Heavy Metal Reduction Study On Sewage Pretreatment By Fe₃O₄ And Sludge Treatment By Electrokinetic Method

Heavy metal pollution is common pollution problem in sewage treatment.The heavy metals in the sewage will greatly affect the treatment effect of sewage,and most of them will be transferred to the excess sludge during the sewage treatment,which will affect the environmental safety and cause serious obstacles to the utilization of the sludge.Therefore,how to effectively deal with the problem of heavy metals in sewage and reduce the heavy metal content in sludge is one of the key points of current water treatment.In this study,chromium(Cr)and copper(Cu),which are widely present and typical in the existence form,were selected as the research object.The adsorption method and the electrokinetic method were The pre-removal of heavy metals in sewage by magnetic adsorption technology and the treatment of heavy metals in sludge by electric technology were used to achieve the purpose of reducing heavy metals in sewage and sludge.Pretreatment of sewage by adsorption method using magnetic magnetite(Fe3O4)as adsorbent to reduce heavy metals entering the sludge from sewage.In this study,the different effect factors including pH,adsorbent dosage,initial concentration of heavy metals,common anions and cations in water on the simultaneous adsorption efficiency of Cr and Cu in sewage were investigated.The adsorption mechanism was studied by analyzing Zeta potential,FTIR infrared of Fe3O4 and the morphological analysis of Cr and Cu under different pH conditions.At the same time,adsorption isotherms,adsorption thermodynamics and kinetics were studied.The results show that Fe3O4 exhibits good adsorption properties for Cr and Cu,the adsorption removal effect varies with pH and other conditions.The pH is a decisive factor,directly changing the zeta potential of Fe3O4 and the existence form of Cr and Cu.The adsorption removal efficiency of Cr and Cu varies with pH,the low pH value facilitates the adsorption removal of Cr,while the high pH value facilitates the adsorption removal of Cu.The optimum pH for adsorption of Cr and Cu are 2 and 7,respectively,and the favorable pH value for combined removal is 4;The increase of adsorbent dosage can increase the adsorption effect of Cr and Cu.With the increase of initial concentration of solution,the removal rate and adsorption amount of Cr and Cu decreased and increased respectively.Under the experimental conditions(initial concentration of Cr and Cu is lmg/L),the adsorption capacity of Cr and Cu were 8.67mg/g and 18.61mg/g,respectively.The change of temperature and the applied magnetic field have little effect on the adsorption results.In the presence of various common anions and cations,phosphorus interfere with the adsorption of Cr.The adsorption process conforms to the Langmuir adsorption equation and the second-order kinetics.Fe3O4 exhibited good adsorption performance of heavy metals in sewage and easy be separated and recovered under magnetic field.The removal rate of Cr and Cu reached 89%and 96%,respectively.Establish a reaction operating system for electrokinetic treatment of Cr and Cu in sludge.By changing the experimental conditions,the influencing factors in the electrolysis process were explored,and the properties of the sludge and the material flow of Cr and Cu were analyzed.The results show that the use of three-slot electrolyzer and the installation of anion and cation membrane can effectively solve the problem of acid-base migration zone and sludge acidification,and achieve effective removal of heavy metals in sludge.The pH is the key influencing factor,the change of Cr and Cu removal rate is opposite with the change of pH,the removal rate of Cr increases with the increase of pH value,and the removal rate of Cu decreases with the increase of pH value.The optimum pH value of the coexistence system is 5?7,which is related to the surface charge of the sludge and the existence of Cr and Cu depending on the pH.The higher the voltage,the better the effect.Considering this,30V electrolysis voltage was used for the experiment.Under favorable conditions,the removal rate of Cr and Cu in sludge by electrokinetic method is 42%and 45%,respectively.