ADVANCED CONVERSION TECHNOLOGIES FOR SUGARS AND BIOFUELS: SUPERIOR FEEDSTOCKS, PRETREATMENTS, INHIBITOR REMOVAL, AND ENZYMES
Location: Bioenergy Research Unit
Title: Shaping reactor microbiomes to produce the fuel precursor n-butyrate from pretreated cellulosic hydrolysates
Submitted to: Environmental Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 15, 2012
Publication Date: October 3, 2012
Citation: Agler, M.T., Werner, J.J., Iten, L.B., Dekker, A., Cotta, M.A., Dien, B.S., Angenent, L.T. 2012. Shaping reactor microbiomes to produce the fuel precursor n-butyrate from pretreated cellulosic hydrolysates. Environmental Science and Technology. 46(18):10229-10238.
Interpretive Summary: Corn fiber is a byproduct of corn wet milling that is enriched for fiber. This paper describes a novel process for converting corn fiber into carboxylic acids for chemical and biofuels applications. Corn fiber was heated in the presence of dilute sulfuric acid so as to hydrolyze the hemicellulose carbohydrates and expose the cellulose fibers. The pretreated corn fiber was neutralized and fed into a bioreactor that contained a microbial consortium suitable for converting the sugars and cellulose into carboxylic acids. The advantages of this approach compared to other fermentation processes is that a mixture of microorganisms were used, which are immune to contamination, and no enzymes were needed for hydrolysis of the cellulose fibers to glucose because the microorganisms naturally produce their own enzymes. The research also examined the effects that operating conditions, substrate composition after biomass pretreatment and bioreactor history had in shaping reactor microbial communities and identified targets for future optimization of the process. This work will be interest to the agricultural processing industry, especially those engaged in corn wet milling.
To maximize the production of carboxylic acids with open cultures of microbial consortia (reactor microbiomes), we performed experiments to understand which factors affect the community dynamics and performance parameters. We operated six thermophilic (55°C) bioreactors to test how the factors: i. biomass pretreatment; ii. bioreactor operating conditions; and iii. bioreactor history (after perturbations during the operating period) affected total fermentation product and n-butyrate performance parameters with corn fiber as the cellulosic biomass waste. The maximum total fermentation production rate of 0.74 g COD l^-1^ d^-1^ and n-butyrate production rate of 0.47 g COD l^-1^ d^-1^ were achieved in bioreactors that were fed with dilute-acid pretreated corn fiber at a pH of 5.5. Computational ecology methods showed that changes in operating conditions to dilute toxic carboxylic acid products, which lead to these maximum performance parameters, also altered the composition of the microbiome, and that the microbiome, in turn, affected the performance. Operating conditions are an important factor (tool for operators) to shape reactor microbiomes, but other factors, such as substrate composition after biomass pretreatment and bioreactor history are also important. Further optimization of operating conditions must relieve the toxicity of carboxylic acids at acidic bioreactor pH levels even more, and this can, for example, be accomplished by extracting the product from the bioreactor solutions.