Degradation rates of benzotriazoles and benzothiazoles under UV-C irradiation and the advanced oxidation process UV/H2O2

Abstract

Benzotriazoles (BTs) and benzothiazoles (BTHs) are extensively used chemicals found in a wide range of household and industrial products. They are chemically stable and are therefore ubiquitous in the aquatic environment. The present study focuses on the potential of ultraviolet (UV) irradiation, alone or in combination with hydrogen peroxide (H2O2), to remove BTs and BTHs from contaminated waters. Six compounds, three out of each chemical class, were investigated using a low-pressure mercury lamp (main emission at 254 nm) as the radiation source. Initially, the direct phototransformation kinetics and quantum yield in dilute aqueous solution was studied over the pH range of 4-12. All BTs and BTHs, except for benzothiazole, exhibited pH-dependent direct phototransformation rate constants and quantum yields in accordance to their acid-base speciation (7.1 < pKa < 8.9). The direct phototransformation quantum yields (9.0 × 10(-4)-3.0 × 10(-2) mol einstein(-1)), as well as the photon fluence-based rate constants (1.2-48 m(2) einstein(-1)) were quite low. This suggests that UV irradiation alone is not an efficient method to remove BTs and BTHs from impacted waters. The second-order rate constants for the reaction of selected BTs and BTHs with the hydroxyl radical were also determined, and found to fall in the range of 5.1-10.8 × 10(9) M(-1) s(-1), which is typical for aromatic contaminants. Finally, the removal of BTs and BTHs was measured in wastewater and river water during application of UV irradiation or the advanced oxidation process UV/H2O2. The latter process provided an efficient removal, mostly due to the effect of the hydroxyl radical, that was comparable to other aromatic aquatic contaminants, in terms of energy requirement or treatment costs.

Degradation of nitro-based pharmaceuticals by UV photolysis: Kinetics and simultaneous reduction on halonitromethanes formation potential

“…To quantitatively analyze the pH dependence of UV photolysis of RNTD and NZTD, the ε was modeled as a function of pH by assigning each protonated/deprotonated species a specific molar absorptivity (ε 0 and ε 1 ), with the apparent absorptivity being the summation of the absorptivity contributed by each species (Eqs. (1)e(3)) (Canonica et al, 2008;Bahnmuller et al, 2015). The specific molar absorptivity for each RNTD and NZTD species was fit by minimizing the sum of differences squared between observed and modeled apparent molar absorptivity.…”

Degradation of benzotriazole by a novel Fenton-like reaction with mesoporous Cu/MnO 2 : Combination of adsorption and catalysis oxidation

“…When the MCM dose was increased from 0.2 to 0.5 g L −1 , there were significant increases in both the adsorption and oxidation. [38], which suggests that the MCM shows higher catalytic activity and usage rate of H 2 O 2 than other catalysts. The effect of the initial concentration of BZA on the performance is shown in Figure 3(E).…”

“…After drying at 70°C overnight, MCM was obtained by calcination in air at 300°C for 7 2 h. Under typical synthetic conditions, the MCM showed a Cu/Mn molar ratio of 1:4.…”

“…Through its widespread application, considerable amounts of BZA have been released into the aquatic environment in direct discharge of effluents from industrial plants [5] and from urban wastewater treatment plants (WWTPs) [6]. The presence of BZA in the aqueous environment is harmful to ecosystems and human health [7]. Recently, BZA has been listed as an emerging contaminant [2], and many studies have documented that the conventional microbiology-based WWTP techniques cannot entirely degrade this compound because of its persistence [8].…”

Oxidation of benzotriazole and benzothiazole in photochemical processes: Kinetics and formation of transformation products

“…Some of the AOPs were also investigated with regards to BTH and BTA, e.g. -monochromatic UV/H 2 O 2 oxidation [20,21], ozonation combined with sorption on activated carbon (O3/AC) [22], oxidation by persulfate and electron beam irradiation [23].…”