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 CH(4) 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.
Perchloroethylene (PCE) and trichloroethylene (TCE) have been commonly used in the repair and maintenance of diesel engine locomotives. Improper handling, storage, and disposal lead to contamination of rail yard soils and groundwater with chlorinated ethylenes. Benzene, toluene, ethyl-benzene, and xylene (BTEX) are also common contaminants at rail yards because of the leakage of diesel fuel storage tanks and spills of diesel fuel. Co-contamination of groundwater with BTEX and chlorinated ethylenes allows for the application of anaerobic/aerobic bioremediation to achieve mineralization of both types of compounds. Bench scale laboratory experiments were run to select and enrich for an undefined, mixed, microbial consortium able to mediate PCE dechlorination to dichloroethylene (DCE), mineralization of the DCE, and mineralization of aromatic compounds. A periodically operated suspended culture reactor created alternating anaerobic/aerobic environments. When glucose was added to the reactor as the sole electron donor, the mixed culture dechlorinated PCE to cis-1,2-dichloroethylene (cDCE) in 24 h. When phenol and glucose were added to the reactor, the mixed culture dechlorinated PCE to cDCE, metabolized the influent phenol, and oxidized 90 percent of the cDCE produced in 24 h. Because both phenol and toluene can induce the enzymes necessary for mineralization of TCE and DCE, an anaerobic/aerobic bioremediation approach has potential application for remediation of groundwater at rail yards co-contaminated with diesel fuel and chlorinated ethylenes.
Methane production from the soluble fraction of distillers' dried grains with solubles, a co-product of ethanol production, was studied in 2-L anaerobic sequencing batch reactors (ASBRs) under 10 different operating conditions. Methane production and chemical oxygen demand (COD) removal were quantified for a wide range of operating parameters. Chemical oxygen demand removals of 64 to 95% were achieved at organic loading rates ranging from 1.5 to 22.2 g COD/L Á d, solids retention times from 8 to 40 days, and food-to-microorganism ratios ranging from 0.4 to 1.9 g COD/g volatile suspended solids (VSS) Á d. Biogas methane content varied from 61 to 74%, with 0.29 L CH 4 produced/g COD removed. Roughly 56% of the influent COD and 84% of the COD removed in the ASBRs was converted to methane. Microbial yield (Y) and decay (b) constants were determined to be Y ¼ 0.126 g VSS/g COD removed and b ¼ 0.032 day À1 , respectively. Methane produced from co-products can reduce the costs and fossil-fuel consumption of ethanol manufacture. Water Environ. Res., 80, 570 (2008).
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