The photodegradation and modeling of a typical NAPL trichloroethene, by monochromatic UV irradiations

In this study, the photodegradation of a typical nonaqueous phase liquid (NAPL)-trichloroethene (TCE) by ultraviolet irradiation was investigated. The decay of NAPL-TCE was studied in a RPR-200 Rayonet photochemical reactor, at three different monochromatic UV lamps (254, 300, and 350 nm). Among the three UV wavelengths used, the highest photodecay rate was obtained at 254 nm. The effect of the initial NAPL dosage was also analyzed to determine the photodecay of NAPL-TCE in batch experiments by ultraviolet irradiation at preselected wavelengths. The direct photolysis of NAPL-TCE followed two-stage pseudo first-order decay kinetics. The photodegradation rates of TCE were found to decrease with the increment of NAPL dosage. It is interesting to find that the NAPL dosage is critical to determine the process performance due to the NAPL size or cage effect, which will control the diffusion of TCE/intermediates between NAPL and aqueous phases and therefore the overall reaction rates. Mathematical models were developed for the prediction of the two-stage photodegradation, in which the remaining fraction of TCE (C/C0) in the system becomes predictable.

The photodegradation of trichloroethylene with or without the NAPL by UV irradiation in surfactant solutions

The photodegradation of trichloroethene (TCE) with or without nonaqueous phase liquids (NAPL) by ultraviolet irradiation in surfactant solutions was examined in this study. The photodecay of TCE was studied at monochromatic 254nm UV lamps. The effects of the type of surfactants, initial surfactant concentrations, pH levels and NAPL concentrations were examined to explore the photodecay of TCE. All the photodegradation of TCE followed pseudo-first-order decay kinetics at various conditions. It was found that Brij 35 overdose and higher initial pH levels may retard or inhibit the photodecay of TCE, mainly due to protons, intermediate generation and change of surfactant structure in the processes. The optimal condition for TCE photodecay was suggested based on the analysis of kinetics data, from which the reaction mechanism of TCE in the presence of NAPL form was also studied. In general, the reactions of TCE in micellar solution and NAPL pool can be considered as independent pathways due to the low molecule diffusion between the two phases.

Antenatal ovarian torsion: a "free-floating" cyst

This case report documents the unusual presentation of an antenatal ovarian torsion followed by auto-amputation of the ovarian tube complex, finally resulting in a free floating abdominal cyst. The differential diagnosis of antenatally diagnosed abdominal cysts is discussed and the surgical management outlined.

Removal of phenylurea herbicide monuron via riboflavin-mediated photosensitization

Photodegradation of the phenylurea herbicide monuron by using riboflavin (Rf), a sensitizer, was investigated by varying the doses of monuron and Rf in this work. An enhanced photochemical effect was observed in the process compared with the direct photolysis by using UV irradiation only. The reaction time was greatly shortened from more than 60 min (direct photolysis) to 8-30 min depending on the doses of initial concentration of monuron ([M]0) and Rf. A modified hyperbola model was found to be useful to determine the reaction kinetics and thereafter the performance on the photodegradation of monuron sensitized by Rf. Two measurable characteristic constants (initial decay rate and total removal index) were used to quantify the reaction. The maximum removal difference compared with the direct photolysis and Rf-sensitization was investigated. It was found that the improvement of the process depended on both the [M]0 and the doses of Rf.

Selection of supported cobalt substrates in the presence of oxone for the oxidation of monuron

The immobilization of cobalt ion on different media to catalyze oxone has been investigated. A probe herbicide, Monuron, was effectively degraded by using Co2+/oxone systems. For Co2+ supported on zeolite, 100% of Monuron could be removed within a 10 min reaction time. However, the recycling of the spent Co-zeolite catalyst using various posttreatments did not give a promising result. This is likely because the zeolite particles in solution have blocked and significantly attenuated the incident UV light from reducing Co3+ to Co2+. On the contrary, the use of cationic resin has minimized these problems. In the process of Co-resin/oxone/UV, faster Monuron decay could be achieved than that in the dark reaction. In the presence of UV, a significant drop of total organic carbon (TOC) was also observed in this approach suggesting an effective and clean process for Monuron mineralization.

Fetoscopy under gas amniodistension: pressure-dependent influence of helium vs nitrous oxide on fetal goats

PURPOSE

Recently, gas amniodistension has been advocated for fetoscopic surgery to employ ergonomics similar to laparoscopy. However, neither the optimal type of gas nor its physiological influence on the fetus have been clearly outlined yet. This study investigates the impact of helium (HE) vs nitrous oxide (N2O) on fetal goats during fetoscopy.

METHODS

We insufflated either HE or N2O in 12 pregnant goats (15 fetuses; HE = 7, N2O = 8), then increased the pressures from 0, 4, 7, to 10 mm Hg in 30-minute intervals and recorded the fetal and maternal vital parameters. Finally, whole-body computed tomography to asses for intracorporeal gas was performed.

RESULTS

All fetuses survived. Mean fetal vital signs showed no significant differences between HE or N2O at specific pressure levels. In detail, HE/N2O at 0 vs 10 mm Hg caused a fetal temperature decrease (32.9 degrees C/33.2 degrees C vs 32 degrees C/32.5 degrees C), heart rate increase in the N2O group (100/102 vs 102/121 beats per minute), and no significant change in arterial pressure (45.8/48.3 vs 53.7/46.7 mm Hg). The PO2 was adequate (3.7/3.3 vs 3.7/2.9 kPa), whereas the pH remained unchanged (7.4/7.3 vs 7.3/7.3). However, fetal pCO2 was elevated in the N2O group before insufflation (5.5/7.2 vs 6.8/8.0 kPa) owing to maternal hypoventilation (maternal PCO2: 4.9/5.8 vs 5.0/5.4 kPa), correction of which was slower in the fetus than in the maternal animal. Computed tomography ruled out intracorporeal gas accumulation.

CONCLUSION

Neither HE nor N2O impose significant physiological harm for the fetus. Heating of the gas and maternal anesthesia seem essential. Considering the potential teratogenicity of N2O, however, HE could be the favorable environment for fetoscopic procedures under gas amniodistension.

Ozonation of endocrine disrupting chemical BHA under the suppression effect by salt additive--with and without H(2)O(2)

The oxidation of fresh and saline wastewater containing an endocrine disrupting chemical (butylated hydroxyanisole, BHA) under different reaction conditions by ozonation and O(3)/H(2)O(2) was investigated at various pH levels. The observed pseudo-first-order reaction kinetics was justified through a combined direct ozone and indirect radical oxidation approach for the ozonation process. The BHA decay rates increased with the increase of the solution pH, but decreased as the NaCl concentration increased because of the consumption of ozone by chloride. A kinetic model was therefore derived for predicting BHA degradation at various initial pH levels and NaCl concentrations. For the O(3)/H(2)O(2) and O(3)/H(2)O(2)/Cl(-) processes, the rate of BHA removal was investigated at hydrogen peroxide concentration ranged from 0.5 to 5mM at pH 7. Different optimal H(2)O(2) dosages and decay rates were found for both processes due to the participation of reactions among O(3), H(2)O(2), OH* and Cl(-) as discussed in the paper.

The role of organic ligands in ferrous-induced photochemical degradation of 2,4-dichlorophenoxyacetic acid

Recent studies have shown that hydrogen peroxide is generated in a ferrioxalate-induced photoreductive reaction, but information about the effect of organic ligands on the photochemical behaviour of ferrous species is limited. The degradation of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) by a ferrous-catalyzed oxidation in the presence of various ligands such as formate, citrate, malelate, oxalate, and ethylenediaminetetra-acetic acid (EDTA) was studied. The experiments were conducted under either dark or irradiated (350n m) conditions. Forty-two percent and 34% of 2,4-D were removed by the Fe(2+)/oxalate/UV and Fe(2+)/citrate/UV processes, respectively, after 30 min of reaction and oxidative intermediates were obtained in both cases. The presence of hydroxylated intermediates suggests that 2,4-D may be attacked by hydroxyl radicals, which are the products of the photo-Fenton-like reaction. As such, hydrogen peroxide was produced by the photolysis of ferrous oxalate or ferrous citrate, referred to hereafter as photogenerated H(2)O(2). As expected, the total removal percentage of 2,4-D jumped to 97% when 1mM of hydrogen peroxide (so-called spiked H(2)O(2)) was externally added to the reaction vessel to initiate the Fe(2+)/oxalate/UV process. Therefore, the treatment of 2,4-D by the Fe(2+)/oxalate/H(2)O(2)/UV system can be operated in two steps: the photolysis of ferrous oxalate first, followed by adding the spiked H(2)O(2) sometime after the commencement of the reaction. A two-phase model has been developed to describe this tandem ferrous-catalyzed photooxidation, which would help to achieve the mineralization of 2,4-D.

The effect of solution pH and peroxide in the TiO2-induced photocatalysis of chlorinated aniline

Chlorinated anilines are frequently used in the industry as starting materials for chemical synthesis. This type of compounds can end up as pollutants in wastewater. 2-Chloroaniline (2-ClA) was selected irradiating under monochromatic UV light at 300nm. The reaction rate could be enhanced by introducing low level of H(2)O(2) into the UV/TiO(2) system. Excess H(2)O(2) could not increase the HO* generation but retarded the reaction rate. The pH effect was also investigated in UV/TiO(2) and UV/TiO(2)/H(2)O(2) systems. All the experimental results show that pH is a sensitive parameter to the rate of degradation. Low reaction rate at acidic pH could be accounted by the dark adsorption test which has also proven the photocatalysis of TiO(2) may contribute to a two-step process: (1) 2-ClA pre-adsorbed onto TiO(2) and (2) photoexcitation of TiO(2). At high pH, rate enhancement could be observed at UV/TiO(2) system because of the increase generation of HO*. However, the introduction of H(2)O(2) slowdown the decay rate at such alkaline medium.

Degradation of atrazine by modified stepwise-Fenton's processes

The removal of atrazine (ATZ) by stepwise Fenton's processes (stepwise-FP) was studied and the system models were developed through the examination of reaction kinetics. The study compared the performance of the removal of ATZ by conventional FP with stepwise-FP, where the total dose of H(2)O(2) was split and inputted into the system at different times and/or quantities. The performance of stepwise-FP was found to be better than that of conventional FP. This was probably due to the minimization of the peak concentration of H(2)O(2) in the solution, which reduced the probability that valuable H(2)O(2) and hydroxyl radicals would be consumed in forming weaker radicals. The reaction kinetics of the decay of ATZ in stepwise-FP was found to be a two-stage process; and in each stage, fast decay followed by stagnant decay was observed. Two characterized constants (the initial decay rate and the oxidative capacity) were introduced and were found to be useful in quantifying the stepwise-FP. The models for predicting stepwise-FP with respect to different dosing times and/or asymmetrical doses were developed, and were found to be very useful for evaluating the system performance and/or for process design.

An image-based approach to measure the ferric ion diffusion coefficient in fricke gel dosimetry

A numerical method was adopted to solve the diffusion equation to determine ferric ion diffusion coefficient in Fricke-agarose gels. A fast MR acquisition technique was employed to avoid smearing of acquired data due to diffusion over an extended time period. Our results show that for a Fricke gel contained 1 mM ammonium ferrous sulfate, 1% agarose, 1 mM sodium chloride and 50 mM sulfuric acid, its ferric ion diffusion coefficient is 1.73 10^-2cm²h^-1in room temperature. This value is consistent with the 1 ~ 2 10^-2cm²h^-1range obtained by previous studies under varying concentrations of gel ingredients.

Reaction pathways and kinetics of butylated hydroxyanisole with UV, ozonation, and UV/O(3) processes

The chemical degradation of the endocrine disrupting chemical, butylated hydroxyanisole (BHA), was investigated by different treatment processes including ultraviolet (UV) irradiation, ozonation (O(3)), and UV/O(3). O demethylation, dimerization, and oxidation have been found to be the main degradation mechanisms. A systematic decay pathway was proposed based on ten identified intermediates in the studied processes, including a unique pathway leading to the formation of precipitates in the ozonation process. An unconventional minimum-type variation of BHA decay rate constants from acidic to caustic range has been found for both ozonation and UV/O(3) processes. The precipitates formed during ozonation can be removed during the process to optimize the treatment, while the UV/O(3) process can offer a relatively fast and clean process to degrade BHA and its associated intermediates.

The use of oxyhalogen in photocatalytic reaction to remove o-chloroaniline in TiO2 dispersion

Photodecay of o-chloroaniline (o-ClA) in various combinations of UV sources, TiO2, and oxyhalogens was investigated. To improve the conventional photocatalytic process by using UV/TiO2, the addition of oxyhalogens (ClO3(-), BrO3(-) and IO3(-)) into UV/TiO2 system was studied and the effect in such addition is very encouraging for all the selected additives. Oxyhalogens are capable of deferring the electron-hole recombination of TiO2 which significantly improved its catalytic performance. The presence of IO3(-) in UV/TiO2 resulted in the fastest o-ClA decay among three oxhalogens at the same dosage. The decay of o-ClA in UV/TiO2/oxyhalogen process is characterized by a two-stage pseudo-kinetics, where a faster initial decay was followed by a retardation state. A mathematics model was successfully established for the prediction of the two-stage decay of o-ClA in UV/TiO2/IO3(-) with any designed [IO3(-)] concentration.

Degradation of the endocrine disruptor carbofuran by UV, O3 and O3/UV

The photodegradation of a carbamate insecticide, Carbofuran (CBF), which has been recognised as a potential endocrine disrupting chemical, was studied via different wastewater treatment processes. This study has shown the efficiency of advanced oxidation process, AOP (UV/O3) than those of the direct UV photolysis and ozonation process, by completely removing 0.2 mM CBF and achieving 24% mineralisation within 30min. The initial decay of CBF by UV/O3 accelerated from 0.05 to 0.16 min(-1) as the initial pH increasing from 3.0 to 11.3. The pH-dependency of CBF has also been shown in both ozonation and UV/O3 process. A linear relationship could be found for the latter process in all pH, while for the former process, two stages of reactions (steady and accelerating) were found in the acidic and alkaline pH condition, respectively.

Tuberculosis intestinal perforation during anti-tuberculosis treatment

Intestinal perforation is an uncommon but potentially fatal complication of intestinal tuberculosis. We report on a 63-year-old HIV-negative man who developed terminal ileal perforation approximately 3.5 months following initiation of anti-tuberculous treatment for pulmonary tuberculosis and a concomitant tuberculous perianal abscess. Clinical and radiological improvements were initially evident following commencement of anti-tuberculous treatment, and the paradoxical response phenomenon was suspected. The patient subsequently underwent surgical resection of the affected bowel segment with primary anastomosis, and made an uneventful recovery. Anti-tuberculous medication was continued for another 12 months, and after a further 12 months there was no evidence of recurrent tuberculosis. This case illustrates that tuberculous intestinal perforation can develop during chemotherapy for tuberculosis. Prompt diagnosis and appropriate surgical treatment are essential to avoid morbidity and mortality.

Enhancement of ozone oxidation and its associated processes in the presence of surfactant: degradation of atrazine

In this study, the degradation of atrazine (ATZ) by ozone (O3) oxidation and its associated processes (i.e. UV, UV/O3) in the presence and absence of surfactant was investigated and compared. A non-ionic surfactant, Brij 35, was selected. It was found that the presence of a low concentration of surfactant could improve the removal of ATZ by increasing the dissolution of ozone and the indirect generation of hydroxyl radicals. The saturated ozone level and the reaction rate constants were increased with increasing the concentration of surfactant and then decreased at higher surfactant doses at pH level of 2.5. A similar trend was observed at pH level of 7.0 in the presence of bicarbonate ion, because it is capable of deactivating the hydroxyl radicals generating at higher pH level. However, when the radical reactions become dominant in the ozonation (at pH 7.0 without bicarbonate), the saturated ozone level was higher than that with bicarbonate and the kinetic rate constants were increased first and levelled off with increasing of the dose of surfactant. Through the examining of a proposed unit performance index, the low concentration of surfactant is surely beneficial to the ozonation process. Besides, the direct photolysis and photo-assisted ozonation were compared to the ozonation. A significant enhancement on the decay rate of ATZ was resulted exclusively by adding the surfactant. An enhancement index for quantifying the improvement of the various processes was developed.

The partitioning and modelling of pesticide parathion in a surfactant-assisted soil-washing system

Soil sorption of organic pollutants has long been a problematic in the soil washing process because of its durability and low water solubility. This paper discussed the soil washing phenomena over a wide range of parathion concentrations and several soil samples at various fractions of organic content (foc) levels. When parathion dosage is set below the water solubility, washing performance is stable for surfactant concentrations above critical micelle concentration (cmc) and it is observed that more than 90% of parathion can be washed out when dosage is five times lower than the solubility limit. However, such trends change when non-aqueous phase liquids (NAPL) is present in the system. Parathion extraction depends very much on the surfactant dosage but is not affected by the levels of foc in the system. In between the extreme parathion dosage, a two-stage pattern is observed in these boundary regions. Washing performance is first increased with additional surfactant, but the increase slows down gradually since the sorption sites are believed to be saturated by the huge amount of surfactant in the system. A mathematical model has included foc to demonstrate such behavior and this can be used as a prediction for extraction.