Assessment of advanced oxidative processes based on heterogeneous catalysis as a detoxification method of rice straw hemicellulose hydrolysate and their effect on ethanol production by Pichia stipitis

Abstract

In the present work, detoxification treatments based on advanced oxidative processes (AOPs) aiming to improve the ethanol production by Pichia stipitis were evaluated. The experimental design was carried out according to a Taguchi L8 orthogonal array in order to evaluate the influences of pH, catalyst type (ZnO or TiO2), UV radiation (UVA or UVC), and oxidant agent (O2 or O3) on aromatic compounds concentration and fermentation performed. The results showed that treatment conditions which most contribute to reducing the toxicity of the hydrolysate in relation to ethanol production were pH 8.0 and the use of O3 as an oxidizing agent. Within the region evaluated, there was no difference between the use of TiO2 or ZnO and or UVA or UVC radiation. The heterogeneous AOPs were able to remove above 49 % of the furan, above 39 % of the total phenolic compounds, and 100 % of the low molecular weight phenolic compounds, without affecting the sugar concentrations in the hydrolysate. Furthermore, heterogeneous processes have provided relevant increases on sugars consumption (148 %) and maximum ethanol concentration (154 %) as compared with untreated hydrolysate. In addition, the AOPs treatment showed advantages such as it does not generate waste, does not degrade hydrolysate sugars, and does not lead to loss of hydrolysate volume due to the treatment. Based on the results, it can be concluded that AOPs are promising processes for application in hydrolysate treatment to reduce toxicity and consequently improve the fermentability of lignocellulosic hydrolysates.