DISINFECTION USING A NOVEL HETEROGENEOUS CATALYST

Hydrogen peroxide (H2O2) is a strong oxidising agent, which is considered environmentally friendly because it can rapidly degrade to the innocuous products of water and oxygen. It is the aim of this work to investigate the potential of a novel catalyst in activating H2O2 so as to reduce the concentration of H2O2 used and the time taken for disinfection. The antimicrobial properties of an iron based novel heterogeneous polyacrylonitrile catalyst (PCat) were examined against Escherichia coli ATCC 10536, Pseudomonas aeruginosa ATCC 15442 and Staphylococcus aureus ATCC 6538 using a modified version of the European suspension test. Experiments were performed at room temperature and at 35oC (with or without bubbled air). H2O2 validation experiments were performed to establish the concentrations at which there is slow inactivation of the organisms. Further studies were then conducted at these concentrations to determine whether the addition of PCat increases the rate of microbial inactivation. H2O2 at 0.2% w/v (against Escherichia coli), 0.5% w/v (against Pseudomonas aeruginosa) and 1% w/v (against Staphylococcus aureus ) resulted in average log reductions of 4.76, 0.97, and 5.37 respectively after 60 minutes exposure at room temperature. Increased activity was seen against all of the organisms at 35oC (after 40 mins exposure time log reductions of >5.39, 4.09 and >5.59 were recorded). Bactericidal activity was significantly increased when PCat was combined with H2O2. At room temperature bactericidal activity was seen at 30 mins (Escherichia coli), 20 mins (Pseudomonas aeruginosa) and10 mins (Staphylococcus aureus); and at 35oC bactericidal activity occurred at 10 mins for all the tested organisms. Overall, greater increases in antimicrobial activity were seen when the tests were carried out at 35oC compared to room temperature. Bactericidal activity was observed 48hrs and 6months after first use of PCat at room remperature and 35oC. However, there was reduction in activity compared to the initial ‘fresh’ PCat tests at room temperature, but no significant (p>0.05) difference in activity at 35oC. Five percent and 7.5% w/v H2O2 with PCat showed sporicidal activity against Bacillus subtilis spores at 2hrs at room temperature, whereas without the catalyst sporicidal activity was absent. In the presence of H2O2, leachate from PCat was found to contain very low amounts of iron which exhibited potent antimicrobial activity similar to that of PCat when it was left in the experimental solution. Traditional homogeneous iron salts of the same strength showed considerably less activity suggesting that there may be a structural conversion of iron in the leached solution resulting in the formation of new antimicrobial compounds.

Electron paramagnetic resonance studies using DMPO as radical scavenger indicated that PCat decomposes H2O2 to generate hydroxyl radicals (.OH radicals). .OH radicals were seen to be involved in the mode of antimicrobial action. These studies have demonstrated the potential biocidal use of the novel PCat when combined with low concentrations of H2O2 (below the current recommended levels). Reuse of the PCat may be possible and it appears to be more effective at 35oC than at room temperature.