Methane production from ethanol co-products in anaerobic SBRs

Methane production from condensed distillers' solubles (CDS, or syrup), a co-product of ethanol production, was studied in 2-l anaerobic sequencing batch reactors (ASBRs) under 10 different operating conditions. Methane production and COD removal were quantified under steady state conditions for a wide range of operating parameters. COD removals of 62–96% were achieved at OLRs ranging from 1.5–22.2 g COD l⁻¹ d⁻¹, SRTs from 8–40 d, and F/M ranging from 0.37–1.95 g COD g⁻¹ VSS d⁻¹. The methane content of the biogas varied from 57–71% with 0.27 l CH₄ produced per g of COD removed. Approximately 54% of the COD fed to the ASBRs, and 83% of the COD removed in the ASBRs was converted to methane. Microbial yield (Y) and decay (b) constants were determined to be approximately Y = 0.127 g VSS g⁻¹ COD removed and b = 0.031 d⁻¹, respectively. Methane recovery from ethanol co-products can reduce the cost and the fossil fuel consumption of ethanol production.