Electrochemical Removal of Zinc and Nickel Ions from Wastewater Using Flat Plate Electrodes

Simulated wastewater containing 20ppm of Zn++, 20ppm of Ni++ was treated using an electrochemical technique. This synthetic wastewater was used to simulate the wastewater from metal finishing industries. A rectangular bath integrated with an electrochemical cell consisting of flat plate electrodes (the stainless steel anode and aluminum cathode) was used in the treatment. Potassium sulfate was used as a supporting electrolyte to enhance the removal of Zn++ and Ni++. The effects of volumetric liquid flux, pH and electrode surface area on Zn++ and Ni++ removal were investigated. All experiments were performed at 25ºC and at an applied voltage of 4V. When volumetric flux was raised from 0.0092 to 0.0277m³.m-².s-¹, an increasing trend of the Zn++ and Ni++ removal was observed. The maximum metal removal was observed at a volumeteric liquid flux of 0.0231m³.m-².s-¹. Zn++ and Ni++ were removed by 80% and 34%, respectively, after 48 hours of electrochemical treatment. Moreover, an increase in the removal of Zn++ and Ni++ was observed when the pH was varied from 3.5 to 6.5. The maximum removal of Zn++ and Ni++, 97% and 62%, respectively, occurred at a volumetric liquid flux of 0.0231m³.m-².s-¹ and a pH of 6.5. The experimental values showed a similar increasing trend in the removal of Zn++ and Ni++, when the electrode surface area was increased from 0.024m² to 0.048m²; the removal of Zn++ and Ni++ improved by 14% and 12%, respectively. However, there was no major change in the removal of Zn++ and Ni++ between flat plate and corrugated plate electrodes.

Electrochemical removal of zinc and nickel ions from wastewater using porous electrodes

Simulated wastewater containing Ni++ and Zn++ was treated using an electrochemical cell. Porous aluminum cathode and porous stainless steel anode were used in a flow-through configuration. For porous catholdes, both aluminium foam and corrugated aluminum plates having perforations were used. To study the effects of applied voltage and volumetric liquid flux on the removal of Ni++ and Zn++, the electrochemical cell was operated for 48 hours at different applied voltages of 5, 10, 15, 20 and 25 V, and at different volumetric liquid fluxes both in the laminar (0.00471 and 0.00943 m³.m-².s-¹) and turbulent regimes (0.01414, 0.01886 and 0.02357 m³.m-².s-¹). For the maximum removal of both nickel and zinc ions, the optimum applied voltage and volumetric liquid flux were found to be 12 V and 0.02357 m³.m-².s-¹, respectively; under these operating conditions, the concentrations of Ni++ and Zn++ in the simulated wastewater were reduced by 85.5% and 98%, respectively. Operating beyond an applied voltage of 12 V, the removal of Zn++ was slightly improved and achieved a maximum value of 99.05% at 25 V; however, an opposite trend was observed in case of Ni++ removal, which finally decreased to 56% at 25 V., because of the excessive precipitation of Ni++ as nickel hydoroxide.

Combined Electrochemical & Biological Treatment of Industrial Wastewater Using Porous Electrodes and a Packed Bed Aerator

Zinc, nickel and propylene glycol methyl ether were simultaneously removed from simulated wastewater in a column containing a counter-current packed bed and an electrochemical cell. Rectangular porous aluminum foam cathode and porous stainless steel anode were used in a plate-in-tank configuration. During combined biological and electrochemical treatment the wastewater flux was 0.00183 and 0.00915 m³.m̈².s̈¹ at a constant volumetric air flux of 0.0518 m³.m̈².s̈¹. Over a 72 hour treatment period the BOD5 was reduced by 32% and 55% for each volumetric liquid flux, respectively; zinc was reduced by 98% for both fluxes, and nickel was reduced by 95% and 82%, respectively. For sole electrochemical treatment of 48 hours, laminar and turbulent flow conditions were studied. Operating in the laminar flow region of 0.00183 and 0.00915 m³.m̈².s̈¹; zinc was reduced by 95% for both fluxes; nickel was reduced by 80% and 60%, respectively. For the turbulent region in the electrochemical cell, the volumetric liquid fluxes were 0.0137, 0.0229, 0.0321 and 0.0366 m³.m̈².s̈¹. Per cent reduction of both zinc and nickel in this region was less than that encountered in laminar flow. For all the fluxes in the turbulent region zinc was reduced by 82%; nickel was reduced by 55% at a flux of 0.0137 m³.m̈².s̈¹ and 60% at a flux of 0.0366 m³.m̈².s̈¹. Increasing electrode surface area as a means of improving heavy metal reduction by using rectangular porous material in a plate-in-tank configuration is not a viable option at higher volumetric liquid fluxes.

Electrochemical removal of zinc and nickel ions from wastewater using porous electrodes

Simulated wastewater containing Ni++ and Zn++ was treated using an electrochemical cell. Porous aluminum cathode and porous stainless steel anode were used in a flow-through configuration. For porous catholdes, both aluminium foam and corrugated aluminum plates having perforations were used. To study the effects of applied voltage and volumetric liquid flux on the removal of Ni++ and Zn++, the electrochemical cell was operated for 48 hours at different applied voltages of 5, 10, 15, 20 and 25 V, and at different volumetric liquid fluxes both in the laminar (0.00471 and 0.00943 m³.m-².s-¹) and turbulent regimes (0.01414, 0.01886 and 0.02357 m³.m-².s-¹). For the maximum removal of both nickel and zinc ions, the optimum applied voltage and volumetric liquid flux were found to be 12 V and 0.02357 m³.m-².s-¹, respectively; under these operating conditions, the concentrations of Ni++ and Zn++ in the simulated wastewater were reduced by 85.5% and 98%, respectively. Operating beyond an applied voltage of 12 V, the removal of Zn++ was slightly improved and achieved a maximum value of 99.05% at 25 V; however, an opposite trend was observed in case of Ni++ removal, which finally decreased to 56% at 25 V., because of the excessive precipitation of Ni++ as nickel hydoroxide.

Combined Electrochemical & Biological Treatment of Industrial Wastewater Using Porous Electrodes and a Packed Bed Aerator

Zinc, nickel and propylene glycol methyl ether were simultaneously removed from simulated wastewater in a column containing a counter-current packed bed and an electrochemical cell. Rectangular porous aluminum foam cathode and porous stainless steel anode were used in a plate-in-tank configuration. During combined biological and electrochemical treatment the wastewater flux was 0.00183 and 0.00915 m³.m̈².s̈¹ at a constant volumetric air flux of 0.0518 m³.m̈².s̈¹. Over a 72 hour treatment period the BOD5 was reduced by 32% and 55% for each volumetric liquid flux, respectively; zinc was reduced by 98% for both fluxes, and nickel was reduced by 95% and 82%, respectively. For sole electrochemical treatment of 48 hours, laminar and turbulent flow conditions were studied. Operating in the laminar flow region of 0.00183 and 0.00915 m³.m̈².s̈¹; zinc was reduced by 95% for both fluxes; nickel was reduced by 80% and 60%, respectively. For the turbulent region in the electrochemical cell, the volumetric liquid fluxes were 0.0137, 0.0229, 0.0321 and 0.0366 m³.m̈².s̈¹. Per cent reduction of both zinc and nickel in this region was less than that encountered in laminar flow. For all the fluxes in the turbulent region zinc was reduced by 82%; nickel was reduced by 55% at a flux of 0.0137 m³.m̈².s̈¹ and 60% at a flux of 0.0366 m³.m̈².s̈¹. Increasing electrode surface area as a means of improving heavy metal reduction by using rectangular porous material in a plate-in-tank configuration is not a viable option at higher volumetric liquid fluxes.

Electrochemical Removal of Zinc and Nickel Ions from Wastewater Using Flat Plate Electrodes

Simulated wastewater containing 20ppm of Zn++, 20ppm of Ni++ was treated using an electrochemical technique. This synthetic wastewater was used to simulate the wastewater from metal finishing industries. A rectangular bath integrated with an electrochemical cell consisting of flat plate electrodes (the stainless steel anode and aluminum cathode) was used in the treatment. Potassium sulfate was used as a supporting electrolyte to enhance the removal of Zn++ and Ni++. The effects of volumetric liquid flux, pH and electrode surface area on Zn++ and Ni++ removal were investigated. All experiments were performed at 25ºC and at an applied voltage of 4V. When volumetric flux was raised from 0.0092 to 0.0277m³.m-².s-¹, an increasing trend of the Zn++ and Ni++ removal was observed. The maximum metal removal was observed at a volumeteric liquid flux of 0.0231m³.m-².s-¹. Zn++ and Ni++ were removed by 80% and 34%, respectively, after 48 hours of electrochemical treatment. Moreover, an increase in the removal of Zn++ and Ni++ was observed when the pH was varied from 3.5 to 6.5. The maximum removal of Zn++ and Ni++, 97% and 62%, respectively, occurred at a volumetric liquid flux of 0.0231m³.m-².s-¹ and a pH of 6.5. The experimental values showed a similar increasing trend in the removal of Zn++ and Ni++, when the electrode surface area was increased from 0.024m² to 0.048m²; the removal of Zn++ and Ni++ improved by 14% and 12%, respectively. However, there was no major change in the removal of Zn++ and Ni++ between flat plate and corrugated plate electrodes.

Effect of temperature and pH on biological oxidation of antifreeze coolant using a packed column aerator

Simulated wastewater containing 0.75% (v/v) antifreeze was treated biologically using a 0.18-m diameter packed column aerator with a 0.4-m higth packed bed of 20-mm polypropylene spheres. Effects of liquid temperature and pH on the biological oxygen demand (BOD₅) removal were investigated. All experiments were performed under an air flux of 0.0080 kg.m-².s-¹ and a liquid flux of 14.8 kg.m-².s-¹. An increasing trend of the BOD₅ removal with temperature was observed when liquid temperature was increased from 16 to 32 ºC by 4-degrees increments. When the wastewater pH was increased from 4 to 10 (by one-pH unit increments), the BOD₅ removal was increased by 18%. The averaged BOD₅ removal in the order of 90% (from the initial value of about 900 mg/L down to 80mg/L) was obtained after 96 hours of treatment. The stripping effect was accounted for about 75 mg/L of the overall BOD₅ change, i.e. about 9% of the overall BOD₅ removal. In addition, the BOD₅ removal due to the biomass in the packed column was also monitored. A decrease of about 15% in the BOD₅ removal was observed without packing in the packed column aerator.

Effect of temperature and pH on biological oxidation of antifreeze coolant using a packed column aerator

Simulated wastewater containing 0.75% (v/v) antifreeze was treated biologically using a 0.18-m diameter packed column aerator with a 0.4-m higth packed bed of 20-mm polypropylene spheres. Effects of liquid temperature and pH on the biological oxygen demand (BOD₅) removal were investigated. All experiments were performed under an air flux of 0.0080 kg.m-².s-¹ and a liquid flux of 14.8 kg.m-².s-¹. An increasing trend of the BOD₅ removal with temperature was observed when liquid temperature was increased from 16 to 32 ºC by 4-degrees increments. When the wastewater pH was increased from 4 to 10 (by one-pH unit increments), the BOD₅ removal was increased by 18%. The averaged BOD₅ removal in the order of 90% (from the initial value of about 900 mg/L down to 80mg/L) was obtained after 96 hours of treatment. The stripping effect was accounted for about 75 mg/L of the overall BOD₅ change, i.e. about 9% of the overall BOD₅ removal. In addition, the BOD₅ removal due to the biomass in the packed column was also monitored. A decrease of about 15% in the BOD₅ removal was observed without packing in the packed column aerator.

Enhancing Ion Flotation through Decoupling the Overflow Gas and Liquid Fluxes

Conventional ion flotation is hydrodynamically constrained by coupling of the gas flux and liquid flux that report to the concentrate. This constraint has greatly limited the industrial application of ion flotation, despite its remarkable effectiveness in extracting ionic species down to very low concentrations, of order 1 ppm. Previous work demonstrated that these hydrodynamic constraints could be significantly relaxed using the reflux flotation cell (RFC), a system incorporating parallel inclined channels to improve bubble-liquid segregation. However, it was found that bubble coalescence placed an additional limit on performance. In this study the impact of coalescence was minimized by reducing the volume reduction from 20 to 5, ensuring sufficient liquid reported to the concentrate with the bubbles. Under these conditions, an equivalent adsorptive recovery was achieved using the RFC at feed fluxes up to four times those in the conventional system. The maximum adsorptive extraction rate achieved with the RFC was three times that for the conventional system. A refined experimental methodology was used to quantify much more accurately the relative hydrodynamic limits of conventional and RFC operation. The previously neglected issue of split-zone segregation, resulting in smaller bubbles in the lower part of the cell, was also investigated.