Reverse osmosis and ultrafiltration of stillage solubles from dry‐milled corn fractions

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Abstract
Grits, flour, degerminated meal and hominy feed from corn were fermented to make ethyl alcohol. The stillage, remaining after distillation of alcohol, was separated by screening and centrifuging into insoluble and soluble fractions. The stillage solubles contained 0.036 to 0.080% nitrogen and 1.4 to 7.2% total solids. Ultrafiltration (UF) membranes separated stillage solubles into permeate and concentrate fractions. Permeates from stillage solubles accounted for 85 to 95% of the original volume, 44 to 67% of the total solids and 40 to 75% of the total nitrogen. Reverse osmosis (RO) membranes separated the UF permeate into RO permeate and RO concentrate fractions. The RO permeate accounted for 70 to 92% of the original volume, 5 to 15% of the total solids and 5 to 21% of the total nitrogen in the UF permeate. Conductivity of some RO permeate fractions was lower than that of tap water. The combination of UF and RO processing of stillage solubles from corn dry‐milled fractions appears to be an attractive method to recover most of the solids and nitrogen in small volumes of concentrate, and produces a final permeate with a low concentration of solids and nitrogen. The RO permeate may be reused as water, treated further or discharged.

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