Whole slurry ethanol fermentation of maleic acid-pretreated EFBs without a detoxification process

The whole slurry fermentation indicates the simultaneous saccharification and fermentation (SSF) of total slurry of pretreated lignocellulose, in which the solids/liquid separation step is eliminated. In most studies, pretreated lignocellulose is used in enzymatic hydrolysis and ethanol fermentation after being washed with water. In this study, the feasibility of whole slurry fermentation was tested for oil palm empty fruit bunches (EFB) using maleic acid as an acid catalyst. The optimal pretreatment conditions were found to be 190°C, 1% (w/v) maleic acid, and 3 min ramping to 190°C in a microwave digester. When comparing the ethanol yield (% of theoretical maximum) of SSF (48 h), which was assessed from the initial glucan input at the pretreatment step, the pretreated and washed EFB gave only 39.0% but the SSF of whole slurry resulted in 61.3%. This significantly higher ethanol yield of the whole slurry fermentation than that of the SSF of washed pretreated EFB may be due to the utilization of both solid and liquid fractions of pretreated EFB slurry. Because of less formation of inhibitors during maleic acid pretreatment and less inhibition by maleic acid salts, the pretreated EFB slurry was proceeded to the SSF only after neutralization. These results imply that 1) maleic acid can be utilized as a suitable catalyst for whole slurry fermentation not requiring inhibitor detoxification or conditioning and 2) the whole slurry fermentation can improve the efficiency of ethanol production by utilization carbohydrates available in both solid and liquid phases.