Effect of iron salt type and dosing mode on Fenton-based pretreatment of rice straw for enzymatic hydrolysis.

Fenton-based processes with four different iron salts in two different dosing modes were used to pretreat rice straw (RS) samples to increase their enzymatic digestibility. The composition analysis shows that the RS sample pretreated by the dosing mode of iron salt adding into H2O2 has a much lower hemicellulose content than that pretreated by the dosing mode of H2O2 adding into iron salt, and the RS sample pretreated by the chloride salt-based Fenton process has a much lower lignin content and a slightly lower hemicellulose content than that pretreated by the sulphate salt-based Fenton process. The higher concentration of reducing sugar observed on the RS sample with lower lignin and hemicellulose contents justifies that the Fenton-based process could enhance the enzymic hydrolysis of RS by removing hemicellulose and lignin and increasing its accessibility to cellulase. FeCl3·6H2O adding into H2O2 is the most efficient Fenton-based process for RS pretreatment.

Ultrasound-assisted alkaline pretreatment for enhancing the enzymatic hydrolysis of rice straw by using the heat energy dissipated from ultrasonication.

Rice straw samples were exposed to ultrasound-assisted alkaline (NaOH) pretreatment by using the heat energy dissipated from ultrasonication to increase their enzymatic digestibility for saccharification. The characterization shows that the pretreatment could selectively remove lignin and hemicellulose without degrading cellulose, and increase porosity and surface area of rice straw. The porosity, surface area and cellulose content of rice straw increased with the increasing concentration of NaOH used. The rice straw sample pretreated by using the heat energy dissipated from ultrasonication has a higher surface area and a lower crystallinity index value than that pretreated by using the external source of heating, and the amount of reducing sugar released from the former sample at 48h of enzymatic saccharification, which is about 3.5 times as large as that from the untreated rice straw sample (2.91vs. 0.85gL-1), is slightly larger than that from the latter sample (2.91vs. 2.73gL-1). The ultrasound-assisted alkaline pretreatment by using the heat energy dissipated from ultrasonication was proved to be a reliable and effective method for rice straw pretreatment.