| Biochar,a kind of highly aromatic organic carbon solid,is produced by pyrolysis of biomass materials under anaerobic or anaerobic conditions.When terra preta was discovered by scientists on the amazon plain in Brazil,it soon set off a research upsurge in biochar.At present,the research on biochar in domestic and overseas is no longer limited to its positive effects on the ecological environment,such as improving soil physical and chemical properties,increasing soil fertility and crop yield,controlling environmental pollution,reducing pollutant bioavailability and ecological toxicity,mitigating global warming,reducing CO2,CH4 and other greenhouse gas emissions.Some researchers have begun to pay attention to the potential pollutants generated by biochar,such as polycyclic aromatic hydrocarbons(PAHs),and their environmental risks in agricultural application.The control and remediation technologies of PAHs pollution have attracted wide attention due to their strong "three-cause"(carcinogenic,induced and mutagenic)effects.Among them,PAHs substances adsorbed by biochar technique has become a research hotspot.However,using biochar for remediation of PAHs pollutants might cause second pollution to the environment because of it contains a certain amount of PAHs.In this study,the effects of different types of biochar produced by different raw materials and temperature on the residual of PAHs in biochar,as well as their impact of application on the content of PAHs in aqueous solution,soil and Chinese cabbage were studied.The main results are as follows:(1)The effects of different raw materials and pyrolysis temperature on the content of PAHs in biochar were analyzed.The content of PAHs was greatly influenced by the source of raw materials.The highest and lowest average total content of PAHs were 21.46 mg kg"1(10.51-29.94 mg kg-1)and 7.70 mg·kg-1(2.29-19.44 mg·kg-1)in straw and living waste biochar,respectively.While,agricultural waste,livestock and poultry manure were,12.49 mg·kg-1(10.51-29.94 mg-kg-1),12.29 mg·kg-1(8.37-14.7 mg·kg-1)and 9.43 mg·kg-1(5.53-13.32 mg-kg-1),respectively.(2)The wheat straw biochar(WBC),pig manure biochar(PBC)and sludge biochar(SBC)were selected as adsorbents,and the typical materials of phenanthrene and pyrene in PAHs were used as adsorbate to study the effect of biochars' adsorption-desorption on phenanthrene and pyrene in solution.The results showed that the dynamic adsorption mechanism of wheat straw,pig manure and sludge biochar on phenanthrene was different from that of pyrene,and the quasi-first order kinetic model could well fit the adsorption effect on phenanthrene(R2>0.96),while the adsorption of pyrene by three kinds of bioochar was more consistent with the quasi-second order kinetic model(R2>0.96).The adsorption isotherm of phenanthrene and pyrene in wheat straw,pig manure and sludge biochars shows that Langmuir equation can fit them better in a certain equilibrium concentration range,compared with Freundlich equation(R2>0.95).The adsorption capacity and linearity degree of wheat straw and pig manure biochar were higher than that of sludge in a certain concentration range.The adsorption capacity of phenanthrene and pyrene was higher than that of SBC,and the adsorption potential of WBC and PBC on phenanthrene and pyrene was higher than that of SBC.In the desorption test,with the increase of desorption time,the desorption rates showed some fluctuations,but the desorption rates of phenanthrene with sludge,pig manure and wheat straw biochar were stable around 10%,8%,9%,respectively.Similarly,the desorption rates of pyrene were stable around 11%,8%and 6%,respectively.Compared with the analytical dynamic diagram of phenanthrene and pyrene,pyrene(4 rings)was more difficult to be desorpted by biochar than phenanthrene(3 rings).(3)On the base of adsorption test,two pot experiments were conducted surpersede,in which the effects of maize straw biochar,wehat straw biochar,pig manure biochar and sludge biochar on PAHs accumulation in Chinese cabbage in both polluted and unpolluted soils were studied systematically.The results are as follows:Maize straw biochar could improved the total residual amount of PAHs in the clean soil,while it showed no similar effect on the amount of PAHs accumulated by Chinese cabbage and no significant effect on the biomass of Chinese cabbage.Through 40d cultivation,soil samples were collected for the determination of available PAHs concentrations.Results showed that treatments with biochars of 18 mesh and 5 mesh decreased soil available PAHs concentrations by 34.4%and 45.1%,respectively.However,there was no significant difference between the 60 mesh of biochar and CK.The results suggested that the PAHs in biochar would not bring ecological risk to clean soil.The three kinds of biochars used in this study all showed certain inhibition effect on PAHs accumulated by Chinese cabbage in polluted soils.Compared with the control,biochar could reduce the PAHs accumulation in Chinese cabbage within the ranges from 14.5%to 49.4%,and the inhibition abilities of biochars showed in the orders of wheat straw biochar>pig manure biochar>sludge biochar.The reduction rates for low molecular weight of PAHs with 2-3 rings with biochar treatments changed from 0 to 30.8%,while it were from 30.7%to 68.1%for high molecular weight PAHs with 4-6 rings.Under the treatment of 2%of wheat straw biochar and pig manure biochar,the biomass of Chinese cabbage was significantly increased by 20.0%and 22.3%.Therefore,the application of biochar can be taken as an effective measure to reduce PAHs uptake meanwhile improve crop yield.Above all,as a kind of environment-friendly adsorbent,biochar could not only effectively absorb PAHs in water/soil,but also prevent crops from absorbing PAHs from contaminated soil.Additionally,soil total PAHs concentrations will be improved by bicohar application with the remained PAHs in the process of bicohar production,while there is no negative effect on soil available PAHs,Chinese cabbage biomass and PAHs uptake.Therefore,the application of biochar in the area of polycyclic aromatic hydrocarbons(PAHs)remediation shows promising prospect in popularization and application. |
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