Efficient Removal Of Phenolic Organics By Swine Bone Derived Biochar: Insight Into The Degradation Mechanism And Toxicity

With the development of industrialization,the water environment problems caused by refractory organic substance urgently needs to be addressed.Advanced oxidation processes（AOPs）is an effiecnt approach,which can fundamentally degrade the pollutants.Among the various AOPs,persulfate（PS）activation system has received much attention,for it could conquer the drawbacks of traditional Fenton system（such as limited p H range and the formation of iron sludge）.Recently,as a simple-design and low-cost carbonaceous materials,biochar has been widely applied as catalyst in persulfate system.However,the catalytic capacity of pristine biochar is limited,heteroatomic doping and transition metal loading have been frequently used to enhance the catalytic capacity of biochar.There is no doubt that it would increase the cost.It is urgent to develop biochar orginrate from different biomass,to achieve high catalytic efficiency with pristine biochar.Consequrntly,biochar derived from swine bone（BBC-900）was applied in persulfate system.Benifiting from the natural porous structure of swine bone,BBC-900 could activate persulfate to degrade 2,4-dichlorphenol（2,4-DCP）efficiently.The pseudo-first-order rate constant was 0.0334 min^-1,which was familiar with the efficiency of the structured carbonaceous materials.The electrochemical experiment and active species capture experiment illustrated that radical(SO₄^·-,·OH and O₂^·-)and non-radical pathway（¹O₂ and electron transfer pathway）were both worked in BBC-900/PS system.The existence of multiple mechanisms helps the BBC-900/PS system to adapt to different conditions.In addition,because of the complex composition of biochar,it is difficult to explore the specific role of various functional structures on biochar in persulfate activation system.To brige this gap,selective inactivation experiment was first involved to investigate the role of oxygen-containing groups in catalysis.Moreover,the influence of annealing temperature and acid treatment to the functional structure and the propotion of different mechanisms were ananlyized.The results showed that 1)-COOH and-OH were the active sites for SO₄^·-and·OH;2)C=O was the active sites for electron transfer process;3)defects and PFRs were the active sites for O₂^·-and ¹O₂;4)the inorganic component of swine bone did little for the catalytic capacity of BBC-900,but only worked as hard template to form porous structure.Noteworthily,the porous sturcure and specific surface area were tightly related to the adsoption capacity of biochar,and they are the base of radical and non radical pathway in persulfate activate system.It has been reported that the phenols degradation process based on SO4^·-would produce intermediate with high toxicity.However,the influence might arise during the degradation of organic pollutants by biochar-based persulfate systems have not been systematically evaluated.In order to understand the toxic effect bringing about by the BBC-900/PS system,applying the suppression ratio of Scendesmus obliquus in 96 h to evaluate the acute toxicity.The results showed that the highly toxic intermediate occur in BBC-900/PS system,and the generation of radicals would also do harm to the growth of plants.Thus,the acute toxicity climbed with the increase of the propotion of radical pathway.However,the excellent adsorption capacity might be able to adsob the high toxic intermediate,which could restrain the acute toxicity of BBC-900/PS system.To sum up,the application of the swine bone derived biochar provides a new strategy for high efficiency green remediation of organic contaminants.Furthermore,understanding the corresponding relationship between active sites and active species would give information to the oriented synthesis of biochar and promote the application of biochar in the field of environmental catalysis.