DISINFECTION OF MUNICIPAL WASTEWATER BY TiO2 PHOTOCATALYSIS WITH UV-A, VISIBLE AND SOLAR IRRADIATION AND BDD ELECTROLYSIS (original) (raw)
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International Journal of Environmental Science and Technology, 2018
Pollution of water sources by pathogens is a major concern worldwide. This study investigated critical disinfection aspects such as bacterial regrowth or decay and evaluation of metal-ion leaching during photocatalytic disinfection. The inactivation of waterborne bacterial pathogens (Escherichia coli, Salmonella species, Shigella species and Vibrio cholerae) using ultraviolet and solar photocatalysis was evaluated. Bare and metal-ion (silver, copper and iron)-doped titanium dioxide photocatalysts were used to explore comparative performance. The influence of photocatalyst concentration (0.1-1.0 g/L), source of radiation (ultraviolet or solar light) and water type (synthetic and municipal wastewater) was examined. The disinfection data were fitted to the pseudo-first-order model. The disinfection efficiency was higher in saline deionized water (99.9998-100%) that was spiked with the target pathogens (10 6 colony forming units/mL), compared to actual wastewater samples. Within 180 min of treatment under solar irradiation, disinfection efficacy of 86.8-100% was achieved, while 99.4-100% disinfection efficacy was attained under ultraviolet irradiation within 60 min. A significant difference (p < 0.05) between ultraviolet and solar photocatalysis was observed, and silver-doped titanium dioxide displayed the best performance under all conditions tested. Nevertheless, after a contact time of 180 min, there was no bacterial regrowth observed even for the solar photocatalysis processes; in fact, bacterial decay occurred. The elution of doping metals into the treated wastewater was insignificant. Therefore, the metal-ion-doped photocatalysts were effective under solar radiation, thus overcoming the limitation of bare titanium dioxide which is only effective under ultraviolet light and preventing bacterial regrowth.
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.
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.
Journal of Hazardous Materials, 2009
In this study the potential application of TiO(2) photocatalysis as primary disinfection system of drinking water was investigated in terms of coliform bacteria inactivation and injury. As model water the effluent of biological denitrification unit for nitrate removal from groundwater, which is characterized by high organic matter and bacteria release, was used. The injury of photocatalysis on coliform bacteria was characterized by means of selective (mEndo) and less selective (mT7) culture media. Different catalyst loadings as well as photolysis and adsorption effects were investigated. Photocatalysis was effective in coliform bacteria inactivation (91-99% after 60 min irradiation time, depending on both catalyst loading and initial density of coliform bacteria detected by mEndo), although no total removal was observed after 60 min irradiation time. The contribution of adsorption mechanism was significant (60-98% after 60 min, depending on catalyst loading) compared to previous investigations probably due to the nature of source water rich in particulate organic matter and biofilm. Photocatalysis process did not result in any irreversible injury (98.8% being the higher injury) under investigated conditions, thus a bacteria regrowth may take place under optimum environment conditions if any final disinfection process (e.g., chlorine or chlorine dioxide) is not used.
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.
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 Pollution, 2019
The photocatalytic inactivation of Escherichia coli (E. coli) under light-emitting diode (LED) light irradiation was performed with P/Ag/Ag 2 O/Ag 3 PO 4 /TiO 2 photocatalyst to investigate the photocatalytic bactericidal activity. Our work showed that this composite photocatalyst possessed remarkable bacterial disinfection ability and could completely inactivate 10 8 cfu/mL of E. coli within just 40 min under the optimum catalyst loading of 0.5 g/L. The effects of different environmental factors, including light wavelength, light intensity, temperature, solution pH and inorganic ions, on the inactivation efficiency were evaluated. The results showed that bacteria inactivation by P/Ag/Ag 2 O/Ag 3 PO 4 /TiO 2 was more favorable with blue colored LED irradiation, light intensity at 750 W/m 2 , temperature in the range of 30 e37 C and pH values at natural or slightly alkaline condition. The existence of different inorganic ions under normal environmental level had no significant impact on the bactericidal performance. In addition, during the inactivation process, the morphology changes of E. coli cells were directly observed by scanning electron microscope (SEM) and further proved by the measurement of K þ leakage from the inactivated E. coli. The results demonstrated that the photocatalytic inactivation caused drastic damage on bacterial cells membrane. Furthermore, the mechanisms of photocatalytic bacterial inactivation were also systemically studied and the results confirmed that the excellent disinfection activity of P/Ag/Ag 2 O/ Ag 3 PO 4 /TiO 2 resulted from the major reactive species: h þ and $O 2 À from photocatalytic process instead of the leakage of Ag þ (0.085 ± 0.005 mg/L) from photocatalyst. These results indicate that P/Ag/Ag 2 O/ Ag 3 PO 4 /TiO 2 photocatalyst has promising potential for real water sterilization application.
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.
Applied Catalysis B: Environmental, 2014
The effect of N-doped TiO 2 (NDT) photocatalysis on the inactivation of an antibiotic resistant Escherichia coli strain selected from a biologically treated urban wastewater effluent was investigated. NDT was prepared by sol-gel method and characterized by thermogravimetric analysis, X-ray diffraction, FTIR and Laser Raman spectra and UV-visible reflectance spectra. XRD analysis revealed that anatase is the only crystalline phase in NDT photocatalyst and UV-visible reflectance spectra showed that the absorption onset shifted toward visible region (about 500 nm). The NDT photocatalyst was compared with commercially available TiO 2 powders (namely Millennium PC50 and PC100), under solar simulated radiation (250 W lamp) and different photocatalysts loadings (0.025-0.5 g L −1). The higher inactivation rate (8.5 × 10 5 CFU 100 mL −1 min −1 , after 10 min of irradiation) of antibiotic resistant E. coli strain was observed for NDT photocatalyst at 0.2 g L −1 dose. Kinetic test at the optimum photocatalyst loading showed that total inactivation can be achieved after 60 min of irradiation. Antibiotic resistant test (Kirby-Bauer) on survived colonies showed that solar photocatalytic process with NDT did not significantly affect resistance of E. coli strain to tetracycline and vancomycin as irradiation time increased, but a decreasing trend (p < ˛ = 0.05) in resistance to ciprofloxacin (p = 0.0311) and sensitivity to cefuroxime (p = 0.0018) was observed.