Heterogeneous photocatalytic treatment of organic dyes in air and aqueous media

This review focuses on the heterogeneous photocatalytic treatment of organic dyes in air and water. Representative studies spanning approximately three decades are included in this review. These studies have mostly used titanium dioxide (TiO2) as the inorganic semiconductor photocatalyst of choice for decolorizing and decomposing the organic dye to mineralized products. Other semiconductors such as ZnO, CdS, WO3, and Fe2O3 have also been used, albeit to a much smaller extent. The topics covered include historical aspects, dark adsorption of the dye on the semiconductor surface and its role in the subsequent photoreaction, semiconductor preparation details, photoreactor configurations, photooxidation kinetics/mechanisms and comparison with other Advanced Oxidation Processes (e.g., UV/H2O2, ozonation, UV/O3, Fenton and photo-Fenton reactions), visible light-induced dye decomposition by sensitization mechanism, reaction intermediates and toxicity issues, and real-world process scenarios. © 2008 Elsevier B.V. All rights reserved.

Anaerobic effluent disinfected with ozone/hydrogen peroxide efluente anaeróbio desinfetado com ozônio/peróxido de hidrogênio

This research aimed at studying the oxidation process, to verify the effectiveness of coliform inactivation and to evaluate the formation of ozonation disinfection byproducts (DBP) in anoxic sanitary wastewater treated with ozone/hydrogen peroxide applied at doses of 2.6 mg O3 L-1 and 2.0 mg H2O2 L-1 with contact time of 10 min and 8.1 mg O3 L-1 and 8.0 mg H2O2 L-1 with contact time of 20 min. The mean chemical oxygen demand (COD) reductions were 7.50 and 9.40% for applied dosages of 2.5-2.8 and 6.4-9.4 mg O3 L-1 + 2.0 and 8.0 mg H2O2.L-1, respectively. The Escherichia coli (E. coli) inactivation range was 2.98-4.04 log10 and the total coliform inactivation range was 2.77-4.01 log10. The aldehydes investigated were formaldehyde, acetaldehyde, glyoxal and methylglyoxal. It was observed only the formation of acetaldehyde that ranged 5.53 to 29.68 μg L-1.

A New and Simple Visual Technique Based on Indigo Dye for Determination of Ozone in Ambient Air

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Toxicity on aquatic organisms exposed to secondary effluent disinfected with chlorine, peracetic acid, ozone and UV radiation

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Ozone and nitrogen dioxide gas sensor based on a nanostructured SrTi0.85Fe0.15O3 thin film

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Effect of low-dose gaseous ozone on pathogenic bacteria

Background: Treatment of chronically infected wounds is a challenge, and bacterial environmental contamination is a growing issue in infection control. Ozone may have a role in these situations. The objective of this study was to determine whether a low dose of gaseous ozone/oxygen mixture eliminates pathogenic bacteria cultivated in Petri dishes. Methods: A pilot study with 6 bacterial strains was made using different concentrations of ozone in an ozone-oxygen mixture to determine a minimally effective dose that completely eliminated bacterial growth. The small and apparently bactericidal gaseous dose of 20 mu g/mL ozone/oxygen (1: 99) mixture, applied for 5min under atmospheric pressure was selected. In the 2nd phase, eight bacterial strains with well characterized resistance patterns were evaluated in vitro using agar-blood in adapted Petri dishes (10(5) bacteria/dish). The cultures were divided into 3 groups: 1-ozone-oxygen gaseous mixture containing 20 mu g of O-3/mL for 5 min; 2- 100% oxygen for 5 min; 3- baseline: no gas was used. Results: The selected ozone dose was applied to the following eight strains: Escherichia coli, oxacillin-resistant Staphylococcus aureus, oxacillin-susceptible Staphylococcus aureus, vancomycin-resistant Enterococcus faecalis, extended-spectrum beta-lactamase-producing Klebsiella pneumoniae, carbapenem-resistant Acinetobacter baumannii, Acinetobacter baumannii susceptible only to carbapenems, and Pseudomonas aeruginosa susceptible to imipenem and meropenem. All isolates were completely inhibited by the ozone-oxygen mixture while growth occurred in the other 2 groups. Conclusion: A single topical application by nebulization of a low ozone dose completely inhibited the growth of all potentially pathogenic bacterial strains with known resistance to antimicrobial agents.

Effect of ozone on periodontopathogenic species--an in vitro study

The in vitro study was aimed to determine the effect of ozone on periodontopathogenic microorganisms. Ozone was generated for 6 s-2 × 24 s (corresponding to 0.56 mg-2 × 2.24 mg of ozone) against 23 mainly anaerobic periodontopathogenic species. Agar diffusion test was used as a screening method. Then, the killing activity was tested in a serum-free environment and with 25% v/v inactivated serum. Further, the effect of ozone on bactericidal activity of native serum was analyzed against Fusobacterium nucleatum, Porphyromonas gingivalis, and Aggregatibacter actinomycetemcomitans. Agar diffusion test showed a high efficacy of ozone against microorganisms, especially against Porphyromonas gingivalis. This result was confirmed by the killing tests; most of the strains in a concentration of 10(5) were completely eliminated after twofold 18-s application of ozone. Only four of the six potentially "superinfecting" species (Staphylococcus aureus, Enterococcus faecalis, Enterobacter cloacae, Candida albicans) survived in part. Addition of heat-inactivated serum reduced the killing rate of ozone by 78% after 6-s and by 47% after twofold 18-s exposures; no strain was completely eradicated after any application of ozone. The bactericidal effect of native serum was enhanced after application of ozone; no effect was visible on the included A. actinomycetemcomitans strain which was found to be completely resistant to the bactericidal action of serum. In conclusion, (a) ozone has a strong antibacterial activity against putative periodontopathogenic microorganisms, and (b) the bactericidal effect is reduced in the presence of serum. Ozone may have potential as an adjunctive application to mechanical treatment in periodontitis patients.

Comparison of the immediate effects of gaseous ozone and chlorhexidine gel on bacteria in cavitated carious lesions in children in vivo

Clinical application of ozone gas has been shown to arrest the progression of dentinal caries in children. In this study, we compare the immediate effects of gaseous ozone and chlorhexidine gel on bacteria in cavitated carious lesions in children. Forty children, each with at least two open occlusal carious lesions, were enrolled in the study. Two teeth were chosen randomly. In one lesion, overlying soft biological material was removed, whilst the other lesion was not excavated. Cavities were rinsed with sterile water and dried with air. A standardised sample was taken from the mesial part of each lesion. Then, gaseous ozone (HealOzone) or 1% chlorhexidine gel (Corsodyl) was applied for 30 s on both lesions of 20 children each, and a second sample was taken from the distal part of each lesion. The anaerobic microbiota was cultivated; the number of colony forming units was calculated per milligram sample. The two-sided paired t test showed no significant (P > 0.05) differences in the reduction of total bacterial counts per milligram comparing samples before and after ozone or chlorhexidine application. The tests also showed no statistically significant difference whether the superficial decayed dentine had been removed before ozone or with chlorhexidine treatment or not. It can be concluded that gaseous ozone or chlorhexidine gel application for 30 s to deep occlusal carious cavities had no significant immediate antimicrobial effects whether the superficial decayed layers dentine were removed or not.

Growth response to ozone of annual species from Mediterranean pastures

Ozone (O3) phytotoxicity has been reported on a wide range of plant species. However, scarce information has been provided regarding the sensitivity of semi-natural grassland species, especially those from dehesa Mediterranean grasslands, in spite of their great biological diversity and the high O3 levels recorded in the region. A screening study was carried out in open-top chambers (OTCs) to assess the O3-sensitivity of representative therophytes of these ecosystems based on the response of selected growth-related parameters. Three O3 treatments and 3 OTCs per treatment were used. Legume species were very sensitive to O3, because 78% of the tested species showed detrimental effects on their total biomass relative growth rate (RGR) following their exposure to O3. The Trifolium genus was particularly sensitive showing O3-induced adverse effects on most of the assessed parameters. Gramineae plants were less sensitive than Leguminosae species because detrimental effects on total biomass RGR were only observed in 14% of the assessed species. No relationship was found between relative growth rates when growing in clean air and O3 susceptibility. The implications of these effects on the performance of dehesa acidic grasslands and on the definition of ozone critical levels for the protection of semi-natural vegetation are discussed.

Assessment of the ozone sensitivity of 22 native plant species from mediterranean annual pastures based on visible injury

Ozone (O3) phytototoxicity has been reported on a wide range of plantspecies, inducing the appearance of specific foliar injury or increasing leaf senescence. No information regarding the sensitivity of plantspecies from dehesa Mediterranean grasslands has been provided in spite of their great biological diversity. A screening study was carried out in open-top chambers (OTCs) to assess the O3-sensitivity of 22 representative therophytes of these ecosystems based on the appearance and extent of foliar injury. A distinction was made between specific O3injury and non-specific discolorations. Three O3 treatments (charcoal-filtered air, non-filtered air and non-filtered air supplemented with 40 nl l−1 O3 during 5 days per week) and three OTCs per treatment were used. The Papilionaceae species were more sensitive to O3 than the Poaceae species involved in the experiment since ambient levels induced foliar symptoms in 67% and 27%, respectively, of both plant families. An O3-sensitivity ranking of the species involved in the assessment is provided, which could be useful for bioindication programmes in Mediterranean areas. The assessed Trifoliumspecies were particularly sensitive since foliar symptoms were apparent in association with O3 accumulated exposures well below the current critical level for the prevention of this kind of effect. The exposure indices involving lower cut-off values (i.e. 30 nl l−1) were best related with the extent of O3-induced injury on these species.

Effect of post-harvest ozone treatments on the skin phenolic composition and extractability of red winegrapes cv Nebbiolo and Berbera

Mestrado Vinifera Euromaster - Instituto Superior de Agronomia - UL