Kinetics of benzenesulfonates elimination by UV and UV/H2O2

Catalytic Ozonation in Arrayed Zinc Oxide Nanotubes as Highly Efficient Mini-Column Catalyst Reactors (MCRs): Augmentation of Hydroxyl Radical Exposure

Reactor design is significant to catalytic ozonation for an efficient mass transfer and exposure of the powerful but short-lived hydroxyl radicals (HO•). Herein, five groups of zinc oxide nanotube arrays with pore sizes from 168 to 10 nm were produced as mini-column catalyst reactors (MCRs) for internal catalytic ozonation, whose performance was comparatively studied on the kinetics of ozone transfer, consumption, and radical probe interaction. Using an R_CT value describing HO• exposure, all the MCRs with sufficient ozone transfer featured an R_CT level of at least 3.2 × 10^-6, which is substantially higher than most values in referenced works (10^-9∼10^-6) and that for microscale reactors in our work (∼10^-8). Furthermore, the HO• exposure dramatically increased with diminishing pore size, causing an elevated R_CT up to 8.0 × 10^-5 for the smallest MCR with 10 nm pore. The interphase formed in this flow-through system might have enriched HO• radicals produced via surface, and for a smaller MCR, the effect would be greater with a more confined microfluidic region. Investigations on electron paramagnetic resonance and the treatment of ozone-recalcitrant organics corroborated the nanoscale effect of MCR on augmentation of HO• exposure. This study offers a new way to design nanotube reactors for internal HO•-based heterogeneous catalysis.

Modeling partial oxidation of a commercial textile surfactant formulation with the H(2)O(2)/UV-C process

In the present study, the reaction conditions required for the partial oxidation of a commercial nonionic textile surfactant, an alkyl polyethoxylate, with the H(2)O(2)/UV-C treatment process were optimized using central composite design and response surface methodology (CCD-RSM). CCD-RSM allowed for the development of empirical quadratic equations that satisfactorily predicted COD and TOC removal efficiencies under all studied experimental conditions. Analysis of variance revealed that the variables "H(2)O(2) concentration" and "initial surfactant COD" were found to be the process independent parameters most positively and negatively affecting the treatment performance, respectively, whereas the process variable "treatment time" had a smaller influence on COD and TOC removal efficiencies. According to the established polynomial regression models, for the degradation of the nonionic surfactant at an initial COD of 450 mg L(-1) and pH of 10.5, the optimized treatment conditions were 15 mM H(2)O(2) and a reaction time of 80 min. In order to achieve the treatment targets (complete surfactant removal accompanied by 60% COD and TOC elimination to meet the national discharge consents into receiving water bodies) either H(2)O(2) concentration or photochemical treatment time had to be increased. Activated sludge inhibition experiments conducted with nonionic surfactant solution being subjected to photochemical oxidation under optimized reaction conditions indicated that the inhibitory effect of the nonionic surfactant could be completely eliminated during H(2)O(2)/UV-C treatment and the partial degradation intermediates were more biodegradable than the original textile surfactant.

Photocatalytic degradation of p-phenylenediamine with TiO2-coated magnetic PMMA microspheres in an aqueous solution

This study investigates the photocatalytic degradation of p-phenylenediamine (PPD) with titanium dioxide-coated magnetic poly(methyl methacrylate) (TiO2/mPMMA) microspheres. The TiO2/mPMMA microspheres are employed as novel photocatalysts with the advantages of high photocatalytic activity, magnetic separability, and good durability. The scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), and transmission electron microscopy (TEM) images of the TiO2/mPMMA microspheres are used to characterize the morphology, element content, and distribution patterns of magnetite and TiO2 nanoparticles. The BET-specific surface area and saturation magnetization of the TiO2/mPMMA microspheres are observed as 2.21 m(2)/g and 4.81 emu/g, respectively. The photocatalytic degradation of PPD are performed under various experimental conditions to examine the effects of initial PPD concentration, TiO2/mPMMA microsphere dosage, and illumination condition on the eliminations of PPD and chemical oxygen demand (COD) concentrations. Good repeatability of photocatalytic performance with the use of the TiO2/mPMMA microspheres has been demonstrated in the multi-run experiments. The photocatalytic kinetics for the reductions of PPD and COD associated with the initial PPD concentration, UV radiation intensity, and TiO2/mPMMA microsphere dosage are proposed. The relationships between the reduction percentages of COD and PPD are clearly presented.

Degradation of DMSO by ozone-based advanced oxidation processes

The present study investigates the oxidation of dimethyl sulfoxide (DMSO) by conventional ozonation and the advanced oxidation processes (AOPs). The major degradation products identified were methanesulfinate, methanesulfonate, formaldehyde, and formic acid in ozonation process. The subsequent degradation of intermediates shows that methanesulfonate is more resistance to ozonation, which reduces the mineralization rate of DMSO. The effect of t-butanol addition and ozone gas flow dosage on the degradation rate was evaluated. The rate constant of the reaction of ozone (k(D)) with DMSO was found to be 0.4162 M(-1)S(-1). In the second part of this study, DMSO degradation and TOC mineralization were investigated using O(3)/UV, O(3)/H(2)O(2) and UV/H(2)O(2) processes. In all theses processes the degradation of target organics is more pronounced than TOC removal. The efficiencies of these processes were evaluated and discussed. The formation of sulfate ion in all AOPs have been identified and compared with other processes. Overall it can be concluded that ozonation and ozone-based AOPs are promising processes for an efficient removal of DMSO in wastewater.

Degradation of xenobiotics originating from the textile preparation, dyeing, and finishing industry using ozonation and advanced oxidation

Effluents from textile preparation, dyeing, and finishing processes contain high concentrations of biologically difficult-to-degrade or even inert auxiliaries. Under these circumstances, it most often becomes inevitable to apply energy-intense and hence "imperative" treatment technologies (so-called advanced oxidation processes, AOPs) to achieve an acceptable reduction in the organic content of the effluent, thereby improving the biocompatibility of the originally refractory wastewater. The present experimental study focused on three problematic dyehouse effluent streams in order to alleviate the problem of toxicity and recalcitrance arising from the use of certain textile chemicals at source. For that purpose, the textile preparation stage was simulated by a nonionic surfactant (NS), the polyamide dyeing stage by a synthetic tannin (syntan; ST), and an aqueous biocidal finishing (BF) solution was employed to mimic typical textile finishing effluent. Synthetic effluent streams bearing NS, ST, or BF were subjected to treatment with different, well-established AOPs (ozonation at varying pH; advanced oxidation with H(2)O(2)/UV-C at varying H(2)O(2) concentrations) in order to degrade the active ingredients of the auxiliary formulations, thereby eliminating their toxicity and recalcitrance. Baseline experiments were conducted in order to optimize AOP conditions that were consecutively applied to observe changes in the originally poor effluent biodegradability and high toxicity. Obtained experimental findings revealed that (i) the COD content of NS could be reduced by at least 50% after H(2)O(2)/UV-C treatment at pH 9.0 accompanied by a nearly twofold improvement in its already fair biodegradability; (ii) the inhibitory effect of the biochemically reluctant ST on heterotrophic biomass was completely eliminated upon ozonation (dose=900 mg h(-1)) at pH 3.5; and (iii) the microbial toxicity exerted by BF totally disappeared after ozonation (dose=600 mg h(-1)) at pH 7.2. However, the achievement of detoxification and/or biodegradability improvement was accompanied with high electrical energy requirements.

Photochemical degradation of diethyl phthalate with UV/H2O2

The decomposition of diethyl phthalate (DEP) in water using UV-H2O2 process was investigated in this paper. DEP cannot be effectively removed by UV radiation and H2O2 oxidation alone, while UV-H2O2 combination process proved to be effective and could degrade this compound completely. With initial concentration about 1.0mg/L, more than 98.6% of DEP can be removed at time of 60 min under intensity of UV radiation of 133.9 microW/cm2 and H2O2 dosage of 20mg/L. The effects of applied H2O2 dose, UV radiation intensity, water temperature and initial concentration of DEP on the degradation of DEP have been examined in this study. Degradation mechanisms of DEP with hydroxyl radicals oxidation also have been discussed. Removal rate of DEP was sensitive to the operational parameters. A simple kinetic model is proposed which confirms to pseudo-first order reaction. There is a linear relationship between rate constant k and UV intensity and H2O2 concentration.