Optimization Of 2,4-Dichlorophenol Removal By Modified Nanoscale Zero-Valent Iron In Groundwater Using Response Surface Methodology

2,4-Dichlorophenol(2,4-DCP)is widely present in printing,dyeing,papermaking,pharmaceuticals,and pesticides wastewater,which enters into groundwater through chemical wastewater discharge,pesticide use,etc.,and causes serious pollution to groundwater.Due to its toxicity and carcinogenic,teratogenic,mutagenic effect,it can lead to great threaten to the environment and humans.There are chlorine atom and aromatic ring in the molecule of 2,4-DCP,so it has strong stability in the environment.As a result,it is difficult to be biodegraded.Many studies have shown that nanoscale zero-valent iron(n ZVI)can commendably remove 2,4-DCP from groundwater,which has received extensive attention.In this study,n ZVI、Pd/Fe、CMC-Fe、CMC-Pd/Fe were prepared by liquid-phase reduction method,and were characterized by SEM,XRD,and FTIR.The dispersion properties and migration properties of CMC-Pd/Fe in porous media by colorimetric tube settlement experiments,settlement curve,sand migration experiments of sand column with multi factors,(such as CMC modification amount,porous media particle size,and flow rate).The removal of 2,4-DCP in groundwater by CMC-Pd/Fe was studied emphatically.The effect of different dosage,palladium ratio,initial p H,contaminant concentration,and Ca2+ ion concentration on the removal of 2,4-DCP in groundwater by CMC-Pd/Fe were investigated through batch experiments.Finally,using a two-parameter pseudo-first-order kinetics model to fit the experimental data.Based on the results of batch experiments,a four-factor and five-level optimization experiment was designed by central composite design(CCD)method using response surface methodology(RSM).The effects of the interactions of CMC-Pd/Fe dosage,initial p H,reaction time,and contaminant concentration on the removal of 2,4-DCP from groundwater by CMC-Pd/Fe were studied.The results show as follows:(1)The prepared four kinds of nano-iron n ZVI,Pd/Fe,CMC-Fe,CMC-Pd/Fe are all nanoscale.The size of nano-iron particles modified with CMC is obvious less than n ZVI、Pd/Fe and its dispersibility is also better.All of the four kinds of nano-iron particles contain Fe0.Four of them all contain Fe0 and Fe2O3 or Fe3O4,forming a spherical structure with a surface shell of iron oxide and a core of elemental zero-valent iron..When CMC is combined with Fe0 or Pd/Fe bimetal,the hydroxyl and carboxyl groups are shifted significantly and the intensity is also correspondingly changed.The results show that CMC is bound to nanoparticles through the chelation of hydroxyl and carboxyl groups with Fe0 or Pd/Fe.(2)The results of the colorimetric tube settlement experiments and settlement curves,show that the dispersion properties of CMC modified nano-iron is better,and that the inorganic catalyst Pd has little effect on the dispersion properties of nano-iron.Under the same conditions,the migration performance of CMC-Fe and CMC-Pd/Fe in porous media is significantly better than n ZVI and Pd/Fe.With the increase of CMC-Pd/Fe concentration,dosage of CMC,injection flow rate,and particle size of porous media,CMC-Pd/Fe has a better migration performance in the porous medium.(3)The order of the removal efficiency for 2,4-DCP by the four kinds nano-iron is n ZVI<Pd/Fe<CMC-Fe<CMC-Pd/Fe.CMC-Pd/Fe has the best removal efficiency.With the increase of dosage and palladium ratio,the decrease of p H and contaminant concentration,the removal efficiency of 2,4-DCP by CMC-Pd/Fe increases.However,if the p H is too low or too high,it is not bennefit to the reaction.The total hardness component in the groundwater Ca2+ can inhibit the removal of 2,4-DCP.The higher the concentration is,the greater the inhibition is.The removal of 2,4-DCP by CMC-Pd/Fe under different conditions can be well described with a two-parameter pseudo-first-order kinetics model.(4)In Response Surface Methodolog(RSM)optimization experiments,according to the results of model fitting,variance analysis and residual verification,the experimental model is significant.There is a good correlation between experimental values and predicted values.RSM can be used to optimize the removal of 2,4-DCP by CMC-Pd/Fe.The effects of the four variables CMC-Pd/Fe dosage,initial p H of the solution,reaction time,and contaminant concentration on the removal rate are significant.The percentage of contribution to 2,4-DCP removal is CMC-Pd/Fe dosage>initial p H of the solution>reaction time>contaminant concentration.There is a certain amount of interaction between variables.