Biogas Production Characteristics And Technology Optimization Of Anaerobic Digestion From Potato Vines

The thesis makes estimates on potato vines（hereafter PVs）and reveals that in 2013,potato production in China was 92,103,800 tons,out of which collectable and usable PVs amounting to 73,683,100 tons and 31,742,700 tons of PVs can be used as new energy.There are 8 provinces（cities and/or autonomous regions）using new energy totaling more than 1,000,000 tons.They are Inner Mongolia,Sichuan,Guizhou,Yunnan,Chongqing,Heilongjiang and Hubei.When analyzing the distribution density of the availability of new energy,there are 15 provinces（cities and/or autonomous regions）go beyond the national average.The top 5 provinces include Heilongjiang（9.88 t/hm²）,Jiangxi（9.24 t/hm²）,Jilin（8.81 t/hm²）,Chongqing（8.48 t/hm²）,and Tibet（8.45 t/hm²）.So far,only 11,818,800 tons of PVs are utilized as fuels,and an approximate of 20,000,000tons PVs are disposed off or burnt.According to FAO statistics in 2014,in China,1,294,700tons of CO₂ emission is caused by PVs,which cast an enormous detriment to agriculture and ecosystem,and this in turn is also a considerable waste of bio-energy resources.As the development of‘strategy to use potatoes as staple food grain’,there certainly will be more resources of PVs.It has become an urgent research task as to how to raise the utilization of PVs as fertilizer,forage,fuels,raw materials and cultivation bases.Hence,the thesis systematically studied PVs capability to produce biogas through anaerobic digestion（AD）.Major research and results are as follow:（1）Make certain PVs biochemical methane potential（hereafter,BMP）and how the change of inoculants may influence PVs anaerobic digestion to produce biogas.The analysis of PVs physicochemical property reveals tremendous amounts of organic components,with 0.87VS/TS,and theoretical methane yield（TMY）of 449.86 mL/gVS.PVs BMP has been investigated under three different circumstances:inoculant non-deaerated,inoculant deaerated and inoculant deaerated with acclimation.Results show that acclimated inoculants prevail over their non-acclimated counterparts in biogas yield,methane yield and biodegradability（BD）of PVs,rising by 26.78%,36.56%and 17.62%respectively.Based on test results,using the models of Gompertz and first order anaerobic digestion to produce biogas dynamics,the simulation of anaerobic digestion（hereafter,AD）of PVs shows the maximum BMP of PVs is 214.15 mL/gVS,and the maximum biochemical methane rate 40.39 m L·g_vs^-1d^-1,lag phase of AD 3.44d.（2）The study demonstrates influences of Ionic liquids（hereafter,ILs）on PVs AD biogas yield after pretreatment.To take ILs[C₂mim]Ac,[C₄mim]Cl and latent solvent DMSO and pretreat PVs under 130℃for 120 mins,the result shows the three-dimensional stable structure with high crystallinity of the PVs cellulose is completely destroyed,making the containment of regenerated cellulose increases by 17.3%-27.5%,and lignin down 31.8%-43.9%.The solubility and removal capacity of lignin,on a descending order is,[C₂mim]Ac>[C₂mim]Ac/DMSO>[C₄mim]Cl/DMSO>DMSO>[C₄mim]Cl.The scale of influences on PVs anaerobic digestion to produce biogas,on descending order:[C₄mim]Cl/DMSO>[C₂mim]Ac/DMSO>[C₂mim]Ac>[C₄mim]Cl>DMSO.PVs lag phase reduces by 9d after pretreatment of ILs.Total biogas yield rises by 3.2%-76.3%,methane yield 14.3%-25.1%,and biodegradability（BD）8.37%-33.90%.（3）Demonstrating how adding buffers influences PVs biogas yield via AD.Taking ammonium acetate as buffer,making HRT 1 d,HRT 3 ds,HRT 5 ds as time lag,using concentration gradients of 22.50 g/L and 45.00 g/L to conduct buffer adding experiment.The result unmasks that the addition of buffer effectively increases the anaerobic microorganism tolerance to ammonia nitrogen（NH₄⁺-N）in anaerobic digestion system（AD system）,and the stability of the system,and facilitates the system’s biogas yield and methane yield.The group of HRT 5ds buffer 2.5 g/L shows the optimal result,with total biogas yield increasing by 37.46%.Daily biogas yield,NH4+-N concentration and pH value fluctuation ranges±60 mL、±0.07 g/L and±0.12 respectively.Other groups with better biogas yield are HRT 5ds buffer 2.5 g/L、HRT5ds buffer 1.25 g/L、HRT 3ds buffer 1.5 g/L、HRT 5ds buffer 5 g/L、HRT 3ds buffer 0.75 g/L.（4）The thesis illustrates optimum process parameters of PVs and corn stalks in anaerobic co-digestion（hereafter,AcoD）.To use substrate concentration A,C/N ratio B and inoculum rate C as factor,total solid（TS）methane yield ratio as response value in the experiment of central composite design（CCD）,the result shows the theoretical model for TS methane yield（PVs and corn stalks AcoD biogas yield）is Y=538.34-20.37A+23.16C-34.89AB-42.71AC-167.39A²-93.31B²-93.04C².The influences of the above three factors rank C>B>A,and all indicate significant relevance.Paired factors interaction’s influences rank AC>AB>BC.The study concludes that the optimal processing conditions for AcoD of PVs and corn stalks are:substrate concentration 9.87%,C/N ratio 18.76:1,inoculum rate 20.84%,estimated TS gas yield 540.98mL/g TS.（5）The thesis reveals the effect of adding biochar in anaerobic digestion biogas yield of PVs.To use corn stalks as raw material,and pretreat the stalks into biochar via low temperature pyrolysis.Later design experiments using biochar with respective particle diameters of 0.83mm,0.38 mm,0.25 mm,and the amount of addition 5%,10%and 20%respectively.According to the results,adding biochar remarkably enhances PVs productivity of anaerobic digestion biogas.Daily maximum methane yield increases by 5.16%-56.94%,Volatile solid（VS）cumulative methane yield increases by 1.65%-37.71%,biodegradability（BD）increases by1.69%-37.62%,COS removal rate increases by 3.47%-16.48%.Maximum daily methane yield reaches 46.58 m L/gVS,and the maximum VS cumulative methane yield reaches 325.14mL/gVS.Different amounts of addition and particle parameters influences on PVs biogas yield rank as follow:20%CB60>20%CB40>20%CB20>5%CB20>10%CB60>5%CB60>5%CB40>10%CB40>10%CB20.By application of the Gompertz model and first order dynamics model,the simulation of the experiment data concludes that the adding of biochar increases methane rate of PVs anaerobic digestion by 62.59%-168.16%,shortens the lag phase by 20.16%-96.12%,and raise the first order hydrolysis rate constant by 0.04-0.08 d^-1.