Kai-Sung Wang

Effects of dissolved oxygen on dye removal by zero-valent iron.

Effects of dissolved oxygen concentrations on dye removal by zero-valent iron (Fe(0)) were investigated. The Vibrio fischeri light inhibition test was employed to evaluate toxicity of decolorized solution. Three dyes, Acid Orange 7 (AO7, monoazo), Reactive Red 120 (RR120, diazo), and Acid Blue 9 (AB9, triphenylmethane), were selected as model dyes. The dye concentration and Fe(0) dose used were 100 mg L(-1) and 30 g L(-1), respectively. Under anoxic condition, the order for dye decolorization was AO7>RR120>AB9. An increase in the dissolved oxygen concentrations enhanced decolorization and chemical oxygen demand (COD) removal of the three dyes. An increase in gas flow rates also improved dye and COD removals by Fe(0). At dissolved oxygen of 6 mg L(-1), more than 99% of each dye was decolorized within 12 min and high COD removals were obtained (97% for AO7, 87% for RR120, and 93% for AB9). The toxicity of decolorized dye solutions was low (I(5)<40%). An increase in DO concentrations obviously reduced the toxicity. When DO above 2 mg L(-1) was applied, low iron ion concentration (13.6 mg L(-1)) was obtained in the decolorized AO7 solution.

Degradation of azo and anthraquinone dyes by a low-cost Fe0/air process

Degradation of two different kinds of dyes, anthraquinone Reactive Blue 4 (RB4) and azo Reactive Black 5 (RB5), by low-cost zero valent iron (Fe(0)) in a N(2) bubbling system (Fe(0)/N(2) process) and air bubbling system (Fe(0)/air process) was investigated. The operating parameters, including initial solution pH, dye concentration and Fe(0) dose, were also evaluated. The Fe(0)/air process shows a higher decolorization rate compared to the Fe(0)/N(2) process. Both RB4 and RB5 solutions at 100 mg L(-1) were rapidly decolorized by Fe(0)/air process within 9 and 3 min, respectively, at initial solution pH 3, Fe dose of 50 g L(-1) and air flow rate of 5 L min(-1). The optimal initial solution pH was 3. The Fe(0)/N(2) process removed only <17% of COD. However, significant COD removals were achieved for RB 4 (87%) and RB5 (43%) by the Fe(0)/air process after 9 min of treatment. Spectra analysis results indicated that the Fe(0)/N(2) process destroyed only the anthraquinone group (A(594)) for the RB4 solution and decreased the azo (A(596)) and naphthalene group (A(310)) for the RB5 solution. However, the Fe(0)/air process rapidly removed A(594), A(370), A(296) (anthraquinone group) and A(256) (aromatic and dichlorotriazine group) for RB4, and A(597) and A(310) (naphthalene group) for RB5. The results indicated that the low-cost Fe(0)/air process is a potential technique for rapid degradation of RB4 and RB5 solutions.

Phytoextraction of cadmium by Ipomoea aquatica (water spinach) in hydroponic solution: effects of cadmium speciation.

Phytoextraction is a promising technique to remediate heavy metals from contaminated wastewater. However, the interactions of multi-contaminants are not fully clear. This study employed cadmium, Triton X-100 (TX-100), and EDTA to investigate their interactions on phytotoxicity and Cd phytoextraction of Ipomoea aquatica (water spinach) in simulated wastewater. The Cd speciation was estimated by a chemical equilibrium model and MINEQL+. Statistic regression was applied to evaluate Cd speciation on Cd uptake in shoots and stems of I. aquatica. Results indicated that the root length was a more sensitive parameter than root weight and shoot weight. Root elongation was affected by Cd in the Cd-EDTA solution and TX-100 in the Cd-TX-100 solution. Both the root length and the root biomass were negatively correlated with the total soluble Cd ions. In contrast, Cd phytoextraction of I. aquatic was correlated with the aqueous Cd ions in the free and complex forms rather than in the chelating form. Additionally, the high Cd bioconcentration factors of I. aquatica (375-2227 l kg(-1) for roots, 45-144 l kg(-1) for shoots) imply that I. aquatica is a potential aquatic plant to remediate Cd-contaminated wastewater.

Enhancement of Rhodamine B removal by low-cost fly ash sorption with Fenton pre-oxidation.

The removal of a basic dye, Rhodamine B (RhB), by fly ash adsorption, Fenton oxidation, and combined Fenton oxidation-fly ash adsorption were evaluated. Even though fly ash is a low cost absorbent, a high dose of fly ash was needed to remove RhB. Only 54% of RhB was removed by 80 g L(-1) fly ash. Solution pH did not significantly affect the RhB sorption by fly ash after 8h. Fenton reagents at H(2)O(2) dose of 6 x 10(-3)M and pH 3 rapidly decolorized 97% of RhB within 2 min, and 72% of COD removal was obtained at 30min reaction time. Spectrum analysis result showed that a large area of UV spectrum at 200-400 nm remained after Fenton reaction. The addition of 1gL(-1) fly ash effectively removed COD from Fenton-treated solution, and the UV absorption spectrum at 220-400 nm totally vanished within 2h. COD removal of RhB by the combined Fenton oxidation and fly ash sorption process was 98%. The COD removal capacity of fly ash for Fenton-treated RhB solution was 41.6 times higher than that for untreated RhB solution. The results indicated that the combined process is a potential technique for RhB removal.

Degradation of Reactive Black 5 using combined electrochemical degradation-solar-light/immobilized TiO2 film process and toxicity evaluation.

The combined electrochemical oxidation-solar-light/immobilized TiO2 film process was conducted to degrade an azo dye, Reactive Black 5 (RB5). The toxicity was also monitored by the Vibrio fischeri light inhibition test. The electrochemical oxidation rapidly decolorized RB5 (55, 110 microM) with a supporting electrolyte of 2 gl(-1) NaCl at current density 277Am(-2) and pH 4. However, TOC mineralization and A(310) removal were low. Additionally, the treated solution showed high biotoxicity. RB5 at 110 microM significantly retarded the de-colorization efficiency by using the solar-light/immobilized TiO2 film process. The combined electrochemical oxidation-solar-light/immobilized TiO2 process effectively increased the removal of color, A(310), and TOC. The toxicity was also significantly reduced after 3h of solar irradiation. The results indicated that the low-cost combined process is a potential technique for rapid treatment of RB5.

Comparison of Source Identification of Metals in Road-Dust and Soil

Source identification of toxic metals is very critical for pollution prevention and human health protection. Many studies only use either road dust metal data or soil metal data to evaluate metal contamination and identify pollution sources, and this may lead to the exclusion of some important information. In this study, the differences of metal spatial distribution and source identification between road dust and associated soil in an industrial area were investigated. Results indicate the metal concentrations in road dust were generally higher than those in soil. Based on the average concentrations, the order for dust metal concentrations was Fe>>Zn>>Pb>Cu>Cr>Ni. The order for soil metal concentrations was slightly different, namely Fe>>Zn>>Cu∼Pb>Ni>Cr. The spatial distributions of metals in the road dust were very different from those in the soil, except for Fe. The GIS results indicate that elevated levels of Fe, Zn, and Pb were present in road dust near a steel plant. High concentrations of Cu, Cr, and Ni appeared at a road intersection. Elevated metal concentrations of Fe, Zn, Pb, Cu, and Cr were present in soil around the steel plant. A coal-fired power plant did not seem to be a significant metal source in this study. Significant correlations for dust metals imply that these were well mixed in the study area. The metal sources identified by PCA with soil metal data were obviously different from those identified with road dust metal data. When road dust metal data were used, the changes of PCA analyzed areas slightly influenced the source identification. The PCA results were obviously influenced by changes of analyzed areas when soil metal data were used.

Treatment of Reactive Black 5 by combined electrocoagulation-granular activated carbon adsorption-microwave regeneration process

Treatment of an azo dye, Reactive Black 5 (RB5) by combined electrocoagulation-activated carbon adsorption-microwave regeneration process was evaluated. The toxicity was also monitored by the Vibrio fischeri light inhibition test. GAC of 100 g L(-1) sorbed 82% of RB5 (100 mg L(-1)) within 4h. RB5-loaded GAC was not effectively regenerated by microwave irradiation (800 W, 30s). Electrocoagulation showed high decolorization of RB5 within 8 min at pH(0) of 7, current density of 277 A m(-2), and NaCl of 1 g L(-1). However, 61% COD residue remained after treatment and toxicity was high (100% light inhibition). GAC of 20 g L(-1) effectively removed COD and toxicity of electrocoagulation-treated solution within 4h. Microwave irradiation effectively regenerated intermediate-loaded GAC within 30s at power of 800 W, GAC/water ratio of 20 g L(-1), and pH of 7.8. The adsorption capacity of GAC for COD removal from the electrocoagulation-treated solution did not significantly decrease at the first 7 cycles of adsorption/regeneration. The adsorption capacity of GAC for removal of both A(265) (benzene-related groups) and toxicity slightly decreased after the 6th cycle.

Effects of UV irradiation on humic acid removal by ozonation, Fenton and Fe0/air treatment: THMFP and biotoxicity evaluation

Effects of UV irradiation on humic acid (HA) removal by Fe(0)/air, ozonation and Fenton oxidation were investigated. The trihalomethane forming potential (THMFP) and toxicity of treated solutions were also evaluated. The experimental conditions were ozone of 21 mg min(-1), H(2)O(2) of 8 × 10(-4)M, Fe(0) of 20 g L(-1), air flow of 5 L min(-1), and UVC of 9 W. Results indicated that Fe(0)/air rapidly removed HA color (>99%) and COD (90%) within 9 min. 51-81% of color and 43-50% of COD were removed by ozonation and Fenton oxidation after 60 min. Both UV enhanced ozone and Fenton oxidation removed HA, but the Fe(0)/air process did not. Spectrum results showed all processes effectively diminished UV-vis spectra, except for ozonation. The THMFP of Fe(0)/air-treated solution (114 μg L(-1)) was much lower than those of Fenton- (226 μg L(-1)) and ozonation-treated solutions (499 μg L(-1)). Fe(0)/air with UV irradiation obviously increased the THMFP of treated solution (502 μg L(-1)). The toxicity results obtained from Vibrio fischeri light inhibition test indicated that the toxicity of Fe(0)/air-treated solution (5%) was much lower than that of ozonation- (33%) and Fenton-treated solutions (31%). Chlorination increased the solution toxicity. The correlation between biotoxicity and chloroform in the chlorinated solution was insignificant.

Phytoremediation of Cr(III) by Ipomonea aquatica (water spinach) from water in the presence of EDTA and chloride: effects of Cr speciation.

Wastewater is often co-contaminated with chromium, chelating agents, and chloride. Influences of Cr(3+) speciation on Cr phytoremediation by Ipomonea aquatica were investigated. MINEQL+ was employed to estimate Cr speciation. Statistic regression was used to investigate the relationships between Cr speciation and accumulation. I. aquatica accumulated high Cr concentration (13,217 mg kg(-1)) in the root at Cr(3+) of 10 mg l(-1) and EDTA of 10(-4) M after 14 d growth. Pearson correlation analysis indicates that root Cr concentration significantly correlated with Cr-EDTA speciation (r = 0.67, p < 0.05) and Cr-Cl speciation (r = 0.91, p < 0.01). Shoot Cr concentration also significantly correlated with Cr-Cl speciation (r = 0.97, p < 0.01). An increase in Cl(-) concentration to 1.72 x 10(-4) M enhanced root Cr concentration; however, the accumulation of root Cr was inhibited at high Cl(-) concentration (5.76 x 10(-5) M). Microscopic image showed that a high portion of Cr(3+) accumulated on the root surface.

Remediation of Metal-Contaminated Soil by an Integrated Soil Washing-Electrolysis Process

Chelating agents such as EDTA and DTPA are often used to remove metals from soil. However, their toxicity, bio-recalcitrance, and problems with recovery of heavy metal and chelating agents severely limit their applications. A biodegradable chelating agent, LED3A, and two surfactants, SDS and Triton X 100, were evaluated as potential alternatives for remediation of metal-contaminated soil. LED3A alone only removed 40% of cadmium the addition of surfactant significantly enhanced its cadmium removal capacity up to 80% for a wide range of pH (5 to 11). The enhancement increased with both surfactant concentrations and LED3A concentrations. Because LED3A had a much higher removal capacity for copper, the synergistic effect of surfactant-LED3A mixture was less obvious. Sequential extraction analysis indicated that the LED3A not only removed copper from carbonate and Fe-Mn oxide fraction, but also from organic fractions. A three-dimension electrolysis reactor could effectively recover both metals and LED3A-SDS within thirty minutes. The combined soil washing by LED3A-surfactants and electrolysis provides a potential approach for remediation of copper- and cadmium-contaminated soils.