but for economic reasons these or other ideas are going to have to realistic on the carbon cycle from the CO2 to a fuel – leaving behind raw carbon compounds will be a huge drag on economic potential.
Another point overlooked is the algae oil. The impact on the oil through these processes isn’t known, nor are the proteins and other parts considered. Algae is a pretty rich trove of carbohydrates, oils and proteins that reason would seem to suggest are quite valuable.
Its much more complex when considering the money needed to farm algae production, process out the products, and balance processes to revenue streams. But research is getting there and these two research projects offer quite a lot to process engineers for contemplating plant designs.
Algae are a wonderful way to recapture carbon using sunlight. Getting to products though, with all the value intact at sensible investment and pricing is a very complex matter. It’s getting there.
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I believe that this production will grow as the technology advances. As the productivity increases, more people are willing to invest in the production. Nice and detailed explanation anyway. Thanks for the great post! Hopefully it will replace the use of fossil fuel in 10 years time 🙂
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