Ming-Yen Wey

Characteristics of two types of stabilized nano zero-valent iron and transport in porous media.

Nano-scale zero-valent iron (NZVI) has been shown to be suitable for remediating contaminated aquifers. However, they usually aggregate rapidly and result in a very limited migration distance that inhibits their usefulness. This study employed poly acrylic acid (PAA) and carboxymethyl cellulose (CMC) to synthesize two types of stabilized styles of NZVI with finer sizes (namely PNZVI and CNZVI). The mobility of stabilized NZVI was also demonstrated on the basis of transport in porous media. The results show that the PNZVI has a uniform particle size of 12 nm. However, tens of CNZVI particles with diameters of 1-3 nm were packed into secondary particles. Both the PNZVI and the CNZVI exhibited amorphous structures, and the stabilizer was bound to particle surfaces in the form of bidentate bridging via the carboxylic group, which could provide both electrostatic and steric repulsion to prevent particle aggregation. This study also proposes presumed stabilized configurations of PNZVI and CNZVI to reasonably illustrate their different dispersed suspension types. On the basis of the breakthrough curves and mass recovery, this study observed that the mobility of PNZVI in classic Ca(2+) concentration of groundwater was superior to CNZVI. Nonetheless, the mobility of CNZVI would be decreased less significantly than PNZVI when encountering high Ca(2+) concentrations (40 mM). Presumably, increasing the pore flow velocity would enhance the mobility of stabilized NZVI. Overall, the results of this study indicate that PNZVI has the potential to become an effective reactive material for in situ groundwater remediation.

The effect of particle size distribution on minimum fluidization velocity at high temperature

Abstract The objective of this research is to study the effect of high temperature and particle size distribution (PSD) on minimum fluidization velocity ( U mf ). Four particle size distributions of silica were fluidized in air at atmospheric pressure between 700 and 900 °C. The particle size distributions evaluated included a narrow cut, a binary mixture, a uniform distribution, and a Gaussian distribution, all with similar means. The experimental results revealed a minimum in U mf near 800 °C. The reason might be that interparticle forces would be changed as temperature rose and increased the minimum fluidization velocity. The binary and uniform size distributions behaved similarly to each other but generally had higher U mf s than the Gaussian and narrow cut distributions.

Catalytic removal of SO2, NO and HCl from incineration flue gas over activated carbon-supported metal oxides

Abstract Activated carbon-supported copper, iron, or vanadium oxide catalysts were exposed to incineration flue gas to investigate the simultaneous catalytic oxidation of sulfur dioxide/hydrogen chloride and selective catalytic reduction of nitrogen oxide by carbon monoxide. The results show that AC-supported catalysts exhibit higher activities for SO2 and HCl oxidation than traditional γ-Al2O3-supported catalysts and the iron and vanadium catalysts act as catalysts instead of sorbents, and can decompose sulfate with evolution of SO3 and then regenerate for more SO2 adsorption to take place. The AC-supported catalysts also display a high activity for NO reduction with CO generated from a flue gas incineration process and the presence of SO2 in the incineration flue gas can significantly promote catalytic activity. Using CO as the reducing agent for NO reduction is more effective than using NH3, because NH3 may be partially oxidized in the presence of excess O2 (12 vol%. in the incineration flue gas used) to form N2, which can decrease the overall extent of NO reduction.

Carbon materials as catalyst supports for SO2 oxidation: catalytic activity of CuO–AC

Copper catalysts supported on acid treated activated carbon (AC) were prepared, characterized and tested in terms of their SO2 oxidation activity. Reactions of CuO–AC in flow systems with sulfur dioxide, oxygen and nitrogen streams were investigated to determine the types of chemical interactions that occur on the sorbent surface. The effects of reaction temperature, acid treatment, metal loading, support particle size, SO2 concentration and O2 concentration on SO2 oxidation activity were evaluated. It was found that carbon materials used as catalyst supports for copper oxide catalysts provided a high catalytic activity for adsorbing SO2 from flue gas and oxidizing it. Acid pretreatment of the carbon supports increased the content of specific surface chemical groups to enhance the catalytic activity for SO2 oxidation. Metal loading, as well as support particle size, have a significant influence on the SO2 activity. The supported metals rather than surface oxygen functional groups on AC may be the active sites for adsorbing SO2.

Pollutants in incineration flue gas

Previous studies have shown that pollutants from incineration include heavy metals, organic compounds, particulate and acid gas. However, most studies on a single pollutant, it is rare for a study to concentrate on all possible pollutants and the relations between these pollutants under various incineration conditions. The objective of this work was to experimentally study the effect of different operating conditions on the pollutants emitted during incineration and the relations between these pollutants. The operating conditions of the experiments included the temperature of the combustion chamber and the species of organics. The findings indicated that the concentration of hydrogen chloride (HCl) in the presence of polyvinyl chloride (PVC) was higher than that of sodium chloride (NaCl). Regardless of what Cl-containing feedstock was added, the concentration of chromium (Cr) was constant. When organic chloride was added, Cr was the main metallic element which influenced the formation of polycyclic aromatic hydrocarbons (PAHs). On the other hand, when inorganic chloride (NaCl) was added, lead (Pb) was the major element.

The adsorption of heavy metals by different sorbents under various incineration conditions

The emission of heavy metals can be controlled by adding solid sorbents into the combustion chamber during incineration processes. The objective of this work was to experimentally study the adsorption efficiency of different sorbents for heavy metals under various incineration conditions. Each sorbent has its optimum operating temperature. Kaolinite and aluminum oxide have the best adsorption efficiency at 800 degrees C, and bauxite is at 700 degrees C. The adsorption efficiencies of the three sorbents for the four heavy metals all follow the sequence of Pb > Cu > Cr > Cd. The presence of inorganic chloride (NaCl) and sulfate (Na2SO4) increases the adsorption efficiency of the sorbents, but organic chloride PVC decreases the adsorption efficiency.

Biotoxicity evaluation of fly ash and bottom ash from different municipal solid waste incinerators

Different types of municipal solid waste incinerator (MSWI) fly and bottom ash were extracted by TCLP and PBET procedures. The biotoxicity of the leachate of fly ash and bottom ash was evaluated by Vibrio fischeri light inhibition test. The results indicate the following: (1) The optimal solid/liquid ratio was 1:100 for PBET extraction because it had the highest Pb and Cu extractable mass from MSWI fly ash. (2) The extractable metal mass from both fly ash and bottom ash by PBET procedure was significantly higher than that by TCLP procedure. (3) The metal concentrations of fly ash leachate from a fluidized bed incinerator was lower than that from mass-burning and mass-burning combined with rotary kiln incinerator. (4) The TCLP and PBET leachate from all MSWI fly ash samples showed biotoxicity. Even though bottom ash is regarded as a non-hazardous material, its TCLP and PBET leachate also showed biotoxicity. The pH significantly influenced the biotoxicity of leachate.

Capture of heavy metals by sorbents in incineration flue gas

Abstract The emission of heavy metals can be controlled by injecting solid sorbents into the flue during incineration processes. Feed waste elemental compositions and types of sorbents influence the controlling efficiency of the sorbents for heavy metal compounds. The objective of this work is to experimentally study the controlling efficiency of different sorbents for heavy metals in the flue of an incineration system, and study the effects of feed waste composition on the controlling efficiency of sorbents. The investigated heavy metals are Pb, Cd, Cu and Cr. The operating parameters evaluated included: (1) different sorbents (kaolinite, limestone, aluminum oxide, and water); (2) the feed waste contained organic chloride (PVC); (3) the feed waste contained inorganic chloride (NaCl); (4) the feed waste contained sulfate (Na 2 SO 4 ); (5) comparing the controlling efficiency of sorbents used in the combustion chamber and injected in the flue of an incineration system. Experimental results indicated that the control efficiency of the four sorbents for heavy metals under various feed waste composition follows the sequence of limestone>water>kaolinite>aluminum oxide. The best sorbent for the four heavy metals is limestone, especially as the feed waste contained organic chloride PVC, because limestone slurry provides a lot of calcium and alkali to react with the metal chlorides and acid gas. The presence of inorganic chloride NaCl and sulfate Na 2 SO 4 in the feed waste is helpful to increase the capture efficiency of the sorbents for heavy metals. By comparison, the capture efficiency of the sorbent injected in the flue is lower than that added in the combustion chamber.

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.

The influence of heavy metals on the formation of organics and HCl during incinerating of PVC-containing waste

Abstract The heavy metal, organic pollutants and HCl emissions from incineration pose a grave threat to human health. However, submicro metal particles and organics in gas phase are removed with difficulty by conventional air pollution control apparatus, and could be released into the atmosphere along with the flue gas. This research studied the formation of organics and HCl (hydrogen chloride) during incineration when the feedstock contained different amounts of PVC and heavy metals. The experiments were performed in a bubbling fluidized bed incinerator with two cyclones and scrubbers. Experimental results indicated that the greatest amount of organic compounds produced were aromatic compounds. The amount of organic compounds and HCl increased when the feedstock contained PVC (polyvinyl chloride), and decreased when the feedstock contained heavy metals.