Earthworms As Effective Assistants For Enhanced Transport Of Nanoscale Zerovalent Iron And Pollutant Removal

Nanoscale zerovalent iron(NZⅥ)particles have received considerable attention forin-situ remediation of contaminated soil and groundwater.NZⅥ particles can effectively degrade chlorinated solvents,organic dyes,organo-chlorine pesticides,and inorganic pollutants,such as perchlorate,nitrate,and heavy metal ions.The advantages of using NZⅥ particles compared to traditional iron powders approaches contaminants include the high surface area,high reactivity,and the transport and delivery properties.These advantages of NZⅥ particles are useful to help it directly access and target the contaminants.NZⅥ particles are known to exhibit a core–shell structure,with an Fe3O4 and Fe2O3 shell around an Fe0 core.Due to the van der Waals attractive force,dipole interactions and the intrinsic ferromagnetism,NZⅥ particles tend to aggregates.Aggregate NZⅥ particles will initially be transported only a few centimeters or less,and it don’t being transported to the target area and can not degrade contaminants,so that it is still difficulties to bringing NZⅥ particles into contact with the contaminants in source treatment applications.The Tufenkji-Elimelech model is the most comprehensive and recognized model to description colloid migration theory,T-E model considered full force include Brownian diffusion,interception,and gravitational sedimentation in the process of particle precipitation.Through the T-E model we can get the porosity affect the transport of NZⅥ particles.Collector efficiency has decreased with the increase of porosity,and collector efficiency is significantly decreased with diameter of particle increase.The transport of NZⅥ could be increased with the decreased of collector efficiency.Chromium(Cr)is a typical toxic heavy metal in soil and groundwater,which has been extensively used in leather tanning,metal finishing,and other industrial applications.As we know,Cr(Ⅵ)is more toxic and soluble than Cr(III),NZⅥ particles has strong reducing ability,and convert Cr(Ⅵ)to Cr(III)quickly.In this work,we want to increase the porosity of quartz sand by the earthworms’ movement to promote the transport of NZⅥ particles in quartz sand.And we investigate Cr(Ⅵ)removal efficiencies by the system of earthworms and NZⅥ in quartz sand.Earthworms as effective assistants for enhanced transport of NZⅥ and groundwater pollutant removal,which the increase of porosity of sand grains was 47.5% through themovements of earthworms,and promote the transport efficiency of NZⅥ particles was34.43%,it is easy to bringing NZⅥ particles into contact with the contaminants in source treatment applications in soil.we investigate Cr(Ⅵ)removal efficiencies by the system of earthworms and NZⅥ in quartz sand,The Cr(Ⅵ)removal efficiency of mixture system was89%,and it is not the simple superimposed,the reason mainly duo to NZⅥ particles could contact with and reduction of Cr(Ⅵ)by the activity of earthworms best.