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Two modified electrodes (Pb/PbO2 and C/PbO2) were prepared by electrodepositing a lead oxide layer on lead and carbon substrates. These modified electrodes were used as anodes for the generation of sodium hypochlorite (NaOCl) from sodium chloride solution. Different operating conditions and factors affecting the treatment process of NaOCl generation, including current density, pH values, conductive electrolytes, and electrolysis time, were studied and optimized. By comparison the C/PbO2 electrode shows a higher efficiency than the Pb/PbO2 electrode for the generation of NaOCl.
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Antimicrobial disinfectants are used as primary treatment options against pathogens on surfaces in healthcare facilities to help prevent healthcare associated infections (HAIs). On many surfaces, pathogenic microorganisms exist as biofilms and form an extracellular matrix that protects them from the antimicrobial effects of disinfectants. Disinfectants are used as all-purpose antimicrobials though very few specifically make biofilm efficacy claims. The objective of this study was to evaluate the efficacy of eight registered disinfectants (six registered by the Environmental Protection Agency and two products registered in by the European Chemical Agency) with general bactericidal claims, but currently no biofilm efficacy claims, against Staphylococcus aureus ATTC-6538 and Pseudomonas aeruginosa ATCC-15442 biofilms. We hypothesized that hydrogen peroxide and sodium hypochlorite disinfectant products would be more effective than quaternary ammonium chlorides.
Overall, sodium hypochlorite and hydrogen peroxide disinfectants had significantly higher bactericidal efficacies than quaternary ammonium chloride disinfectants. We also found that all tested disinfectants except for quaternary ammonium chloride disinfectants met and exceeded the EPA standard for bactericidal efficacy against biofilms.
In general, bactericidal efficacy against biofilms differed by active ingredient. The efficacies of sodium hypochlorite and hydrogen peroxide disinfectants did not vary between strains, but there were significant differences between strains treated with quaternary ammonium chloride disinfectants.
Disinfectants are primary intervention options against pathogenic organisms on surfaces in healthcare facilities [7, 14] and are used as broad-spectrum antimicrobials [19]. Common antimicrobials used for disinfecting surfaces in healthcare facilities include quaternary ammonium compounds, hydrogen peroxide, and chlorine-based products [6, 17]. There are few published studies that investigate the efficacy of disinfectants on bacterial biofilms at label use concentrations. The objective of this study was to evaluate the efficacy of eight registered disinfectants with general bactericidal claims, but no current biofilm efficacy claims, against S. aureus ATTC-6538 and P. aeruginosa ATCC-15442 biofilms. We hypothesized that accelerated hydrogen peroxide disinfectant products would be more effective than quaternary ammonium compounds and that sodium hypochlorite disinfectants would be the most effective at eliminating biofilms.
In this study, we tested eight registered disinfectants under label use conditions against S. aureus and P. aeruginosa biofilms using EPA methods MB-19 and MB-20. We found statistically significant quantitative differences among disinfectant active ingredients and products against S. aureus and P. aeruginosa. Specifically, we found (i) statistically significant differences in disinfectant efficacy among disinfectants, (ii) similar performance of hydrogen peroxide and sodium hypochlorite-based products against S. aureus and P. aeruginosa biofilms, and iii) significantly higher bactericidal efficacy of quaternary ammonium-based products against S. aureus than P. aeruginosa. Bacterial biofilms are common on a wide range of surfaces made of different materials and have been reported to be present in drains, metal pipes [10], sanitizing bottles, trolleys and clipboards [23] thus are potential sources of HAIs.
Hydrogen peroxide and sodium hypochlorite disinfectants were effective against P. aeruginosa and S. aureus biofilms at the EPA required reduction levels. Hydrogen peroxide and sodium hypochlorite disinfectants have been reported to destroy both the biofilm matrix and the bacteria cells within, making them better anti-biofilm agents [31, 32]. Specifically, sodium hypochlorite disinfectant products irreversibly kill bacterial cells in biofilms by denaturing proteins in the biofilm matrix and inhibiting major enzymatic functions in bacterial cells. Although sodium hypochlorite disinfectants at concentrations as low as 0.0219% are effective against the formation of S. aureus biofilms [33], the use of sub-lethal concentrations of some sodium containing disinfectants could actually promote the formation of biofilms on environmental surfaces [34]. In a study conducted by West et al. [22], hydrogen peroxide products and sodium hypochlorite products were more effective against both S. aureus and P. aeruginosa planktonic cells compared to quaternary ammonium. On another note, surfaces disinfected with hydrogen peroxide based antimicrobials have demonstrated significantly lower chances of bacterial regrowth than those disinfected with quaternary ammonium compounds [35]. To this effect, the study by Boyce et al. [35] concluded that the risk of the incidence of HAIs was lower with hydrogen peroxide disinfectants than with the use of quaternary ammonium compounds. Our data suggest that hydrogen peroxide or sodium hypochlorite products should be used in healthcare facilities for routine use, particularly on surfaces prone to biofilm development. However, hydrogen peroxide disinfectants have also been reported to be corrosive on medical equipment such as flexible endoscopes [36] and can discolor metal finishes [37]. Despite these limitations, Alfa et al. [38] also demonstratated that a 0.5% hydrogen peroxide antimicrobial is highly efficient at disinfecting medical devices. Moreover, hydrogen peroxide disinfectants are neither irritating or malodorous [37].
We found that hydrogen peroxide and sodium hypochlorite products are effective against S. aureus and P. aeruginosa biofilms, which can be common in healthcare facilities. However, quaternary ammonium chloride compounds are not as effective against S. aureus and P. aeruginosa biofilms grow on hard non-porous surfaces and did not achieve a minimum 6 log10 CFU reduction. While further research is warranted to evaluate more complex biofilms in hospital environements, test the efficacy of disinfectants against dry biofilms, and to optimize the bactericidal effects of a combination of different ready to use antimicrobials, infection preventionists should consider the use of hydrogen peroxide and sodium hypochlorite products on surfaces at risk of biofilm development to prevent HAIs.
There are several types of chlorine sources that water treatment plants can use: chlorine gas, liquid sodium hypochlorite, or onsite production. Chlorine gas can be more cost effective, but a growing number of states are converting to bulk sodium hypochlorite or bleach. If chlorine gas is more economical, why would water treatment plants convert to sodium hypochlorite?
Flowering of trees at the WRS treated with KClO3, NaClO2, bleach, and bleach plus CuCl2 began 5 weeks (22 Oct. 2004) after treatment. By 12 weeks after treatment, trees stopped production of panicles and the number of flowering terminals was determined. Nontreated control trees did not flower and KClO3, NaClO2, bleach, and bleach plus CuCl2-treated trees exhibited 97.8% (484 flowering/495 total terminals), 91.8% (462 flowering/503 total terminals), 84.7% (326 flowering/385 total terminals), and 96.9% (493 flowering/509 total terminals) flowering, respectively. The means for each treatment were not significantly less than the KClO3 treatment (P > 0.27) for NaClO2, bleach (P > 0.18), and bleach plus CuCl2 (P > 0.43) as analyzed by SAS PROC GLIMMIX using Dunnett's adjustment for multiplicity. This demonstrates that chlorate, chlorite, and hypochlorite can effectively induce off-season flowering of longan.
Hypochlorite enhances flowering in longan similar to potassium chlorate (Sritontip et al., 2005a), and we demonstrate that it can also effectively induce off-season flowering. NaOCl degradation occurs through two pathways. The first pathway leads to the production of oxygen, whereas the second leads to chlorate formation (Adam and Gordon, 1999). The incorporation of copper (Cu2+) to the bleach solution, an ion that catalyzes both degradation pathways of hypochlorite to chlorate or oxygen (Adam and Gordon, 1999), appeared to induce flowering to the same degree as KClO3 treatment or bleach treatments alone, suggesting chlorate in bleach contributed to the promotion of longan flowering.
In addition to hypochlorite and chlorate, sodium was also added to the soil during the bleach treatment. Soil analyses from trees treated with bleach and control trees at Onomea showed that at 14 weeks after treatment, soil from bleach-treated trees contained 151.3 36.8 ppm of Na+, whereas soil from untreated control trees contained 37.7 2.9 ppm of Na+. Soil pH and salinity were not significantly different in soil samples from bleach-treated and untreated trees and no visible signs of sodium toxicity could be detected. One year after bleach treatment, there was no significant difference between soil samples of bleach-treated trees, 24.4 2.9 ppm, and untreated trees, 24.3 4.8 ppm, suggesting that sodium did not accumulate in the soil.
Therefore, we conclude that chlorate, chlorite, and bleach are able to induce flowering in longan. Bleach is an effective alternative to potassium chlorate for producing off-season longan fruits. The decomposition of hypochlorite to chlorate in the bleach contributes to the floral induction without sodium accumulation in soil 1 year after application in a high rainfall environment.