Bio-ethanol production by Zymomonas mobilis using pretreated dairy manure as a carbon and nitrogen source

Dairy manure contains high levels of cellulose, hemicellulose and a nitrogen source. These properties make dairy manure a potential biomass source for ethanol production. In this study, a dilute NaOH pretreatment and enzymatic hydrolysis were carried out for the degradation of lignocellulose from dairy manure. The response surface method and Box-Behnken design were first applied in order to optimize the NaOH pretreatment. Under the optimization conditions, 21.14 g L-1 of glucose and 9.48 g L-1 of xylose were obtained from continuous enzymolysis. The maximum ethanol concentration achieved reached 10.55 g L-1 when using ethanologenic Zymomonas mobilis without an additional nitrogen source. This produced a 71.91% ethanol yield from manure hydrolysate medium. These results demonstrate the economic benefits of using nitrogen from a dairy manure source for balancing the C/N ratio, without the need for an additional nitrogen source. The results from this study could extend beyond cellulosic ethanol for the production of other chemicals.