Anaerobic Digestion Potential for Ethanol Processing Residues

The production of corn-based ethanol in the U.S. is dramatically increasing, and consequently so is the quantity of byproduct materials generated from this processing sector. These coproduct streams are currently solely utilized as livestock feed, which is a route that provides ethanol processors with a substantial revenue source and significantly increases the profitability of the production process. With the construction and operation of many new plants in recent years, these residuals do, however, have much potential for value-added processing and utilization in other sectors as well. This option holds the promise of economic benefit for corn processors, especially if the livestock feed market eventually becomes saturated with byproduct feeds. Anaerobic digestion, which has been successfully utilized to produce methane from a variety of food and organic processing residues, has not yet been used in the ethanol industry. The objective of this study, therefore, was to assess the potential for using ethanol processing residue streams as feedstocks for anaerobic digestion. Toward that end, laboratory testing of anaerobic digestibility has been conducted and biochemical methane yields have been measured during a 45 day trial. Results indicate that whole stillage and thin stillage produced acceptable levels of methane, but CDS was the most promising coproduct. It yielded a BMP of 45% that of theoretical, which is remarkably high, and thus should be examined further in follow-up studies.