Effects Of Biochars Derived From Different Pyrolysis Temperatures On Environmental Behaviors Of Polycyclic Aromatic Hydrocarbons In Soils

Polycyclic aromatic hydrocarbons(PAHs)are a kind of persistent organic pollutants produced in people's life.They are highly carcinogenic,teratogenic and mutagenic.They are widely distributed in the soil and water environment because they are hard to be biodegraded and they can endanger human health and ecological security through soil-animal and soil-plant systems.Biochar is a type of highly aromatic material with high carbon content,which is produced by the pyrolysis of biomass under the artificial control conditions of complete or partial anoxia.It is a new type of environmental functional adsorbent that can be applied to environmental pollution remediation.In this study,seven kinds of biochar BC100~BC700 with pyrolysis temperature of 100~700 were prepared from wheat straw in Tianjin.And then the physicochemical properties and structures of these prepared biochars were analyzed and identified,and select phenanthrene and pyrene as the representative to measure the adsorption of biochar on PAHs.On this basis,BC100,BC300,BC500and BC700 were selected to study the effect of pyrolysis temperature of biochar on the microbial availability and removal of PAHs in soil so as to explore the structure-activity relationship.The study results of this thesis can provide the technical guidance and theoretical supporting for the pollution control of PAHs in soil.The main conclusions of this study are as follows:(1)The structural characterization of these seven pyrolysis temperature biochars were studied.The results showed that with the increase of pyrolysis temperature,the degree of charcoalization of wheat straw increased,the yield decreased,the ash content and the aromaticity of biochar increased,the hydrophilicity and polarity decreased,the specific surface area and porosity of biochar increased,the average pore size decreased.(2)The adsorption capacity of PAHs by different pyrolysis temperature biochar was determined.The results showed that with the increase of carbonization temperature,the adsorption capacity of biochar to PAHs increased gradually,the adsorption isotherm tended to be nonlinear and the degree of nonlinearity increased gradually.The Freundlich N index showed a good positive linear correlation with biochar's aromaticity.And the LgK_f exhibited a good negative linear correlation with biochar's aromaticity and a good positive linear correlation with the specific surface area of biochar.The adsorption of composite PAHs on biochar has a competitive effect.Compared with the adsorption of single PAHs,the adsorption capacity of biochar to organic compounds decreases and the adsorption isotherm increases linearly.(3)In the study of the effect of biochar pyrolysis temperature on the microbial availability and removal of PAHs in soil,the results showed that adding biochar can significantly reduce the microbial bioavailability of PAHs in soil,and the higher the pyrolysis temperature,the better the biochar effect.The addition of low-temperature pyrolysis of biochar to the soil inhibits the degradation of PAHs in the soil,whereas the addition of high-temperature pyrolytic biochar do not significantly inhibit the biodegradation of PAHs by soil microorganisms.This may be due to the superior structural properties of high-temperature biochar which provide a more suitable space for the growth and reproduction of PAH-degrading bacterias in the soil,making biochar not only a repository of PAHs but also a site of degradation.