Preparation Of Hydrothermal Carbonaceous Materials From Food Waste And Study On Adsorption Behavior Of Per-and Polyfluoroalkyl Substances

With the acceleration of my countrys urbanization process and rapid population growth,the output of food waste has increased sharply.Food waste is rich in organic matter and nutrients,and has the dual attributes of pollution and resources.If it is effectively treated,it can be used as resources.In recent years,the hydrocharization technology has the advantages of converting materials with high moisture content into carbonaceous materials and solid fuels,and has broad application prospects in the resource treatment of food waste.Its solid phase product（hydrochar）is mainly carbon element,and has pore structure and rich functional groups.It not only realizes carbon fixation and energy production,but also may prevent and control new pollutants in environmental media such as soil.Per-and polyfluoroalkyl substances（PFASs）are a class of global new pollutants with alkyl carbon chain structure as the skeleton,and hydrogen atoms are fully or partially replaced by fluorine atoms.The soil is an important sink of PFASs.the PFASs present in the soil will enter the groundwater through leaching and affect water quality and safety.Existing studies mostly focus on the occurrence,concentration level and behavioral mechanism of long-chain PFASs such as Perfluorooctane sulfonic acid（PFOS）and Perfluorooctanoic acid（PFOA）.A report on the control of PFASs by hydrocharaceous materials from food waste.Therefore,this paper uses low-value biomass food waste as the research object,selects PFASs with different carbon chain lengths and functional group structures,and carries out the preparation of food waste hydrocharaceous materials and the study on the adsorption behavior of PFASs,which is the food waste hydrochar The future potential applications of quality materials to control the migration of PFASs in soil provide basic theoretical data support.The main research contents and results are as follows:（1）Using the food waste in the transfer station as the experimental raw material,the hydrochar is prepared by the hydrothermal carbonization method,and the modified carbon is prepared by the zinc chloride（Zn Cl₂）high-temperature activation method.The element composition analysis,surface functional group qualitative,physical conformation observation and other characterization methods are used,Prove the composition and structural characteristics of hydrochar and modified carbon.The results show that the specific surface area of hydrothermal carbon is only 5.54m²/g,and the pore volume is as low as 0.01cm³/g.After the hydrothermal carbon is modified by Zn Cl₂ at high temperature,the pore structure changes significantly,and the specific surface area and pore volume are as high as 206.97 m²/g and 0.12cm³/g,with obvious microporous structure(V_micropores/V_{total pores}=66.67%),and compared with hydrochar,the degree of aromatization of hydrothermal modified carbon of food waste is increased,and its polarity If it becomes lower,it has the potential to become a soil remediation material.（2）Due to the strong hydrophobicity of PFASs,it may be adsorbed on the walls or filter membranes of the main instrument containers used in the pretreatment,resulting in loss of PFASs concentration during analysis.The current research only reports on the influence of the pretreatment process of traditional long-chain PFASs such as PFOS and PFOA on the quantitative results.There is still a lack of research on the influence of the pretreatment process of short-chain and new PFASs on the quantitative results.Therefore,the short-chain perfluorinated chain between C3 and C6 is selected.Polyfluorinated compounds and perfluorinated compounds with ether bonds in the perfluorocarbon chain are the research objects,and the influence of the pretreatment process on the analysis results of PFASs is explored.The results showed that after 96hours of adsorption of PFASs in polypropylene（PP）centrifuge tubes,the concentration of 10 PFASs at 96 hours was found to account for 91.88%～100.24%of the initial concentration,and the adsorption loss was negligible.By measuring the concentration of PFASs before and after the filtration of the nylon membrane,it was found that the concentration of PFASs before and after filtration was distributed near the 1:1 line,indicating that the nylon membrane basically did not intercept PFASs during the pretreatment.The standard addition recovery experiment was carried out under the pretreatment conditions of using PP material centrifuge tube and nylon membrane filtration.The standard addition recovery rate of 10 kinds of PFASs was72.96%～122.56%,indicating that this method has good accuracy and accuracy for the determination of 10 kinds of PFASs.（3）Select PFASs that take into account the difference in functional group and carbon chain length as the adsorbent,and use the modified hydrochar of food waste as the adsorbent,carry out the shake flask adsorption experiment,obtain the adsorption coefficient characterizing its solid-liquid phase partition,and study the effect of PFASs Adsorption-desorption behavior of food waste modified hydrochar.The results showed that the adsorption of PFASs by the modified hydrochar reached adsorption equilibrium within 96 hours,and the adsorption distribution coefficient（log K_d）of 10 PFASs was1.33～5.49 L/g.Both the carbon chain length and functional groups of PFASs would produce log K_d.influences.In the study of adsorption kinetics,it was found that the longer the carbon chain length of PFASs,the faster the removal rate of adsorption kinetics.The adsorption-desorption curve of 10 kinds of PFASs in the food waste modified hydrochar has obvious non-overlapping phenomenon,indicating that the adsorption-desorption behavior is irreversible.From the analysis of the desorption hysteresis coefficient of the modified hydrochar,it can be found that,except The desorption hysteresis coefficients of PFBA and HFPO-DA at low concentrations are in the range of 0.7～1,and the other desorption hysteresis coefficients are all less than 0.7,indicating that the desorption hysteresis of 10 kinds of PFASs is relatively significant,so it can be It is speculated that when the food waste modified hydrochar is added to the soil,it can effectively prevent the impact of PFASs leaching and reduce the environmental risks caused by PFASs.