Chih-Ta Wang

Removal of COD from laundry wastewater by electrocoagulation/electroflotation.

The removal efficiency of COD in the treatment of simulated laundry wastewater using electrocoagulation/electroflotation technology is described. The experimental results showed that the removal efficiency was better, reaching to about 62%, when applying ultrasound to the electrocoagulation cell. The solution pH approached neutrality in all experimental runs. The optimal removal efficiency of COD was obtained by using the applied voltage of 5V when considering the energy efficiency and the acceptable removal efficiency simultaneously. The Cl(-) concentration of less than 2500ppm had a positive effect on the removal efficiency. The performance of the monopolar connection of electrodes was better than that of the bipolar connection in this work. In addition, the removal efficiency of using Al electrodes was higher in comparison with using Fe electrodes in the study. The highest COD removal amount per joule was found to be 999mgdm(-3)kWh(-1) while using two Al electrodes, although the removal efficiency increased with the number of Al plates.

Effect of operating parameters on indium (III) ion removal by iron electrocoagulation and evaluation of specific energy consumption

The aim of this study is to investigate the effects of operating parameters on the specific energy consumption and removal efficiency of synthetic wastewater containing indium (III) ions by electrocoagulation in batch mode using an iron electrode. Several parameters, including different electrode pairs, supporting electrolytes, initial concentration, pH variation, and applied voltage, were investigated. In addition, the effects of applied voltage, supporting electrolyte, and initial concentration on indium (III) ion removal efficiency and specific energy consumption were investigated under the optimum balance of reasonable removal efficiency and relative low energy consumption. Experiment results indicate that a Fe/Al electrode pair is the most efficient choice of the four electrode pairs in terms of energy consumption. The optimum supporting electrolyte concentration, initial concentration, and applied voltage were found to be 100 mg/l NaCl, 20 mg/l, and 20V, respectively. A higher pH at higher applied voltage (20 or 30V) enhanced the precipitation of indium (III) ion as insoluble indium hydroxide, which improved the removal efficiency. Results from the indium (III) ion removal kinetics show that the kinetics data fit the pseudo second-order kinetic model well. Finally, the composition of the sludge produced was characterized with energy dispersion spectra (EDS).

Study of COD and turbidity removal from real oxide-CMP wastewater by iron electrocoagulation and the evaluation of specific energy consumption

This study explores the feasibility of reducing COD and turbidity from real oxide chemical mechanical polishing (oxide-CMP) wastewater. Based on the dynamic characteristics of batch electrocoagulation, three operating stages (lag, reactive, and stabilizing) are proposed to identify the relationships among the zeta potential of the silica particles, solution turbidity, and the corresponding mean particle size. Experiment results show that the silica particles were destabilized and settled at the critical electrolysis time, which was estimated to be about 12 min under an applied voltage of 20 V and a supporting electrolyte of 200mg/L. The corresponding turbidity removal occurred mostly during the reactive stage. The process variables, including applied voltage and electrolyte concentration, were investigated in terms of COD removal efficiency and turbidity removal. In addition, the effects of applied voltage and supporting electrolyte on COD removal efficiency and specific energy consumption were evaluated. Under the optimum balance, satisfactory removal efficiency and relatively low energy consumption were obtained. The optimum electrolyte concentration and applied voltage were found to be 200mg/L NaCl and 20 V, respectively. Under the optimum conditions, COD and turbidity decreased by more than 90% and 98% in real oxide-CMP wastewater, respectively.

Silica particles settling characteristics and removal performances of oxide chemical mechanical polishing wastewater treated by electrocoagulation technology

The purpose of this study was to explore the feasibility of removing silica particles and reducing turbidity from oxide chemical mechanical polishing (oxide-CMP) wastewater. Based on the dynamic characteristics of batch electrocoagulation, three operating stages (lag, reactive, and stabilizing) are proposed to identify the relationships among the zeta potential of the silica particles, solution turbidity, and the corresponding mean particle size of the silica. Experimental results show that the silica particles were destabilized and settled at the critical mean particle size, which was estimated to be above 520nm after 10min, and the corresponding turbidity removal mostly occurred during the reactive stage. Furthermore, the corresponding mean particle size varied from 520 to 1900nm as the treatment time progressed from 10 to 20min, which also occurred during the reactive stage. Several parameters, including different electrode pairs, electrolyte concentration, applied voltage, and the optimum condition of power input were investigated. Experimental results indicate that a Fe/Al electrode pair is the most efficient choice of the four electrode pair combinations in terms of energy consumption. The optimum electrolyte concentration and applied voltage were found to be 200ppm NaCl and 30V, respectively.

Adsorption treatment of oxide chemical mechanical polishing wastewater from a semiconductor manufacturing plant by electrocoagulation

In this study, metal hydroxides generated during electrocoagulation (EC) were used to remove the chemical oxygen demand (COD) of oxide chemical mechanical polishing (oxide-CMP) wastewater from a semiconductor manufacturing plant by EC. Adsorption studies were conducted in a batch system for various current densities and temperatures. The COD concentration in the oxide-CMP wastewater was effectively removed and decreased by more than 90%, resulting in a final wastewater COD concentration that was below the Taiwan discharge standard (100 mg L(-1)). Since the processed wastewater quality exceeded the direct discharge standard, the effluent could be considered for reuse. The adsorption kinetic studies showed that the EC process was best described using the pseudo-second-order kinetic model at the various current densities and temperatures. The experimental data were also tested against different adsorption isotherm models to describe the EC process. The Freundlich adsorption isotherm model predictions matched satisfactorily with the experimental observations. Thermodynamic parameters, including the Gibbs free energy, enthalpy, and entropy, indicated that the COD adsorption of oxide-CMP wastewater on metal hydroxides was feasible, spontaneous and endothermic in the temperature range of 288-318 K.

Paired removal of color and COD from textile dyeing wastewater by simultaneous anodic and indirect cathodic oxidation

The anodic and indirect cathodic removals of color and COD from real dyeing wastewater were investigated simultaneously using a stacked Pt/Ti screen anode and a graphite packed-bed cathode in a divided flow-by electrochemical reactor. The anodically generated hypochlorite and cathodically generated hydrogen peroxide were the main species used to remove color and COD in the wastewater. Various experimental operating factors that can affect the removal efficiency were investigated, including the applied current density, the amount of NaCl added, the solution pH in alkaline ranges and the temperature. The color and COD removal efficiencies in the anodic chamber were much higher than those in the cathodic chamber. The overall (anodic plus cathodic) removal efficiencies increased with the applied current density, the amount of NaCl added and the temperature. In contrast, increasing the solution pH decreased the overall removal efficiency. The anodic and cathodic current efficiencies at 20 mA/cm(2) were 63.50% and 19.57%, respectively. In this work the total treatment cost for removing 1g COD was US

Performance of COD removal from oxide chemical mechanical polishing wastewater using iron electrocoagulation

0.643 when an air cylinder was used.

Treatment of Polyvinyl Alcohol from Aqueous Solution via Electrocoagulation

This study investigated the feasibility of chemical oxygen demand (COD) abatement from oxide chemical mechanical polishing (oxide-CMP) wastewater. The process variables, including applied voltage, electrolyte concentration and temperature, were evaluated in terms of COD removal efficiency. In addition, the effects of applied voltage, supporting electrolyte, and temperature on electric energy consumption were evaluated. Under the optimum balance of variables, satisfactory COD removal efficiency and relatively low energy consumption were achieved. The optimum electrolyte concentration, applied voltage, and temperature were found to be 200 mg/L NaCl, 20 V, and 25°C, respectively. Under these conditions, the COD concentration in oxide-CMP wastewater decreased by more than 90%, resulting a final wastewater COD concentration that was below the Taiwan discharge standard (100 mg/L). Since the processed wastewater quality exceeded the direct discharge standard, the effluent could be considered for reuse. COD removal rates obtained during the electrocoagulation process can be described using a pseudo-kinetic model. The present study results show that the kinetic data fit the pseudo first-order kinetic model well. Finally, the morphology and composition of the sludge produced were characterized using scanning electron microscopy (SEM) and energy dispersion spectra (EDS).

Chemical and physical properties of plasma slags containing various amorphous volume fractions

This study investigates the feasibility of removing the chemical oxygen demand (COD) from a solution containing polyvinyl alcohol (PVA) by electrocoagulation. Several parameters—including the current density, supporting electrolyte, and temperature—were evaluated in terms of COD removal efficiency. The effects of these parameters on the electrical energy consumption were also investigated. The optimum current density, supporting electrolyte concentration, and temperature were found to be 5 mA/cm2, 0.012 N NaCl, and 298 K, respectively. The experimental data were also tested against different adsorption isotherm models to describe the electrocoagulation process; the COD adsorption studied here best fit the Freundlich adsorption isotherm model. Thermodynamic parameters, including the Gibbs free energy, enthalpy, and entropy, indicated that the adsorption of COD on metal hydroxides was feasible, spontaneous, and endothermic in the temperature range of 288 K to 318 K.

Effect of NaOH on the vitrification process of waste Ni–Cr sludge

In this study, municipal solid waste incinerator fly ash was vitrified using a plasma torch. The fly ash contained rich Ca, causing a high basicity of 2.43. Pure quartz was used as an additive to adjust the basicity. BET surface area analysis, X-ray diffraction analysis, and a scanning electron microscope were used to examine the physical properties of slags. The chemical stability and the acid resistance of slags were evaluated using the toxicity characteristics leaching procedure and tests of acid bathing. The results indicate that the plasma torch effectively vitrified the fly ash. Anthropogenic metals with low boiling points, such as Cd, Pb, and Zn, were predominately vaporized into flue gas. Most of the metals with high boiling points, such as Cr, Cu, and Mn, remained in the slag. After the vitrification, hazardous metals were noticeably immobilized in all slags. However, the slags with higher amorphous volume fractions were more effective in metal immobilization and in resisting acid corrosion. This indicates that SiO(2) enhanced the formation of the glassy amorphous phase and improved the resistance of acid corrosion and the immobilization of hazardous metals.