Chen-Yu Chang

The pH and anion effects on the heterogeneous photocatalytic degradation of o-methylbenzoic acid in TiO2 aqueous suspension.

This investigation used UV light of 365 nm and titanium dioxide in aqueous suspension to study the photocatalytic reaction of o-methylbenzoic acid under the influence of pH values, anion additives and the varieties of titanium dioxide. From experimental results, under the condition of 5 g/l TiO2, pH 3 and light intensity of 2.45 mW/cm2, 0.1 mM of o-methylbenzoic acid could be completely decomposed in 2 h. The reaction was faster with lowering pH, and was found to be apparent first-order following Langmuir-Hinshelwood model. In the presence of anion additives, the inhibitive effect of chloride ions was larger than that of sulfate ions under acidic condition for Degussa brand titanium dioxide, but without influence using Janssen brand. Both brands, however, promoted the mineralization of o-methylbenzoic acid (o-MBA).

The reaction pathway for the heterogeneous photocatalysis of trichloroethylene in gas phase.

Trichloroethylene (TCE) has been widely used in industry. It is considered a hazardous and carcinogenic air pollutant. In this investigation, TCE photocatalytic reactions were performed in a packed bed reactor configured as a continuous flow reactor and a FT-IR sample cell used as a batch reactor to determine the intermediates under irradiation by 365 nm UV light. In this study, the intermediates detected during these reactions were phosgene, dichloroacetyl chloride (DCAC), chloroform, hexachloroethane, alcohols, esters, aldehydes, carbon monoxide, and carbon dioxide. The possible reaction mechanisms began with the Cl- subtraction. The Cl radicals then interacted with TCE to form various intermediates and products.

The formation of disinfection by-products in water treated with chlorine dioxide

In this study, chlorine dioxide (ClO(2)) was used as an alternative disinfection agent with humic acid as the organic precursor in a natural aquatic environment. The major topics in this investigation consisted of the disinfection efficiency of ClO(2), the formation of disinfection by-products (DBPs), and the operating conditions. The results indicated that the pH value (pH 5-9) did not affect the efficiency of disinfection while the concentration of organic precursors did. The primary DBPs formed were trihalomethanes (THMs) and haloacetic acids (HAAs). The distribution of the individual species was a function of the bromide content. The higher the ClO(2) dosage, the lower the amount of DBPs produced. The amount of DBPs increased with reaction time, with chlorite ions as the primary inorganic by-product.

The organic precursors affecting the formation of disinfection by-products with chlorine dioxide

The object of this research was to study the formation of disinfection by-products by using chlorine dioxide (ClO2) as a disinfectant reacting with different properties of organic substance in natural aquatic environment. The adsorbent resin (XAD-4, XAD-7) was used to divide the organic matters in raw water into three groups. The influence of the function groups on structure, reaction tendency, and formation of disinfection by-products generated by the reaction of these organic substances with chlorine dioxide was explored. The experimental results show that the three different organic groups formed using adsorbent resin were hydrophobic substance, hydrophilic acid, and non-acid hydrophilics in proportions of 43%, 41%, and 16%, respectively. Within the raw water in our study, the hydrophilic substance had a higher distribution proportion than that described in general articles and journals, which indicates that this water was contaminated with pollution from human beings. The exploration of the reactivity of the three different organic substances with chlorine dioxide shows that the unit consumption of disinfection agent per unit organic matters (represented by ClO2/DOC) is in the following sequence hydrophobic substance > hydrophilic substance > non-acid hydrophilics. It indicated that larger molecular organic precursors had larger consumption of disinfectant. We also discovered that after the reaction of the three different organic substances with chlorine dioxide, the largest amount of disinfection by-products were generated by the non-acid hydrophilics.

Photocatalytic degradation of wastewater from manufactured fiber by titanium dioxide suspensions in aqueous solution

This investigation concerned the use of titanium dioxide irradiated with UV light of 365 nm wavelength in a jacketed cylindrical glass reactor for the removal of organic pollutants from the final settling tank of wastewater from manufactured fiber production. The controlling factors of the feasibility studies included the amount of titanium dioxide, pH value, light intensity, and aeration on the decomposition. The results indicated that, with 0.25 g/L TiO2, optimum decomposition could be attained. An excess amount of TiO2 could block the light passage and lower the efficiency. The lower the pH value, the better the decomposition. The decomposition of organic pollutants was in proportion to the light intensity, while aeration was a decisive controlling factor, with dissolved organic carbon (DOC) removal efficiency from 30% without aeration to 75% with aeration.

The formation and control of disinfection by-products using chlorine dioxide

In this study, chlorine dioxide (ClO2) was used as an alternative disinfectant with vanillic acid, p-hydroxybenzoic acid, and humic acid as the organic precursors in a natural aquatic environment. The primary disinfection by-products (DBPs) formed were trihalomethanes (THMs) and haloacetic acids (HAAs). Under neutral conditions (pH = 7) for vanillic acid, more total haloacetic acids (THAAs) than total trihalomethanes (TTHMs) were found, with a substantial increase during the later stages of the reaction. In the case of p-hydroxybenzoic acid, the amount of THAAs produced was minimal. Raising the concentration of ClO2 was not favorable for the control of THAAs in low concentrations of vanillic acid. ClO2 could reduce the total amount of TTHMs and THAAs for higher concentration of vanillic acid. It was found that the humic acid treatment dosage was not significant. Under alkaline conditions (pH = 9), the control of TTHMs and THAAs for the treatment of vanillic acid was better and more economical, however, an appreciable amount of inorganic by-products were observed. Under the same alkaline condition, the control of THAA for the treatment of p-hydroxybenzoic acid was not beneficial and for the treatment of humic acid was not significant.