Comparison of SHF and SSF Processes under Fed Batch Mode on Ethanol Production from Pretreated Vegetable Processing Residues

Abstract

Vegetable wastes containing high starch in contrast to lignocellulosic biomass cause environmental threat due to non-judicious disposal and have not been exploited for bioethanol production. The ethanol production from steam or dilute sulphuric acid (DSA) pretreated residues was compared under fed-batch Separate Hydrolysis and Fermentation (F-SHF) or Simultaneous Saccharification and fermentation (F-SSF). The volumetric ethanol productivity, ethanol yields and ethanol contents (g/L) were higher from DSA than steam pretreatment in F-SHF, while latter two did not differ significantly between the pretreatments under F-SSF mode. High RS utilization was observed towards the last phase (72-120 h) in steam pretreatment under F-SSF. Fermented broth from F-SSF had higher levels of inhibitors such as phenolics, furfural and Hydroxymethyl furfural compared to F-SHF and also in the DSA pretreatment. A comparison of the ethanol production from the processes vis-a-vis enzyme and yeast feeding and pretreatment conditions, overall processing time etc. showed that F-SSF had higher requirement of enzymes and yeast than F-SHF. Possibility to curtail fermentation at 24 h under F-SHF mode due to very low ethanol production after 24 h equated the processing time under the two modes to 120 h and this made F-SHF the most advantageous process for the selected residues.