Is Not It Time to Stop Using Chlorine for Treating Water?

Djamel Ghernaout^1,2, Noureddine Elboughdiri^1,3

¹Chemical Engineering Department, College of Engineering, University of Ha’il, Ha’il, KSA.
²Chemical Engineering Department, Faculty of Engineering, University of Blida, Blida, Algeria.
³Département de Génie Chimique de Procédés, Laboratoire Modélisation, Analyse, et Commande des systèmes, Ecole Nationale d’Ingénieurs de Gabès (ENIG), Rue Omar Ibn-Elkhattab, Gabès, Tunisia.

DOI: 10.4236/oalib.1106007                

Abstract

Chlorine is largely used as a disinfectant in the water and wastewater treatment industries through the world despite the fact that is greatly poisonous for hu-man beings. Its toxicity is more extended to generating disinfection by-products during its microorganisms’ killing and action on organic matter present in water. More importantly, recent studies proved the potential impacts of disinfection on transmission of antibiotic resistance genes (ARGs), particularly for free-living ARGs in final disinfected effluent of urban wastewater treatment plants. Indeed, Escherichia coli concentration prior to chlorination depicted a powerful positive correlation with the extracellular ARGs plenty in the final effluents; however, lower temperature and higher ammonium concentration were suggested to relate with intracellular ARGs. Chlorination could elevate the plenty of ARGs, therefore, inducing danger of the diffusion of antibiotic resistance in nature. Consequently, chlorine toxicity is more and more proved, which appeals its urgent stopping from using it in the treatment of both water and wastewater. The same conclusion was also obtained at least for UV and UV/H2O2 disinfection. Chemical disinfection should be urgently avoided or at least deeply revised. For removing pathogens and treating water, safe multi-barrier methods, such as distillation and membrane processes, have to be adopted.

Keywords

Antibiotic-Resistant Bacteria (ARB), Antibiotic Resistance Genes (ARGs), Wastewater Treatment, Disinfection, Oxidation, Escherichia coli

1. Introduction

Antibiotic resistance has caused massive dangers to public health globally [1]. Every year, more than 700,000 persons die from antimicrobial-resistant infections worldwide; nevertheless, the envisaged disaster number risks to attain 10 million by 2050 if no measures are made immediately [2]. Even if the diffusion of antibiotic resistance in clinic environments has appealed considerable worries, the appearance and propagation of antibiotic resistance bacteria (ARB) or antibiotic resistance genes (ARGs) in natural environments have been disregarded yet [3].

Urban wastewater treatment plants (UWWTPs) remain at the interface joining the human population and the aquatic/soil mediums [4] - [10]. They can supply an exemplary environment for the procuration and dispersal of antibiotic resistance [11] [12] [13]. Due to an assorted blend of antibiotics and different contaminants, their metabolites and resistant bacteria attain UWWTPs via wastewater discharges from hospitals, households, industries, and animal farms [14]. The spread of ARB and ARGs in UWWTPs has caught more and more awareness lately [15] [16] [17] [18]. Especially, biological reactors [19] [20] [21] in activated sludge setups are considered as one of the serious boxes in nursing both ARB and ARGs [22] [23], via picking below subjection of antibiotic or resistance transfer between bacteria through horizontal gene transfer (HGT) [24] [25]. In particular, it has been mentioned that UWWTPs display restricted potential to eliminate or restrain ARGs and ARB [17] [26] [27]. More importantly, not only does the effluent constitute a huge tank comprising diverse ARGs, but also the plenties of several exemplary ARGs are surprisingly higher in effluent than that in influent through the treatment techniques, such as blaCTX-M, blaTEM and qnrS [28] [29]. As a result, UWWTPs have been established to function a key part in the transmission of ARB and ARGs in nature, therefore causing hazards to public health [1].

To dominate the prevalence of microorganisms, different disinfection techniques have been largely employed in UWWTPs. Several investigations have studied the demobilization of ARGs via disinfection technologies like chlorination and ultraviolet (UV) irradiation [30] [31] [32] [33]. Nevertheless, not many new investigations mentioned that chlorination, as a largely utilized disinfection method, might co-select antibiotic resistance. As an illustration, Shi et al. [29] affirmed that the chlorination method augmented the plenties of ampC and tetA following metagenomic sequencing. Further, Xu et al. [34] published that chlorination elevated the comparative plenty of ARGs from 6.4- to 109.2-fold in tap water contrasted to the final water. On the other hand, Lin et al. [35] proposed that ARGs were more possibly eliminated rather than co-selected via chlorine, where they monitored 225 ARGs; however, only six were elevated following chlorination. Even if paradoxical deductions were gained concerning the effect of chlorination on ARGs, a small number of researches have been devoted to discerning among intracellular ARGs (iARGs) and extracellular ARG (eARGs). Indeed, disinfection techniques (like chlorination) may destroy ARB; however, at the same time, DNA will be liberated into the water, where eARGs may remain existing in the free-living DNA. The presence of iARGs can assist ARB dispersal through conjugation and transduction; however, the competent non-resistant bacteria in the biofilm and sedimentation can take up eARGs stability in the aquatic medium for quite a time, that way conducting to the diffusion of antibiotic resistance through transformation [36] [37] [38]. Consequently, eARGs in the effluent from UWWPTs are also possible to raise ARGs and ARB transmission in environmental mediums. Nevertheless, the influence of chlorination on eARGs stays ambiguous because of the shortage of an efficacious procedure to extract extracellular DNA (eDNA), which is too small to collect in treated water. Lately, Wang et al. [38] presented a procedure to collect eDNA via employing a novel kind of nucleic acid adsorption particle (NAAP) with an elevated potential, which may attain an eARG recuperation average of more than 95% from 10 L of water samples. This advanced procedure may let us examine the effect of disinfection on eARGs [1].

2. Chlorination Augments Both iARGs and eARGs

Liu et al. [1] examined the impacts of chlorination on the presence and concentration of both eARGs and iARGs in a full-scale UWWTP during twelve months. They indicated that the concentrations of both eARGs and iARGs could be elevated via disinfecting with chlorine dioxide (ClO₂). More importantly, chlorination preferentially augmented the plenties of eARGs versus macrolide (ermB), tetracycline (tetA, tetB and tetC), sulfonamide (sul1, sul2 and sul3), β-lactam (ampC), aminoglycosides (aph(2’)-Id), rifampicin (katG) and vancomycin (vanA) up to 3.8 folds. In the same way, the plenties of iARGs were also elevated up to 7.8 folds following chlorination. In terms of correlation analyses, the plenty of Escherichia coli prior chlorination depicted a powerful positive correlation with the total eARG concentration; however, lower temperature and higher ammonium concentration were supposed to be linked with the concentration of iARGs. Liu et al. [1] concluded the chlorination could elevate the plenties of both iARGs and eARGs, just like that causing danger of the diffusion of antibiotic resistance in nature.

3. Microbial Selectivity of UV Treatment on Antibiotic-Resistant Bacteria

To comprehend the influence of UV disinfection on antibiotic-resistant bacteria, Guo et al. [39] investigated both total heterotrophic bacteria, and antibiotic-resistant bacteria (comprising cephalexin-, ciprofloxacin-, erythromycin-, gentamicin-, vancomycin-, sulfadiazine-, rifampicin-, tetracycline- and chloramphenicol-resistant bacteria) in secondary effluent samples from a domestic wastewater treatment plant (Figure 1). Bacteria resistant to both erythromycin and tetracycline were selected as the specimen of multiple-antibiotic-resistant

Figure 1. Treatment process of the municipal wastewater treatment plant (A²/O: Anaerobic-Anoxic-Oxicprocess; BAF: Biological Aerated Filter) [39].

bacteria and their properties following UV application were also examined. They found that UV disinfection conducts to performant demobilization of total heterotrophic bacteria, as well as all antibiotic-resistant bacteria. Following UV application at a fluence of 5 mJ/cm², the log decreases of nine types of antibiotic-resistant bacteria changed from 1.0 ± 0.1 to 2.4 ± 0.1. Bacteria resistant to both erythromycin and tetracycline had an identical fluence reaction as did total heterotrophic bacteria. Their results propose that UV disinfection could remove antibiotic resistance in wastewater treatment effluents and therefore guarantee public health security. Guo et al. [39] mentioned that UV disinfection conducted to the enrichment of bacteria with resistance to sulfadiazine, vancomycin, rifampicin, tetracycline and chloramphenicol; however, the fractions of cephalexin-, erythromycin-, gentamicin- and ciprofloxacin-resistant bacteria in the wastewater diminished. This illustrates the microbial selectivity of UV disinfection for antibiotic-resistant bacteria.

4. Antibiotic Resistance Diffusion Capacity by UV/H₂O₂ Technique

Ferro et al. [40] assessed the influence of an advanced oxidation process (particularly UV/H₂O₂) [41] - [46] on antibiotic resistance diffusion capacity. They performed UV/H₂O₂ disinfection trials on real wastewater samples to estimate the: 1) demobilization of Total Coliforms, E. coli, and antibiotic-resistant E. coli as well as 2) probable elimination of objective ARGs (that is, bla_TEM, qnrS and tetW) (Figure 2). Especially, DNA was extracted from both antibiotic-resistant E. coli bacterial cells (intracellular DNA), grown on selective culture media, and the whole water suspension (total DNA) collected at various treatment periods. Polymerase chain reaction (PCR) check was realized to discover the absence/presence of the selected ARGs. Real Time quantitative Polymerase Chain Reaction (qPCR) was employed to measure the studied ARGs in terms of copies/mL. Regardless of the bacterial demobilization and a diminution of ARGs in intracellular DNA following 60 min treatment, UV/H₂O₂ method was not performant in eliminating ARGs from water suspension (total DNA). More importantly, an augmentation up to 3.7 × 10³ copies/mL (p N 0.05) of bla_TEM gene was noted in total DNA following 240 min treatment; however, no variation (p > 0.05) was observed for qnrS gene among the initial (5.1 × 10⁴ copies/mL) and the final sample (4.3 × 10⁴ copies/mL) (Figure 3). Following their findings, Ferro et al. [40] concluded that the examined disinfection technique might not be able to diminish antibiotic resistance diffusion capacity.

Figure 2. Relative abundance of bacterial population during UV/H₂O₂ treatment and AntibioticResistant E. coli percentages calculatedwith respect to total coliforms (upper placed values) and E. coli [40].

Figure 3. Results of electrophoretic run of PCR product on gel agarose: 16S rRNA gene (a); bla_TEM gene (b); qnrS gene (c); tet Wgene (d). P.C. = positive control; N.C. = negative control [40].

5. Electrodis Infection of Bacteria

Electrodisinfection has been illustrated to be an efficacious technique with low needed residence period for treating potable water supplies, industrial raw water supplies, liquid foodstuffs, and wastewater effluents [47] - [52]. Ghasemian et al. [53] explored the electrodis infection of saline water polluted with bacteria in chloride-containing solutions employing Sb-doped Sn_80%-W_20%-oxide anodes. They focused on the impact of current density, bacterial load, initial chloride concentration, solution pH, and the kind of bacteria (E. coli D21, E. coli O157: H7, and E. faecalis) on disinfection performance. They tested the influence of the natural organic matter [54] - [60] and a radical scavenger on the disinfection efficiency. They found that their electrochemical setup was greatly efficient in demobilizing bacteria for a 0.1 M NaCl solution polluted with ~10⁷ CFU/mL bacteria via implementing a current density ≥ 1 mA/cm² over the cell. They attained 100% demobilization of E. coli D21 during less than 60 s and power consumption of 48 Wh/m³, via implementing a current density of 6 mA/cm² in a 0.1 M NaCl solution polluted with ~10⁷ CFU/mL. Reactive chlorine species as well as reactive oxygen species (such as hydroxyl radicals) [61], formed in situ throughout the electrochemical technology, were discovered to be in charge of demobilizing bacteria.

6. Conclusions

The main points drawn from this work may be given as:

1) Chlorination augmented both eARGs and iARGs contamination in a full-scale UWWTP. E. coli concentration prior to chlorination depicted a powerful positive correlation with the eARGs plenty in the final effluents; however, lower temperature and higher ammonium concentration were suggested to relate with iARGs. Chlorination could elevate the plenty of ARGs, therefore inducing danger of the diffusion of antibiotic resistance in nature [1].

2) As the UV fluence used in actual WWTPs for disinfecting wastewater is usually less than the design parameters, regarding the life span and running circumstances of UV lamps, the potential hazard augmented by ARB following implementations of low fluences still needs awareness. For this reason, ARB removal researches of UV disinfection or different disinfection techniques in WWTPs are necessitated [39].

3) Consequently, chlorine toxicity is more and more established. This implicates its urgent stopping from using it in the treatment of both water and wastewater [62]. Chemical disinfection should be deeply avoided or at least revised [63] - [68]. For removing pathogens and treating water, safe multi-barrier processes, such as distillation and membrane processes [69] - [78], have to be adopted for the best future of humankind [79] [80] [81].

Conflicts of Interest

The authors declare no conflicts of interest regarding the publication of this paper.

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[59]	Ghernaout, D., Al-Ghonamy, A.I., Naceur, M.W., Boucherit, A., Messaoudene, N.A., Aichouni, M., Mahjoubi, A.A. and Elboughdiri, N.A. (2015) Controlling Coagulation Process: From Zeta Potential to Streaming Potential. American Journal of Environmental Protection, 4, 16-27. https://doi.org/10.11648/j.ajeps.s.2015040501.12
[60]	Ghernaout, D. and Boucherit, A. (2015) Review of Coagulation’s Rapid Mixing for NOM Removal. Journal of Research & Developments in Chemistry, 2015, Article ID: 926518. https://doi.org/10.5171/2015.926518
[61]	Ghernaout, D. (2019) Aeration Process for Removing Radon from Drinking Water: A Re-view. Applied Engineering, 3, 32-45.
[62]	Ghernaout, D. (2017) Environmental Principles in the Holy Koran and the Sayings of the Prophet Muhammad. American Journal of Environmental Protection, 6, 75-79. https://doi.org/10.11648/j.ajep.20170603.13
[63]	Boucherit, A., Moulay, S., Ghernaout, D., Al-Ghonamy, A.I., Ghernaout, B., Naceur, M.W., AitMessaoudene, N., Aichouni, M., Mahjoubi, A.A. and Elboughdiri, N.A. (2015) New Trends in Disinfection By-Products Formation upon Water Treatment. Journal of Research & Developments in Chemistry, 2015, Article ID: 628833. https://doi.org/10.5171/2015.628833
[64]	Ghernaout, D. (2018) Disinfection and DBPs Removal in Drinking Water Treatment: A Perspective for a Green Technology. International Journal of Advanced and Applied Sciences, 5, 108-117. https://doi.org/10.21833/ijaas.2018.02.018
[65]	Ghernaout, D., Touahmia, M. and Aichouni, M. (2019) Disinfecting Water: Elec-trocoagulation as an Efficient Process. Applied Engineering, 3, 1-12.
[66]	Ghernaout, D. (2017) The Holy Koran Revelation: Iron Is a “Sent Down” Metal. American Journal of Environmental Protection, 6, 101-104. https://doi.org/10.11648/j.ajep.20170604.14
[67]	Ghernaout, D., Aichouni, M. and Touahmia, M. (2019) Mechanistic Insight into Disinfection by Electrocoagulation: A Review. Desalination and Water Treatment, 141, 68-81. https://doi.org/10.5004/dwt.2019.23457
[68]	Ghernaout, D. (2019) Greening Electrocoagulation Process for Disinfecting Water. Applied Engineering, 3, 27-31.
[69]	Ghernaout, D. and El-Wakil, A. (2017) Requiring Reverse Osmosis Membranes Modifica-tions—An Overview. American Journal of Chemical Engineering, 5, 81-88. https://doi.org/10.11648/j.ajche.20170504.15
[70]	Ghernaout, D. (2017) Reverse Osmosis Process Membranes Modeling—A Historical Overview. Journal of Civil, Construction and Environmental Engineering, 2, 112-122.
[71]	Ghernaout, D., El-Wakil, A., Alghamdi, A., Elboughdiri, N. and Mahjoubi, A. (2018) Membrane Post-Synthesis Modifications and How It Came about. Interna-tional Journal of Advanced and Applied Sciences, 5, 60-64. https://doi.org/10.21833/ijaas.2018.02.010
[72]	Ghernaout, D., Alshammari, Y., Alghamdi, A., Aichouni, M., Touahmia, M. and AitMessaoudene, N. (2018) Water Reuse: Extenuating Membrane Fouling in Membrane Processes. International Journal of Environmental Chemistry, 2, 1-12. https://doi.org/10.11648/j.ajche.20180602.12
[73]	Ghernaout, D. (2019) Brine Recycling: Towards Membrane Processes as the Best Available Technology. Applied Engineering, 3, 71-84.
[74]	Ghernaout, D. and Elboughdiri, N. (2019) Electrocoagulation Process Intensification for Disinfecting Water: A Review. Applied Engineering, 3, 140-147.
[75]	Ghernaout, D. and Elboughdiri, N. (2019) Iron Electrocoagulation Process for Disinfecting Water: A Review. Applied Engineering, 3, 154-158.
[76]	Ghernaout, D., Naceur, M.W. and Aouabed, A. (2011) On the Dependence of Chlorine By-Products Generated Species Formation of the Electrode Material and Applied Charge during Electrochemical Water Treatment. Desalination, 270, 9-22. https://doi.org/10.1016/j.desal.2011.01.010
[77]	Ghernaout, D. (2011) Water Treatment Chlorination: An Updated Mechanistic Insight Review. Chemistry Research Journal, 2, 125-138.
[78]	AitMessaoudene, N., Naceur, M.W., Ghernaout, D., Alghamdi, A. and Aichouni, M. (2018) On the Validation Perspectives of the Proposed Novel Dimensionless Fouling Index. International Journal of Advanced and Applied Sciences, 5, 116-122. https://doi.org/10.21833/ijaas.2018.07.014
[79]	Ghernaout, D., Alghamdi, A., Aichouni, M. and Touahmia, M. (2018) The Lethal Water Tri-Therapy: Chlorine, Alum, and Polyelectrolyte. World Journal of Applied Chemistry, 3, 65-71. https://doi.org/10.11648/j.wjac.20180302.14
[80]	Ghernaout, D., Ghernaout, B. and Naceur, M.W. (2011) Embodying the Chemical Water Treatment in the Green Chemistry: A Review. Desalination, 271, 1-10. https://doi.org/10.1016/j.desal.2011.01.032
[81]	Ghernaout, B., Ghernaout, D. and Saiba, A. (2010) Algae and Cyanotoxins Removal by Coagulation/Flocculation: A Review. Desalination and Water Treatment, 20, 133-143. https://doi.org/10.5004/dwt.2010.1202