Comparison of acid and hydrothermal pretreatments of date waste for value creation

Abstract

Abstract The production of date syrup yields a substantial amount of date press cake (DPC), fibrous and moisturising material with great potential for generating value through bioprocessing. However, the recalcitrant structure of DPC affects the yield of products in bioprocesses. To boost the accessibility of the structure as well as increase the soluble fraction of carbohydrates and facilitate further enzymatic hydrolysis, hydrothermal and dilute acid (0.5% (v/v) sulfuric acid) pretreatments as cost-effective and feasible methods were applied on DPC at relatively low temperatures (80, 100, 120 and 140 °C) and reaction times (60 and 90 min). The success in pretreatment was then evaluated by a post-enzymatic treatment using an enzyme cocktail of cellulases and hemicelluloses. Based on total accessible sugar with minimum produced inhibitors, an optimal operating condition was considered acid pretreatment at 120 °C for 90 min with a 55.02% increase in total sugar yield. To explore the potential use of pretreated DPC, an anaerobic digestion was conducted on untreated and acid-pretreated DPC at 120 °C for 90 min. The results showed that pretreatment increased the total bioproduct yield, including hydrogen, ethanol, and volatile fatty acid yields, by 59.75%. This demonstrates the significant impact of pretreatment on product yields in a bioprocess.

Keywords

• Acid pretreatment
• Anaerobic digestion
• Date press cake
• Enzymatic hydrolysis
• Fermentable sugar
• Hydrothermal pretreatment