Photodynamic Approaches to Water Disinfection

Authored by: Michela Magaraggia , Giulio Jori

CRC Handbook of Organic Photochemistry and Photobiology

Print publication date:  March  2012
Online publication date:  March  2012

Print ISBN: 9781439899335
eBook ISBN: 9781466561250
Adobe ISBN:

10.1201/b12252-68

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Abstract

The question of water supply and distribution is becoming of utmost importance worldwide from both a social and a scientific point of view. Actually, a growing number of countries around the world, especially developing countries but also several Mediterranean countries, face increasingly difficult situations concerning the availability of irrigation, industrial, and drinking water from both surface and groundwater stocks. Many water sources are heavily polluted by hazardous chemicals, which are known to be harmful to humans and a variety of animal and vegetal ecosystems, as well as by several kinds of pathogenic microorganisms, such as bacteria, fungi, molds, viruses, and parasitic protozoa. Potential contaminants include agricultural runoff, landfill leachates, and industrial activities [1,2]. Therefore, there is an urgent need for the definition of efficacious and environmentally safe techniques yielding an efficient water purification and disinfection. Currently, the most commonly adopted approaches are based on physical methods (e.g., filtration, heating, or irradiation with ultraviolet [UV] light or x-rays), even though reliance is mainly placed on chemical treatments with oxidizing species, such as chlorine, chlorine dioxide, or ozone [3]. However, such methods often exhibit a number of negative aspects, in particular the formation of endoperoxides or trihalomethanes as by-products of the reaction between the chemical disinfectant and organic matter, or the selection of multidrug resistant microbial strains upon repeated treatment of waters characterized by a large microbial flora [4,5]. Moreover, chlorine is often phytotoxic [6], while the use of ozone proved to be moderately expensive and involve a high consumption of energy, thereby making its implementation on a large scale a not very attractive endeavor. The evolvement of resistance by microbial cells represents a particularly challenging problem as a consequence of the truly large variety of mechanisms, which have been found to be developed by pathogenic agents in order to increase their defensive strategies against external insults: these include a thickening of their outer wall, encoding of new proteins that prevent the penetration of drugs, onset of mutants deficient in those porin channels allowing the influx of externally added chemicals, etc. [7]. The transfer of such resistance to human pathogens represents a potentially serious threat to public health [8]. Therefore, it is by now apparent how difficult it is to identify a comprehensive strategy.

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