Study On The Removal Of Organic Contaminants By Chitosan/surfactant/clay Supported Catalyst

Organic pollutants such as nitroaromatic compounds and oily substances are improperly disposed and are discharged into the environmental water bodies,causing serious damage to the ecological environment and human health.Studies have shown that the use of enzyme-catalyzed hydrolysis and mineral-bound Fe(II)catalytic reduction can remove or degrade these organic contaminants.However,there are also problems such as the inactivation of free enzymes,their inability to be reused,and the need to increase the catalytic activity of mineral-bound Fe(II).Therefore,in this paper,chitosan/clay composite microsphere supported lipase was prepared by using natural polymer chitosan and clay mineral as raw materials to improve the stability and reusability of lipase-catalyzed hydrolysis of oily substances;Surfactants including cation(CTAB),anion(SDBS),non-ion(TX-100)and(Tween-80)influence Fe(II)-reduced nitrobenzene contaminants bound on iron-containing clay minerals.The analysis of changes in active Fe(II)during reaction,the composition of secondary minerals on the surface of clay minerals,the change in electrode potential of the reaction system,and the effect of clay minerals on the adsorption performance of pollutants were investigated by means of analytical methods such as M?ssbauer spectra,XPS,and ORP.The effect mechanism of active agent on the mineral-reduced Fe(II)reduction activity provides a theoretical basis for the development of in-situ remediation technology based on surfactant-enhanced nitrobenzene contaminants.The research results were lists as follows:(1)An appropriate addition ratio of chitosan to clay(8:1,5:1,3:1)not only enhanced the adsorption of olive oil on the carrier,but also enhanced thebiocompatibility between chitosan and lipase,to improve the catalytic activity of immobilized lipase as much as possible.(2)The addition of clay can raise the structural rigidity of the immobilized lipase,improve its catalytic stability to heat and pH changes,and enhance the reusability of lipase in the hydrolysis of olive oil.(3)The different effects of various surfactants on the removal of the same contaminant by clay minerals/Fe(II)were obsevered.The presence of CTAB,TX-100 or Tween-80 promoted the reduction of nitrobenzene and p-nitrotoluene,while SDBS showed inhibitory effect,and the order of effect was ranked as follows:CTAB >Tween-80 > TX-100 > SDBS.As for the reduction of p-nitrchlorobenzene by clay minerals/Fe(II),these surfactants all showed positive effect at different degrees,and the order of effect were ranked as follows: CTAB> SDBS> Tween-80> TX-100.(4)The effect mechanism of surfactant on the reduction of nitrobenzene contaminants by clay minerals/Fe(II)was mainly related to the formation edge surface bound Fe(II),secondary mineral composition on clay surface,and adsorption of contaminants by clay.The presence of CTAB,TX-100,or Tween-80 can promote the formation of edge surface bound Fe(II)and reactive magnetite as secondary minerals,and increase the adsorption efficiency of contaminants by clay,contributing to the removal of contaminants by clay minerals/Fe(II).The promotion degree of surfactants on formation edge surface bound Fe(II),secondary mineral composition on clay was consistent with the order of their effects on the removal of contaminants.The inhibitory effect of SDBS on nitrobenzene and p-nitrotoluene was mainly due to the decrease of the edge surface bound Fe(II),which was a dominant active species to reduce both contaminants.(5)The effect mechanism of surfactants on the removal of nitrobenzene contaminants by iron minerals/Fe(II)was also related to the hydrophobicity and electron-deficiency of the contaminants themselves.The highest of hydrophobicity of p-nitrochlorobenzene and electron-deficiency of its nitro group contributed to the highest removal efficiency of p-nitrochlorobenzene by iron minerals/Fe(II).The improved enrichment of contaminant on the reaction interface by surfactant was a dominant factor for the removal of p-nitrochlorobenzene.Therefore,the presence of SDBS also promoted the removal of p-nitrochlorobenzene.Although the hydrophobicity of p-nitrotoluene was higher than that of nitrobenzene,theelectron-deficiency of nitro group of p-nitrotoluene was lower than that of nitrobenzene,leading to the lowest reduction efficiency of p-nitrotoluene by iron minerals/Fe(II),and the lowest promotion of surfactant on the removal of iron minerals/Fe(II).Therefore,the effect of the same surfactant on the reduction of these three contaminants was listed in the order of p-nitrochlorobenzene > nitrobenzene >p-nitrotoluene.