Based On The Research Of Anaerobic Co-digestion Of Green Algae And Sludge And Collaborative Purification Technology Of Biogas And Biogas Slurry

The rapid consumption of energy,the reduction of fossil fuel reserves and the new situation and new requirements based on carbon peaking and carbon neutrality have increased the demand for alternative and renewable energy sources.Therefore,the development and use of renewable energy from various biomass has received extensive attention in recent years.As a biomass source that can be used to produce biofuel,green algae has become the preferred raw material for anaerobic digestion to produce biogas due to its high productivity and strong environmental tolerance.In this study,chlorella and sludge were mixed for anaerobic co-digestion to explore the optimal ratio of chlorella and sludge.On this basis,chlorella and sludge were treated by hydrothermal pretreatment,and the effects of different temperatures of hydrothermal pretreatment on the mixed anaerobic digestion of chlorella and sludge were explored,so as to further improve the gas production effect and determine the optimal pretreatment temperature.In addition,in order to improve the biogas methane content and effective removal of contaminants in the biogas slurry,the research of chlorella and scenedesmus to optimize culture conditions and determine the biogas slurry of best chlorella and scenedesmus growth and carbon dioxide（CO₂）concentration dilution condition,on this basis,the selection of chlorella and scenedesmus best initial inoculation amount so as to realize the collaborative biogas,biogas slurry purification.The conclusions are as follows:（1）The effect of different VS ratio mixture of Chlorella and sludge on anaerobic digestion gas production was studied.The results showed that when the mixing ratio was2:1,the effect of anaerobic digestion gas production was the best,and the cumulative gas production was 250.98 mL/g VS,which was 1.37 times and 1.65 times higher than that of the single sludge group and the single Chlorella group,respectively.In addition,the mixed group had a higher concentration of VFAs,up to 2956.45 mg/L.Fitzhugh first-order kinetic model and modified Gompertz model were used to fit the cumulative gas production of all experimental groups.It was found that the mixed anaerobic co-digestion of Chlorella and sludge increased the methane production potential and maximum gas production rate,and the 2:1 mixed group had the highest methane production potential and maximum gas production rate.423.48 mL/g VS 33.21 mL/g VS d,respectively.Based on this experiment,the effect of hydrothermal pretreatment temperature on anaerobic digestion of 2:1 mixed Chlorella and sludge was investigated.The results show that the maximum cumulative gas production is 481.23 mL/g VS when the hydrothermal temperature is 180℃.At this temperature,the content of VFAs is also high,up to 5463.52 mg/L.According to Fitzhugh first-order kinetic model and modified Gompertz model,hydrothermal pretreatment can improve gas production potential and shorten the lag period of anaerobic digestion,indicating that hydrothermal pretreatment is conducive to hydrolytic acidification of chlorella biomass and decomposition of macromolecular organic matter into short chain small molecules to promote anaerobic digestion.Macrowhole genome sequencing results of the experimental groups before and after hydrothermal treatment showed that hydrothermal pretreatment significantly improved the abundance of hydrolytic acidified bacteria such as Chloroflexi,Proteobacteria and Acidobacteria at phylum level,and the experimental group at 180℃had the highest abundance.They were 4.13%,55.84%and 0.82%,respectively,indicating that hydrothermal pretreatment can accelerate the degradation capacity of sugars and organic matter,and promote the acid production stage of anaerobic digestion.（2）According to the effect of initial nitrogen and phosphorus concentration on the growth of Chlorella and Scenedesmus,different biogas slurry dilution conditions were determined,and the effects of CO₂ concentration and biogas slurry dilution on the growth of Chlorella and Scenedesmus were explored,and the optimal CO₂ concentration and biogas slurry dilution conditions were determined for biogas slurry and biogas collaborative purification.The results showed that chlorella and Scenedesmus grew best at 250 mg/L initial nitrogen concentration,and their maximum dry weights were 47.19and 31.03 mg/L,respectively.The dry weight of Chlorella and Scenedesmus was 304.02and 151.46 mg/L,respectively,at 75 mg/L P initial concentration.Under these conditions,different proportion of biogas slurry was determined,and it was found that50%biogas slurry was the most suitable for the growth of Chlorella and Scenedesmus,and the highest dry weight of chlorella and Scenedesmus were 268.61 and 115.35 mg/L,respectively.At the end of the experiment,the removal rates of TN,TP and COD in chlorella group were 60.76,92.70,44.35%,and 55.84,88.26,59.27%in chlorella and Scenedesmus group,respectively.The optimal CO₂ concentration was 5%,and the dry weight was 629.02 mg/L and 307.36 mg/L,respectively.The 20%CO₂ concentration significantly inhibited the growth of Chlorella and Scenedesmus.（3）The effects of different initial inoculations of Chlorella and Scenedesmus(OD₆₈₀=0.05,0.1,0.2,0.3)on biogas and biogas co-purification under the optimal CO₂concentration and biogas dilution conditions were investigated.The results showed that at the end of the experiment,the dry weight of Chlorella was 0.3>0.2>0.1>0.05 in the experimental group,and the dry weight of Scenedesmus was 0.3>0.2>0.05>0.1in the experimental group.When the initial inoculation amount of Chlorella and Scenedesmus was 0.3,the removal efficiency of COD,TN and TP of Chlorella was90.6%,83.03%and 99.84%,and that of Scenedesmus was 77.71%,66.35%and 98.74%,respectively.In addition,when the initial inoculation amount was 0.3,the carbon sequestration capacity of Chlorella and Scenedesmus was the highest,and the highest carbon sequestration rate was 18.03%and 11.05%,respectively.