Study On The Effect Of The Reflux Of Biogas Slurry On The Anaerobic Fermentation Characteristics Of Corn Straw

Straw is the largest and most abundant biomass resource.Currently,the country is leading and promoting the development of large-scale straw biogas projects.The environmental and energy benefits of straw preparation of biogas have drawn increasing attention as a by-product of biogas projects.The emergence of fluids has become an important factor constraining the development of biogas projects.Biogas slurry recycling is the most effective way to reduce the displacement of biogas slurry and save water resources.Therefore,this paper uses corn stalk as the main raw material and sets different biogas slurry return ratios A?0%?,B?25%?,C?50%?,D?75%?,E?100%?,at 37°C,fermentation TS concentration10%,organic load 2gL^-1d^-1 using CSTR full-mix reactor anaerobic fermentation test,through the fermentation process pH value,TOC content,gas production,methane percentage,viscosity,volatile acid,the detection of Kjeldahl nitrogen,ammonia nitrogen,etc.,explored the effects of biogas slurry return on the anaerobic fermentation characteristics and acid production and nitrogen transformation of corn stover.The main conclusions are as follows:?1?Through the analysis of the cumulative gas production,it is found that the 25%biogas liquid reflux can increase the cumulative gas production by 6.40%,50%biogas liquid reflux can increase the gas production rate by 4.53%,75%biogas liquid reflux can increase the gas production rate by 9.95%,and 100%biogas liquid reflux can increase the gas production rate of 4.69%.The biogas production of VS in each group is 303.14mL/g,322.5 mL/g,316.89mL/g,333.31mL/g and 317.35mL/g respectively.Among them,75%biogas slurry return to increase VS production capacity is the best and the fermentation process is stable.The methane content of methane methane produced in group 1¹0d,A and D had a peak value,which reached 66.46%,68.03%,A and D group 19⁶1d between 51.76%⁵6.1%,and the variation trend of methane content in B and E groups are the same,the highest values in the early stage of fermentation are 54.72%and 56.63%lower than A and D groups.The quantity is up,and the difference between the A and D group is little.H₂S gas content in each group is low,fluctuating between 15⁹0ppm,and H₂S gas content in A and B groups increased slowly.The change trend of H₂S in C,D and E groups is relatively stable,and the fluctuation range is also small,which is significantly lower than that in A and B groups.?2?The pH values of each group are in the range of 6.8⁷.5,and the pH values of each group is basically the same.After the mid fermentation,the decrease rate of the pH value of the reflux group is slower than that of the unreflux group.With the increase of feed times,the viscosity of the biogas slurry reflux group increased rapidly,and the A group slowly increase to 43mPa·s.The B group rose to 72mPa·s.The C group viscosity 16⁴0 day was raise from28mPa·s to 89mPa·s.It finally arrives at 104mPa·s.Group D 13³7 day increased rapidly from 22mPa·s to 99mPa·s,and finally reache 124mPa·s.In group E,31 day reach 105mPa·S,and then rose to 144mPa·s at the end of fermentation.Biogas slurry reflux will significantly improve the viscosity of fermentation system.The reflux of biogas slurry can effectively improve the removal rate of TOC.20%,50%,75%and 100%of biogas slurry reflux group increase TOC removal rate by 6.87%,7.32%,10.92%and 6.93%respectively.?3?In the early stage of fermentation,biogas slurry reflux significantly increases the concentration of acetic acid,but there is no significant difference in acetic acid concentration at the later stage.The decrease rate of propionic acid in B,D and E groups was faster than that in A group.The reflux of biogas liquid could accelerate the degradation of propionic acid and prevent the accumulation of propionic acid to inhibit the activity of methanogenic bacteria.The effects of biogas slurry reflux on butyric acid,isobutyric acid,n-Valerate,isovalerate and hexanic acid were not obvious.These acids are lower than those of acetic acid and propionic acid.The total VFAs concentration does not change significantly after biogas slurry refluxing.The total volatile acid content decrease rapidly after the beginning of biogas slurry reflux,and fluctuated at 400mg/L in later stage.?4?The concentration of Kjeldahl nitrogen in each group has a rising trend in 13d before fermentation,and the concentration of Kjeldahl nitrogen decrease to the end of fermentation in each group.The decrease of each group reache 66.7%,58.12%,46.72%,43.05%and48.19%,respectively.Biogas slurry reflux slowe down the consumption of Kjeldahl nitrogen.?5?The difference of ammonia nitrogen concentration in the former 13 days was not obvious,and the concentration of ammonia nitrogen is at a high point.With the fermentation,the reduction rate of ammonia nitrogen concentration in the reflux group is significantly slower than that of the non reflux group.With the increase of biogas slurry reflux ratio,the degree of ammonification of organic nitrogen increase significantly.The degree of ammonification of organic nitrogen decreased in the first 13d group from 90%to 70%.After a HRT,the A group droppe to 57.80%.Group B increased from 70.91%22d to 81.66%,and C group reache 82.95%.D group 46⁶1d fluctuates in the 81.53%⁸6.20%range.D group46⁶1d fluctuates in the 81.53%⁸6.20%range.The 52⁶1d in group E fluctuate around 85%.The ammoniation of organic nitrogen is obviously enhance by the reflux of biogas slurry in the middle and late fermentation,and the content of nitrogen in the anaerobic fermentation of corn straw is low,and the ammonia nitrogen is not inhibited,and the degree of ammoniation of organic nitrogen is high.