Sulfamethoxazole exposure to simulated solar radiation under continuous flow mode: Degradation and antibacterial activity.

Among pharmaceuticals, the occurrence of antibiotics in the environment is a subject of special concern due to their environmental impact, namely the development of bacterial resistance. Sulfamethoxazole (SMX) is one of the most commonly used antibiotics and it is regularly found, not only in effluents from sewage treatment plants (STPs), but also in the aquatic environment. Photodegradation appears as an alternative process for the removal of this type of pollutants from contaminated waters. In order to be used for a remediation purpose, its evaluation under continuous flow mode is essential, as well as the determination of the final effluent antibacterial activity, which were assessed in this work. As compared with batch operation, the irradiation time needed for SMX elimination under continuous flow mode sharply decreased, which is very advantageous for the target application. Moreover, the interrelation between SMX removal, mineralization and antibacterial activity was evaluated before and during photodegradation in ultrapure water. Although mineralization was slower than SMX removal, bacterial activity increased after SMX photodegradation. Such increase was also verified in environmental water matrices. Thus, this study has proven that photodegradation is an efficient and sustainable process for both (i) the remediation of waters contaminated with antibiotics, and (ii) the minimization of the bacterial resistance.

The design of a sunlight-focusing and solar tracking system: A potential application for the degradation of pharmaceuticals in water.

Photolysis is considered one of the most important mechanisms for the degradation of pharmaceuticals. Photodecomposition processes to remove pharmaceuticals in water treatment presently use artificial UV light incorporated in advanced oxidation processes. However, UV lighting devices consume a substantial amount of energy and have high operational costs. To develop low energy treatment systems and make good use of abundant sunlight, a natural energy resource as a green technology is needed. As such, a system that combines sunlight focusing, solar tracking and continuous reaction was designed and constructed in the present study, and its application potential as a pharmaceutical water treatment option was tested. Two representative photolabile pharmaceuticals, ciprofloxacin and sulfamethoxazole, were chosen as the target pollutants. The results indicate that the sunlight-focusing system consisting of a UV-enhancing-coated parabolic receiver can concentrate solar energy effectively and hence result in a more than 40% improvement in the direct photolysis efficiency of easily photoconvertible ciprofloxacin. The sunlight-focusing coupled with a solar tracker (SFST) system can improve the sunlight-focusing efficiency by more than 2-fold, thus leading to the maximization of the efficient use of solar energy. Sulfamethoxazole, which is difficult to photoconvert, was successfully degraded by more than 60% compared to direct photolysis through the designed SFST system in the presence of persulfate. The treatment system exhibited good and consistent performance during clear and cloudy days of summer. It is proven that the UV-enhanced coated SFST system with the addition of persulfate indeed has development potential for application in the degradation of pharmaceuticals in water.

One-step construction of heterostructured metal-organics@Bi2O3 with improved photoinduced charge transfer and enhanced activity in photocatalytic degradation of sulfamethoxazole under solar light irradiation.

A facile one-step assembly method was developed for the preparation of metal-organics @Bi2O3 composites for photocatalysis. Two kinds of metal-organics (Ti-bdc and Cu-btc)@Bi2O3 composites were synthesized via the coordination of btc3-/bdc2- and metal ions (Ti4+/Cu2+) as well as OH on the surface of Bi2O3. Compared with pure Bi2O3, Ti-bdc@Bi2O3 shows a 1.7 times higher photocatalytic activity in the degradation of sulfamethoxazole (SMX) under a simulated solar irradiation with a cumulative removal of 62% within 60 min. The high photocatalytic activity could be attributed to the high charge separation, enhanced electron transfer as well as the low recombination rate of photo-generated electrons and holes due to the construction of hetero-structures. The stability test showed that Ti-bdc@Bi2O3 is more stable in water than Cu-btc@Bi2O3. Furthermore, through the radical-trapping experiments and main intermediates detection, it is demonstrated that the photo-generated holes as well as the OH and O2- formed dominate the photocatalytic decomposition of SMX. These findings demonstrate the potential usage of a facile method to synthesize metal-organics and metal oxides composites, some of which possess high water stability and thus could be employed for water treatment.

Influence of ionizing radiation on the antimicrobial activity of the antibiotics sulfamethoxazole and trimethoprim.

The response of the antimicrobial compounds sulfamethoxazole (SMX) and trimethoprim (TMP) - individually and in mixtures - to ionizing radiation was investigated using laboratory prepared mixtures and a commercial pharmaceutical formulation. The residual antibacterial activity of the solutions was monitored using Staphylococcus aureus and Escherichia coli test strains. Based on antibacterial activity, SMX was more susceptible to ionizing radiation as compared to TMP. The antibacterial activity of SMX and TMP was completely eliminated at 0.2 kGy and 0.8 kGy, respectively. However, when SMX and TMP were in a mixture, the dose required to eliminate the antibacterial activity was 10 kGy, implying a synergistic antibacterial activity when these are present in mixtures. Only when the antibiotic concentration was below the Minimum Inhibitory Concentration of TMP (i.e., 2 µmol dm-3) did the antibacterial activity of the SMX and TMP mixture disappear. These results imply that the synergistic antimicrobial activity of antimicrobial compounds in pharmaceutical waste streams is a strong possibility. Therefore, antimicrobial activity assays should be included when evaluating the use of ionizing radiation technology for the remediation of pharmaceutical or municipal waste streams.

UV direct photolysis of sulfamethoxazole and ibuprofen: An experimental and modelling study.

Photodegradation characteristics of pharmaceuticals and personal care products (PPCPs) during UV irradiation are of practical and scientific importance in selecting operational parameters during water treatment processes. In this study, the molar extinction coefficient (ε), quantum yield (φ), and degradation kinetics of neutral/anionic forms of sulfamethoxazole (SMX) and ibuprofen (IBU) were compared by varying solution pH. The degradation kinetics of the target compounds were observed to reversely correlate to the energy gap between highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) values of the target compounds. Then, a kinetic model for predicting the direct photolytic rates at different solution pH was established based on ε and φ of neutral/anionic species. The root mean squared errors for the modeled values suggest that the model exhibits good predictive power. Finally, in order to evaluate the electrical energy consumption during the UV direct photolysis process, the electrical energy per order (EE/O) was assessed. The experimental and modelling results are important to elucidate the mechanism of degradation of target PPCPs under UV irradiation and allow for the selection of optimal conditions in water treatment processes.

Direct and indirect photolysis of seven micropollutants in secondary effluent from a wastewater lagoon.

The photodegradation of seven micropollutants commonly found in municipal wastewater, namely caffeine, carbamazepine, diuron, simazine, sulfamethoxazole, triclosan and 2,4-D, was investigated in pure water and secondary effluent to understand the direct and indirect photolysis of these compounds under natural sunlight irradiation. Sulfamethoxazole and triclosan were readily photodegraded with half-lives of 5.8 and 1.8 h, respectively, whilst the others were relatively resistant towards sunlight irradiation. Enhanced degradation was observed in secondary effluent compared with in the pure water matrix for all compounds, except for triclosan. It was confirmed that hydroxyl radicals played an important role in the photodegradation of the micropollutants while singlet oxygen may also play a role. The contribution of hydroxyl radical to the overall degradation of the five compounds that were resistant to direct sunlight accounted for 32%-70%. The impact of humic acid and nitrate, two known photosensitisers and wastewater components, on the photodegradation of the seven micropollutants in pure water was investigated under simulated solar radiation. The presence of nitrate promoted the photochemical loss of all seven micropollutants, however, humic acid caused promotion or inhibition, depending on the characteristics of the micropollutant. Humic acid enhanced the photolytic degradation of caffeine, sulfamethoxazole and diuron, while it hindered the photodegradation of the other four compounds by absorbing the available irradiation energy and/or reforming the parent compound. Furthermore, it was shown that there was only a small increase (up to 15%) in photodegradation of the compounds at 25 °C compared with that at 10 °C in the simulated system.

Dye-sensitized TiO2-catalyzed photodegradation of sulfamethoxazole under blue or yellow light.

Visible light-induced photocatalysis is potentially advantageous and could be an efficient approach to degrade contaminants because it can be used to selectively target specific wavelength for decomposition of organic contaminants in water and wastewater. This study demonstrates the photodegradation of sulfamethoxazole (SMX) using [Pt(3,3'-dicarboxy-2,2'-bpy)(1,2-benzenedithiolate)] (Complex 1)-sensitized and [Pt(4,4'-dicarboxy-2,2'-bpy)(1,2-benzenedithiolate)] (Complex 2)-sensitized titanium dioxide (TiO2) under blue or yellow light (420 or 580 nm, respectively) irradiation in water. The Complex 1-sensitized TiO2 photocatalytic oxidation of SMX reached almost 100 % removal under 420 nm irradiation for 3 h in water. In addition, the formation of hydroxyl radicals can be facilitated by bubbling O2 during the photodegradation in which an effective decomposition of SMX was observed. Based on HPLC and UV-Vis studies of the decomposed products, it was found that SMX underwent cleavage of aromatic rings during the photodegradation process.

Decomposition of sulfamethoxazole and trimethoprim by continuous UVA/LED/TiO2 photocatalysis: Decomposition pathways, residual antibacterial activity and toxicity.

In this study, continuous LED/UVA/TiO2 photocatalytic decomposition of sulfamethoxazole (SMX) and trimethoprim (TMP) was investigated. More than 90% of SMX and TMP were removed within 20min by the continuous photoreactor (with the initial concentration of 400ppb for each). The removal rates of SMX and TMP decreased with higher initial antibiotics loadings. SMX was much easier decomposed in acidic condition, while pH affected little on TMP's decomposition. 0.003% was found to be the optimum H2O2 dosage to enhance SMX photocatalytic decomposition. Decomposition pathways of SMX and TMP were proposed based on the intermediates identified by using LC-MS-MS and GC-MS. Aniline was identified as a new intermediate generated during SMX photocatalytic decomposition. Antibacterial activity study with a reference Escherichia coli strain was also conducted during the photocatalytic process. Results indicated that with every portion of TMP removed, the residual antibacterial activity decreased by one portion. However, the synergistic effect between SMX and TMP tended to slow down the antibacterial activity removal of SMX and TMP mixture. Chronic toxicity studies conducted with Vibrio fischeri exhibited 13-20% bioluminescence inhibition during the decomposition of 1ppm SMX and 1ppm TMP, no acute toxicity to V. fischeri was observed during the photocatalytic process.

Integration of nickel doping with loading on graphene for enhanced adsorptive and catalytic properties of CdS nanoparticles towards visible light degradation of some antibiotics.

Water dispersible, highly efficient nickel doped CdS nanoparticles anchored on graphene nanosheets as a photocatalyst for cephalexin and sulfamethoxazole photodegradation have been prepared in a facile microwave-furnace assisted method. Each one of the two modifications has played a critical role in nanocomposite functioning. Defects originated by dopant boosted the lifetime of carriers and thereupon graphene matrix transferred them to contribute effectively the photocatalytic process. Characterization results revealed the formation of monocrystalline hexagonal phase of all products and that both doping and loading on graphene have red-shifted the absorption edge of CdS towards the visible light region. Furthermore, FTIR confirmed the successful reduction of graphene oxide by the subsequent preparation steps. Adsorption isotherms revealed the role of graphene in enhancing substrate adsorption. Nevertheless, dissimilar pathways of catalytic degradation were observed on the doped composite as cephalexin oxidation was principally mediated by the hole-hydroxyl radical mechanism, sulfamethoxazole oxidation favored the superoxide radical mechanism. This composite has shown, however, a high photostability and minimized ions release of the composite.

Removal of trimethoprim, sulfamethoxazole, and triclosan by the green alga Nannochloris sp.

Trimethoprim (TMP), sulfamethoxazole (SMX), and triclosan (TCS) are widely used and continuously released into aquatic environments. Freshwater algae can be responsible for the uptake and transfer of the contaminants because they are a major food source for most aquatic organisms. This research applied incubation studies to evaluate the removal efficiency of TMP, SMX, and TCS by the green alga Nannochloris sp. The results showed that the hydrophilic antibiotics TMP and SMX remained in the algal culture at 100% and 68%, respectively, after 14days of incubation, and therefore were not significantly removed from the medium. However, the lipophilic antimicrobial TCS was significantly removed from the medium. Immediately after incubation began, 74% of TCS dissipated and 100% of TCS was removed after 7days of incubation. Additionally, over 42% of TCS was found associated with the algal cells throughout the incubation. The results demonstrate that the presence of Nannochloris sp. eliminated TCS in the aquatic system, but could not significantly remove the antibiotics TMP and SMX. The removal mechanisms of SMX and TCS were found to be different in the algal culture. Algae-promoted photolysis was the primary process for removing SMX and algae-mediated uptake played a major role in removing TCS.

Biodegradation of sulfamethoxazole photo-transformation products in a water/sediment test.

Occurrence of the antibiotic sulfamethoxazole (SMX) in the aquatic environment is of concern due to its potential to induce antibiotic resistance in pathogenic bacteria. While degradation of SMX can occur by numerous processes, the environmental fate of its transformation products (TPs) remains poorly understood. In the present work, biodegradation of SMX photo-TPs was investigated in a water/sediment system. Photo-TPs were produced by exposing SMX to artificial sunlight for 48 h. The resulting mixture of 8 photo-TPs was characterized using a combination of ultra-high performance liquid chromatography coupled to high-resolution mass spectrometry and tandem mass spectrometry, and then used in biodegradation experiments. Significant differences in transformation among SMX photo-TPs were observed in the water/sediment system, with four photo-TPs displaying evidence of biodegradation (dissipation half-lives [DT50] of 39.7 d for 3-amino-5-methylisoxazole, 12.7 d for 4-nitro-sulfamethxoazole, 7.6 d for an SMX isomer and 2.4 d for [C10H13N3O4S]), two displaying primarily abiotic degradation (DT50 of 31 d for sulfanilic acid and 74.9 d for 5-methylisoxazol-3-yl-sulfamate), and two photo-TPs behaving largely recalcitrantly. Remarkably, TPs previously reported to be photo-stable also were persistent in biodegradation experiments. The most surprising observation was an increase in SMX concentrations when the irradiated solution was incubated, which we attribute to back-transformation of certain photo-TPs by sediment bacteria (85% from 4-nitro-sulfamethoxazole). This process could contribute to exposure to SMX in the aquatic environment that is higher than one would expect based on the fate of SMX alone. The results highlight the importance of considering TPs along with their parent compounds when characterizing environmental risks of emerging contaminants.

Photolytic degradation of sulfamethoxazole and trimethoprim using UV-A, UV-C and vacuum-UV (VUV).

The photolytic degradation of the non-degradable pharmaceuticals sulfamethoxazole (SMX) and trimethoprim (TMP) in an aqueous solution was investigated using three kinds of low-pressure mercury lamp UV-A (352 nm), UV-C (254 nm), and vacuum-UV (VUV, 185 nm and 254 nm). The degradation rates were highly dependent on the target compounds as well as the UV sources. No degradation of the target compounds was observed using UV-A treatment, because there was no overlap between the UV-A emission spectrum and absorption spectrum of the target compounds. On the other hand, UVC and VUV revealed higher reactivity. The results also indicated that SMX had a greater potential to react photochemically than TMP. Among the UV sources, VUV was the most effective process for the degradation of target compounds. Furthermore, the addition of oxidants such as hydrogen peroxide (H2O2) and sodium persulfate (Na2S2O8) to the reaction system improved the overall degradation rate significantly.The experimental results for the VUV-irradiated samples with the addition of methanol as a hydroxyl radical scavenger revealed that hydroxyl radicals contribute significantly to the elimination of the target compound. Overall, the degradation rate of the target compounds was in the order: VUV = UV-C > UV-A for sulfamethoxazole and VUV/H2O2 > VUV/ Na2S2O8 > VUV >UV-C >UV-A for trimethoprim.

Sunlight-induced transformation of sulfadiazine and sulfamethoxazole in surface waters and wastewater effluents.

Sulfadiazine (SD) and sulfamethoxazole (SMX) are widely used sulfonamide antibiotics, which are present as contaminants in surface waters and are known to undergo phototransformation. This kinetic study was conducted to identify the processes responsible for their phototransformation in sunlit surface waters. Water samples from the Thur River (Switzerland) and from a pilot wastewater treatment plant, as well as aqueous solutions of two well-characterized natural dissolved organic matter (DOM) extracts, namely Suwannee River and Pony Lake fulvic acids (SRFA, PLFA), were examined. Both sulfonamides were found to undergo direct and indirect phototransformation, with contributions of excited triplet states of DOM and of effluent organic matter (EfOM) and possibly of hydroxyl radical and other unidentified reactive species. Under simulated sunlight, SMX mainly reacted through direct phototransformation, with a certain contribution of indirect phototransformation occurring for a wastewater effluent. The behavior of SD was found to be more diverse. For river waters, wastewater effluents and PLFA solutions, indirect phototransformation was predominant, while for SRFA solutions direct phototransformation prevailed. The rates of phototransformation of SD were interpreted as the result of a complex interplay between the photosensitizing and the inhibitory effect of DOM/EfOM, with an additional component related to the nitrite ion as a source of photoproduced hydroxyl radical. For typical conditions found in surface waters comparable to the Thur River, phototransformation half-lives on the order of 3-13 d were estimated for the two studied sulfonamides.

Phototransformation of wastewater-derived trace organic contaminants in open-water unit process treatment wetlands.

Open-water cells in unit process treatment wetlands can be used to exploit sunlight photolysis to remove trace organic contaminants from municipal wastewater effluent. To assess the performance of these novel systems, a photochemical model was calibrated using measured photolysis rates for atenolol, carbamazepine, propranolol, and sulfamethoxazole in wetland water under representative conditions. Contaminant transformation by hydroxyl radical ((•)OH) and carbonate radical ((•)CO3(-)) were predicted from steady-state radical concentrations measured at pH values between 8 and 10. Direct photolysis rates and the effects of light screening by dissolved organic matter on photolysis rates were estimated using solar irradiance data, contaminant quantum yields, and light screening factors. The model was applied to predict the land area required for 90% removal of a suite of wastewater-derived organic contaminants by sunlight-induced reactions under a variety of conditions. Results suggest that during summer, open-water cells that receive a million gallons of water per day (i.e., about 4.4 × 10(-2) m(3) s(-1)) of nitrified wastewater effluent can achieve 90% removal of most compounds in an area of about 15 ha. Transformation rates were strongly affected by pH, with some compounds exhibiting faster transformation rates under the high pH conditions associated with photosynthetic algae at the sediment-water interface and other contaminants exhibiting faster transformation rates at the circumneutral pH values characteristic of algae-free cells. Lower dissolved organic carbon concentrations typically resulted in increased transformation rates.

Degradation of sulfonamides antibiotics in lake water and sediment.

Degradation of three sulfonamides (SAs), namely sulfamethoxazole (SMX), sulfamethazine (SMZ), and sulfadimethoxine (SDM) in surface water and sediments collected from Taihu Lake and Dianchi Lake, China was investigated in this study. The surface water (5-10 cm) was collected from the east region of Taihu Lake, China. Two sets of degradation experiments were conducted in 3-L glass bottles containing 2 L of fresh lake water and 100 µg/L of individual SAs aerated by bubbling air at a rate of approximately 1.2 L/min, one of which was sterilized by the addition of NaN3 (0.1%). Sediment samples were taken from Taihu Lake and Dianchi Lake, China. For the sediment experiment, 5 g of sediment were weighed into a 50-mL glass tube, with 10 mg/kg of individual SAs. Different experimental conditions including the sediment types, sterilization, light exposure, and redox condition were also considered in the experiments. The three SAs degraded in lake water with half-lives (t 1/2) of 10.5-12.9 days, and the half-lives increased significantly to 31.9-49.8 days in the sterilized water. SMZ and SDM were degraded by abiotic processes in Taihu and Dianchi sediments, and the different experimental conditions and sediments characteristics had no significant effect on their declines. SMX, however, was mainly transformed by facultative anaerobes in Taihu and Dianchi sediments under anaerobic conditions, and the degradation rate of SMX in non-sterile sediment (t 1/2 of 9.6-16.7 days) were higher than in sterilized sediment (t 1/2 of 18.7-135.9 days). Under abiotic conditions, degradation of SMX in Dianchi sediment was faster than in Taihu sediment, probably due to the higher organic matter content and inorganic photosensitizers concentrations in Dianchi sediment. High initial SAs concentration inhibited the SAs degradation, which was likely related to the inhibition of microorganism activities by high SAs levels in sediments. Results from this study could provide information on the persistence of commonly used sulfanomides antibiotics in lake environment.

Direct photolysis of human metabolites of the antibiotic sulfamethoxazole: evidence for abiotic back-transformation.

The presence of potentially persistent and bioactive human metabolites in surface waters gives rise to concern; yet little is known to date about the environmental fate of these compounds. This work investigates the direct photolysis of human metabolites of the antibiotic sulfamethoxazole (SMX). In particular, we determined photolysis kinetics and products, as well as their concentrations in lake water. SMX, N-acetyl sulfamethoxazole, sulfamethoxazole ß-D-glucuronide, 4-nitroso sulfamethoxazole, and 4-nitro sulfamethoxazole were irradiated under various light sources and pH conditions. All investigated metabolites, except sulfamethoxazole ß-D-glucuronide were found to be more photostable than SMX under environmentally relevant conditions. Between two and nine confirmed photoproducts were identified for SMX-metabolites through ultraperformance liquid chromatography/high-resolution mass spectrometry. Interestingly, photolytic back-transformation to SMX was observed for 4-nitroso-SMX, indicating that this metabolite may serve as an environmental source of SMX. Moreover, two human metabolites along with SMX were regularly detected in Lake Geneva. The knowledge that some metabolites retain biological activity, combined with their presence in the environment and their potential to retransform to the parent compound, underlines the importance of including human metabolites when assessing the effects of pharmaceuticals in the environment.

Degradation and toxicity assessment of sulfamethoxazole and chlortetracycline using electron beam, ozone and UV.

Recently, the occurrence of antibiotics in sewage treatment plant effluent, as well as drinking water, has raised concern about their potential impacts on the environment and public health. Antibiotics are found in surface and ground waters, which indicate their ineffective removal by conventional wastewater treatment processes. Therefore, advanced oxidation processes (AOPs) have received considerable attention for the removal of antibiotics. This study was conducted to evaluate the degradation and mineralization of antibiotics (sulfamethoxazole and chlortetracycline) using an electron beam, ozone and UV, and the change of toxicity. Also, the electrical energy consumption based on the EE/O parameter (the electrical energy required per order of pollutants removal in 1 m(3) wastewater) was used to quantify the energy cost associated with the different AOPs (electron beam, ozone and UV) for the degradation of antibiotics. The results showed that an electron beam effective for the removals of both sulfamethoxazole and chlortetracycline in aqueous solutions. However, degradation of the target compounds by ozone and UV showed different trends. The oxidation efficiency of each organic compound was very dependent upon the AOP used. Algal toxicity was significantly reduced after each treatment. However, based on the electrical energy, the electron beam was more efficient than ozone and UV. Electron beam treatment could be an effective and safe method for the removal of antibiotic compounds.

Phototransformation of selected pharmaceuticals during UV treatment of drinking water.

The kinetics of Ultraviolet C (UV-C)-induced direct phototransformation of four representative pharmaceuticals, i.e., 17alpha-ethinylestradiol (EE2), diclofenac, sulfamethoxazole, and iopromide, was investigated in dilute solutions of pure water buffered at various pH values using a low-pressure and a medium-pressure mercury arc lamp. Except for iopromide, pH-dependent rate constants were observed, which could be related to acid-base equilibria. Quantum yields for direct phototransformation were found to be largely wavelength-independent, except for EE2. This compound, which also had a rather inefficient direct phototransformation, mainly underwent indirect phototransformation in natural water samples, while the UV-induced depletion of the other pharmaceuticals appeared to be unaffected by the presence of natural water components. At the UV-C (254 nm) drinking-water disinfection fluence (dose) of 400 Jm(-2), the degree of depletion of the select pharmaceuticals at pH=7.0 in pure water was 0.4% for EE2, 27% for diclofenac, 15% for sulfamethoxazole, and 15% for iopromide, indicating that phototransformation should be seriously taken into account when evaluating the possibility of formation of UV transformation products from pharmaceuticals present as micropollutants.

Sulfamethoxazole abatement by photo-Fenton toxicity, inhibition and biodegradability assessment of intermediates.

The objective of this work was to study the abatement of 200mgL(-1) sulfamethoxazole (SMX) solution by means of photo-Fenton process. Biodegradability of the treated solutions was followed by the ratio biochemical oxygen demand at five days/chemical oxygen demand (BOD(5)/COD) and toxicity by Microtox and inhibition tests. Experiments with different initial concentration of H(2)O(2) were carried out. The initial amount of Fe(2+) and pH of the solution were set at 10mgL(-1) and 2.8 respectively. The temperature of the reactor was kept constant in all the experiments (25+/-0.8 degrees C). Photo-Fenton process is thought to be a successful treatment step to improve the biodegradability of wastewater containing SMX. The complete antibiotic removal was achieved for a H(2)O(2) dose over 300mgL(-1). Biodegradability (BOD(5)/COD) rose from zero (SMX solution) to values higher than 0.3 (treated solutions). Toxicity and inhibition tests pointed out in the same direction: oxidized intermediates for initial H(2)O(2) dose over 300mgL(-1) showed no toxicity effects on pure bacteria and no inhibition on activated sludge activity.

Photodegradation of sulfamethoxazole: a chemical system capable of monitoring seasonal changes in UVB intensity.

Sulfamethoxazole (SMX) in its nonionized form in aqueous solution has ultraviolet (UV) absorption that is maximal at 268 nm but extends through the ultraviolet-B (UVB) region. It was found to be extremely susceptible to photodegradation when exposed to artificial UV radiation through a Pyrex filter or to unfiltered natural sunlight. The SMX anion was more stable. The quantum yields of the photodegradation of both forms were determined by use of monochromatic light and ferrioxalate chemical actinometry, the values of 0.47 (pH 3.0) and 0.084 (pH 9.0) at the maximum absorption wavelengths (268 and 257 nm, respectively) being obtained. Using literature data on sunlight intensity, the photochemical shelf-life of SMX solutions exposed to direct sunlight was calculated for Sydney (latitude 33.5 degrees S) as a function of season of the year and verified experimentally. A fixed correlation was established between the rate constant for SMX degradation and UVB intensity measured by a radiometer, suggesting the capacity of this chemical system to monitor changes in the UVB region of sunlight.