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May 20, 2024

L'efficacité du chlore

npj Clean Water volume 4, Numéro d'article : 48 (2021) Citer cet article 6666 Accès 7 Citations 8 Détails Altmetric Metrics Les solutions de chlore sont largement utilisées pour la production de produits biologiques.

npj Clean Water volume 4, Numéro d'article : 48 (2021) Citer cet article

6666 Accès

7 citations

8 Altmétrique

Détails des métriques

Les solutions chlorées sont largement utilisées pour la production d’eau potable biologiquement sûre. La capacité des systèmes de traitement de l’eau potable au point d’utilisation [POU] a suscité un intérêt dans les endroits où les systèmes de traitement centralisés et les réseaux de distribution ne sont pas pratiques. Cette étude a examiné l'activité antimicrobienne et anti-biofilm de trois désinfectants à base de chlore (ions hypochlorite [OCl-], acide hypochloreux [HOCl] et solutions activées électrochimiquement [ECAS]) destinés à être utilisés dans les applications d'eau potable POU. L'activité antimicrobienne relative a été comparée dans des tests de suspension bactéricide (BS EN 1040 et BS EN 1276) utilisant Escherichia coli. L'activité anti-biofilm a été comparée en utilisant Pseudomonas aeruginosa sessile établi dans un réacteur à biofilm du Center for Disease Control [CDC]. HOCl a présenté la plus grande activité antimicrobienne contre E. coli planctonique à > 50 mg L−1 de chlore libre, en présence d'une charge organique (albumine sérique bovine). Cependant, ECAS a présenté une activité anti-biofilm significativement plus élevée que OCl et HOCl contre les biofilms de P. aeruginosa à ≥ 50 mg L−1 de chlore libre. Sur la base de ces preuves, les désinfectants dans lesquels HOCl est l'espèce de chlore dominante (HOCl et ECAS) seraient des désinfectants alternatifs appropriés à base de chlore pour les applications d'eau potable POU.

La consommation d’eau biologiquement contaminée1 constitue une source majeure de maladies humaines. Cela est particulièrement pertinent pour les pays à faible revenu (c'est-à-dire que le revenu national brut [RNB] par habitant est < 1 025 dollars) et les pays les moins avancés (46 pays à faible revenu confrontés à de graves obstacles structurels au développement durable) où, selon les estimations, 30 % de la population, en moyenne, avoir accès à des services d’assainissement de base2. Cela contraste avec les pays de la classe moyenne supérieure (RNB par habitant de 4 036 $ à 12 475 $) et à revenu élevé (RNB par habitant > 12 476 $) qui utilisent principalement des systèmes centralisés de traitement de l’eau potable pour assurer la production et l’approvisionnement en eau biologiquement sûre3. Le rôle principal de la désinfection de l’eau potable est de contrôler les micro-organismes pathogènes et de garantir que l’eau traitée est biologiquement potable. Le chlore, sous forme d'hypochlorite de sodium [NaOCl], est le désinfectant le plus courant en raison de son faible coût et de ses propriétés antimicrobiennes efficaces4. La présence de chlore résiduel (0,5 à 5 mg L−1) dans les réseaux de redistribution limite la repousse microbienne, contribuant ainsi à maintenir une eau biologiquement sûre au point de livraison3. Les organismes indicateurs tels que Escherichia coli, les coliformes totaux, les entérocoques et Clostridium perfingens3,5, qui déduisent la présence de matières fécales, sont surveillés pour garantir l'efficacité des processus de traitement de désinfection. La limite recommandée pour ces organismes indicateurs dans l’eau traitée est de zéro UFC 100 mL−1, en raison de leur potentiel pathogène3,5. Malheureusement, l’utilisation de désinfectants chlorés donne lieu à la formation de sous-produits de désinfection [SPD]6,7 tels que les trihalométhanes8 et les acides haloacétiques9. Ces sous-produits sont connus pour présenter des propriétés mutagènes et cancérigènes10 et sont donc hautement indésirables.

Point-of-use [POU] drinking water treatment systems do not require distribution networks and therefore negate the need to maintain residual chlorine levels. The World Health Organization recommends free chlorine concentrations of between 0.2 and 0.5 mg L−1 at point of delivery and use3. The use of conventional chlorine-based disinfectants, such as hypochlorite (OCl-), within POU water disinfection requires the storage and transportation of hazardous chemicals and can also cause the formation of harmful DBPs and the deterioration of taste and odour11. Ultraviolet and ozone are well established as disinfection technologies within both decentralised/POU12,13 and large scale drinking water treatment14,3.3.CO;2-1." href="/articles/s41545-021-00139-w#ref-CR15" id="ref-link-section-d367130989e520"15, but an added benefit of implementing electrochemcially activated solutions [ECAS] is it has capability to be used externally to water treatment systems as part of food production16,17 or in healthcare settings18,19. A limited number of studies have compared ECAS against commonly used chlorine agents for decentralised disinfection applications20,21. Although these preliminary studies were promising, neither study reported the pH of the ECAS studied or their effectiveness against biofilms./p>95%), and dissolved chlorine [Cl2] (<5%)25,26. Additional metastable antimicrobial species including; OH-, O3, H2O2 and O2- are also theorised to be generated although there lifetime and activity within active solutions is debated27,28. The antimicrobial properties of ECAS result from a combination of HOCl and the metastable species that give rise to the observed high ORP values. The mode of action of such solutions is then physical rupture of the inner and outer cell membranes19,29, leading to disruption and failure of microbial functionality, such as energy generation mechanisms23./p>5-log reduction) and there was no significant difference between the three disinfectants, whereby HOCl resulted in a complete log reduction, for OCl- a log reduction of 7.871 ± 0.74 log10 CFU mL−1 was achieved whilst ECAS achieved a 6.806 ± 1.09 log10 CFU mL−1 reduction. At 50 mg L−1 FC, OCl- did not achieve the required 5-log reduction (4.531 ± 0.15 log10 CFU mL−1), resulting in significantly lower antimicrobial activity compared to both HOCl and ECAS (p < 0.0001), whereby there was no significant difference between HOCl and ECAS treatment (p > 0.05). At the lowest FC concentration tested (25 mg L−1) ECAS was the only disinfectant to reduce the bacterial load ≥5 log10 CFU mL−1 (Fig. 2), resulting in a 6.077 ± 1.441 log10 CFU mL−1 log reduction. The log reductions obtained for OCl- and HOCl treatment were both significantly less than ECAS (p < 0.001), whereby HOCl resulted in a 3.207 ± 0.505 log10 CFU mL−1 log reduction, which was significantly greater than the 1.945 ± 0.222 log10 CFU mL−1 log reduction exhibited by OCl- (p = 0.0011). The 5-log reduction CT values for OCl-, HOCl and ECAS with a low organic load demonstrated that NaOCl exhibited the highest CT value (88.96 mg min L−1), followed by HOCl (34.78 mg min L−1) and then ECAS (20.94 mg min L−1)./p> 0.05). However, ECAS resulted in the greatest log reduction (1.606 ± 0.954 log10 CFU mL−1), followed by HOCl (0.978 ± 0.202 log10 CFU mL−1) and OCl- (0.025 ± 0.004 log10 CFU mL−1). The organic loading tested under dirty conditions does not represent concentrations expected within POU drinking water systems. However, results highlight the need to reduce organics present to ensure sufficient antimicrobial activity throughout disinfection stages of drinking water treatment./p> 0.05). In fact, there was no significant reduction in biofilm density between 0 (control) and 5 mg L−1 FC (p > 0.05) for any test disinfectant. Overall, the results demonstrate a dose-response of increasing antimicrobial efficacy with increasing FC concentrations. Interestingly, for ECAS the greatest increase in antimicrobial activity (p = 0.009) occurred at ≥25 mg L−1 FC, whereas the greatest increases for HOCl and OCl- were observed between 0 and 25 mg L−1 (p < 0.0001)./p>25 mg L−1 (i.e. 50, 100, 150 mg L−1). Interestingly, there was no significant difference in the antimicrobial activity exhibited by ECAS at an FC concentration of 25 mg L−1 in either the presence or absence of low organic loading (clean BSA conditions). This shows that low concentrations of organic matter do not unduly interfere with the mechanism of action for ECAS under these experimental conditions. ECAS exhibits very high ORP value (>+1100 mV), due to both reactive chlorine and oxygen species, which in turn drives rapid oxidation reactions. However, the presence of higher concentrations of organic matter will ultimately reduce the ORP through oxidation-reduction reactions50, contributing to a resultant reduction in antimicrobial activity of ECAS, as has been previously observed50,51. Interestingly, previous work by Robinson et al. in 201352 demonstrated that antimicrobial activity of ECAS could be maintained when stored for a 398 day period at 4 °C in the dark, despite showing no detectable FC after 277 days (e.g. < 0.01 mg L−1). This demonstrates the importance of the additional antimicrobial species, other than those that are chlorine derived, contributing to an increased antimicrobial activity. Thus, helping explain the greater antimicrobial activity of ECAS at a FC of 25 mg L−1 in the presence of clean BSA conditions when compared to equivalent HOCl and NaOCl solutions. Further increasing the organic loading of BSA (3.0 g L−1; dirty BSA conditions) within the bactericidal assay greatly reduced the antimicrobial activity of OCl- and ECAS at all FC concentrations tested. In comparison the antimicrobial activity of HOCl was not significantly reduced at FC concentrations >25 mg L−1. Therefore, it is clear that HOCl produced via the dissolution of NaDCC demonstrates a greater antimicrobial activity against planktonic bacteria under dirty BSA conditions. Chemically derived HOCl is more stable than electrochemically generated HOCl solutions, as they do not possess metastable antimicrobial species, that form at the anodic surface53. Chemically derived HOCl also degrades at a slower rate when exposed to sunlight (UV)54, in comparison to electrochemically generated HOCl which degrade at an increased rate55. This highlights the importance of selecting the most appropriate disinfectant for use in POU treatment systems. For example, in instances where filtration or removal of organic matter from bulk water is not standard practice or is difficult, HOCl would provide greater antimicrobial efficacy, compared to NaOCl or ECAS./p>3.3.CO;2-1./p>