The Research Of Hydrothermal Carbonization Technology Of Food Waste And Product Properties

With the growth of the economy and people’s life,the production of food waste in China has also increased sharply.The water content,oil content and organic matter content of food waste are high.Due to the high organic load in the process of anaerobic digestion,a large number of biogas slurry and biogas residue will be produced.If not properly treated,it will cause secondary pollution.How to dispose the food waste is an urgent problem.Hydrothermal carbonization technology（HTC）is a new technology to treat biomass.It can convert biomass into solid,liquid and gas under the condition of high moisture content,so it can be used in the treatment of food waste.This paper combined hydrothermal carbonization technology and anaerobic digestion technology to realize the efficient utilization of food waste.Firstly,the influencing factors of starch during hydrothermal carbonization process were studied.The results show that the carbon content in the hydrochar increased from44.44%to 62.79-70.97%,HHV increased from 17.68 MJ/kg to 24.36-26.64 MJ/kg,H/C and O/C atomic ratio were dreased from 1.67 to 0.62-0.93 and 1.11 to 0.35-0.51.The decrease of atomic ratio indicates that hydrochar has better combustion properties.The influence of temperature is stronger than residence time and moisture content.The increase of temperature will accompany the dissolution of hydrochar and the formation of secondary carbon.Prolonging the residence time can improve the strength of condensation reaction and the high moisture content will affect the distribution of hydrochar.The liquid phase recycling can improve the mass yield of hydrochar.After the sixth cycle,the mass yield of hydrochar was increased from 23.4%to 31.65%.Secondly,the food waste was used as raw material to maximize the energy yield of hydrochar by response surface method.The results show that the optimal preparation conditions for energy yield were as follows:temperature of 260°C,contact time of 4 h and moisture content of 80%,and the energy yield could reach 66.1%.Also,carbon emissions during hydrothermal carbonization,incineration,landfill and composting were calculated.It is concluded that HTC can significantly reduce the carbon emissions,and the carbon emission of HTC is 0.15-0.25 g CO₂/g food waste.Subsequently,the application of hydrotchar in combustion and anaerobic process were studied.The results show that the carbon content in the hydrochar increased from51.94%to 65.97-71.08%,O content decreased from 35.29%to 11.85-21.03%,HHV increased from 22.18 MJ/kg to 28.36-31.11 MJ/kg.Van Krevelen indicates that dehydration and decarbonization were happened during hydrothermal carbonation process.O/C and H/C atomic ratio were dreased from 0.51 to 0.15-0.24 and 1.53 to 0.89-1.15,and the activation energy required in the initial stage of hydrochar combustion is also significantly reduced.The anaerobic digestion experiments show that hydrochar could increase the gas production of hydrothermal liquid.When the addition of hydrochar was 10 g/L,the cumulative methane yield could reach 251.52±16.47 m L CH₄/g-COD,which increased by 101%compared with the control group.The addition of hydrochar increases the abundance of microbial communities,such as Clostridia,Syntrophomonas,Methanosphaera,and the oxygen-containing functional groups on the surface of hydrochar can enrich microorganisms,which provides a platform for direct electron transfer of microorganisms.Finally,the technology of hydrothermal carbonization coupled anaerobic digestion to treat food waste was studied.It was found that the combination of two technologies could significantly improve the utilization value of food waste,and the energy generated was 19.95%higher than that of anaerobic digestion.At the same time,the whole process can reduce the production of landfill gas and leachate.