The Preparation Of Nano-composite Beads And Its Research Of Adsorption Effect On Typical Pollutant Removal In Runoff

Stormwater runoff pollution seriously threatens the water environment of the city.The filtration system is one of the effective technologies to control the stormwater pollution to the receiving water,and the infiltration materials is the core component of the system to remove pollutants.Conventional infiltration materials have low energy efficiency for the removal of heavy metals,polycyclic aromatic hydrocarbons,and nitrogen,phosphorus and other pollutants contained in runoff rainwater.Therefore,the development and improvement of infiltration materials are particularly important.Based on the previous research which was successfully synthesized the nano zero-valent iron beads,this paper comprehensively investigates the removal efficiency and mechanism of heavy metal Pb²⁺,Cu²⁺,and Zn²⁺by nano-zero-valent iron beads.The kinetic adsorption of three kinds of heavy metals on the nano-zero-valent iron beads is more consistent with the pseudo-second-order model,indicating that chemical adsorption is a key factor affecting the adsorption rate,and the order of the adsoption rate is Cu²⁺>Pb²⁺>Zn²⁺,which is consistent with their respective reduction potentials.The isothermal adsorption of Pb²⁺,Cu²⁺,Zn²⁺by nano zero-valent iron beads is in line with the Langmuir model.The maximum adsorption capacity of the three heavy metals is Pb²⁺?16.02 mg/g?>Cu²⁺?5.24 mg/g?>Zn²⁺?2.31 mg/g?.The pH value of the solution has a great influence on the adsorption of heavy metals by the nano-zero-valent iron beads,and the ionic strength has no significant effect.In order to improve the removal effect of the small beads on mixed inorganic and organic contaminants,carbon nanotubes were added during the synthesis of nano-zero-valent iron beads.The effect of many factors on their performance was examined,and the composition of each component was determined.The best ratio of component is zero-valent iron powder/Pumice/Carbon nanotubes/Polyvinyl alcohol?1:0.5:0.1:3,g/g?.The effect of the removal of phenanthrene and Pb²⁺alone and in common was studied.Kinetic studies have shown that the effect of composite beads on the adsorption of phenanthrene and Pb²⁺is different.The isotherms indicated that the composite beads had superior phenanthrene and Pb²⁺removal efficiency and all fitted to the Langmuir model.The adsorption capacities of the composite beads for phenanthrene and Pb²⁺and in mixture systems were 0.16 mg/g and 11.6 mg/g,respectively.The effect of p H and ionic strength on the removal of phenanthrene and Pb²⁺for composite beads is relatively small,and the nanocomposite beads have strong environmental adaptability.The prepared nanocomposite beads basically have the removal efficiency of NO3^--N,TN and TP up to 80%.The nano zero-valent iron beads have higher NO3^--N removal ability than the composite beads,and the mechanisms include redox and co-precipitation.For TN and TP,the removal effect of nano-composite beads is better.In particular,the adsorption amount of TP is much higher than that of nano-zero-valent iron beads.The changes of pH and ion amount have little effect on the removal of NO3^--N,TN,and TP by composite beads.Based on all the above results,it can be shown that the nanocomposite beads can be used as infiltration materials to control rainwater pollution in each infiltration facilities.