Toxicity Of Persistent Free Radical Containing-biochar And Its Removal Effect On P-nitrophenol

As a new type of functional material,biochar has attracted much attention.In recent years,its application in water and soil remediation has gradually increased.However,it was reported that biochar contains a large number of persistent free radicals(PFRs),which can can act as redox mediators to promote the degradation and transformation of pollutants and heavy metals,and also stimulate oxidative stress in organisms.At present,there is still no detailed and in-depth study on the environmental behavior of PFRs of biochar in the degradation system of pollutants and its degradation effect on the target pollutants.In addition,due to the common use of biochar,it will enter the nature water in different ways during application and processing.But the adverse effects of PFRs-containing biochar on aquatic organisms have not got enough attention.In this study,biochar pyrolyzed from pine needle under oxygen-limited conditions.The effects of pyrolysis temperature and time on the concentration and type of PFRs in biochars were investigated,and environmental stability analysis(decay)also was analyzed.At the same time,the effects of organic matter in the biomass feedstock on the concentration of PFRs was also investigated.The Scenedesmus obliquus(S.obliquus)and the luminescence of Photobacterium phosphoreum(P.phosphoreum)were used as the test organisms,the toxicity of PFRs-containing biochars were expressed with the following endpoints: cell growth,chlorophyll-a(Chl-a),reactive oxygen species(ROS),superoxide dismutase(SOD)content of S.obliquus and the luminescence of P.phosphoreum.On the other hand,we synthesized a new kind of nZVI composite material with PFRs-containing biochars as the support(called nZVI/BC composite)to remove P-Nitrophenol(PNP).The composite mass ratio,solution pH material dosage,and the role of PFRs on the effect of PNP removal were investigated.It was found that the formation of PFRs in biochars depend on the content of organic matter in biomass feedstock.The pyrolysis temperature greatly influenced the concentration and type of PFRs.We can see that the concentration of PFRs in biochar was increased when the pyrolysis temperature increased from 200 to 500 °C,but decreased when the pyrolysis temperature further increased to 600 °C,reached the highest at 500 °C.For the type of PFRs,the oxygen-centered radicals were dominant at relatively low pyrolysis temperatures,whereas carbon-centered radicals with an adjacent oxygen atom were predominant at relatively high temperature.Moreover,PFRs-containing biochars prepared in our study can produce toxic effects on S.obliquus and P.phosphoreum,and our results show that the toxicity of biochar is significantly correlated with the concentration of FRs in biochar particles.In this study,a new kind of nZVI composite material with PFRs-containing biochars as the support(nZVI/BC)was successfully synthesized,which can effectively remove PNP in water under acidic conditions of pH=3.Particularly,the removal rate of PNP can reach 100% when the mass ratios of nZVI and biochar was 1:1.·OH was detected in the removal system,it was found that the concentration of hydroxyl did not significantly increase with the increase of the concentration of the material used,but the removal rate of PNP significantly increased with the increase of the material concentration,which means that ·OH was not the only way of PNP degradation.The PFRs in biochar could accelerate the removal of PNP by nZVI/BC composites,and improve the removal rate.In summary,the results of this study provide a basis for further understanding the environmental behavior and application of PFRs containing biochar,provide basic data for ecological risk assessment of organisms in actual water environments,and lays the foundation for the application of biochar in environmental remediation.