Enhanced enzymatic hydrolysis of wheat straw by two-step pretreatment combining alkalization and adsorption

Wheat straws (WS) were pretreated by a two-step pretreatment for enhanced enzymatic hydrolysis. The raw wheat straw (RWS) was firstly soaked in microwave-assisted NaOH solution at the presence of a mixed solution of H₂O₂ and hexadecyl trimethyl ammonium chloride (HTAC), and the residue was put into methyl orange (MO) solution to obtain the final substrate for enzymatic hydrolysis. It was interesting to find that the WS after the first step of the pretreatment could effectively remove MO in the second step of the pretreatment with the highest removal efficiency of 98.86% at the MO concentration of 25 mg/L and at the adsorbent-adsorbate ratio of 0.8%. Meanwhile, the enzymatic hydrolysis efficiency of the WS that was pretreated by the two steps was higher than that of the RWS as well as the first-step-pretreated WS. Enzymatic hydrolysis experiment showed that the glucose concentration after 48-h hydrolysis was 4.85 g/L at the solid loading of 5%, compared with the RWS of 0.90 g/L and the first-step-pretreated WS of 4.33 g/L. This suggested that the two-step pretreatment method could not only make WS as a good adsorbent but also a more biodegradable lignocellulosic material. Characterization analysis showed that the specific surface area and the cellulose content of the WS were both increased after the two-step pretreatment, indicating that the pretreatment method was significant to properly utilizing WS as biosorbent and biofuel. Besides, a possible mechanism for the effect of the pretreatment on the WS was proposed.