446
S. Das et al.
generally associated with the presence of dissolved refractory organic components,
suspended solids and fecal coliforms that are both annoying and expensive to get rid
of (Viessman et al. 1998). Universal water treatment technologies like adsorption
or coagulation simply concentrate the pollutants, transferring them to other harmful chemical forms, face problems for complete elimination and decontamination
(Padmanabhan et al. 2006). Conventional methods like membrane filtration technologies, sedimentation, and chemical treatment involve greater operating costs and
produce lethal secondary pollutants into the aquatic ecosystem (Gaya and Abdullah
2008). These unnecessary secondary pollutants are apprehensive worldwide due to
the growing environmental consciousness and legislatures. Thus remedies include
chemical treatment methods like chlorination and ozonation and other treatment like
UV light has been most commonly and widely used disinfection process.
1.3.1 Chlorination
Chlorination is one of the most universally used practises for disinfection owing its
economical factors. It is used in the final step of WWTP which involves addition
of gaseous chlorine (Cl 2 ), calcium, or sodium hypochlorite (Ca(OCl) 2 )/(NaOCl), to
water which ultimately acts in disinfection of waterborne pathogens with the generation of hypochlorous acid (HOCl). The mechanism of action generally involves oxidation of bacterial germ cells, and cell membranes, along with inhibition of enzyme
activity. Regrettably, chlorination has been scarce for effective inactivation of viral
pathogens (Kitajima et al. 2010). He reported the presence of enteroviruses in nearly
58% of the samples and adenoviruses in nearly all samples collected from six different WWTP after chlorination process. Since 1970s the effect of chlorination MDR
bacteria has been studied. More recently, Huang et al. showed that the though inactivation rates of MDR bacteria (namely, chloramphenicol-, rifampicin-, tetracyclineresistant bacteria) stayed comparatively high with respect to other heterotrophs but
the fraction of MDR increased numerously after chlorination (Huang et al. 2013).
This includes increased resistance toward of E. coli tetracycline antibiotics, whose
inactivation rates with Cl 2 (1.5 mg/L) have been lesser in comparison to the sensitive
ones. This may lead to selectivity of resistant strains in drinking and wastewater.
Studies performed by Munir et al. from five WWTPs in Michigan (USA), reports
no significant involvement of this technique to MDR and ARG reduction. Consequently, the mechanism of how chlorine action toward MDR and ARG assortment in
wastewater is greatly unidentified and further insights into this research is required
(Munir et al. 2011).
1.3.2 Ozonation
Ozonation is a typical process used for oxidative disinfection of water and polluted
waters. Ozone effectually incapacitates survivors of chlorination process, i.e., protozoans like Cryptosporidium and Giardia (Rennecker et al. 1999; Von Gunten 2003).
S. Das et al.
generally associated with the presence of dissolved refractory organic components,
suspended solids and fecal coliforms that are both annoying and expensive to get rid
of (Viessman et al. 1998). Universal water treatment technologies like adsorption
or coagulation simply concentrate the pollutants, transferring them to other harmful chemical forms, face problems for complete elimination and decontamination
(Padmanabhan et al. 2006). Conventional methods like membrane filtration technologies, sedimentation, and chemical treatment involve greater operating costs and
produce lethal secondary pollutants into the aquatic ecosystem (Gaya and Abdullah
2008). These unnecessary secondary pollutants are apprehensive worldwide due to
the growing environmental consciousness and legislatures. Thus remedies include
chemical treatment methods like chlorination and ozonation and other treatment like
UV light has been most commonly and widely used disinfection process.
1.3.1 Chlorination
Chlorination is one of the most universally used practises for disinfection owing its
economical factors. It is used in the final step of WWTP which involves addition
of gaseous chlorine (Cl 2 ), calcium, or sodium hypochlorite (Ca(OCl) 2 )/(NaOCl), to
water which ultimately acts in disinfection of waterborne pathogens with the generation of hypochlorous acid (HOCl). The mechanism of action generally involves oxidation of bacterial germ cells, and cell membranes, along with inhibition of enzyme
activity. Regrettably, chlorination has been scarce for effective inactivation of viral
pathogens (Kitajima et al. 2010). He reported the presence of enteroviruses in nearly
58% of the samples and adenoviruses in nearly all samples collected from six different WWTP after chlorination process. Since 1970s the effect of chlorination MDR
bacteria has been studied. More recently, Huang et al. showed that the though inactivation rates of MDR bacteria (namely, chloramphenicol-, rifampicin-, tetracyclineresistant bacteria) stayed comparatively high with respect to other heterotrophs but
the fraction of MDR increased numerously after chlorination (Huang et al. 2013).
This includes increased resistance toward of E. coli tetracycline antibiotics, whose
inactivation rates with Cl 2 (1.5 mg/L) have been lesser in comparison to the sensitive
ones. This may lead to selectivity of resistant strains in drinking and wastewater.
Studies performed by Munir et al. from five WWTPs in Michigan (USA), reports
no significant involvement of this technique to MDR and ARG reduction. Consequently, the mechanism of how chlorine action toward MDR and ARG assortment in
wastewater is greatly unidentified and further insights into this research is required
(Munir et al. 2011).
1.3.2 Ozonation
Ozonation is a typical process used for oxidative disinfection of water and polluted
waters. Ozone effectually incapacitates survivors of chlorination process, i.e., protozoans like Cryptosporidium and Giardia (Rennecker et al. 1999; Von Gunten 2003).