Comparison of liquid hot water, very dilute acid and alkali treatments for enhancing enzymatic digestibility of hazelnut tree pruning residues

Abstract

The effect of pretreatments on the composition of the hazelnut tree pruning residue (HTPR) and on the digestibility of the cellulose was investigated. The liquid hot water (LHW) and the very dilute acid (VDA) treatments were effective in solubilizing hemicellulose. The cellulose conversion increased up to around 60% (corresponding to 32-36 g/L glucose) with decreasing hemicellulose concentration in the pretreated HTPR. The alkali treatment provided partial delignification, however, the glucose production was comparably lower. Combining the hemicellulose removal and the delignification effect of different pretreatments in two-stage processes (LHW-alkali and VDA-alkali treatments) enhanced the cellulose concentration in the solids, but not the amount of glucose released in the enzymatic digestion. These results suggested that the hemicellulose was the main barrier against the conversion of cellulose in the LHW and VDA treated HTPR and the glucose in the hydrolysis medium inhibited the cellulase activity, which prevented the complete conversion of cellulose.

Enhancement and modeling of enzymatic hydrolysis on cellulose from agave bagasse hydrothermally pretreated in a horizontal bioreactor

“…It can be observed that at temperatures of 190°C and 220°C hemicellulose was completely solubilized, disappearing from the solid phase. Sabanci and Buyukkileci (2018) found hemicellulose content reduction on the solid fraction with the increment of temperature and time of liquid hot water pretreatment. They also reported almost complete solubilization of hemicellulose at 210°C.…”

One-Step or Two-Step Acid/Alkaline Pretreatments to Improve Enzymatic Hydrolysis and Sugar Recovery from Arundo Donax L.

“…Moreover, the ALP samples obtained from relatively severe conditions (1.0%~1.2% NaOH) indicated lower lignin contents compared to those observed in AP and FP (Table 1). Effective lignin removal has also been observed in previous alkaline pretreatments of various biomass wastes [6,13,16].…”

“…The bioconversion process is still constrained due to the recalcitrance of these energy crops. Different pretreatment strategies such as pretreatments using acid, alkaline or hot water, explosion pretreatments with steam or ammonia, and biological pretreatment have been reported for reducing the recalcitrance of lignocellulosic biomass wastes, and hence, enhancing the digestibility of these biomass wastes [12][13][14][15][16][17][18]. Chemical pretreatment has been extensively investigated, from lab-scale studies to large-scale ethanol fermentation applications, especially those using low lignin biomass (e.g., agricultural wastes) as substrates [15][16][17][18].…”

“…Acid pretreatment, which has substantial advantages such as its low cost and high efficiency, is a commonly used technique [12,16]. It is usually performed with acid addition of 0.01~5% (w/w) at 120~210 • C for 5~120 minutes, and it cleaves the glucosidic bonds of polysaccharides and effectively removes hemicellulosic components with less impact on lignin [12][13][14][15][16][17]. The main drawbacks of acid pretreatment with inorganic acids (e.g., sulfuric acid) are the formation of inhibitory compounds and its requirement for corrosion-resistant reactors [12].…”

“…On the other hand, alkaline pretreatment has less corrosion problems in comparison with these processes that involve acid addition. Alkaline pretreatment, which can effectively remove lignin from lignocellulosic biomass, has significantly improved the enzymatic hydrolysis of various wastes [13,15,16].…”