Removal Mechanism Of Endosulfan By Biochar Derived From Emergent Plants

In December 2016,China announced the "13th Five-Year" and required the elimination of endosulfan until 2020.Moreover,the development of extensive operation of constructed wetland system has been launched worldspread.However,due to the pollution caused by unharvest wetland plants in time,the matrix clogged.It was six kinds of biochars(canna indical,acorus calamus,phragmites autralias,zizania aquatic,thalia dealbata and arundo donax)derived from wetland plants that were pyrolyzed without oxygen.In addition,the mechanism of endosulfan removal from biochars were further elucidated by exploring enhancing hydrolytic effect and the influence of ash and dissolved organic matter.The main conclusions were as follows:(1)The results showed that the ash contents were higher than that of other agricultural wastes,rangeing from 10.88 to 31.11%.The results also suggested that the biochars had a mass of aromatic domains and pores on the surface of biochars.The pores were mainly mesopores and partly fragmented.(2)The adsorption coefficient(logKd)ranged from 1.47 to 11.91 mL/g,of which the logKd of CAIB,ACCB and PHAB was relatively higher among six biochars.As the equilibrium concentration of endosulfan increased,the logKac decreased,indicating that the adsorption mainly based on the adsorption of organic matter on the surface.The biochar pore size had a significant positive correlation with the adsorption coefficient logKd of ?-endosulfan and ?-endosulfan(P>0,0.7839 and P>0,0.8003),while the specific surface area and its correlation was poorly weak(P<0,0.1644 and P<0,0.0368),indicating pore distribution and diffusion effect functioned.In addition,the hydrophobic interactions,distribution effect and electrostatic attraction were also involved in.In a word,considering adsorption strength and reused times,the CAIB,ACCB and PHAB hold a relatively perfect performance.(3)Moreover,biochar could catalyze the hydrolysis of endosulfan with an increase of hydrolysis efficiency about 16.57?72.57%under the condition of neutral solution.After deashed,the affinity between biochars and ?-endosulfan or a-endosulfan weakened and the adsorption capacity was limited(logKF ranged from 6.74 to 11.11 mg/g).In addition,the value of(O+N/C)decreased,the proportion of surface-C and bulk-C increased,indicating that deashing could increased the hydrophobicity.After adding to supernatant,the endcsulfan adsorption by deashed biochars dramatically improved.(4)In fact,the DOM of ARDB contained more high molecular aromatic humus substances,the fluorescence peak shifted to the V part,considering the proportions of P(?,n)and P(?,n),r(A,C)and the dissolved organic carbon,the DOM of ARDB,CAIB,and PHAB posed a more enhanced hydrophobic effect.