Amaranth lignocellulose as feedstock for bioethanol production: effect of microwave-assisted alkaline pretreatment on reducing sugar yield

Abstract

A new class of lignocellulose derived from amaranth (Amaranthus Cruentus) represents a potential feedstock for bioethanol production. The lignocellulose material can be pretreated to yield high monomeric sugar concentrations and also be able to release lignin that normally has inhibiting effects during hydrolysis and fermentation in the bioethanol production process. The objective of the present study was to evaluate the pretreatment of amaranth lignocellulose by assessing the yields of total reducing sugars. Milled amaranth roots and stems, ­1 ­1 containing 363.5 g Kgcellulose and 124.9 g Kghemicellulose were pretreated using microwave irradiation in the presence of different alkaline catalysts. Microwave pretreatment was conducted at varying power inputs and energy densities using NaOH, KOH or Ca(OH)2 as alkaline pretreatment at varying concentrations (10 to 50 g kg­1). The liquid fraction was analyzed for 5 and 6­ring sugar content using high performance liquid chromatography (HPLC). The overall results showed that pretreatment with KOH followed by enzymatic hydrolysis gave the highest total sugar yield (488.23 g Kg­1 based on original biomass loading). Microwave­ assisted alkali pretreatment of lignocellulose remains the most affordable and effective method for delignification and hydrolysis of lignocellulosic biomass compared to conventional heating. The results from this study show that Amaranthus cruentus has potential for high concentrations of fermentable sugars and is a viable feedstock for bioethanol production through microwave pretreatment