High productivity and specificity in anaerobic digesters arise because complex microbiomes organize into a metabolic cascade to maximize energy recovery and to utilize the advantage that the gaseous end product methane freely bubbles out of the system. These lessons were applied to ascertain whether a reactor microbiome could be shaped to produce a different end product. The liquid product n-caproic acid was chosen, which is a 6-carbon-chain carboxylic acid that is valuable and that has a relatively low maximum solubility concentration for product recovery. Acetoclastic methanogenesis was inhibited by pH control and a route was provided for n-caproic acid extraction by implementing selective, in-line recovery. Next, ethanol was supplemented to promote chain elongation, which is a pathway in which short-chain carboxylic acids are elongated sequentially into medium-chain carboxylic acids with two-carbon units derived from ethanol. The reactor microbiome developed accordingly with the terminal process catalyzed by chain-elongating bacteria. As a result, n-caproic acid production rates increased to levels comparable to anaerobic digestion systems for solid waste treatment.
Development of a highly specific and productive process for n-caproic acid production: applying lessons from methanogenic microbiomes
M. T. Agler, C. M. Spirito, J. G. Usack, J. J. Werner, L. T. Angenent; Development of a highly specific and productive process for n-caproic acid production: applying lessons from methanogenic microbiomes. Water Sci Technol 1 January 2014; 69 (1): 62–68. doi: https://doi.org/10.2166/wst.2013.549
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