Influencing Factors On Transport And Deposition Of Microplastics And Escherichia Coli In Saturated Porous Media

Because of their surface hydrophobicity and large specific surface area,microplastic particles are important carriers of organic pollutants.Meanwhile the pathogenic microorganism represented by E.coli widely exists in the drinking water source,which poses a serious threat to the safety of water quality.In this paper,microplastics and E.coli are taken as the research objects,and the four main influencing factors on the transport and deposition are comprehensively explored,including medium particle size,colloid particle size,medium surface charge property and ionic strength.The separate and synergistic transport experiments of E.coli and microplastics in saturated porous media under different conditions were carried out and the influencing mechanism of each factor was analyzed and discussed.The main results were summarizes as the follows:When the microplastics transport in porous media,both the decrease of media particle size and the increase of microplastics size can reduce the suction ratios of the breakthrough curves(the BTCs)and inhibit the transport.When the particle size ratio reaches a certain degree,the influence of straining is gradually reflected,and the increase of ionic strength in the system has a significant promotion on the straining effect.The modified glass beads have lower Zeta potential,which leads to stronger transport of microplastics,while the aluminum spheres have obvious inhibition effect on the transport of microspheres due to their surface positive charged,which indicated that the surface charge properties is dominant at this time.The positive surface charged coarse media can improve the retention and even make the retention rate of coarse media reach that of fine media.When E.coli transports in porous media,the BTCs of the two colloidal particles with similar Zeta potential are quite different.It is judged that the biological characteristics of E.coli are the main reason for the difference,which results in that the suction ratios of the BTCs of E.coli are higher.It was found that the media with lower Zeta potential,the transport of E.coli was weakly affected by the media particle size and ionic strength,indicating that the surface charge properties is dominant,and there is a critical secondary energy minimum between E.coli and strong negative surface charged media.When the same concentration of E.coli and microplastics transported in the porous media at the same time,the BTCs of 1.0μm microsphere has no obvious change,while the E.coli suction ratio decreased significantly,and the E.coli is more obvious affected by water environment factors than the individual transport.Therefore,it is speculated that microplastics are more susceptible to adsorption with porous media due to their uniform chemical properties.Moreover,it is very likely that there is a possibility of agglomeration and bridging between E.coli and microplastics,the hydraulic radius is increased,and the energy barrier and the initial(secondary)energy well of the interaction between the agglomerate and the medium particles are changing,which will lead to the development of favorable deposition and the decrease of transport.