Adsorption Of Microcystin-LR On Biochars

Microcystins (MCs) are a group of cyclic heptaptide hepatoxins produced by died cyanobacteria. If dringking water sources contain tiny MC contaminants, it will do serious harm to public health. Biochar, containing much porous structures and surface functional groups, is widely used for removal of pollutants.In this work, biochars (named as Z-300and Z-700) are produced from the carbonization of jujube-wood at300and700℃, respectively. The influences of temperature, pH and dissolved organic matter on the adsorption of biochars are investigated. The main results are listed as follows:As the temperature increases from10℃to40℃, adsorption of Z-300and Z-700increases, indicating the higher temperature contributes to the more MC-LR adsorption. However, MC-LR adsorption decreases as the solution pH increases, which is due to the strengthened electrostatic attractions and the formation of hydrogen bonds under lower pH. In addition, the coexisting dissolved organic matters (fulvic acid and tannic acid) will reduce MC-LR adsorption, due to the repulsion of MC-LR and direct site-competing on Z-700.To explore MC-LR adsorption mechanisms, the influences of different competitors (inorganic salt, compounds containing carboxyl group and guanidine group) on the adsorption of MC-LR by Z-700are experimented as well. The main results are listed as follows:(1) Ionic strength may affect the electrostatic interaction between Z-700and MC-LR;(2) Carboxyl and guanidine groups on MC-LR play significant roles in adsorption process.Finally, the difficult desorption of MC-LR from Z-700and Taihu sediment implies the reduced exposure risks of MC-LR.As a result, MC-LR adsorption on biochars is influenced by temperature, pH, ionic strength and the coexisting dissolved organic matters. The adsorption mechanism is involved by the electrostatic interaction between the biochar surfaces and MC-LR molecules, and the binding of MC-LR’s carboxyl and guanidine groups to the surface functional groups of Z-700. Chemisorption may occur due to the existence of the resisted desorption of MC-LR from both Z-700and biochar-contained Taihu sediment.