Adsorption Performance Of Pretreated Wheat Straw On Cd(?) And Methyl Orange From Aqueous Solutions And Consequent Enzymatic Hydrolysis

Heavy metal and dye pollution in water both could cause great harm to and have potential adverse effects on animals,plants and humans.With the improvement of environmental awareness and requirements for sustainable development,how to properly treat industrial wastewater which contains toxic and hazardous substances has become a focus and difficulty in current research.As a simple and efficient wastewater treatment method,adsorption has broad application prospects,especially the use of cheap and readily available green adsorbent to treat wastewater has received much attention in recent years.Crop straws come from a variety of sources and can be regenerated,which is an ideal raw material for preparing biosorbent.Proper pretreatment methods can not only improve the adsorption performance of straw,but also have a positive effect on its enzymatic hydrolysis ability.This study used wheat straw as raw material to synthesize novel biosorbents NHWS and NMHWS by washing,grinding,microwaving,swelling by dilute alkaline solutions and graft copolymerization of surfactant.NHWS and NMHWS were used to adsorb Cd(?)and methyl orange from aqueous solutions,and consequent enzymatic hydrolysis experiment were also conducted to compare the yield of reducing sugars.Three major parts included in this paper are listed as follows.The first part mainly describes the preparation procedures and characterizations of modified wheat straw,namely,NHWS and NMHWS.Characterization analyses showed that both NHWS and NMHWS had obvious changes of surface structure,their surface became more broken and rough,besides,more pores could be found in the images of scanning electron microscope.Besides,the BET surface areas of NHWS and NMHWS both increased.The Fourier Transform Infrared Spectroscopy analysis suggested that the function groups of wheat straw were changed,the number of hydroxyl decreased,and quaternary ammonium groups were introduced to the cellulose.The second part was the adsorption experiments of NHWS and NMHWS.The adsorption capacity of NMHWS was higher than that of the NHWS,and the adsorption was rapid at the beginning and gradually slowed down until reaching adsorption equilibrium in both adsorption of Cd(?)and methyl orange.The pseudo-second-order model and Langmuir isotherm best fit the adsorption of Cd(?)by NHWS and NMHWS,and the adsorption was an exothermic,spontaneous and feasible process.NMHWS had a maximum removal efficiency of methyl orange of 99.32%.The third part investigated the enzymatic hydrolysis of NHWS and NMHWS after adsorbing methyl orange.The results showed that the suitable enzymatic hydrolysis time was 48 h,and the optimal solid loading was 5%.The compositional analysis of wheat straw indicated that both pretreatment and adsorption of methyl orange could increase the cellulose content of the wheat straw,dissolve some lignin and degrade part of hemicellulose.NMHWS-MO had the highest cellulose content and thus obtained the highest reducing sugar concentration.