Cassava pulp enzymatic hydrolysis process as a preliminary step in bio-alcohols production from waste starchy resources

Abstract

Tapioca starch factories generate a large amount of wastewater and solid waste which take several steps of waste treatment to manage. The solid waste in particular contains a high level of starchy-lignocellulosic biomass, especially cassava pulp (CP). The wastewater, above mentioned, contains also residual cassava constituents and, usually are named cassava wastewater (CWW). These residual resources are potentially promising substrates for the production of biofuels (renewable energy carriers), such as products resulted from acetone-butanol-ethanol (ABE) fermentation process. The conventional combination steps between acid hydrolysis and enzymatic hydrolysis of starchy- lignocellulosic substrate, before fermentation process, generate complicated problems such as acid contaminated waste and spending of a long time (several hours) for hydrolysis reaction process. To address these problems, cassava pulp (CP) alone or supplemented with cassava starch wastewater (CWW) was used as a model feedstock (raw material) and an adapted one step enzymatic hydrolysis was created. This one step enzymatic hydrolysis process shows a shortened optimum treatment time (2 h) and yielded a reducing sugar level that was equal to that previously reported for the two stage combination between of acid hydrolysis and enzymatic hydrolysis. After adapted one step enzymatic hydrolysis of the starch the reducing sugar solution was fermented using either Saccharomyces cerivisiae TISTR5339 or Clostridium butyricum TISTR1032 for ethanol and ABE production, respectively. The ethanolic fermentation (by using S. cerevisiae) of CP (67 g/L) in sterilized wastewater solution, yielded a bioproduct mixture having a content consisting (beside other components) from 8.8 g/L of ethanol, but this ethanol concentration was increased to 12.9 g/L with the replacement of the water by CWW. Fermentation of the saccharified CP alone or with CWW with C. butyricum yielded a total ABE production of 9.65 g/L and 10.24 g/L, respectively, but the ethanolic production was reduced from 9 g/L (93% of the solvent composition) to 1.64 g/L (16% solvent composition) by the addition of the CWW, with butanol as the major product (53.2%; 2.5 g/L). © 2012 Elsevier Ltd. All rights reserved.