Shang-Lien Lo

Characterization of arsenate adsorption on hydrous iron oxide using chemical and physical methods

Abstract The adsorption of arsenate by hydrous iron oxide was investigated by both chemical and physical energy dispersive analysis of X-rays (EDAX) and Fourier transform infrared (FTIR) methods. The chemical methods for characterizing arsenate adsorption sites on hydrous iron oxide surfaces in this work were investigations of the effect of ionic strength and zeta potential measurements of iron oxide systems containing various arsenate concentrations over the pH range 4–10. An inner-sphere complexation at the aqueous arsenate/iron oxide interface was identified from the results of the ionic strength effect and the shift in isoelectric point of the system. Evidence for direct coordination of arsenate to the surface of iron oxide was obtained by EDAX and FTIR techniques. Results from these physical methods showed that arsenate was chemisorbed on the iron oxide surface. Specific adsorption could therefore be deduced, on the basis of both chemical and physical methods, to occur at the aqueous arsenate and solid iron oxide interfaces.

Effects of co-existing anions on fluoride removal in electrocoagulation (EC) process using aluminum electrodes

Batch experiments with bipolar aluminum electrodes and potentiodynamic polarization tests with monopolar systems were conducted to investigate the effects of the type and concentration of co-existing anions on defluoridation in electrocoagulation (EC) process. The results demonstrate that the type of the dominant anion directs the EC defluoridation reaction. The defluoridation efficiency was almost 100% and most of the fluoride removal reaction occurred on the surface of the anode in the solution without the co-existing anions, due to the electro-condensation effect. In the solutions with co-existing anions, most of the defluoridation took place in bulk solution. The residual fluoride concentration is a function of the total mass of Al(III) liberation from anodes and the types of the functions in the solutions with and without co-existing anions are different. The existence of sulfate ions inhibits the localized corrosion of aluminum electrodes, leading to lower defluoridation efficiency because of lower current efficiency. The presence of chloride or nitrate ions prevented the inhibition of sulfate ions, and the chloride ions were more efficient. Different corrosion types occurred in different anion-containing solutions and the form of corrosion affected the kinetic over-potential. The bypass flow causes the decrease of current efficiency and the proportion of the bypass flow of current increased due to a rise of the kinetic over potential and the conductivity of the solution.

Total recovery of resources and energy from rice straw using microwave-induced pyrolysis

This article presents the application of microwave-induced pyrolysis to total recovery of resources and energy from rice straw. The microwave power and particle size of feedstock were both key parameters affecting the performance of microwave-induced pyrolysis. Under 400-500W microwave power, the reduction of fixed carbon in the biomass was significant. From the experimental results of specific surface area, zeta potential, and Cu2+ adsorption, the applications of solid residues in the water and wastewater treatment could be expected. The major compositions in gaseous product were H2, CO2, CO, CH4 of 55, 17, 13, 10vol.%, respectively. The high H2 content might imply that microwave-induced pyrolysis of biomass waste has the potential to produce the H2-rich fuel gas. Alkanes, polars, and low-ringed polycyclic aromatic hydrocarbons were three primary kinds of compounds in the liquid product.

Diagnosing reservoir water quality using self-organizing maps and fuzzy theory

Since trophic status assessment of water quality is very important for the water resources management, the assessment results obtained from using only one parameter may easily mislead or bias the decision makers or managers. Even when using a multivariable index, how to determine the weights of all factors is debatable. In this research, one complementary evaluation method, self-organizing map (SOM), for diagnosing water quality has been used to develop a trophic state classifier and is illustrated with a case study of trophic status assessment for Fei-Tsui Reservoir in Taiwan. The historical database was collected from the management agency of Fei-Tsui Reservoir from 1987 to 1995. The results of SOM are compared with those of the Carlson index and Fuzzy synthetic evaluation, showing that the inconsistent records can be mapped to the conflicting data zone of the SOM output map. In addition, SOM creates a diagnostic axis on the map to express the trophic status of the water body. As long as the SOM model is well-trained, new records can be assessed and classified as either one of three trophic levels or speciarcases. If special water quality conditions are expressed on the SOM output, those data can reveal that either total phosphorus (TP) or chlorophyll A (chl a) is higher than usual.

Efficient decomposition of perfluorocarboxylic acids in aqueous solution using microwave-induced persulfate.

The microwave-hydrothermal decomposition of persistent and bioaccumulative perfluorooctanoic acid (PFOA) in water with persulfate (S(2)O(8)(2-)) at 60, 90, and 130 degrees C was examined to develop an effective technology for treating PFOA pollution. S(2)O(8)(2-) is an efficient oxidant for degrading PFOA even at the room temperature of 27 degrees C. Higher temperature accelerates the PFOA decomposition rate, but an extremely high temperature (130 degrees C) will lead to the formation of significant amounts of radical oxidants that are released rapidly to consume most remaining persulfate thus causing a lower mineralization efficiency. The solution pH value is another important factor to influence the degradation rate; there is almost no PFOA decomposition reaction under alkaline conditions. The decomposition rate in acidic conditions is 1.1-7.4 times faster than in alkaline condition. Additionally, the proposed method is also effective in decomposing other PFCA species such as the C2-C7 perfluoroalkyl groups.

Hydrogen-rich fuel gas from rice straw via microwave-induced pyrolysis

This study aimed to research the productivity of H(2)-rich fuel gas from rice straw using the microwave-induced pyrolysis. The formation constituents of gas product and the mechanism of its production were also discussed. The primary components of gas product were H(2), CO(2), CO, and CH(4), with average percentages of 50.67, 22.56, 16.09, and 7.42vol.%, respectively. According to the TA-MS analysis, it was suggested that focused heating by microwaves made the microwave-induced pyrolysis different from the traditional pyrolysis. A chemical equation could be nearly balanced to illustrate the gas composition generated from rice straw. From the viewpoint of energy consumption, close to 60% of the input energy could be derived and utilized as bioenergy.

Competitive adsorption of molybdate, chromate, sulfate, selenate, and selenite on γ-Al2O3

Competitive adsorption of molybdate, selenite, selenate, chromate, and sulfate onto γ-Al2O3 was investigated in the present study. Binary-solute systems of MoO42−/SeO32−, CrO42−/SO42−, and CrO42−/SeO42− as well as single anion systems were evaluated for the relative influence on competitive adsorption on oxide surface. As would be expected, the adsorption density of each anion in the binary-solute systems decreases, as compared to the respective density in a single anion system. Furthermore, MoO42− inhibits SeO32− adsorption in acidic condition and that SO42− or SeO42− depresses CrO42−. The order of the relative retainment of anions on oxide surface is molybdate>selenite>selenate∼sulfate>chromate, which corresponds to the magnitude of the overall proton coefficient of the corresponding anions.

Microwave-hydrothermal decomposition of perfluorooctanoic acid in water by iron-activated persulfate oxidation

The microwave-hydrothermal decomposition of persistent and bioaccumulative perfluorooctanoic acid (PFOA) in aqueous solution using persulfate activated by zero-valent iron (ZVI) at 60 and 90 degrees C was examined. The results of laboratory study reveal that when PFOA is treated with 5mM persulfate (PS) and ZVI at 90 degrees C for 2h, 67.6% of PFOA is effectively decomposed to form shorter-chain perfluorinated carboxylic acids (PFCAs) and fluoride ions, with 22.5% defluorination efficiency. Introducing ZVI into the PFOA solution with PS addition will lead to synergetic effect that accelerates the PFOA decomposition rate, and reduces the reaction time. ZVI not only decomposes PFOA, but also releases ferrous ions to lower the activation energy of PS while forming sulfate free radicals at a lower reaction temperature. The combined use of ZVI and persulfate will lead to significant savings in energy consumption and reduction of process time.

Application of two-stage fuzzy set theory to river quality evaluation in Taiwan.

An indicator model for evaluating trends in river quality using a two-stage fuzzy set theory to condense efficiently monitoring data is proposed. This candidate data reduction method uses fuzzy set theory in two analysis stages and constructs two different kinds of membership degree functions to produce an aggregate indicator of water quality. First, membership functions of the standard River pollution index (RPI) indicators, DO, BOD(5), SS, and NH(3)-N are constructed as piecewise linear distributions on the interval [0,1], with the critical variables normalized in four degrees of membership (0, 0.33, 0.67 and 1). The extension of the convergence of the fuzzy c-means (FCM) methodology is then used to construct a second membership set from the same normalized variables as used in the RPI estimations. Weighted sums of the similarity degrees derived from the extensions of FCM are used to construct an alternate overall index, the River quality index (RQI). The RQI provides for more logical analysis of disparate surveillance data than the RPI, resulting in a more systematic, less ambiguous approach to data integration and interpretation. In addition, this proposed alternative provides a more sensitive indication of changes in quality than the RPI. Finally, a case study of the Keeling River is presented to illustrate the application and advantages of the RQI.

Adsorption of Se(IV) and Se(VI) on an iron-coated sand from water

Abstract This study was aimed at developing a method for coating hydrated iron-oxide onto the surface of quartz sand. Two coating parameters were investigated: the pH at which iron-oxide was synthesized and the coating temperature. According to the results, a larger quantity of iron was coated onto quartz sand in the lower pH range (0.5 – 2.0). This iron-oxide-coated sand (IOCS) produced at low pH was more difficult to dissolve in acidic and basic solution and had better Se(IV) and Se(VI) adsorption efficiencies than did IOCS produced at high pH (8.0 – 11.0). Adsorption experiments showed that Se(IV) adsorption by IOCS was specific and Se(VI) adsorption was nonspecific. In kinetic experiments, pseudo-equilibrium of Se(IV) adsorption was attained within 10 minutes while Se(VI) adsorption needed 1.5 hours. Higher concentrations of NaOH solution could increase the desorption rate of Se(VI) but could not increase the total desorbed quantity. In addition, adsorption isotherm results indicated that the adsorption capacity of IOCS from pH 4.0 to 6.5 was 0.014 – 0.017 mmole Se/g sand for Se(IV) and was 0.013 – 0.014 mmole Se/g sand for Se(VI).