Study On Preparation Of Bioethanol And Activated Carbon From Different Growth Phases Of Mushroom Substrate

The cultivation substrate of edible fungi is based on raw biomass such as wheat stalk,bran,wood and so on.During the growth process,edible fungi absorb nutrients needed for their own growth through the decomposition of lignocellulose in the culture medium,and the remaining solid by-products after they are mature and picked are edible fungus residue.Biomass is mainly composed of cellulose,hemicellulose and lignin,which are closely connected by hydrogen bonds and chemical bonds.Lignin,which is similar to adhesives,forms protective shells to wrap the cellulose into complex compounds,which can be degraded and fermented to obtain bioethanol.Lignin is the biggest barrier to acid and cellulase degradation of cellulose.The pretreatment can destroy the structure of lignocellulose and increase the contact area between acid or cellulase and cellulose,so as to achieve effective degradation of cellulose.At present,physical methods(such as mechanical grinding and steam blasting),chemical methods(strong acid and strong base)and biological methods(bacteria)are mostly used for pretreatment of lignocellulose.There are many reports on the pretreatment of lignocellulose by biological methods,but relatively few studies on the pretreatment of lignocellulose by edible fungi.In this study,the fungus residues of Pleurotus ostreatus corn cob and Shiitake sweet gum at different growth stages were used as experimental materials,and the study was carried out from five aspects:composition content,lignocellulase activity,physical and chemical structure characteristics,polysaccharide degradation process conditions and resource utilization of spent mushroom substrate.Firstly,the composition content and extracellular enzyme activity of the samples were analyzed by chemical titration and UV-Vis spectrophotometry.The morphological characteristics,surface functional groups and crystal phase structure of the samples were analyzed by scanning electron microscopy(SEM),Fourier transform infrared spectroscopy(FT-IR)and X-ray diffractometry(XRD).The results showed that the lignocellulose was selectively degraded by Pleurotus ostreatus and Shiitake during their growth,and the lignocellulose structure was destroyed.The yield of corn cob and sweetgum were 29.53%and 29.38%,respectively.The yield of corn cob and sweet gum increased rapidly after pretreatment by edible fungi,and the best yield was 79.07%and 85.26%after secondary phases,respectively.Secondly,Box-Behnken response surface design experiment was conducted to optimize the five main factors affecting the enzymatic hydrolysis process of the second batches of Pleurotus ostreatus substrate(SPS)and second batches of Shiitake substrate(SSS),such as time,additional amount of cellulase,temperature,solid-liquid ratio and initial p H.It was found that the order of the influence of SPS cellulase hydrolysis rate was as follows:The amount of enzyme>solid to liquid ratio>enzymolysis time=enzymolysis temperature=p H,and time had significant interaction with both temperature and p H.The order of influence on the yield of SSS cellulase was as follows:enzyme amount>enzymatic hydrolysis time>enzymatic hydrolysis temperature=solid-liquid ratio=p H,and time had significant interaction with both temperature and p H,and enzyme amount and temperature had significant interaction.The optimum conditions of SPS enzymatic hydrolysis were as follows:enzymatic hydrolysis time(60h),cellulase amount(80 FPU·g^-1),enzymatic hydrolysis temperature(40?),solid-liquid ratio(1:20)(g·m L^-1),p H(4.6),and the yield of SPS was 80.73%.The enzymatic hydrolysis time(60 h),the amount of cellulase(107.5FPU·g^-1),hydrolysis temperature(44?),solid-liquid ratio(1:15.5)(g·m L^-1),p H(4.73)of SSS were obtained,and the yield of SSS was 78.43%.Considering the feasibility of practical operation,the p H of SPS was changed to 4.6,the temperature of SSS was changed to 44?,the solid-liquid ratio was changed to1:15.5(g·m L^-1),and the p H was changed to 4.7.Under the optimal conditions of SPS hydrolysis and fermentation,the ethanol yield was(7.15±1.03)g/100 g SPS.The ethanol yield of SSS was(4.62±0.81)g/100g SSS.Finally,orthogonal experiment was used to optimize the preparation and adsorption conditions of biochar.It was found that the best preparation conditions of Pleurotus ostreatus carbon(PC)were:carbonization temperature(280?),carbonization time(80min),activation temperature(60?),activation time(3h),Na OH concentration(12%).Shiitake carbon(SC)were:carbonization temperature(300?),carbonization time(60min),activation temperature(70?),activation time(4.5h)and Na OH concentration(15%)were obtained.Under the optimal adsorption conditions,the removal efficiency and adsorption capacity of methylene blue by PC were 82.16%and 221.83 mg·g^-1,respectively.The removal efficiency and adsorption capacity of methylene blue by SC were 80.16%and 168.34 mg·g^-1,respectively.The adsorption model of biocar showed that its physical structure and surface electronegativity jointly promoted the adsorption of methylene blue.Thermodynamic analysis showed that the adsorption process was a spontaneous endothermic reaction.In a certain temperature range,increasing the temperature was beneficial to the adsorption.In conclusion,the pretreatment of corn cob and sweet gum by Pleurotus ostreatus and Shiitake can effectively destroy the lignocellulose structure and improve the yield of enzymatic hydrolysis of cellulose.The preparation of biochar from spent mushroom substrate can be used as environmental protection remediation agent.This study provided a theoretical reference for the pretreatment of other lignocellulosic and the resource utilization of spent mushroom substrate.