Chasing Nature

If someone were to ask you, ”What do helicopters, hypodermic needles, airplane wings and sonar have in common?”, do you think you could come up with the answer? At first glance the answer may not seem clear, but upon closer inspection a hidden similarity emerges. While all of these items do represent enormous leaps in human technological advancement, the design behind them is by no means original. Millions of years before the notion of these technologies were even conceived, dragonflies and hummingbirds hovered in midflight, vipers injected venom through hollow fangs into unsuspecting prey and dolphins used echolocation to locate fish. In fact a vast majority of modern technology is directly copied from designs in nature. Despite our best attempts, these imitations always pale in comparison to the real thing. It is really not much of a surprise then, when technology fails to match the most complex biological processes which, in themselves took millions of years to develop through evolution
One of the most complex and intricate of these systems is the digestive tract, specifically that found in ruminants. Since the emergence of grass as a dominant plant species, ruminants have continued to be the dominant group of herbivores. The secret of this success lies in the unique digestive system of this group of animals. Cellulose, is one of the main components of grass and plant cell walls, and since it is primarily comprised of carbohydrates, it has a lot of stored potential energy. The trouble is that cellulose is very difficult to digest and as a result all of that stored energy is virtually unattainable. Ruminants however, have evolved a highly complex digestive system which can digest tough cellulose so that energy may be extracted. Recently, humans have also recognized the enormous energy potential of cellulosic plant biomass specifically in the production of ethanol. Ethanol has many industrial applications, but its primary use is as a fuel additive. When ethanol is added to fuel, the amount of hydrocarbon and volatile organic emissions decreases. Up until recently, corn has been the primary source of ethanol. Unfortunately, corn alone cannot supply the necessary amount of ethanol required for a worldwide demand. Consolidated bioprocessing(CBP) of biomass is a process which utilizes anaerobic bacteria to decompose and ferment cellulose plant biomass into ethanol. Currently, CBP systems still require many improvements before the process can become a viable ethanol production source. Researchers from the University of Wisconsin-Madison and the USDA-ARS-US Dairy Forage Research Center have set out to observe the digestive system of the cow, which has a very efficient cellulose digestive system, in order to determine how CBP systems can be improved. After observation, 3 main areas of improvement were identified:
1. Pre-treatment of the cellulose fibre
2. Anaerobic bacteria
3. Usage of by-products as possible alternate energy sources

Even for the species of bacteria which can produce cellulase, cellulose must first be pre treated in order to weaken the tough protein lignin found in the cell walls of plantcells. In CBP this is achieved chemically, however, the systems and the chemical agents all require significant costs. In addition, chemical pre treatment also results in the loss of some carbohydrate from the mixture as well as waste which requires disposal. The system in cows is much more primitive, yet more effective. By physically grinding the plant material, and then re-chewing the regurgitated cud, cows are able to reduce the particle size so much that there is an estimated 104 fold increase in total surface area(Weimer 2009). However, in order to thoroughly breakdown the cellulose cows were found to chew for 200 min/kg of fibre intake which adds up to 10-13 hours of ruminating per day or as high as 20 hours per day(Weimer 2009)! Remarkably the energy expended in ruminating is actually quite small. But currently there is no mechanical system which matches the efficiency of the cow in grinding plant biomass, so efforts are continuing to be focused on a chemical pre treatment. However, this research may provide the information which could be used in the future to create a more efficient grinding system which closely mimics the cow.
The process of cellulose hydrolysis is made possible by enzymes produced by anaerobic bacteria. In cows these vital bacteria are located in a large organ called the rumen where the chewed plant fibre can remain for up to 72 hours(Weimer 2009). This gives the bacteria in the rumen plenty of time to properly digest the treated plant matter. In the low-no oxygen conditions, fermentation occurs and the main products are volatile fatty acids(VFA), which the cow absorbs through its gut wall(Weimer 2009). The cellulose is degraded faster depending on the available surface area. Plant cell walls are composed of many different components and yet almost every single type of enzyme required to digest the material can be produced by at least one of the bacterial species found in the rumen. In contrast, artificial systems lack this diversity of microflora, and cannot digest plant matter as thoroughly as ruminants.
Perhaps the most important focus of this study was the examination of utilizing the fermentation by products other than ethanol as alternative energy sources. Two of the major by products produced by the fermentation process are methane and VFAs. Methane, which is excreted as gas by ruminants, could be captured in CBP systems and used as an alternate fuel source. VFAs on the other hand have a low volatility, but have a large amount of stored energy therefore have a potential as another energy source. Most systems currently focus on primarily ethanol production however, the addition of these by products could contribute enormously to the biomass energy yield.
Improvements on current CBP systems need to be made before this process becomes a viable source of ethanol. Current research provides a valuable insight regarding the direction to advance this technology. Equally important, the effort towards developing this technology also presents alternatives for waste management. For industries where high cellulose biomass is produced as waste such as agriculture, forestry or even maintenance of green spaces the advancement of CBP systems represents a potentially effective and even beneficial waste management strategy other than composting.

References
Weimer J. Paul, Russell B. James, & Muck E. Richard. (2009). Lessons from the cow: What the ruminant animal can teach us about consolidated bioprocessing of cellulosic biomass. [Lessons from the cow: What the ruminant animal can teach us about consolidated bioprocessing of cellulosic biomass] Bioresource Technology, 100(21), 5323-5331.