Effects Of Microwave Hydrothermal/Microbial Electrocatalysis On The Characteristics For Corn Straw Of Anaerobic Digestion

The excessive use of fossil fuels and the increasing demand for energy make the world face the crisis of energy exhaustion.As a clean and low-carbon fuel,biogas can be used to mitigate the energy crisis and improve the global ecosystem effect.Anaerobic digestion is considered to be an efficient and environmentally friendly channel of converting inexpensive and abundant lignocellulosic feedstock into biogas.Due to the unique crosslinking structure of lignocellulosic raw materials,the hydrolysis process of anaerobic digestion is limited and the conversion efficiency is disappointed.Therefore,the pretreatment technology has become one of the research hotspots to improve the conversion efficiency of biomass.In addition,profiting from the unique bioelectrochemical system of the microbial electrocatalytic anaerobic reactor,the applied voltage can improve the treatment effect of anaerobic digestion.In this paper,microwave hydrothermal pretreatment of corn stalks was carried out to study the effects of pretreatment on the physicochemical properties and biogas production of corn stalks,and to reveal the effects of different applied voltages on the running performance for the microbial electrocatalytic anaerobic reactor.The research contents and main results are as follows:（1）Effect of microwave hydrothermal pretreatment on physicochemical properties of corn straw.The changes of physicochemical properties of corn straw were studied by microwave hydrothermal pretreatment.The results showed that with the increase of temperature and time of microwave hydrothermal pretreatment,the dense bundle lignocellulose structure of corn straw was destroyed,and the roughness and crack increased.The content of cellulose and hemicellulose increased while the content of lignin decreased,and the weight loss reached 19.00～50.80%.The vibration intensity of the surface functional groups decreased continuously,the corresponding lateral order index was 1.70～4.78,and the total crystallinity index was 0.86～2.43.The X-ray diffraction peak is deformed more sharply and the diffraction intensity is increased continuously,and the corresponding crystallinity index is 24.14～47.49%.However,there was no significant change in the position of the 002plane microcrystalline in the cellulose,and the corresponding microcrystalline size perpendicular to the 002 plane was 2.74～5.93 nm.This means that the microwave hydrothermal pretreatment destroys the lignocellulosic crosslinking structure of corn stalks and contributes to the improvement of anaerobic digestion biogas production.（2）Effect of microwave hydrothermal pretreatment on biogas production characteristics of corn stalk in anaerobic digestion.The changes of biogas production characteristics of pretreated corn stalks were studied by anaerobic digestion.The results showed that the p H value of anaerobic digestion ranged from 5.62 to 8.31.The trend of biogas production per day in each experimental group was roughly the same.The peak of biogas production per day in the anaerobic digestion of corn straw pretreated at 150℃for 10 min was 794.82 m L,which was 43.38%higher than 554.33 m L in the control group.The cumulative methane production was 260.24 m L/g?VS_added,which was 73.08%higher than 150.36 m L/g?VS_added in the control group.The modified Gompertz model was used for kinetic fitting analysis of cumulative methane production in each treatment group.The fitting effect was fine and the retention periodλvalue decreased.This means that microwave hydrothermal pretreatment can improve the methane production rate for anaerobic digestion of corn straw.（3）Effects of microbial electrocatalysis on methane production characteristics of anaerobic digestion of corn straw.The influence for the applied voltage on the methane production characteristics of the microbial electrocatalytic anaerobic reactor was studied.The results showed that the microbial electrocatalytic anaerobic reactor possessed nice start-up performance,better Coulomb efficiency and electrochemical contribution rate,and faster anodic reaction rate at 1.0 V applied voltage.Under the applied voltage of 0.8 V,the microbial electrocatalytic anaerobic reactor had a better operation effect.The utilization rate of acetic acid reached 60.41%,the removal rate of COD reached 81.42%,and the total phenol removal rate reached 76.24%.besides,the total methane production was 27.10 m L,which was 36.66%higher than that of the control group.Cyclic voltammetry test showed that there were more electroactive microorganisms in the anaerobic reactor under the applied voltage of 1.0 V.AC impedance spectrum analysis showed that the reactor held a smaller charge transfer resistance with an applied voltage of 0.8 V,and the time constant in the normalized imaginary part capacitor was relatively small,which was 0.26 s.Electrochemical characteristics analysis showed that the reactor had a lower internal resistance of 472.43Ωand a higher power density of 46.0 m W/m³ at an applied voltage of 0.8 V.This means that the anaerobic reactor produces more methane yield under the applied voltage of 0.8 V.