Removal of Pb(Ⅱ) from Wastewater and Polluted Soil by Electrical Technologies
【摘要】：In the present study, the removal of Pb~(2+)from wastewater and polluted soil was carriedout using the principles of electroremediation. In the first section (wastewater treatment) theintegrated electrodialysis, electrolysis, and adsorption on cation exchange membrane wasproposed to achieve (a) secure outlet discharge complying with the established legislationlevels of1mg L~(-1), water reuse, and recovery of Pb~(2+)with high purity. However, in the secondsection (polluted soil remediation) a new process for soil electrokinetic remediation (SEKR)known as perforated cathode pipe SEKR system (PCPSS) was introduced to (a) overcomeSEKR drawbacks and (b) improve pollutant removal.
The integrated between wastewater treatment and polluted soil remediation wasproposed owing to (a) during SEKR the pollutants move through soil fluid; accordinglyrealistic simulations require study the behavior of metal ions in the water system and (b) thehigh affinity between wastewater and polluted soil i.e., soil pollution occurs as a result ofuntreated wastewater and vice versa. So, both wastewater and polluted soil treatments shouldto be carried out simultaneously. To study the effect of influential parameters quite preciselyTaghuci approach was utilized. Also, this approach offers prediction of the optimal level forthese parameters, and providing an estimate for the relative contribution of each factor.
After determining the optimal levels of electrodialysis (ED) influential parameters theoutlet dilute solution can be reduced to15.7~(-1)7.1mg L~(-1)from initial concentration600mg L~(-1).Meanwhile, the associated NO_3
Ncoming from the source of Pb(NO3)2was alsodecreased to4-5mg L~(-1)from initial concentration173.8mg L~(-1). According to theinternational legislation permission level of Pb~(2+)containing solutions the outlet discharge ofPb~(2+)must be lower than1mg L~(-1). Pb~(2+)concentration of15~(-1)7mg L~(-1)was processed viaadsorption of cation exchange membrane (CEM). This was carried out by circulating thedilute solution coming from ED dilute inside another ED unit that regenerated with tap water at60V for one hour. Circulating the dilute solution inside another ED unit can be decreasedPb~(2+)concentration to1.0~(-1).3mg L~(-1)and1.3~(-1).9mg L~(-1)for the dilute and concentrate outletstreams, respectively. During the performance of ED the concentrate solution should to betreated. Accordingly, electrolysis treatment was proposed to process the concentrate solution.High concentration of Pb~(2+)(1500mg L~(-1)) rapidly decreased during the first90min, afterwardthe outlet solution kept constant at138~(-1)56mg L~(-1)which represented89-91%recovery rate.The associated NO_3Nalso depleted with a removal rate of30-33%in form of gases.
Soil electrokinetic remediation (SEKR) is a proven technique for treating inorganic,organic, and radionuclide pollutants, particularly in fine-grained soils. The main obstacle toimplementing SEKR is the high pH zone adjacent to the cathode surface, which adverselyaffects electromigration and electroosmosis mechanisms. There have been many attempts toovercome this drawback, but most of the intended solutions are impractical due to excessivecost or the need for chemical additives. We developed a new process for soil electrokinetictreatment in which the cathode is a vertical perforated pipe inserted into the soil. Theremovals of Pb~(2+)and Zn~(2+)from kaolinite were evaluated using the Taguchi approach, inwhich the effects of five four-level parameters (operation time, electrical potential, cathodegap, concentration, and hydrostatic head) were analyzed. The perforated cathode pipe SEKRsystem (PCPSS) was designed to investigate vertical soil electrokinetic remediation, whichhas not been extensively studied. The formation of [PbO_2H]-was the main obstacle hinderedthe migration of Pb~(2+)towards the cathode in either horizontal or vertical system. The removalof Zn~(2+)was much more satisfactory compared with Pb~(2+). The highest removed Pb~(2+)was42.7%, however the highest removed Zn~(2+)was93.5%. Improved electroosmosis throughcavitation was observed. In the PCPSS the formation of insoluble Pb~(2+)electrodeposits nearthe cathode that may be used to form a barrier to prevent waste leakage. Finally, theperformance of SEKR horizontal system in terms of Pb~(2+)removal and acid advection wasmuch better when experiments were performed without hydrostatic water head.