Inactivation and injury of total coliform bacteria after primary disinfection of drinking water by TiO2 photocatalysis (original) (raw)
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Disinfection of spring water and secondary treated municipal wastewater by TiO2 photocatalysis
The photocatalytic disinfection of spring water and secondary treated municipal wastewater by means of UV-A irradiation over TiO 2 suspensions was investigated. Water samples were taken from a spring supplying water to the city of Chania, Western Crete, Greece, while wastewater samples were collected from the outlet of the secondary treatment of Chania municipal wastewater treatment plant. The effect of various operating parameters such as photocatalyst type (rutile, anatase, mixture of anatase and rutile) and concentration (0.5-1 g/L), contact time (up to 60 min) and sample pH (6-8) on the disinfection as assessed in terms of faecal indicator microorganisms (total coliforms and enterococci) inactivation was examined. A commercially available Degussa P25 TiO 2 powder, consisting of 75% anatase and 25% rutile, was found substantially more active than pure anatase or rutile for both groups of bacteria inactivation which increased with increasing contact time and catalyst concentration, whereas small pH changes had little effect on destruction. For both groups of bacteria tested, inactivation followed a first order kinetic expression with the gram positive Enterococcus sp. being considerably more resistant to photocatalytic disinfection than total coliforms.
Environmental and Climate Technologies
Water contamination by various bacteria, viruses and other pathogens is a great threat to human health. Amongst other Advanced Oxidation Processes TiO2 photocatalysis is considered as one of the most efficient treatment for the polluted wastewater disinfection. Usually, the wastewater produced by higher risk objects, such as hospitals, implicates diverse contaminants, but efficiency of most of the Advanced Oxidation Processes is tested by using only single pathogens and information on inactivation of bacteria mixtures is still limited. In this study, photocatalytical inactivation of three commonly found bacterial pathogens (gram-positive (Micrococcus luteus) and gram-negative (Salmonella enterica, Escherichia coli)) was investigated. Efficiency of traditional photocatalytic disinfection process using single bacterial pathogens was compared to the one observed for their mixtures. The impact of photocatalytical process parameters and treatment time on bacteria disinfection efficiency ...
Catalysis Today, 2005
This paper reports the photocatalytic disinfection of water contaminated by a mixture of Escherichia coli and Bacillus sp. as well as that of wastewater containing a larger microbial community. The photocatalytic reactions were carried out in a coaxial photocatalytic reactor called CAPHORE, using TiO 2 P-25 of Degussa. E. coli is more sensitive than Bacillus sp. to photocatalytic treatment. Bacterial inactivation was dependent on organic matter and dissolved oxygen (DO) concentration. Of the bacterial community present in partially treated wastewater, E. coli appears to be more sensitive to the treatment than Enterococcus sp., coliforms (other than E. coli), and Gram-negative (other than coliforms). After photocatalytic treatment, no bacterial recovery of previous groups was observed for 24 h in the dark. However a very low bacterial inactivation rate was observed for the whole bacterial population present in wastewater and detected by non-selective media. The effective disinfection time (EDT), the time necessary for total inactivation of bacteria without re-growth in a subsequent dark period referenced at 24 h (or 48 h), was reached only for Enterococcus sp., and coliform groups. EDT 24 was not reached for the whole population.
Research on Chemical Intermediates, 2007
The use of semiconductor photocatalysis for treatment of water and air has been the topic of intense research activity over the past 20 years. This powerful process has also been extended to the disinfection of environments contaminated with pathogenic micro-organisms. This review summarizes recent developments concerned with the photocatalytic treatment of water contaminated with pathogenic micro-organisms presenting a potential hazard to animals and human beings.
In this study, the semiconductor photocatalytic disinfection of spring water and of secondary treated municipal wastewater was investigated. Natural water from a spring in Chania prefecture, which is used for the water supplies for the city of Chania, Crete, and samples from the effluents of the secondary settling tank of the municipal wastewater treatment plant of Chania were collected. The samples were exposed to UV-A irradiation in the presence of TiO 2. The parameters examined in this study were the length of TiO 2 / UV-A treatment for effective disinfection, the microorganism type (total coliforms, enterococci), the relative bactericidal activity of three different types of TiO 2 , the amount of the catalyst needed, and the pH of the samples. The results presented here show that commercial TiO 2 powder Degussa P25 is the most effective catalyst of the three used. Enterococci showed a stronger resistance to photocatalytic disinfection, whereas small pH changes do not seem to have a significant effect on it.
A Review on TiO 2 Photocatalytic Disinfection of Water with Pathogenic Micro-organisms
During disinfection, the formation of byproducts such as trihalomethanes and other chlorinated byproducts are a major concern. The best alternative to avoid the byproducts formation is photocatalysis. In the past two decades, the studies on photocatalysis have been done using a semiconductor for the treatment of air and water. Among the various semiconductors, TiO 2 is used in various industries as it gives the highest efficiency with the highest stability at a lower cost. This is a powerful process used for disinfecting environment contaminated with pathogenic microorganisms. In this study, a review of previous developments made in the TiO 2 photocatalysis for the disinfection of water contaminated with pathogenic microorganisms is carried out. This paper concludes that TiO 2 photocatalysis can be used in different ways either in suspension or in the form of thin films to disinfect water contaminated with pathogenic microorganisms presenting a potential hazard to animals and human ...
Inactivation of Escherichia coli in water by TiO2-assisted disinfection using solar light
Journal of the Brazilian Chemical Society, 2007
Estudou-se a desinfecção de águas de abastecimento por fotocatálise heterogênea usando um reator de fluxo em um sistema composto por uma placa de vidro com TiO 2 P 25 (Degussa) imobilizado e luz solar como fonte de radiação. Foram utilizados dois modos de operação do reator: passagem única e recirculação. Os experimentos foram conduzidos utilizando inicialmente uma água preparada em laboratório e posteriormente água coletada em poços e lagos de uma região próxima à Campinas, SP. Estudou-se a influência de fatores, tais como, o modo de operação do reator, a cor e turbidez da água, os quais influenciam significativamente na eficiência fotocatalítica de descontaminação e, portanto, na viabilidade da aplicação do processo. Em dias ensolarados, alcançou-se uma redução na carga bacteriológica de cerca de 100% do valor inicial de Escherichia coli (2 × 10 3 NMP per 100 mL) para soluções de água sintética, e, 80% do valor inicial de Escherichia coli (16.6 to 22.2 × 10 3 MPN per 100 mL) para água in natura, através da fotocatálise heterogênea usando TiO 2. TiO 2-assisted heterogeneous photocatalysis and photolysis were evaluated for the disinfection of water samples using a glass reactor with immobilized TiO 2 (catalyst), solar light and E. coli as an indicator microorganism of the efficiency of disinfection. Parameters such as color and turbidity of the water, level of coliform bacteria (by the Colilert ® method), inclination angle of the solar reactor, solar light intensity, flow rate and retention time were controlled during the experiments. Two different operational modes were used for the solar reactor: single pass mode and recirculation mode. First, synthetic water was used in the disinfection tests as a model system; second, tests were conducted using natural samples specifically groundwater collected from a lake and a well. In bacterial suspensions in synthetic water in the absence of color and turbidity, heterogeneous photocatalysis was responsible for the reduction of approximately 100% of the initial concentration of E. coli. Only a 56.5% reduction was obtained by photolysis during the same solution recirculation time, which indicated a better efficiency using the catalyst. From the natural samples, total inactivation was not achieved in the studied cases. However, photocatalysis using TiO 2 /solar light was shown to be quantitatively efficient in the destruction of the total coliforms in water, reaching values up to around 80% inactivation in natural waters with initial levels of total coliforms ranging from 16.6 to 22.2×10 3 MPN per 100 mL.
Evaluation of photocatalytic disinfection of crude water for drinking-water production
Journal of Photochemistry and Photobiology A-chemistry, 2002
TiO 2 -photocatalysis disinfection experiments were carried out with both E. coli in distilled water and natural water samples from the Cauca River (Cali, Colombia). The experiments performed with E. coli in distilled water showed no increase in cell concentration after the treated solution was left in the dark for 24 h. However, the experiments carried out with natural water samples showed drastic culturable cell concentration increase 24 h after stopping the irradiation. This shows the lack of residual effect of TiO 2 -photocatalysis.
The photocatalytic disinfection of urban waste waters
Chemosphere, 2000
In this paper we present the results of the photocatalytic disinfection of urban waste water. Two microbial groups, total coliforms and Streptoccocus faecalis, have been used as indexes to test disinfection eciencies. Dierent experimental parameters have been checked, such as the eect of TiO 2 , solar or UV-lamp light and pH. Disinfection of water samples has been achieved employing both UV-lamp and solar light in agreement with data shown by other authors. The higher disinfection rates obtained employing an UV-lamp may be explained by the stronger incident light intensity. Nevertheless no consistent dierences have been found between TiO 2-photocatalysis and direct solar or UV-lamp light irradiation at natural sample pH (7.8). At pH 5 the presence of TiO 2 increases the relative inactivation rate compared with the absence of the catalyst. After the photocatalytic bacterial inactivation, the later bacterial reappearance was checked for total coliforms at natural pH and pH 5, with and without TiO 2. Two h after the photocatalytic treatment, CFU increment was almost nill. But 24 and 48 h later an important bacterial CFU increment was observed. This CFU increment is slower after irradiation with TiO 2 at pH 5 in non-air-purged samples.
Catalysis Today, 2009
The performances of different configurations of photoreactors were compared for the photocatalytic disinfection of E. coli aqueous suspensions and methylene blue photodegradation. Titania was immobilized in an annular reactor in two different ways: on the inner reactor wall and on the packing of a fixed bed. The influence of the increase in the TiO 2 layer thickness has been studied, and the results have been compared with those obtained with TiO 2 slurries of increasing concentration. Experimental results for methylene blue degradation were in agreement with those expected from the characterization data of the immobilized systems, but they did not fit with the variation of the activity for microorganisms inactivation. The increase in the density of the TiO 2 film caused by the heat treatment carried out after every coating cycle reduce the TiO 2 surface available for the interaction with bacteria, although it remains accessible for the dye molecules. Although immobilized systems show a lower disinfection activity in deionized water than TiO 2 slurries, they show a lower inhibition by the presence of organic matter, leading to comparable irradiation times to reach bacterial concentrations below the detection limit in the treatment of wastewater treatment plant effluents. Moreover, immobilized systems have shown that they are stable and do not present deactivation after several cycles of reuse, being readily applicable for continuous water treatment systems.