Study Of Anaerobic Fermentative Hydrogen Production Process For Food Residues

The production of food residues is increasing dramatically in China cities due to the habits of Chinese and their food structures.According to the local regulations,food residues can't be used as feedstuff for livestock as it contains hazardous bacteria and virus,which is paid attention all over the world.Concerning environmental protection and recovery resource,anaerobic digestion is considered to be a favorable option for the effective treatment of the wastes in which process methane gas and fertilizer can be produced while the wastes are stabilized.Anaerobic digestion of organic wastes has characteristics of reducing waste production,recovering cleaner energy(H₂ or CH₄)and producing organic fertilizer which is according with economizing energy,reducing waste production,cleaner production and cyclic economy.Biological hydrogen production from the wastes using anaerobic digestion is highlighted which is a common ideal among all countries.Therefore,Study on enhancement of anaerobic digestion for hydrogen and methane is of significant theory and application.On basis of the acidiferous characteristic for food residues,the batch fermentative hydrogen production influence of food residues were studied by food residues pretreatment,inoculum pretreatment,inoculation volume,initial pH value,bentonites etc.The methanogenesis process of fermentative hydrogen production residue was investigated by inoculation volume and initial pH value in this dissertation.Moreover, the experiment results were regressed by correctional Gompertz model using CurveExpert 1.3 software.The contents and conclusions are as follows:(1)This dissertation analysed the source,production,chemical and physical characteristics,environmental influences and disposal actualities of the food residues by correlative literatures,which indicates biologic technology will become the leading applied and developmental direction.And this dissertation analysed the basic theory and influencing factors(ecological factors)of fermentative hydrogen production,which discusses substrate pretreatment,volume pretreatment,inorganic nutriment dosages in order to improve the two-stage fermentation process for hydrogen and methane.(2)Results of fermentative hydrogen production indicated that hydrogen potential of food residues pretreated by microwave(600W,4min)and potassium hydroxide (pH=9.0)is optimum under the conditions of 80%inoculum preheated at 80℃for 15min,initial pH value of 8.5,and bentonite dosages 0.25%(m/m,wet substrate).The lag-phase time(λ),the maximal specific hydrogen rate,the specific hydrogen potential and the hydrogen contents of biogas were 4.03h,18.58mL/gVS·h,254.89mL/gVS,54.6%v/v,respectively,which exceed literature results.The experiment result of optimizing condition for fermentative hydrogen production shows that:â‘ In the system of fermentative hydrogen production,there are extraordinary connection between the specific hydrogen rate and pH value.According to the transformation of the specific hydrogen rate and pH value,the kinetic constants of pH model by regression are respectively R_max(21.9mL/(gVS·h)),K_H(1.63×10^-5mol/L)and K_OH(1.45×10^-6mol/L).Therefore,pH value at 5.31 is the optimal pH value of continuous fermentative hydrogen production for food residue.â‘¡There are linear connection between the oxygen reduction potential(ORP)and pH value (R²=0.9906).Moreover,ORP value at -315.08mV is the optimal ORP value of continuous fermentative hydrogen production for food residue.â‘¢Normal butyrate was the main acid product in the fermentative end products,and the percentages of butyrate and acetate at tested volatile fatty acid(VFA)concentrations account for 56.7%,26.5 %respectively.Therefore,the butyrate-type fermentation is the main fermentative type.(3)With the methanogenic process of single factor for fermentative hydrogen production residue,the experiment results show that:â‘ For methane production,the lower inoculation volumes at 15%can inhibit the methanogenesis.However,the higher at 30%,45%,60%especially at 60%can consumingly enhance the methanogenesis.â‘¡By varying the initial pH value in this system,the using efficiency of reactors can be enhanced.In other words,the ability of methane production is stable while the inoculation volumes are reduced from 60%to 45%.â‘¢With the initial pH value at 7.0 and the inoculation volume at 45%,λ,the maximal specific methane rate,the specific methane potential and the maximal methane contents of biogas are 4.02h,50.20mL/gVS.h,379.28mL/gVS,82.2%v/v,respectively.â‘£In this research,the maxium methane content of biological gas surpasses 80%v/v,which is more than normal digestion process(75%v/v).The reason may be that CO₂ from the digestion reaction partly dissolves the system making up the partial acidity by the using of VFA, which can be demonstrated by the pH value(6.80～6.90)of anaerobic digestion residues.(4)The analysis of the livelong process of fermentative hydrogen production in terms of entropy illustrates that:The processes of the collecting,the hydrolyze acidification,the methanogenesis of the residue for fermentative biohydrogen production and the output of methanogenesis are the process of entropy increasing.However,the processes of the separating,the enhancement of the substrate and the hydrogen-producing acetogens are the process of entropy decreasing,which are often becoming the restrictive approach to the anaerobic fermentative hydrogen production.