Component Analysis Of Slurry/Residue And Comprehensive Evaluation For Biomethane System

With the rapid development of China’s economy,energy consumption is increasing day by day.However,the traditional fossil energy is not renewable,and will bring serious environmental pollution.In addition,China is a large agricultural and breeding country,which produces a large number of straw and livestock manure waste.Biomethane system can produce methane from organic wastes,which can not only treat agricultural wastes,but also generate renewable energy.The biomethane system has developed rapidly and the scale has increased in the past twenty years.However,the biomethane system have some disadvantages,such as complex raw material source,low utilization rate of organic matters,large amounts and unknown components of biogas slurry and biogas residues.Therefore,it is very important to clarify the components of raw materials,biogas slurry and biogas residues and evaluate the biomethane system,which are of great significance to optimize biomethane system and reduce pollutant emissions.In the present study,the biogas slurry of twenty-seven cities in China was analyzed and evaluated.Then,the biomethane system of typical raw materials was established.The components of raw materials,biogas,biogas slurry and biogas residues were analyzed.Moreover,the comprehensive evaluation of biomethane system with green degree,methane yield,contamination degree of heavy metals and potential ecological risk was constructed.Finally,the green degree of digestate treatments was evaluated.The following results were obtained.（1）The analysis and evaluation of sixty-nine biogas slurry samples from biogas engineering and household biogas in twenty-seven cities in China were explored.When chicken manure（CHM）was used as raw material,the concentrations of chemical oxygen demand（COD）,ammonia nitrogen（NH₄⁺-N）and phosphate(PO₄^3-)in slurry of biogas engineering were 7092±1268 mg·L^-1,4609±2972 mg·L^-1 and 172.0±78.8 mg·L^-1,respectively,which were significantly higher than those of other raw materials.More important,the concentration of antibiotics in biogas slurry from swine manure（SM）was the highest,mainly sulphonamides,quinolones and tetracyclines.The potential ecological risk of biogas slurry was moderate because of arsenic contamination.With the same fermentation materials,contamination degree and potential ecological risk of slurry of household biogas were more serious than that of biogas engineering.The quadratic polynomial stepwise regression model can quantitatively describe the correlation between the concentrations of seven heavy metals in biogas slurry and NH₄⁺-N,PO₄^3-.（2）The comprehensive component analysis and evaluation of biomethane systems with five typical biomass raw materials were conducted:cattle manure（CAM）,SM,straw（St）,kitchen waste（KW）and CHM.The results indicated that the biomethane system of CHM and SM were similar with high methane yield（183± 18 mL/g VS and 212±19 mL/g VS respectively）,NH₄⁺-N concentration of biogas slurry(1859± 163 mg·L^-1 and 1162± 137 mg·L^-1 respectively),contamination degree of heavy metals of biogas residue.The systems of CAM and St also had some similarities with high cellulose and lignin proportion of raw materials and low COD,NH₄⁺-N,PO₄^3-concentrations of biogas slurry.The considerable green degree in biomethane system of CAM is close to that of SM（0.200 and 0.222 respectively）.（3）The results of biomethane systems from mixed biomass raw materials（SM+St,CAM+SM,St+CHM and SM+CHM）indicated that co-digestion can make up the deficiency of biomethane system using a single substrate.SM mixed with St or CAM can modify the contamination degree of heavy metals and potential ecological risk of single SM substrate.CAM mixed with SM can amend the methane yield of single CAM substrate.St mixed with SM or CHM can improve the green degree and methane yield of single St substrate.CHM mixed with SM or St can optimize the green degree,contamination degree of heavy metals and potential ecological risk of single CHM substrate.With the comprehensive consideration of four evaluation indicators,the co-digestion ratios were recommended:SM to St were 2:1 and 1:1（The green degree of SM:St=2:1 was highest,reaching 0.239.The methane yield of SM:St=1:1 was highest,reaching 218±18 mL/g VS.）;CAM to SM were 2:1 and 1:1（The contamination degree and potential ecological risk of digestate in CAM:SM=2:1 was low.The green degree and methane yield of CAM:SM=1:1 were highest,0.277 and 179±13 mL/g VS,respectively.）;St to CHM was 2:1（The methane yield was highest,reaching 213±36 mL/g VS.Furthermore,the contamination degree and potential ecological risk of digestate was low.）;SM to CHM were 3:1 and 2:1（The green degree and methane yield of SM:CHM=3:1 were highest,0.263 and 224±32 mL/g VS,respectively.The contamination degree and potential ecological risk of biogas slurry in SM:CHM=2:1 was lowest.）.（4）The green degree of digestate treatments from biomethane systems was acquired.Among the slury treatments,microalgae and liquid fertilizer（LF）were relatively outstanding.The green degree of biochar and compost was best among the residue treatments.All three groups digestate coupling treatments（microalgae+biochar,microalgae+compost and LF+compost）can significantly improve the green degree of biomethane system and reduce environmental pollution.After the microalgae+compost treatments,the green degree of the biomethane systems with single SM and single St can increase 97%and 244%,respectively.After the microalgae+biochar treatments,the green degree of the biomethane systems with SM:St=2:1 and SM:St=l:1 can increase 71%and 88%,respectively.