Comparison of Low-Temperature Alkali/Urea Pretreatments for Ethanol Production from Wheat Straw

Abstract

NaOH/urea (NU) pretreatment at lower than 0 °C has been frequently applied for improving bio-conversion of lignocellulose, but the wastewater generated from the pretreatment process is hard to dispose. KOH/urea (KU) pretreatment for enhancing bioconversion of lignocellulose has recently attracted researchers’ attention due to the recycling of wastewater for facilitating crops’ growth. This study compared the effects of NU and KU pretreatments at cold conditions on the enzymatic hydrolysis and bioethanol yield from wheat straw (WS). By using response surface methodology an optimal pretreatment with an equal ratio of alkali/urea (4% w/v) at −20 °C for 3 h was established. The enzymatic hydrolysis of KU-treated WS was 81.17%, which was similar to that of NU-treated WS (83.72%) under the same condition. It means that KU pretreatment has equal ability to NU pretreatment to improve enzymatic saccharification of lignocellulose. KU pretreatment has the promising potential to replace NU pretreatment for facilitating bioconversion of lignocellulose in cold conditions due to the clean way to recycle its wastewater as fertilizer for crop growth. Hence, KU pretreatment combined with enzymatic hydrolysis and fermentation could be a promising green way to cellulosic ethanol production with zero waste emission.