Enhanced upstream processing of rice straw by an integrated alkaline pretreatment and enzymatic saccharification

Abstract

The efficient conversion of lignocellulosic biomass into platform chemicals through enzymatic hydrolysis is often hindered by biomass recalcitrance and limited enzyme accessibility to cellulose. While several studies have addressed individual aspects of rice straw valorization, such as pretreatment, enzymatic hydrolysis, or hydrolysate fermentation, there remains a need for comprehensive research that systematically links pretreatment efficiency, enzyme economy, rapid process kinetics, and mechanistic understanding. Here, we present a systematic, integrated study combining mild NaOH pretreatment of rice straw (1 % NaOH, 73 ◦C, 4.5 h) with a deliberate pursuing of minimal enzyme dosage, achieving rapid and highly efficient saccharification. Key process variables, pretreatment conditions, enzyme dosage, and processing time, were thoroughly investigated to identify a suitable operation window that balances mild pretreatment with low enzyme input (as low as 6.5 mg protein/g solid, ~4.4 FPU/g), enabling up to 90 % glucose yield within just 8 h—using 50–80 % less enzyme and a much shorter processing time than those commonly reported. Importantly, the study also addresses black liquor reuse, demonstrating pretreatment scale-up and translation to increased solid concentrations (7.5 % w/w DS –dry solid-). Comprehensive kinetic, compositional, and structural analyses—including XRD, SEM, confocal fluorescence microscopy, and enzyme adsorption assays—were integrated to provide new insights into the relationship between substrate modification, enzyme accessibility, and saccharification efficiency.