Mineralization of Para-Chlorobenzoic Acid in Water by Cobalt-Incorporated MCM-41 Catalyzed Ozonation

Cobalt-incorporated MCM-41(Co-MCM-41) was used as a heterogeneous catalyst for the ozonation of para-chlorobenzoic acid (p-CBA) in aqueous solution. Cobalt oxide supported on MCM-41(Co/MCM-41) was synthesized for comparison. Their textural properties were elucidated by various characterization techniques to understand the relationship between surface texture and catalytic activity. TOC removal at 60 min reached 91% with Co-MCM-41, 83% with Co/MCM-41 and only 52% with ozone alone, respectively. Observations from diffuse reflection spectroscopy demonstrated that different metal phases were formed in these cobalt-modified molecular sieves samples. Radical scavenger experiments indicated the formation of hydroxyl radicals that were responsible for the effective degradation of p-CBA. An integrated approach to the catalytic mechanism was proposed by considering the variation of pH in the course of ozonation as well as its subsequent influence on the dissociation of targeted compounds and surface charge of the catalyst. In the reusability experiments, the reused Co-MCM-41 was able to regain the same catalytic capability as the fresh one within 5 cycles. X-ray photoelectron spectroscopy results indicated that a part of Co²⁺ was oxidized to Co³⁺ after oxidation reaction.     

The Chemistry of Water Treatment Processes Involving Ozone,Hydrogen Peroxide and Ultraviolet Radiation

Advanced oxidation processes are defined as those which involve the generation of hydroxyl radicals in sufficient quantity to affect water purification. The theoretical and (practical yield of OH from O₃ at high pH, 0₃/H₂0₂, O₃/UV and H₂O₂/UV systems is reviewed. New data is presented which illustrates the importance of direct photolysis in the O₃/UV process, the effect of the H₂0₂:0₃ ratio in the O₃/H₂O₂ process, and the impact of the low extinction coefficient of H₂O₂ in the H₂0₂/UV process.     

Natural organic matter and sunlight accelerate the degradation of 17ß-estradiol in water

Nanomolar concentrations of steroid hormones such as 17β-estradiol can influence the reproductive development and sex ratios of invertebrate and vertebrate populations. Thus their release into surface and ground waters from wastewater facilities and agricultural applications of animal waste is of environmental concern. Many of these compounds are chromophoric and susceptible to photolytic degradation. High intensity UV-C radiation has been demonstrated to degrade some of these compounds in engineered systems. However, the degradation efficacy of natural solar radiation in shallow fresh waters is less understood. Here photolytic experiments with 17β-estradiol demonstrated modest photodegradation (~ 26%) when exposed to simulated sunlight between 290 and 720 nm. Photodegradation significantly increased (~ 40-50%) in the presence of 2.0-15.0 mg/l of dissolved organic carbon (DOC) derived from humic acids of the Suwannee River, GA. However, rates of photodegradation reached a threshold at approximately 5.0 mg/l DOC. Observed suppression of photolysis in the presence of a radical inhibitor (i.e. 2-propanol) indicated that a significant proportion of the degradation was due to radicals formed from the photolysis of DOC. Although photodegradation was greatest in full sunlight containing UV-B (290-320 nm), degradation was also detected with UV-A (320-400 nm) and visible light (400-720 nm) alone.     

Indeno-Polycyclic Aromatic Hydrocarbons: A Versatile New Synthetic Route

Acylation of a polycyclic aromatic hydrocarbon (PAH) adjacent to a ring junction with 2-bromobenzoyl chloride followed by Flash Vacuum Pyrolysis (FVP) of the resulting bromoketone affords the corresponding indeno-annulated PAH. The new method is illustrated by syntheses of indeno[1,2,3-cd]pyrene (1) from pyrene and indeno[1,2,3-cd]fluoranthene (2) from fluoranthene. The formation of indeno[1,2,3,4-defg]chrysene (11) from FVP of 8-(2-bromobenzoyl)-fluoranthene (10), and as a secondary product from FVP of 3-(2-bromobenzoyl)fluoranthene (9), reveals the ability of phenyl groups to migrate around the periphery of a didehydro-PAH. Mechanisms involving reversible hydrogen atom transfers are proposed. Diacylation of fluoranthene with 2-bromobenzoyl chloride followed by FVP gives the previously unknown, nonplanar, nonalternant, C₂₈H₁₄ PAH diindeno[1,2,3,4-defg: 1,2,3-rs]chrysene (21) in just two steps.     

Gamma irradiation of pharmaceutical compounds, nitroimidazoles, as a new alternative for water treatment

The main objectives of this study were: (1) to investigate the decomposition and mineralization of nitroimidazoles (Metronidazole [MNZ], Dimetridazole [DMZ], and Tinidazole [TNZ]) in waste and drinking water using gamma irradiation; (2) to study the decomposition kinetics of these nitroimidazoles; and (3) to evaluate the efficacy of nitroimidazole removal using radical promoters and scavengers. The results obtained showed that nitroimidazole concentrations decreased with increasing absorbed dose. No differences in irradiation kinetic constant were detected for any nitroimidazole studied (0.0014-0.0017 Gy⁻¹). The decomposition yield was higher under acidic conditions than in neutral and alkaline media. Results obtained showed that, at appropriate concentrations, H₂O₂ accelerates MNZ degradation by generating additional HO; however, when the dosage of H₂O₂ exceeds the optimal concentration, the efficacy of MNZ degradation is reduced. The presence of t-BuOH (HO radical scavenger) and thiourea (HO, H and e_aq⁻ scavenger) reduced the MNZ irradiation rate, indicating that degradation of this pollutant can take place via two pathways: oxidation by HO radicals and reduction by e_aq⁻ and H. MNZ removal rate was slightly lower in subterranean and surface waters than in ultrapure water and was markedly lower in wastewater. Regardless of the water chemical composition, MNZ gamma irradiation can achieve i) a decrease in the concentration of dissolved organic carbon, and ii) a reduction in the toxicity of the system with higher gamma absorbed dose.     

Characterization of Natural Water for Potential to Oxidize Organic Pollutants with Ozone

A laboratory study has been designed to investigate the decomposition of ozone in natural water and to determine its potential to produce hydroxyl free radicals for the oxidation of micropollutants during the ozonation process of drinking water. This report describes the first data obtained using a continuous flow reactor capable of observing reactions with relatively short time scales (Q = 34 mL/min; 1.4 < t_c < 27 sec). Rates of ozone decay were studied in fulvic acid solution in the presence, or in the absence of radical scavenger (tert-butyl alcohol) or of promoter of ozone decomposition (formic acid), and a micropollutant of interest (tetrachloroethylene). Also, three natural waters were studied, illustrating that OH radical formation depends on chemical composition of the waters.     

Preliminary Investigation of Manganese-Catalyzed Ozonation for the Destruction of Atrazine

A preliminary experimental study conducted with a conventional bubble ozonation contactor column has shown that small amounts of Mn(II) greatly enhanced the destruction of atrazine by ozone. There is an inversely linear relationship between the dosed Mn(II) concentration and the residual ozone concentration at a specific reaction time. The ozone transfer efficiency into water is greater with the increase of Mn(II) dosage. Hydrous manganese dioxide prepared by reacting permanganate with manganese sulfate, also was shown to be effective in catalyzing the destruction of atrazine by ozone. The efficiency of catalytic activity for the destruction of atrazine caused by preformed hydrous Mn(IV) is slightly lower than the case of Mn(II). A lower residual ozone value using manganese dioxide compared to the case of ozone alone suggests that ozone also may be decomposed by hydrous Mn(IV). However, a commercial MnO₂ did not show any catalytic activity for atrazine destruction. The very much greater degree of atrazine oxidation by manganese-catalyzed ozonation compared to ozone alone is speculated to be the result of the generation of highly oxidative intermediate species such as hydroxyl radicals during the reaction between ozone and manganese species.     

Hydrogen-enriched non-premixed jet flames: Compositional structures with near-wall effects

The species concentrations of non-premixed hydrogen and syngas flames were examined using results obtained from direct numerical simulation technique with flamelet generated manifold chemistry. Flames with pure H₂ and H₂/CO mixtures are discussed for an impinging jet flame configuration. Single-point data analyses are presented illustrating the effects of fuel composition on species concentrations. In general, scatterplots of all species show the effects of fuel variability on the flame compositional structures. The behaviours of major combustion products and key radicals species indicate the effects of CO concentration on the 2/CO syngas combustion. In particular, high concentration of CO tends to induce local extinction in the 2/CO flames in which critical chemical reactions of the fuel mixture such as CO + OH become important. The unsteady fluctuations of species profiles in the wall jet region characterise the complexity of the distributions of compositional structures in the near-wall region with respect to the effects of CO concentration on the combustion of hydrogen-enriched fuels.     

Decomposition of Ethylene Glycol by the Combined Use of Ozone Oxidation and Electrolytic Methods

Decomposition of ethylene glycol by the combined use of an ozone oxidation and an electrolytic method was studied. The overall order of reaction was 0.8 with respect to the concentration of ethylene glycol, and 0.7 to that of ozone in the feed gas. Glycolaldehyde, glyoxal, glyoxylic acid, and formaldehyde were detected as reaction products, and the removal of total organic carbon (TOC), which was not attained by either of the two methods alone, was attained at the same time. The reaction pathway was estimated, and it was considered that the removal of TOC via formic acid was more important than that via oxalic acid. The synergistic effect of the combined use was considered to be caused by reactive radicals formed during the process of a reaction. The removal of TOC was greatly affected by the quality and quantity of salt added.     

Treatment of Malodorants in Air by the UV/Ozone Technique

Laboratory work has shown that a gas scrubber using UV/ozone as the oxidant was effective in destroying model compounds, and that the UV radiation was better applied in the sump liquor rather than in the spray section. A field trial on a plant making selective weed killers has demonstrated that the technique was able to reduce the concentration of malodorants (mainly chlorophenols) by two to three orders of magnitude in a single pass.