Optimization of the Effects of Zn2+, Cu2+ and Mn2+ on Ligninase Enzyme's Activities for Pretreatment of Rice Straw in Conversion to Bio-ethanol

The production of bioethanol from lignocellulosic biomass could be considered as an appropriate and economic option to remove environmental disasters and improve energy security. In fact، lignocellulosic material is mainly composed of cellulose، hemicellulose and lignin. Lignin works as the adhering prevents the bioconversion of cellulose into sugars and ultimately to ethanol. To address the problem، various chemical، physical، physicochemical and biological methods have been suggested. Enjoying convenient operating conditions، production of non-hazardous wastes، and having no harmful side effects، make the biological methods a potentially proper option. Unfortunately، the biological methods are slower and less efficient in comparison with the other processes. In the present study، an attempt is made to resolve this problem in an enzymatic degradation of lignin of a rice straw sample. Several peroxidase enzymes were produced by a white rot fungus، and their effects on lignin removal from the biomass samples were investigated in shaking flasks. Lignin concentration and enzymes'' activity were measured by the acetyl bromide-soluble lignin spectrophotometric method and optical density method using special reagents، respectively. The results revealed that the enzymatic treatment could remove at least 30% of the lignin content of the lignocellulosic biomass. To achieve the maximum activity of the enzymes، The chemical composition of the culturing medium was optimized for the concentration of important metal ions including Cu2+، Mn2+ and Zn2+ through Box Behnken response surface methodology. The enzymes'' activity at the obtained optimal conditions increased four times for Manganese peroxidase، and lignin peroxidase.