Effect Of Escherichia Coli On Co-transport Of Environmental Nanoparticles And Heavy Metal Chromium

"The construction of ecological civilization is a fundamental plan for the sustainable development of the Chinese nation."With rapid economic development,industrial pollution worsens,leading to a lot of pollutions in soils and groundwater.The widespread use of plastic products and the discharge of a large amount of chromium-containing wastewater in industrial have caused the pollution of microplastics and heavy metals in soil and groundwater.Iron nanoparticles（nFe）are widely used for Cr（VI）remediation due to the high reactivity and unique adsorption and reduction capacity.In situ remediation by injecting nFe particles directly into the contaminated place has attracted more and more attention because of its economical,and whether nFe particles can transport to the target area become the focus of research.Meanwhile,Micro/Nano-plastic（NPs）,as pollutants,will transport and ultimately affect the safety of the ecosystem through bio-enrichment.Therefore,it is necessary to investigate the transport behavior of nFe and NPs in environmental systems.Because the soil environment contains complex factors such as microorganisms,clay minerals and phosphate,the transportability of nFe and NPs in soil is not well understood.In this study,the influence of E.coli and phosphate on the transport and retention of nFe and NPs in the quartz sand column and the transport mechanism were investigated by column experiments.With the measurement of Zeta potential and hydraulic radius,adsorption kinetics and adsorption equilibrium experiments,the result was explained in detailed.The two-site kinetic attachment model（TSKAM）was used to simulate the breakthrough curves（BTCs）of two environmental nanoparticles in different systems to further explain their transport behavior.Moreover,by studying the co-transport of nFe and Cr（VI）,the mechanism was revealed and provided guide for engineering applications.The results of the experiment were as follows:（1）The influence of E.coli and phosphate on the transport behavior of NPs of two sizes was investigated.The Sedimentation of NPs was investigated by aggregation experiments.The results indicated that the higher mobility of NPs of 20 nm,and the presence of phosphate would promote the agglomeration of NPs.With the addition of phosphate,ionic strength（IS）in the solution was enhanced and the transport of NPs decreased.With the addition of E.coli,the surface of NPs carried more negative charges and the mobility of NPs was better.In 200m M Na Cl,the phosphate was adsorbed by E.coli instead of 80 nm NPs in the coexistence of E.coli and P,leading to the transportability was the same as that of E.coli alone;while the 20 nm NPs agglomerated with E.coli,most of the phosphate exists in the solution,which increases the ionic strength,leading to the transport of NPs decreased.In 1 m M CaCl₂,the transport of 80 nm and 20 nm NPs was decreased in the presence of E.coli and phosphate.（2）The influence of the presence of E.coli and phosphate on the transport behavior of green synthetic nFe particles under different conditions was investigated.Transport experiments indicated that the transport of nFe decreased with the increase of ion concentration（IC）.Meanwhile,under the same IC,nFe particles performed better mobility at pH 8.0,which was related to the surface surface of the nFe under alkaline conditions due to the effect of compressing the duplex layer.E.coli has different effects on the transport of nFe under different pH conditions.At pH 6.0,E.coli caused the nFe carry more negative charges on the surface and enhanced the transport.At pH 8.0,nFe agglomerated with E.coli,and the aggregation blocked the pores of the quartz sand and inhibited the transport of nFe.Similarly,phosphate enhanced the transport of nFe at pH 6.0 rather inhibited the transport of nFe at pH 8.0 due to the adsorption of phosphate to nFe particles was different in different pH.Moreover,the nFe adsorbed phosphate,which enhanced the transport of nFe When E.coli and phosphate are present at the same time at pH 6.0.At pH 8.0,E.coli preferentially adsorbed phosphate,resulting in the retention of nFe increasing on the quartz sand.（3）E.coli and phosphate were selected as influencing factors to study the mechanism of the co-transport of nFe and chromium.By exploring the co-transport of nFe and Cr（VI）under different conditions,the ability and transport ability of nFe to removal heavy metals under different environmental systems are investigated.In ternary system of E.coli and phosphate,both inhibited the transport of nFe.However,the presence of E.coli promoted the adsorption and the presence of phosphate promoted the reduction of Cr（VI）by nFe particles.The transport of nFe in the coexistence of E.coli and P was the same as that with E.coli alone.The mechanism of the co-transport of nFe particles and Cr（Ⅲ）under different systems was further studied.In presence of E.coli and phosphate inhibited the transport of nFe,and the presence of E.coli also inhibited the transport of Cr（Ⅲ）.Because of competitive adsorption of phosphate and Cr（Ⅲ）by nFe,Cr（Ⅲ）was not adsorbed by nFe particles,so the transport of Cr（Ⅲ）increased.