Degradation of perfluorinated compounds by sulfate radicals - New mechanistic aspects and economical considerations.

Perfluorinated organic compounds (PFC) are an important group of pollutants, which are difficult to be degraded in conventional water treatment. Even hydroxyl radical based processes are not capable to degrade these compounds. Sulfate radicals can oxidize a group of PFC, i.

Reaction of 2-propanol with ozone in aqueous media.

This paper deals with reactions occurring in the aqueous system of 2-propanol/ozone. The considered reactions are discussed from thermodynamic and kinetic points of view. The major finding refers to the fact that 2-propanol reacts with O mainly via hydride transfer: (HO)(HC)CH + O → [(HO)(HC)C + HO] → (HO)(HC)C + HO → (HC)CO + HO + O Arguments supporting this proposed mechanism are: high exergonicity of reaction (ΔG = -234 kJ mol for the first two steps), low HO yield - (2.

Hydroxyl radical yields in the Fenton process under various pH, ligand concentrations and hydrogen peroxide/Fe(II) ratios.

The Fenton process, one of several advanced oxidation processes, describes the reaction of Fe(II) with hydrogen peroxide. Fe(II) is oxidized to Fe(III) that reacts with hydrogen peroxide to Fe(II) and again initiates the Fenton reaction. In the course of the reactions reactive species, e.

Ozonation of anilines: Kinetics, stoichiometry, product identification and elucidation of pathways.

Anilines as archetypes for aromatic amines, which play an important role in the production of, e.g., dyestuffs, plastics, pesticides or pharmaceuticals were investigated in their reaction with ozone.

A New Reaction Pathway for Bromite to Bromate in the Ozonation of Bromide.

Ozone is often used in the treatment of drinking water. This may cause problems if the water to be treated contains bromide as its reaction with ozone leads to the formation of bromate, which is considered to be carcinogenic. Bromate formation is a multistep process resulting from the reaction of ozone with bromite.

Degradation of chlorotriazine pesticides by sulfate radicals and the influence of organic matter.

Atrazine, propazine, and terbuthylazine are chlorotriazine herbicides that have been frequently used in agriculture and thus are potential drinking water contaminants. Hydroxyl radicals produced by advanced oxidation processes can degrade these persistent compounds. These herbicides are also very reactive with sulfate radicals (2.

Carbohydrate radicals: from ethylene glycol to DNA strand breakage.

Radiation-induced DNA strand breakage results from the reactions of radicals formed at the sugar moiety of DNA. In order to elucidate the mechanism of this reaction investigations were first performed on low molecular weight model systems. Results from studies on deoxygenated aqueous solutions of ethylene glycol, 2-deoxy-d-ribose and other carbohydrates and, more relevantly, of d-ribose-5-phosphate have shown that substituents can be eliminated from the β-position of the radical site either proton and base-assisted (as in the case of the OH substituent), or spontaneously (as in the case of the phosphate substituent).

Formation of bromate in sulfate radical based oxidation: mechanistic aspects and suppression by dissolved organic matter.

Sulfate radical based oxidation is discussed being a potential alternative to hydroxyl radical based oxidation for pollutant control in water treatment. However, formation of undesired by-products, has hardly been addressed in the current literature, which is an issue in other oxidative processes such as bromate formation in ozonation of bromide containing water (US-EPA and EU drinking water standard of bromate: 10 μg L(-1)). Sulfate radicals react fast with bromide (k = 3.

Reaction of gadolinium chelates with ozone and hydroxyl radicals.

Gadolinium chelates are used in increasing amounts as contrast agents in magnetic resonance imaging, and their fate in wastewater treatment has recently become the focus of research. Oxidative processes, in particular the application of ozone, are currently discussed or even implemented for advanced wastewater treatment. However, reactions of the gadolinium chelates with ozone are not yet characterized.

The (•)OH radical yield in the H2O2 + O3 (peroxone) reaction.

The peroxone process is one of the AOPs that lead to (•)OH. Hitherto, it has been generally assumed that the (•)OH yield is unity with respect to O3 consumption. Here, experimental data are presented that suggest that it must be near 0.

Standard Gibbs free energies of reactions of ozone with free radicals in aqueous solution: quantum-chemical calculations.

Free radicals are common intermediates in the chemistry of ozone in aqueous solution. Their reactions with ozone have been probed by calculating the standard Gibbs free energies of such reactions using density functional theory (Jaguar 7.6 program).

Degradation of ozone-refractory organic phosphates in wastewater by ozone and ozone/hydrogen peroxide (peroxone): the role of ozone consumption by dissolved organic matter.

Ozonation is very effective in eliminating micropollutants that react fast with ozone (k > 10(3) M(-1) s(-1)), but there are also ozone-refractory (k < 10 M(-1) s(-1)) micropollutants such as X-ray contrast media, organic phosphates, and others. Yet, they are degraded upon ozonation to some extent, and this is due to (•)OH radicals generated in the reaction of ozone with organic matter in wastewater (DOM, determined as DOC). The elimination of tri-n-butyl phosphate (TnBP) and tris-2-chloroisopropyl phosphate (TCPP), added to wastewater in trace amounts, was studied as a function of the ozone dose and found to follow first-order kinetics.

Reaction of ozone with hydrogen peroxide (peroxone process): a revision of current mechanistic concepts based on thermokinetic and quantum-chemical considerations.

The reaction of ozone with the anion of H(2)O(2) (peroxone process) gives rise to (*)OH radicals (Staehelin, J.; Hoigne, J. Environ.

The reaction of ozone with the hydroxide ion: mechanistic considerations based on thermokinetic and quantum chemical calculations and the role of HO4- in superoxide dismutation.

The reaction of OH(-) with O(3) eventually leads to the formation of *OH radicals. In the original mechanistic concept (J. Staehelin, J.

Ozonolysis of lignin models in aqueous solution: anisole, 1,2-dimethoxybenzene, 1,4-dimethoxybenzene, and 1,3,5-trimethoxybenzene.

The lignin models anisole, 1,2-dimethoxybenzene, 1,4-dimethoxybenzene, and 1,3,5-trimethoxybenzene were reacted with ozone in aqueous solution, and major products were identified and quantified with respect to ozone consumption when reference material was available. Hydroxylation products in yields equivalent to those of singlet oxygen and muconic products (in analogy to the Criegee mechanism) dominate. The formation of quinones points to the release of methanol.

Ozonation of wastewater: rate of ozone consumption and hydroxyl radical yield.

For the prediction of the elimination efficiency of micropollutants from wastewater by ozone, the ozone rate constants of the micropollutants and the kinetics of the reaction of ozone with wastewater must be known. The latter is multiphasic with k = 0.071 (mg DOC)(-1) s(-1) for the first mg/L ozone (at a DOC of 7.

Oxidation of some typical wastewater contaminants (tributyltin, clarithromycin, metoprolol and diclofenac) by ozone.

The rate constants of the reactions of O(3) with some typical wastewater pollutants (tributyltin, the macrolide antibiotic clarithromycin, the beta blocker metoprolol and the analgesic diclofenac) were determined and some mechanistic aspects were elucidated. Except for tributyltin compounds that react only slowly with O(3) (k=4-7 M(-1) s(-1)), the compounds react fast (k>10(4) M(-1) s(-1)) and can be eliminated at low O(3) doses. Clarithromycin reacts at its dimethylamino group and yields the corresponding N-oxide that is no longer biologically active.

Photoprocesses of chloro-substituted p-benzoquinones.

The photochemistry of chloro-(ClBQ), dichloro-(2,5- and 2,6-Cl 2BQ), and trichloro-1,4-benzoquinone (Cl 3BQ) was studied in aqueous solution and/or in mixtures with acetonitrile. Final products are the corresponding hydroquinones (QH 2s) and 2-hydroxy-1,4-benzoquinones (QOHs). Three transients were detected by UV-vis absorption spectroscopy.

Oxidation of diclofenac with ozone in aqueous solution.

Ozonation of diclofenac in aqueous solution in the presence and absence of an *OH scavenger, tertiary butanol (t-BuOH), was studied, and the most important reaction intermediates and products were identified. The second-order O3 rate constantwas determined by competition with buten-3-ol and was found to be 6.8 x 10(5) M(-1) s(-1) at 20 degrees C.

Guanine-derived radicals: dielectric constant-dependent stability and UV/Vis spectral properties: a DFT study.

Upon successive deprotonation of the guanine radical cation, various neutral radicals and radical anions can be formed. Their relative stability and UV/Vis absorption spectra have been calculated by DFT in the vacuum and in aqueous solution. Good agreement with experimental data is obtained when solvent effects are taken into account.

The energetics of rearrangement and water elimination reactions in the radiolysis of the DNA bases in aqueous solution (eaq- and *OH attack): DFT calculations.

DFT calculations on the relative stability of various nucleobase radicals induced by e(aq)(-) and (*)OH have been carried out for assessing the energetics of rearrangements and water elimination reactions, taking the solvent effect of water into account. Uracil and thymine radical anions are protonated fast at O2 and O4, whereby the O2-protonated anions are higher in energy (50 kJ mol(-1), equivalent to a 9-unit lower pK(a)). The experimentally observed pK(a)=7 is thus that of the O4-protonated species.

Quantification and modeling of the elimination behavior of ecologically problematic wastewater micropollutants by adsorption on powdered and granulated activated carbon.

The adsorption on powdered activated carbon (PAC) of ecotoxic or potentially ecotoxic micropollutants (ten pharmaceuticals, four X-ray contrast media, and eight industrial chemicals) present in a biologically treated municipal wastewater is studied. All but the X-ray contrast media are eliminated with high efficiency at an economically feasible PAC dosage of 10 mg/L. Based on the experimental data, the competition between the background organic matter and the micropollutant for the active sites of the adsorbent is modeled with the help of the adsorption and tracer analysis supported by the Ideal Adsorption Solution Theory.

Degradation of macrolide antibiotics by ozone: a mechanistic case study with clarithromycin.

Macrolide antibiotics are widely used (in the order of 1g per person per year). They pass the body largely unchanged and are also not degraded in wastewater treatment plants. With not too much effort, they may be eliminated from their effluents by ozonation.