Experimental Study On The Removal Of Polychlorinated Biphenyls And Chromium Compound Pollution In Groundwater By Modified Nano-zero Valent Iron

Heavy metals such as chromium,copper,lead,and persistent organic matter such as polychlorinated biphenyls enter the soil and groundwater,deteriorating the ecological environment of the groundwater,and seriously threaten human health.Modified nano-zero-valent iron is selected to carry out experimental research on the removal of polychlorinated biphenyls and chromium pollution in groundwater.Improve the removal effect of nano-iron on target pollutants through metal modification.Nano-iron materials are coated with sodium alginate to improve the antioxidant capacity of nano-iron materials.At the same time,the nano-iron material coated with sodium alginate is easy to separate from the reaction system to avoid blocking the infiltration reaction wall.The nano iron used in the experiment was prepared by the liquid-phase reduction method of reducing ferrous salt with potassium borohydride.The preparation method of metal-modified nano-iron is a two-step method,and the loading rate of the modified metal is3%.After the prepared nano iron material is added to the 2% sodium alginate solution and stirred evenly,it is transported by a peristaltic pump to a high place and dropped into a 5%calcium chloride solution to finalize the shape.Tetrachlorobiphenyl(PCB77)was used as the representative of PCB to study the removal of PCB77 by sodium alginate coated nickel modified nano-iron(SA-Ni/nZVI)in the experiment.From the aspects of SA-Ni/nZVI material dosage,initial PCB77 concentration,reaction temperature,initial pH,etc.,single-factor and multi-factor influence experiments were carried out on the effect of SA-Ni/nZVI material to remove PCB77.The conclusion is as follows,the removal rate of PCB77 by SA-Ni/nZVI material increases with the increase of the dosage of SA-Ni/nZVI material.When the concentration of SA-Ni/nZVI material is 3.00g/L,the highest removal rate of PCB77 by SA-Ni/nZVI material is 93.33%.The removal of PCB77 by SA-Ni/nZVI material is mainly based on the catalytic degradation of PCB77 by Ni/nZVI,and the adsorption and removal of PCB77 by sodium alginate is auxiliary.The remaining concentration of PCB77 decreases with the increase of the initial PCB77 concentration.The removal of PCB77 by SA-Ni/nZVI material is the fastest within 0.5h of the beginning of the reaction.Normal temperature conditions are conducive to the removal of PCB77;the removal rate of PCB77 first increases and then decreases with the increase of pH.Neutral conditions are conducive to the removal of PCB77 by SA-Ni/nZVI materials.After the reaction,the pH in the reactor tends to be weakly acidic.Under multi-factor conditions,after removing PCB77 from SA-Ni/nZVI material,the biggest influence on the remaining concentration of PCB77 is the initial PCB77 concentration.The biggest influence on the total iron concentration is the initial pH.The biggest influence on the nickel concentration of the reaction system is the dosage of SA-Ni/nZVI material.The experiment uses sodium alginate coated nano-iron(SA-nZVI)material to study the removal of hexavalent chromium.Design single-factor and multi-factor effects experiments to explore the effects of SA-nZVI material dosage,initial hexavalent chromium concentration,reaction temperature,initial pH and other conditions on the removal of hexavalent chromium from SA-nZVI materials.The effects of aging time,reuse and nZVI coating amount on the removal of hexavalent chromium from SA-nZVI materials are also analyzed.The conclusion is as follows,the removal rate of hexavalent chromium by SA-nZVI material increases firstly and then decreases with the increase of the concentration of SA-nZVI material.When the dosage of SA-nZVI material is 0.32g/L,it has the highest removal rate of hexavalent chromium,which is 99.20%.The removal of hexavalent chromium by SA-nZVI is mainly based on the chemical reduction and removal of hexavalent chromium by nZVI,which is accompanied by the adsorption of sodium alginate to hexavalent chromium.The removal rate of hexavalent chromium by SA-nZVI decreases with the increase of the initial concentration of hexavalent chromium.A higher initial concentration of hexavalent chromium can make SA-nZVI material give full play to its ability to remove hexavalent chromium;The lower initial concentration of hexavalent chromium can make the SA-nZVI material fully remove hexavalent chromium.The removal of hexavalent chromium by SA-nZVI material decreases with the increase of the initial pH;a lower initial pH is beneficial to increase the removal rate of hexavalent chromium by SA-nZVI material.Higher reaction temperature accelerates the removal of hexavalent chromium by SA-nZVI material,however,the SA-nZVI material did not improve the removal rate of hexavalent chromium.The removal rate of hexavalent chromium by SA-nZVI material decreases as the ageing time of SA-nZVI material increases.The sealing conditions are conducive to the preservation of SA-nZVI materials.The oxidation of SA-nZVI material is related to the oxygen in the air or water that the material comes into contact with.When the amount of sodium alginate coated nano iron is higher,the removal rate of hexavalent chromium by SA-nZVI material is faster and the removal rate is lower;When the amount of sodium alginate coated nano-iron is low,the removal rate of hexavalent chromium by SA-nZVI material is slower and the removal rate is higher.The highest utilization times of SA-nZVI and nZVI materials for removing hexavalent chromium is twice.Under multi-factor conditions,SA-nZVI material has the greatest influence on the removal rate of hexavalent chromium is the initial concentration of hexavalent chromium.The most important influence on the total iron concentration of the reaction system is the dosage of SA-nZVI material.Finally,the paper explored the removal rules and removal effects of SA-Ni/nZVI materials on PCB77 and hexavalent chromium under the PCB77 and hexavalent chromium compound pollution system.Study the effect of SA-Ni/nZVI material dosage,hexavalent chromium/PCB77 concentration ratio,reaction temperature and initial pH on the removal of PCB77 and hexavalent chromium by SA-Ni/nZVI material,and the total iron and nickel concentration of the reaction system after the end of the reaction.The conclusions are as follows.After the SA-Ni/nZVI material acts on the reaction system,the concentration ratio of Cr(?)/PCB77 is the biggest influence on the remaining PCB77 of the reaction system under the compound pollution condition.The presence of hexavalent chromium has little effect on the removal of PCB77 by SA-Ni/nZVI.The biggest influence on the remaining hexavalent chromium is the concentration of SA-Ni/nZVI material.The biggest influence on the total iron concentration is the Cr(?)/PCB77 concentration ratio,and the biggest influence on the nickel concentration is the initial pH.