The potential for biomimetic application of rumination to bioreactor design

Pretreatment of biomass feedstocks is considered necessary to increase their conversion to biofuels and other bioproducts. However, even the best chemical and physical pretreatments have disadvantages that make the development of alternative strategies to improve biomass fermentability a worthy pursuit. An interesting natural process is that of rumination, by which ruminant animals regurgitate their food for re-chewing to reduce particle size, increase surface area, and accelerate its biodegradation by the animal's mutualistic microbial community. Detailed examination of the process reveals that it is a unique, unusually effective, and energy-efficient type of physical treatment of fibrous biomass. Effectiveness and energy efficiency are gained by several unappreciated aspects of the process, including: full wetting of the biomass prior to its exposure to re-chewing; a hypsodont dentition pattern and jaw movement designed to maximize shearing and delamination (rather than cutting) of the biomass; and an effective feed sorting mechanism that results in a preferential processing of the larger particles that are in need of further grinding, rather than smaller particles whose additional grinding would provide little benefit. These nuances of the rumination process suggest designs for accomplishing similar particle size reduction and surface area increases within bioreactors during cellulosic biomass fermentation (“co-treatment”). While the rumination process has evolved within the context of allowing the ruminant animal to exploit widely available but highly fibrous feeds, it has the potential for broad applicability and improved efficiency for industrial conversion of cellulosic biomass by both pure and mixed cultures.