Ozone unmasked20 May 2021
The use of ozone in laundry applications has taken on more significance as its very real benefits as a destroyer of harmful pathogens puts it centre stage in the Covid-19 age. Richard Neale of LTC Worldwide investigates
The history of ozone in laundering has been marred by early claims that ozone enabled significant reductions in heat energy, chemicals and water consumption, implying that the primary driver for its use was saving money. This missed the greatest feature of ozone, which is its power as a very effective laundry disinfectant. Perhaps it is only now that its effectiveness as a destroyer of harmful pathogens is being fully investigated, driven by the present Covid pandemic.
The successful implementation of ozone requires changes to the wash chemistry and process conditions. These changes do indeed save energy and water, with reduced consumption of specialist chemicals, because ozone must be properly dissolved in the process water and kept in solution for the requisite time (which requires careful control of chemicals and temperature). This month we look at some of the changes needed and the importance of precise chemistry and expert control of the wash process. It is the expertise of leading suppliers of laundry chemicals and machinery which must be coupled with sound laundry management to achieve the undoubted benefits available with ozone injection.
What is ozone?
Ozone is a gas which occurs naturally, from the effect of sunlight on the oxygen in the air and from the discharge of lightning in electrical storms (thunderstorms), for example. It occurs under ultraviolet sunray lamps and elsewhere in man-made electrical items. It can safely be made, in the commercial quantities needed in laundering, by corona discharge. In order to get the concentrations needed for disinfection in laundering, the oxygen content of the gas feed into the corona discharge apparatus must first by increased from 21% (normal air) to 90%, by elimination of most of the nitrogen content of the air. When the oxygen-rich gas stream is then fed through the corona arc, a useful percentage is converted from normal oxygen with two oxygen atoms into ozone with three oxygen atoms. The generating equipment for this is small enough to be installed in the care home laundry alongside the washing machinery, wall-mounted if need be. An important feature of a many installations is a fail-safe system in the generation, which sounds an alarm should the ozone system fail to operate correctly. It is now possible to monitor down to a few parts per billion to ensure safety in the workroom (ozone is poisonous in high concentrations), right up to 200 parts per million (to verify that the corona discharge unit is giving enough ozone for assured disinfection in the wash). In the event of any malfunction, the launderer would revert temporarily to previous systems of disinfection until the fault was fixed.
Ozone has found favour as a disinfectant in a variety of systems. It is becoming disinfectant of choice in modern swimming pools, it is used in Changi airport (dissolved in water) for floor and urinal cleaning in restrooms and it is generally acknowledged as a superior disinfectant to chlorine, when used correctly.
Research and development, by commercial laundry equipment suppliers in the UK, pioneered the use of ozone in care homes, using on-site washer extractors. They demonstrated that when ozone was correctly dissolved in all of the water used in the wash process, both for washes and rinses, then its power as a disinfectant translated into an estimated 5 log10 reduction in viable bacteria. This meets the criteria of the UK NHS for an effective wash process for infective healthcare textiles. Also reported were reductions in some spore forming pathogens such as C.diff., which is a major bonus, as spore formers of this type are not destroyed by implied thermal disinfection.
These findings were translated into commercial washer extractor systems to meet the needs of the UK care home sector, providing washing machines, ozone generation equipment (with full monitoring) and wash chemicals from a single supplier. This integrated approach was designed to ensure that the systems worked seamlessly, providing a philosophy for others to follow. Early monitoring work by LTC confirmed the ability of these systems to achieve very significant improvements in care home disinfection, especially in homes where it had been difficult to achieve implied thermal disinfection previously. Not only did the destruction of pathogens increase markedly, but the odour in the home also became much fresher. The unpleasant smells associated with bacterial excrement were greatly reduced.
It was demonstrated that for maximum effectiveness, the temperature of the water needed to be below 40C to enable maximum ozone concentrations to be reached and maintained. It was also found that the concentration of certain ions in the water needed to be limited. This called for the development of wash products which relied on intelligent design rather than on the crude effect of high alkalinity at high temperature. It also called for reliable generation of ozone in the necessary quantity and the dissolving of this into a working wash process. Success resulted from the partnership between the care home laundry teams, the equipment designer and the process chemistry. These systems appear to have withstood the test of time – the earliest have now been in service for many years.
Further research was undertaken by de Montfort University in Leicester, UK, to determine whether the successful ozone processes would also destroy Covid-19, the source of so much illness and death in the care home sector over the last 12 months. The results were interesting because they not only demonstrated that the ozone process tested resulted in effective destruction of the Covid virus. They also demonstrated that the ozone injection played a part in this destruction, with poorer kill rates when the ozone was deliberately omitted. De Montfort workers reported a contribution by ozone to the kill rate of the Covid-19 virus of 0.6 log10.
Research by Christeyns in Bradford, UK, which was reported in LCN in the October 2018 issue, indicated their success in developing a wash process and chemistry to work with ozone injection. This is important , because Christeyns supply the wash chemistry for a large percentage of the healthcare laundering carried out in the UK. Results obtained by LTC confirmed a kill rate of over 5 log10, for Enterococcus faecium (using the D.E.S. Controller), matching that reported in the nursing home sector.
As far as LCN is aware, no one in the UK has yet tackled the use of ozone for disinfecting contaminated textiles in a tunnel washer. Work by Ralph Daniels has been carried out in the United States (in New Hampshire), but LCN has not yet received any details of the level of disinfection achieved or of how the ozone injection copes with the ‘moving target’ of counterflow tunnel washer waterflows. This would be of major interest to the acute hospitals in the UK and their rental launderers, particularly in view of the encouraging results obtained by de Monfort University in commercial washer extractors.
Other workers have found that the Norovirus is also attacked by ozone, with a kill rate of above 3 log10. This could be of major interest to on-board cruise liner laundries, which have for many years been plagued with periodic outbreaks of this infection and latterly, Covid-19 in addition. Most cruise liners still rely on washer extractors, for which the designs for successful ozone injection have already been developed and proved.
LCN is aware of continuing research into ozone based laundering systems in other UK university partnerships and hopes to be able to publish the results of this in due course.
In all of the research described so far in this article, no one has clearly established the efficacy of ozone-based processes in terms of complete process validation, covering healthcare disinfection (including destruction of Covid-19), soil and stain removal, whiteness maintenance, textile life and process safety. It is hoped that research now in progress will tackle this and produce formal accredited data in terms not only of functionality but also covering health and safety issues. This should not be difficult.
Uses of ozone in fire and flood Recovery
One of the major problems facing specialist cleaners who offer commercial recovery of fire and flood affected textiles is that of achieving disinfection and ensuring that cleaned work is essentially decontaminated, with residual micro-organisms (and the odours they generate) reduced to a very low level. Leading specialists in the UK hang cleaned goods in an ozone chamber (typically overnight) and have found that this gives remarkable improvements and renders the majority of cleaned goods acceptable, even to the most discerning customer. Care has to be taken with certain components (such as leather trim and some metal ancillaries), which can be affected by ozone, but the main bulk of the goods benefit significantly.
Safety of ozone
Ozone is toxic and the maximum allowable concentration in the workroom in the UK is 0.2ppm. This is the Workplace Exposure Limit, assessed by averaging over a 15-minute period. Since ozone is a highly reactive substance, any adverse health effects will be found essentially at the sites of initial contact: the respiratory tract (nose, throat and airways) and the lungs (and at higher concentrations, the eyes). The principal health effects are produced by irritation of and damage to the small airways of the lung. However, people have considerable variation in sensitivity. In laundries which have been using ozone for some years, there does not appear to be any problem, with the correct equipment and procedures, in maintaining safe and pleasant working conditions.
There are undoubtedly benefits in utilising ozone in a washing process. It can be a superb disinfectant in the washing machine, meeting the general NHS requirement of a 5 log10 reduction in micro-organisms measured using Enterococcus faecium. Achieving the necessary wash process conditions automatically involves low temperature washing and improves the laundry’s carbon footprint. This is accompanied in a care-home environment by a noticeable improvement in odours within the entire laundry area and this improvement often translates into a wider reduction in unpleasant smells throughout the establishment. Reduced tonnage of the specialist chemistry needed for ozone washing leads to a reduction in chemical discharges to drain, representing another useful environmental benefit. Because there is much reduced warm-up time, there is a significant reduction in wash process cycle time when compared with processes which rely on implied thermal disinfection. This reduction in cycle time is of even more value in those care homes which depend on rapid cycles to complete the daily workload and which in the past might have tolerated reduced disinfection (by washing on a low-temperature cycle with little disinfection power) as a consequence of this.
The present pandemic has awakened strong interest in thorough disinfection throughout the laundry sector catering for hospitality textiles, for restaurants and hotels. “Does you process guarantee to kill Covid?” has been the start of many conversations between launderers and their clients.
This has led to something of a revolution in this aspect of wash quality, to the general benefit of all, especially the hospitality guest. So, if you are considering ozone in your laundry check out the data when choosing your supplier. Not all ozone systems give the same results.
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