Research On Biogas Anaerobic Fermentation By Using Stalk Materials

Embarking from the problems that may encounter in actual biogas project, researching characteristics of producing biogas by fermentation with straw materials through pilot device in laboratory. Using the conical flask that the volume is1000ml as fermentation tank for static anaerobic fermentation in the experiments, collecting biogas produced by fermentation by the method of drainage, determining the component of biogas by infrared gas analyzer, determining the change of main chemical components of raw materials before and after the fermentation. The experiment studyed on the effects of of biogas fermentation by pretreatment and condition of fermentation and coefficient of alcohol addition. The methods to increase the yield of biogas and content of methane, and the characteristics of fermentation of different materials were considered, aimed to provide reference and basis for optimizing technology and reducing consumption of energy and increasing benefit in biogas project.Before the test,we got three species inoculum that the original optimum temperature were mesotherm (35℃and45℃) and thermophilic (53℃) through the habituated culture. The activity of the culture is better than pig manure or sludge and the inoculum itself does not produce biogas. Inoculum adapted to the fermentation temperature making it start faster after inoculation and it will not effect determination of biogas production rate of raw materials and can obtain more accurate test data.The main conclusions as the following:(1)Used rape stalk and cotton stalk that grow in Hubei and bagasse as the materials when do the research of effect of fermentation by compost time, pulverizing each material to the grain size of3cm, found that rape stalk can start and ferment without compost, the optimum compost time of cotton stalk and bagasse is7days-(2) Used bagasse as the material to do the experiments of anaerobic fermentation, found out the optimum parameter of fermentation is that the initial pH is7.8, the inoculum rate is30%and adding suitable stir, ensuring the initial temperature of culture is fit the ferment temperature. The fermentation start slowly and biogas production rate is low when the initial pH is less than7, When the inoculation rate less than30%the biogas production is the1/3of the production in the inoculation rate of50%, effect of fermentation changed little when the inoculation rate is more than50%. Biogas production rate increased12.81%and11.55%respectively at room temperature and35℃fermentation at the same fermentation condition by adding stirring,it improved the degradation rate significantly and shortened the fermentation cycle time.Rising fermentation temperature is helpful to degradation of organic compounds but the chemical oxygen demand value of residue is larger than500mg·L-1when the fermentation temperature is45℃and53℃.(3) Using spartina alterniflora as fermentation material found that adding ethanol can make the gas production rate increased2-3times and maintain3-5days, the methane content reached80%and maintained for15days, adding ethanol can let the content of methane reach60%in the third day at the start stage of fermentation. The optimum adding amount of the ethanol is0.75%by fermentation volume.It will lead to fermentation stop when the ethanol addition exceed2.0%. adding alcohol had no affecte to degradation of organic matter, the ethanoi conversion rate is74%.(4) The optimum total solid concentration is17.5%in dry fermentation, fermentation is unable to start when the total solid concentration higher than17.5%in mesophilic fermentation, but it can successfully start at thermophilic temperatures fermentation. We can restore gas production by adding fermentation residual or NaOH solution when fermentation is acidification. Adding fermentation residual can make the biogas production rate recovery to normal production but adding NaOH solution can only make the gas production rate recovery to1/2of normal gas production rate.(5) Compared with the other materials in the process of produce biogas by anaerobic fermentation, air-dried spartina alterniflora was found to be the best material of producing biogas with a biogas production ratio of622.82ml·g-1in35℃by anaerobic fermentation. Biogas production rate of yellow maize straw and yellow spartina alterniflora perfomed better when in the mesophilic fermentation conditions, biogas production rate of ensiling maize straw and ensiling spartina alterniflora is better when in the thermophilic fermentation conditions. Fermentation result of cotton stalk that grew in XinJiang is better than Hubei cotton stalk, The methane content in fermentation of air-dried spartina alterniflora is the highest by67.32%.Bagasse is a good raw material for anaerobic fermentation but papermaking sludge is not suitable for biogas production by anaerobic fermentation for the low biogas production rate.