A Novel Approach For Solving Various Environmental

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4147 Journal of Applied Sciences Research, 8(8): 4147-4155, 2012 ISSN 1819-544X This is a refereed journal and all articles are professionally screened and reviewed

ORIGINAL ARTICLES Photocatalysis- A Novel Approach For Solving Various Environmental And Disinfection Problems: A Brief Review Ranjit K. Nath, M. F.M .Zain, Abdul Amir H. Kadhum, Department of Chemical & Process Engineering, Department of civil and Structural Engineering, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor,Malaysia. ABSTRACT The photocatalytic technique is a versatile and efficient disinfection process capable of inactivating a wide range of harmful microorganisms in various media. In photocatalysis processes a heterogeneous semiconductor material is used as a photocattalyst. To the clean nature of the process the power requirements of the technique can be relatively low, with some reactions requiring only light. It is a safe, nontoxic, and relatively inexpensive disinfection method whose adaptability allows it to be used for many purposes. Research in the field of photocatalytic disinfection is very diverse, covering a broad range of applications. This paper presents an overview of photocatalytic process in different sectors. Key words: Photocatalysis, disinfection, oxidation, environmental friendly, micro-organism. Introduction Photocatalytic processes are widely recognized as viable solutions for environmental problems (K. Yogo and M. Ishikawa, 2000). Disinfection of bacteria is of particular importance, because traditional methods such as chlorination are chemical intensive and have many associated disadvantages. For example, in water treatment applications, chlorine used for disinfection can react with organic material to generate chloro-organic compounds that are highly carcinogenic (H. J. Kool et al., 1985 and P. S. M. Dunlop et al., 2002). Other treatment alternatives such as ozonalysis and irradiation using germicidal lamps (254 nm) have their own problems and limitations, such as the lack of residual effect (W. J. Masschelin, 2002) and generation of small colony variants (J. M. C. Robertson et al., 2005) for the latter and production of toxic disinfection by products for the former (W. J. Huang et al., 2005). In the photocatalytic process a semiconductor is commonly used, which is nontoxic, chemically stable, available at reasonable cost, and capable of repeated use without substantial loss of catalytic ability (M. A. Fox et al., 1985). Upto now heterogeneous semiconductor materials like ZnO, Fe2O3, CdS, ZnS, TiO2, SnO2, WO3, LiNbO3 are used as photocatalyst, Beside many tested photocatalyst TiO2 is widely used for photocatalysis in different sectors. Hetero-geneous photo catalysis using titanium dioxide is a safe, nonhazardous, and ecofriendly process which does not produce any harmful by products. Extensive research in this field has been done in the area of photocatalytic removal of organic, inorganic, and microbial pollutants (A. Fujishima et al., 2000 and A. G. Rincon et al., 2005). The mechanism of bactericidal action of TiO2 photocatalysis, as reported by Sunada et al. is attributed to the combination of cell membrane damage and further oxidative attack of internal cellular components, ultimately resulting in cell death (K. Sunada et al., 2003). Heterogeneous photocatalysis is a rapidly developing field in the environmental engineering. Research efforts are being made to improve the efficiency of the TiO2 catalyst by means of doping with various metals (A. Vohra et al., 2005) and nonmetals (J. C. Yu et al., 2005 and G. Li et al., 2007). Other parameters which can be varied in a photocatalytic process, such as the source of ultraviolet irradiation and factors affecting process efficiency (T. P. T. Cushnie et al., 2009) have also been under investigation. Additionally, there are countless reactor designs and configurations (Y. S. Choi et al., 2000 and M. Subrahmanyam et al., 2008) used to exploit photocatalytic disinfection for a wide range of applications, as this process can be used in both water and air matrices (C. Guillard et al., 2008). The current review will focus on developments in photocatalytic disinfection for application in the following contexts: Photocatalysis in Building Materials, Photocatalysis and Microbial Fungi, Photocatalysis in Medical application, Photocatalysis in Laboratory and Hospital, Photocatalysis in Food Industry, Photocatalysis in Plant protection, Photocatalysis and Effluents and Photocatalysis in Water Treatment.

Corresponding Author: Ranjit K. Nath, Department of Chemical & Process Engineering, Department of civil and Structural Engineering, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor,Malaysia. E-mail: [email protected]

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Photocatalysis in Building Materials: The addition of photocatalyst to ordinary building materials such as concrete, creates environmental friendly materials by which air pollution as well as corrosion problem of Reinforcement concrete can be diminished. Improve of air quality: Photocatalytic oxidation (PCO) (Carp 2004a, Linsebigler & L.u.Yates 1995) is promising technologies for air purification because the pollutants can be oxidised to H2O and CO2. However, thermally catalytic oxidation requires high temperatures of 200–1200 °C for efficient operation and hence expensive. Furthermore, thermally catalytic oxidation is not economically feasible at low pollutant concentrations. Titanium dioxide has been used as a catalyst for the UV induced photocatalysis of pollutants in recent years. Photocatalytic reactions are attractive because they do not require high temperature operational conditions and they can be very selective in radiation absorption. photocatalysis has beneficial characteristics, such as its chemical and physical stability, as well as the oxidizing power of the photogenerated holes. It has become apparent that organic compounds can be oxidized to CO2 by hydroxyl radicals generated on the TiO2 surfaces (Hashimoto & Fujishima 1997). Multiple aspects of TiO2 photocatalytic oxidation of organic compounds in the gas phase have been addressed by a profuse scientific literature over the past 20 years.

Fig. 4: Photocatalysis process The development of photocatalysis processes offers a significant number of perspectives especially in gaseous phase depollution (Ranjit K. Nath et al., 2012) It is proved that the photo-oxidizing properties of photocatalyst activated by UV plays an important role in the degradation of volatile organic compounds (VOC). Heterogeneous photocatalysis is based on the absorption of UV radiations by the photocatalyst. This phenomenon leads to the degradation and the oxidation of the compounds, according to a mechanism that associates the pollutant’s adsorption on the photocatalyst and radical degradation reactions. M.M. Ballari et al. focused their work on NO and NO2 degradation by photocatalytically active concrete. The application of photocatalytic concrete containing TiO2 in urban streets is a method to improve the air quality in highly polluted areas. By using this technology it is possible to degrade a wide range of air contaminants, like nitric oxide (NO) and nitrogen dioxide (NO2), mainly emitted by automobiles (M.M. Ballari et al., 2010). In their work paper, the photocatalytic degradation of NO and NO2 was experimentally studied, and the atmospheric reactions involving nitrogen oxides and solar radiation were analyzed as well. In addition, the influence of different system parameters, such as inlet pollutant concentration, relative humidity, and irradiance was investigated in detail. The study performed by J. Chen and C.S. Poon pointed to photocatalytic activity of TiO2 in modified concrete materials and the influence of glass cullets used as aggregates (J. Chen et al., 2009). NO degradation was the measure of photoactivity. The glass cullets enhanced the photocatalytic activity of concrete, but a loss of 20% in photoactivity of surface layers was observed after 56 days curing. Another study of the same authors focused on fundamentals and applications of photocatalytic construction and building materials (J. Chen et al., 2009). Reducing Corrosion of RC: Addition of photocatalytic materials to the RC structure during its construction phase could reduce the corrosion problem of RC materials. This material hinders calcium oxide to form acidic compound. When any cement-based material in contact with the embedded reinforcing steel is carbonated, then the steel surface is

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depassivated (R. Cigna et al., 1994). Therefore, the reinforcing steel is no longer protected from corrosion. Corrosion may also commence when chloride, phosphate, moisture and oxygen gain access to the steel surface (B. El-Jazairi et al., 1990 and A. Raharinaivo et al., 1997). The structural features of metal oxide surfaces are very important for their reactivity in heterogeneous catalysis. For optical applications dense TiO2 films with smooth surfaces are required, whereas for photocatalytic applications of Mixed ZnO and TiO2 films exhibiting roughness and high surface areas may be advantageous to improve their performance and market acceptance outside the current field of optical coatings. The combination of photocatalysis and super-hydrophilicity allows grease and dirt to be swept away with water in presence of ZnO (Ranjit K. Nath et al., 2012). In practice, carbon dioxide (CO2) initiates reinforcement corrosion, when the concrete cover in contact with this steel is carbonated and rather wet (even in a nonpermanent way). Chlorides which induce metal corrosion, are ions dissolved in the pore solution ("free chlorides"). The mixing of ZnO with TiO2 increased the pH of concrete and higher pH value increased the photocatalytic property, which could reduce the corrosion problem of RC materials (Ranjit K. Nath et al., 2012). Photocatalysis and Microbial Fungi: Photocatalytic oxidation can inactivate infectious microorganisms which can be airborne bioterrorism weapons, such as Bacillus anthracis (Anthrax) (J. H. Kau et al., 2009). A photocatalytic system was investigated by Knight in 2003 to reduce the spread of severe acute respiratory syndrome on flights (H. Knight, 2003) following the outbreak of the disease. Inactivation of various gram-positive and gram-negative bacteria using visible light and a doped catalyst (D. Mitoraj et al., 2007) and fluorescent light irradiation similar to that used in indoor environments was studied (A. Pal et al., 2007) and shows great promise for widespread applications. It was also shown that E. coli could be completely mineralized on a TiO2 coated surface in air (W. A. Jacoby et al., 1998). Carbon mass balance and kinetic data for complete oxidation of E. coli, A. niger, Micrococcus luteus, and B. subtillus cells and spores were subsequently presented (E. J. Wolfrum et al., 2002).A comprehensive mechanism and detailed description of the TiO2 photokilling of E. coli on coated surfaces in air has been extensively studied in order understand to a considerable degree and in a quantitative way the kinetics of E. coli immobilization and abatement using photocatalysis, using FTIR, A FM, and CFU as a function of time and peroxidation of the membrane cell walls (V. A. Nadtochenko et al., 2005). Novel photoreactors and photo-assisted catalytic systems for air disinfection applications such as those using polyester supports for the catalyst (M. P. Paschoalino and W. F. Jardim, 2008), carbon nanotubes (V. Krishna et al., 2005), combination with other disinfection systems (S. A. Grinshpun et al., 2007), membrane systems (A. Pal et al., 2005), use of silver bactericidal agents in cotton textiles (T. Yuranova et al., 2003, T. Yuranova et al., 2006 and M. I. Mejia et al., 2010) for the abatement of E. coli in air, high surface area CuO catalysts (M. Paschoalino et al., 2008), and structure silica surf aces (A. Moncayo-Lasso et al., 2008) have also been reported. In terms of environmental health, the antifungal capability of TiO2 photocatalysis against mold fungi on coated wood boards used in buildings was confirmed (F. Chen et al., 2009) using A. niger as test microbe, and UV irradiation. Photocatalysis in Medical application: Photocatalysis is able to kill animal cells, such as in the antitumor activity shown using subcutaneous titania injection onto skin tumours followed by 40 minutes of UV illumination (Y. Kubota et al., 1994). This procedure produced a tenfold tumour volume reduction after three weeks, where the catalyst and light alone control runs showed tumor increases in volume by factors of 30–50. The use of photocatalysis for cancer cell treatment has also been documented elsewhere (H. Irie et al., 2004). For the disinfection abilities of photocatalytic processes, they are being explored for use in medical applications. Shiraishi et al. explored the photocatalytic activity of S. aureus, a common pathogenic bacterium in implantrelated infection, using TiO2 film on stainless steel and titanium substrates (K. Shiraishi et al., 2009). The bactericidal effect of the coating was confirmed upon UV irradiation, and the use of these coated photocatalytic substrates present a useful strategy for the control of such infections associated with biomedical implants. Photocatalysis in Laboratory and Hospital: Particularly in microbiological laboratories and in areas in intensive medical use, frequent and thorough disinfection of surfaces is needed in order to reduce the concentration of bacteria and to prevent bacterial transmission. Conventional methods of disinfection with wiping are not long-term effective, and are staff and

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time intensive. These methods also involve the use of harsh and aggressive chemicals. Disinfection with hard ultraviolet light is usually unsatisfactory, since the depth of penetration is inadequate and there are occupational health risks (K. P. Kuhn et al., 2003). Photocatalytic oxidation on surfaces coated with titanium dioxide offers an alternative to traditional methods of surface disinfection. Research has examined the biocidal activity of thin films of titania anchored to solid surfaces (Y. Kikuchi et al., 1997 and P. Evans et al., 2007). The effectiveness of this process was demonstrated using bacteria relevant to hygiene such as E. coli, P. aeruginosa, S. aureus, and E. faecium (K. P. Kuhn et al., 2003). The inactivation of E. coli cells deposited on membrane filters during irradiation with fluorescent light was also shown as an application of self-disinfecting surfaces (L. Caballero et al., 2009). Another application of photocatalysis in a hospital setting is for the control of Legionnaire’s disease, which is associated to hot water distribution systems containing bacteria of the Legionella species (Y. W. Cheng et al., 2007). In laboratory scale studies, it was shown that photocatalytic oxidation using TiO2/UV was able to mineralize the cells of four strains of L. pneumophilia serogroup 1 (strain 977, strain 1009, strain1004, and ATC C 33153) upon prolonged treatment. This implies that the process used might be a viable alternative to the traditional disinfection processes used for the control of Legionella bacteria in hospital hot water systems, such as thermal eradication and hyperchlorination (Y. W. Cheng et al., 2007). Photocatalysis in Food Industry: Due to the antibacterial applications of TiO2-mediated photooxidation, this process shows promise for the elimination of microorganisms in areas where the use of chemical cleaning agents or biocides is ineffective or is restricted by regulations, for example in the food industries (E. V. Skorb et al., 2008). TiO2 is nontoxic and has been approved by the American Food and Drug Administration for use in human food, drugs, cosmetics, and food contact materials (C. Chaweng and Y. Hayata, 2008). Surface disinfection is also of importance to food processing, as foodborne infections can be caused by the proliferation and resistance to cleaning procedures of pathogenic germs on surfaces of the production equipment in such industries. Studies with E. coli strains (A. K. Benabbou et al., 2007) synthesizing curli, a type of appendage that allows the bacteria to stick to surfaces and form biofilms, were able to inactivate this organism using titania and various types of UV irradiation. In dark events studies, following the bacterial inactivation, no bacterial cultivability was recovered after 48 hours, indicating that the durability of the disinfection was adequate. Nitrogen doping of the titania photocatalyst was also reported in a separate study (Y. Liu et al., 2007) with the use of visible light to inactivate E. coli and biofilm bacteria. Disinfection of E. coli using TiO2containing paper and UV fluorescent irradiation has also been shown (H. Matsubara et al., 1996). Photocatalysis and Effluents: Photocatalysis is also useful for disinfection of sewage containing organisms which are highly resistant to traditional disinfection methods, such as Cryptosporidium parvum (M. Otaki et al. 2000 and Tapashi G. Roy et al., 2009) and noroviruses (T. Kato et al., 1992). Municipal wastewater effluents from a sewage disposal plant in Hannover, Germany were treated in a slurry TiO2 reactor under UV irradiation to simultaneously detoxify and disinfect the samples (R. Dillert et al., 1998). The photo catalytic treatment was able to diminish the concentration of dissolved organic pollutants (indicated by TOC and COD), and as well inactivate pathogenic microorganisms. A similar result was obtained from studies monitoring Faecal streptococci and total coliforms using slurry TiO2 systems with UV lamps and solar irradiation, respectively (J. A. Herrera Melian et al., 2000). Photocatalysis in Water Treatment: Photocatalysis has been proven to be effective in the removal of chemical compounds and microbiological pathogens from water. The current discussion will focus on the various applications of photocatalysis in water disinfection. Surface Water treatment: While the majority of photocatalytic disinfection studies reported are carried out with distilled water or buffer solutions (C. Mccullagh et al., 2007), there have been attempts to quantify the effects of the chemical constituents of natural surface waters on TiO2 photocatalysis (A. G. Rincon et al., 2004 and, J. Marugan et al., 2008). It has been shown, using surface water samples, that the presence of inorganic ions and humic acids decrease the photocatalytic disinfection rate of E. coli (J. Marugan et al., 2008). Other efforts have been made to evaluate photocatalysis applications using real waters (J. C. Ireland et al., 1993 and J. Wist et al., 2002). For

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example, the integration of TiO2 photocatalysis into traditional water treatment processes for the removal of organic matter, which has variable levels during the year, was studied in the UK using three surface water samples (C. A. Murray et al., 2007). In studies done on surface water samples by Ireland et al. it was concluded that inorganic-radical scavengers can have a major negative impact on the efficacy of the photocatalytic process, and the presence of organic matter in the water samples also degrades the E. coli inactivation kinetics. Ground water Treatment: The ability of photocatalysis to break down and detoxify harmful organic chemicals has been exploited for groundwater treatment, as shown by engineering scale demonstrations using solar photo catalysis to remediate groundwater contaminated from leaking underground storage tanks (D. Y. Goswami et al., 1993). The disinfecting abilities of photocatalytic processes for application to treating groundwater contaminated with microorganisms such as F. Solani (P. Fernandez-Ibanez et al., 2009) was also investigated and shown to be effective for the removal of such microorganisms. Natural well water containing the F. Solani species and solar illumination and employing CPCs was also explored as a process configuration for this application (M. I. PoloLopez et al., 2010). Waste water Treatment: Photocatalysis has been used in engineering scale for solar photocatalytic treatment of industrial nonbiodegradable persistent chlorinated water contaminants (S. Malato et al., 2007), and in field scale for treatment of effluents from a resins factory (J. Blanco and S. Malato, 1994.). This process has also shown to be effective for treatment of wastewaters from a 5-fluororacil (a cancer drug) manufacturing plant (M. Anhegen et al., 1995), distillery wastewater (A. H. Zaidi et al., 1995), pulp and paper mill wastewater (C. S. Turchi et al., 1999), dyehouse wastewater, and oilfield produced water (G. Li et al., 2007). However, the disinfection capabilities of photocatalytic processes have not thoroughly been exploited for treatment of wastewaters. Wastewater reclamation and reuse is of growing importance, especially in areas where the freshwater supply is limited, and so effective disinfection of wastewaters is necessary. Any technical means of sewage use is limited by persistent organic pollutants and microorganisms which are not removed by the conventional mechanical and biological treatment train (O. Seven et al., 2004). Additional treatment is therefore necessary before any reuse can take place. An inexpensive approach to synthesizing a novel nitrogen-doped TiO2 photocatalyst has also been developed (Y. Liu et al., 2006) for improving the efficiency of visible light-induced disinfection of wastewaters, and introducing a new generation of catalysts for this application. Photocatalysis in Plant protection: Photocatalytic disinfection is potentially very important in the control and inactivation of pathogenic species present in the nutritive solution in circulating hydroponic agricultures (J. Blanco et al., 2009). Many plant pathogens can be transmitted by irrigation and recycled waters used in hydroponic agriculture. Conventional bactericidal methods often apply chemical pesticides to disinfect these pathogens, but these are often harmful to animals, humans, and the environment due to their residual toxicity (K. S. Yao et al., 2007). Photocatalytic disinfection of these plant pathogens using TiO2 may be used as a new tool for plant protection and an alternative to the use of harsh chemicals. Solar photocatalytic disinfection using batch process reactors and titania photocatalysts was also shown to be effective for the disinfection of five wild strains of the Fusarium genus (F. equiseti , F. oxysporum, F. anthophilum, F. verticilloides, and F. solani), a common plant pathogen (C. Sichel et al., 2007). In this case, natural solar radiation was used and the photocatalytic solar disinfection was compared to solar-only disinfection for these fungi. The photocatalytic process was found to be faster than the solar-only disinfection in all trials. The disinfecting ability of titania photocatalyst films was also tested on pathogens of mushroom diseases: Trichoder maharzianum, Cladobotry umvarium, Spicellum roseum, and P. tolaasii. The disinfection of these species was confirmed by experiments conducted in mushroom growing rooms under black light irradiation, and subsequently, white light irradiation (D. Sawada et al., 2005). Conclusion: Due to the superior ability of photocatalysis to inactivate a wide range of harmful microorganisms, it is being examined as a viable alternative to traditional disinfection methods such as chlorination, which can

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produce harmful by products. Photocatalysis is a versatile and effective process that can be adapted for use in many applications for disinfection in both air and water matrices. Additionally, photocatalytic surfaces are being developed and tested for use in the context of “self-disinfecting” materials. The use of photocatalysis was shown to be effective for various air- cleaning applications to inactivate harmful airborne microbial pathogens. The effectiveness of photocatalytic disinfection for inactivating microorganisms of concern for each of these applications was presented, high lighting key studies and research efforts conducted. While the performance of this technology is still to be optimized for the specific applications, based on the literature presented, it is abundantly evident that photocatalysis should be considered as a viable alternative to traditional disinfection methods. Acknowledgments At first, the authors wish to express gratitude to Almighty God for beginning this research. The authors would like to express special thanks to Universiti Kebangsaan Malaysia; and Faculty of Engineering and Built Environment (FKAB) for allocating funds for research. The first author expresses honest appreciation to Chittagong University of Engineering and Technology (CUET), Chittagong, Bangladesh for providing him leave for this research. References Benabbou, A.K., Z. Derriche, C. Felix, P. Lejeune and C. Guillard, 2007. “Photocatalytic inactivation of Escherischia coli .Effect of concent ration of TiO2 and microorganism, nature, and intensity of UV irradiation,”Applied Catalysis B, 76(3-4): 257-263. Anhegen, M., D.Y. Goswami and G. Svedberg, 1995. “Photocatalytic treatment of wastewater from 5-fluoracil manufacturing,” in Proceedings of the ASME/JSME/JSES International Solar Energy Conference, Maui, Hawaii. Ballari, M.M., Q.L. Yu, H.J.H. Brouwers, 2010. Experimental study of the NO and NO2 degradation by photocatalytically active concrete, Catalysis Today. Blanco, J. and S. Malato, 1994. “Solar photocatalytic mineralization of real hazardous waste water at preindustrial level,” in Proceedings of the ASME/JSME/JSES International Solar Energy Conference, D. E. Klett, R. E. Hogan, and T. Tanaka, Eds., pp:103–109, San Francisco, Calif, USA. Blanco, J., S. Malato, P. Fernandez-Ibanez, D. Alarcon, W. Gernjak, and M.I. Maldonado, 2009. “Review of feasible solar energy applications to water processes,” Renewable and Sustainable Energy Reviews, 13(67): 1437-1445. Caballero, L., K.A. Whitehead, N.S. Allen, and J. Verran, 2009. “Inactivation of Escherichia coli on immobilized TiO2 using fluorescent light,”Journal of Photochemistry and Photobiology A, 202(2-3): 92-98. Chaweng, C. and Y. Hayata, 2008. “Development of TiO2 powder-coated food packaging film and its ability to inactivate Escherichia coli in vitro and in actual tests,” International Journal of Food Microbiology, 123(3): 288-292. Chen, F., X. Yang, and Q. Wu, 2009. “Antifungal capability of TiO2 coated film on moist wood,” Building and Environment, 44(5): 1088-1093. Chen, J., C.S. Poon, 2009. Photocatalytic activity of titanium dioxide modified concrete materials –Influence of utilizing recycled glass cullets as aggregates, Journal of Environmental Management., 90: 3436-3442. Chen, J., C.S. Poon, 2009. Photocatalytic construction and building materials: From fundamentals to applications, Building and Environment, 44: 1899-1906. Cheng, Y.W., R.C.Y. Chan and P.K. Wong, 2007. “Disinfection of Legionella pneumophila by photocatalytic oxidation,” Water Research, 41(4): 842-852. Choi, Y.S. and B.W. Kim, 2000. “Photocatalytic disinfection of E. coli in a UV/TiO2 -immobilised optical-fibre reactor,” Journal of Chemical Technology and Biotechnology, 75(12):1145-1150. Cigna, R., G. Familiari, F. Gianetti, E. Proverbio, 1994. Corrosion and Corrosion Protection of Steel in Concrete (ed, R. N. Swamy), Sheffield, UK, pp: 848. Cushnie, T.P.T., P.K.J. Robertson, S. Officer, P.M. Pollard, C. McCullagh and J.M.C. Robertson, 2009. “Variables to be considered when assessing the photocatalytic destruction of bacterial pathogens,” Chemosphere, 74(10): 1374-1378. Dillert, R., U. Siemon and D. Bahnemann, 1998. “Photocatalytic disinfection of municipal wastewater,” Chemical Engineering and Technology, 21(4): 356-358. Dunlop, P.S.M., J.A. Byrne, N. Manga and B.R. Eggins, 2002. “The photocatalytic removal of bacterial pollutants from drinking water,” Journal of Photochemistry and Photobiology A, 148(1–3): 355-363. El-Jazairi, B. and N.S. Berke,1990. Corrosion of Reinforcement in Concrete (eds. C. L. Page, K. W. J. Treadaway, and P. B. Bamforth), Elsevier Applied Science, pp: 571.

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