Dilute acid pretreatment and fermentation of sugar beet pulp to ethanol

Sugar beet pulp (SBP) is the residue of beet sugar processing and is a promising feedstock for fuel ethanol production. Response surface methodology was used to investigate the effects of temperature, acid concentration and solid loading on dilute sulfuric acid pretreatment and enzymatic hydrolysis of SBP. Mass balances on cellulose, hemicellulose, pectin, and protein were performed and sugar degradation products such as 5-hydroxymethylfurfural (HMF), furfural and acetic acid were monitored. Scanning electron microscopy was used to study changes in the physical structure of SBP upon pretreatment. Acid pretreatment increased the enzymatic digestibility of SBP from 33% (raw) to 93% (treated). Pretreatment at optimum conditions (temperature = 120 °C, acid concentration = 0.66% and solid loading = 6%) resulted in 93% enzymatic hydrolysis yield and 62% total reducing sugar yield. The ethanol yield from pretreated SBP under the optimum conditions was 0.4 g ethanol/g dry matter in a simultaneous saccharification and fermentation (SSF) process employing Escherichia coli KO11.