Energy costs
Drying distillers grain and solubles is an energy consuming process: 40.4% of the thermal energy used in an ethanol plant that produces DDGS can be used in the drying process. However, wet distillers grain spoils quickly and the dried form is preferable in spite of high energy costs: 63% of DGS produced by the US dry-milling ethanol industry are sold dried (US EPA, 2010).
Volatile organic compounds
Drying distillers grain produces volatile organic compounds that may cause serious health problems. These emissions can be reduced (up to 95%) by the installation of thermal oxidizers in ethanol plants (US EPA, 2011).
Industrial waste reduction
Corn distillers grain fed to livestock remove huge amounts of by-products that would otherwise have to be eliminated by other means (Lyons, 2003).
Reduction of methane emissions
Corn distillers grain is a more efficient ingredient than maize grain in cattle and has been shown to decrease methane produced from enteric fermentation when they replace it. This reduction has been estimated at 3.2 g CO2eq/MJ ethanol per head of cattle fed DGS (US EPA, 2010).
Genetically modified maize by-products
Corn distillers grain is mainly produced in the USA and may result from processing of genetically modified maize (in 2005, about 50% of maize acreage in the USA was sown with transgenic plants) (Fernandez-Cornejo et al., 2006). The European Union used to be the main export market and imported more than 90% of US maize DDGS every year between 1995 and 2000. As a result of the de facto moratorium on the approval of new genetically modified varieties and the following introduction of new labeling and traceability requirements for animal feed in 2004, exports of US corn distillers grain to the EU decreased by 80% between 2005 and 2008 (Fox, 2008).