Study On The Anaerobic Co-digestion Characteristics Of Corn Stalk With Hydrothermal Wastewater Pretreatment

As the most common agricultural waste in China,the utilization technology of corn stalk has attracted extensive attention at home and abroad.However,the dense lignocellulose structure of corn stalk restricts its utilization efficiency,so pretreatment is often needed to improve the pore structure and components of corn stalk.Among the methods of pretreatment,acid pretreatment can effectively remove the lignocellulose components in corn stalk and improve the gas production performance of corn stalk in the process of anaerobic digestion.However,conventional acid pretreatment often needs the assistance of high temperature and high pressure,which increases the cost of acid pretreatment.Therefore,in this study,a kind of stalk hydrothermal wastewater was used as the pretreatment liquid.The wastewater contains a lot of acidic substances.A severe environmental pollution will be detected if it is treated inappropriately.Using it as an alternative acid pretreatment of corn stalk can effectively avoid the waste of resources and improve the yield of methane in the process of anaerobic digestion.That is because of the high acidity and thermal energy.Therefore,this paper was carried out for the experiment of using corn stalk hydrothermal wastewater for acid pretreatment and using it for anaerobic digestion.The best hydrothermal wastewater pretreatment condition was preliminarily explored.The central composite design（CCD）was carried out according to the preliminary optimal pretreatment conditions,further optimized the above pretreatment conditions according to the optimization results of response surface.And supplemented the verification experiment for verification.At the same time,the stability of anaerobic digestion system is analyzed.The main conclusions are as follows:（1）Corn stalk hydrothermal wastewater pretreatment can break the dense structure of corn stalk and increase the degradation rate of lignocellulose.The hemicellulose degradation rates of7.92%-21.74%,cellulose degradation rates of 3.25%-10.66%and lignin degradation rates of1.11%-2.44%.In addition,the reducing sugars,p H and VFAs used in the pretreatment of the slurry all provided material security for the anaerobic digestion process.A modified Gompertz model was fitted to show a high fitting result（R²>0.97）for all experimental groups,showing that the highest pretreatment condition of 35°C and 6h was achieved at 189.14 m L g VS^-1.It was 55.17%higher compared with CK group.（2）The above optimal pretreatment conditions were further optimized.After optimization,the optimal pretreatment conditions for the pretreatment of corn stalk with hydrothermal wastewater were obtained.The pretreatment temperature was 43℃,and the optimal pretreatment time was 7 h.Under this condition,the optimal response value（calculative methane production）was 176.62 ml g VS^-1.The verification experiment was further carried out under this experimental condition,and the actual cumulative methane yield was 184.32 ml g VS^-1.After digestion,through the analysis of the physical and chemical properties of the digestion broth（p H,volatile fatty acids,alkalinity and VFA/TA）,it is found that all indexes can be maintained in a normal state.And it is concluded that there is no rancidity in the digestion process,which can ensure the stability of the system in the whole anaerobic digestion process.