Effects On Anaerobic Digestion Characteristics Of Corn Stalks With Ultrasonic/Aerobic Hydrolysis

The use of corn stalks to produce methane by anaerobic fermentation is the main method of high-value energy utilization,and the difficult degradation of lignocellulose of corn stalks is the bottleneck in the anaerobic fermentation process,resulting in low fermentation substrate concentration,long start-up time,and gas production.Low rate and other issues.Therefore,there is an urgent need to find an efficient and pollution-free treatment method to treat corn stalks.This paper takes corn stalks as the treatment object,studies the anaerobic digestion characteristics of corn stalks by ultrasonic-aerobic hydrolysis and aerobic hydrolysis pretreatment,discusses the synergistic effect of ultrasonic and aerobic hydrolysis on the treatment of corn stalks,and analyzes the treated corn stalks.Water absorption characteristics of straw,degradation rate of lignocellulose,reducing sugar content,volatile fatty acid(VFAs)content,pH and cumulative methane production content.The ultrasonic-aerobic hydrolysis pretreatment group with the highest content of VFAs was selected to compare with the aerobic hydrolysis pretreatment group,and the cumulative methane production and pretreatment time were analyzed,and the results were applied to the biogas project for energy consumption comparison analysis.The main findings are as follows:(1)The test results of aerobic hydrolysis pretreatment of corn stalks show that the water absorption rate and lignocellulose degradation rate are significant.Among them,the water absorption rate of corn stalks in the first 2 h is higher,and the water absorption rate gradually becomes after 12 h.Stable,the T9group(45 ℃×16 h)can achieve the highest water absorption rate of 250.30%;the degradation rate of hemicellulose in the corn stalk lignocellulose is 21.66%-30.35%,and the degradation rate of cellulose is28.16%-35.48%.The degradation rate of lignin is 3.50%-7.76%.Scanning electron microscopy showed that the cell wall of corn stalks was severely damaged under the action of aerobic hydrolysis,and hairy scales appeared.After pretreatment,the reducing sugar content in the feed solution is between8.07-11.41 mg/mL,the content of VFAs is between 9.07-14.06 g/L,and the pH is between 5.51-7.02.(2)The results of the anaerobic fermentation test of aerobic hydrolysis pretreatment corn stover showed that the reducing sugar content decreased first and then maintained at a certain value fluctuating,the main acidification product acetic acid accounted for 58.15% of the total VFAs,and the pH was between 6.75-7.11.The cumulative methane production was fitted by a modified Gompertz model,and the fitting coefficient R2 reached 0.97,indicating a good degree of fitting.The lag time of methane production is between 0.42-1.47,and the stronger the aerobic hydrolysis intensity,the shorter the lag time.The cumulative methane production content of the T8 group(45 ℃×12 h)can reach 178.31 mL/g VS,which is comparable to CK(135.32 mL/g VS)compared with an increase of 31.77%.(3)The results of the ultrasonic-aerobic hydrolysis pretreatment corn stalk test showed that the water absorption rate of corn stalks in the C9 experimental group(400 W×20 min)reached 267.4%,but the water absorption rate of corn stalks dropped to 241.7% after 12 h.The water retention of corn stalks after ultrasonic-aerobic hydrolysis treatment is reduced.The degradation rate of hemicellulose in corn stover lignocellulose is 15.58%-30.17%,the degradation rate of cellulose is 28.29%-38.51%,and the degradation rate of lignin is 3.52%-7.83%.After ultrasonic-aerobic hydrolysis treatment,the reducing sugar content in the feed solution is generally between 8.31-12.62 mg/mL,the content of VFAs is between 8.45-16.24 g/L,and the pH is low due to the accumulation of VFAs.(4)Use RSM(response surface optimization method)to optimize the ultrasonic-aerobic hydrolysis treatment conditions,and use VFAs as the response index to perform variance analysis.The results show that the effect of ultrasonic power is better than that of ultrasonic time,and the highest VFAs is achieved.The optimal pretreatment conditions for the content of 16.24 g/L are 309 W and 26 min,and the cumulative methane production content is 198.56 mL/g VS.The comparative analysis results show that the VFAs and methane output of corn stover after ultrasonic-aerobic hydrolysis pretreatment are better than those of aerobic hydrolysis pretreatment.Energy consumption analysis shows that the electric energy required for ultrasonic-aerobic hydrolysis(17.18 k J/g VS)is more than the electric energy required for aerobic hydrolysis(8.03 k J/g VS),but the time required for ultrasonic-aerobic hydrolysis(1.7 h)is much less than the time required for aerobic hydrolysis(12 h);there is no significant difference in energy consumption between aerobic hydrolysis and ultrasonic-aerobic hydrolysis pretreatment in medium and small biogas projects,while aerobic hydrolysis and ultrasonic hydrolysis in large and super large biogas projects are good.The energy consumption of oxygen hydrolysis pretreatment differs significantly.Compared with aerobic hydrolysis pretreatment,ultrasonic-aerobic hydrolysis pretreatment can obtain higher VFAs content and cumulative methane production content in a shorter time.Applying it to the pretreatment process of anaerobic fermentation of corn stover can speed up Start-up cycle,shorten pretreatment time and increase methane output are of great significance to biogas projects.