Opting for Ozone

Ozone has remarkable oxidising properties. Hilary Ayshford spoke to Waterwise Technology's Jon Fletcher about its potential uses in pharmaceutical manufacturing

Traditionally, chemicals have been used to kill undesirable organisms - whether in a production line for food or pharmaceuticals or in air conditioning systems. But ozone - an allotropic form of oxygen - is a readily available alternative that is cheap to manufacture, a highly potent oxidant and degrades within 20-30 minutes to leave no residues.

Ozonated water, is used increasingly by the pharmaceutical manufacturing sector to disinfect production lines as well as for incorporation in the product itself. 'It is a fascinating product,' says Jon Fielder, director of UK company Waterwise Technology.

handling issues

Ozone is the second most powerful oxidising disinfectant available - exceeded only by fluorine - and offers a number of advantages over conventional chemical disinfection methods.

One of its main benefits is its safety. The FDA has given it GRAS status for all applications except contact with milk, and it breaks down quickly and naturally to oxygen without any residual chemicals, toxins or contaminants. And as it is produced at the point of use, there are no issues relating to storage or handling hazards. The only substance added to water is oxygen, making it suitable for process water without adversely affecting the final product.

A second benefit is its cost effectiveness. Once the initial capital investment has been made, there are no consumable chemicals to be purchased as the ozone is created by extracting oxygen from the water or the air. Nor is there a great energy requirement as there is for heat sanitisation techniques. Ozone systems are also very reliable and maintenance requirements are low.

Even more importantly, there is little or no need for downtime while disinfection takes place. The high oxidation power of ozone means that disinfection is rapid and highly penetrative, treating the internal surfaces and equipment throughout the water system and destroying biofilm.

In the past, the system was shut down and flushed through with chemical disinfectant, which then had to be purged from the pipework before production could resume. Apart from the downtime, Fielder explains, significant amounts of product could be lost if the chemicals were not completely removed. But if ozonated water is used to clean the system, manufacturing can restart at once as the ozone will have dissipated.

The breakdown of the ozone can be accelerated by the use of UV light. To disinfect the system the UV light is turned off and ozonated water allowed to flow round the system while production is suspended - for example, overnight. When production is ready to resume, the light is turned on again. 'There is no draining of the system, no shut-down so it is a much smoother operation,' Fielder points out.

short half-life

There are two main methods of creating the ozone. The first is to split the oxygen molecule in the water and use a low voltage, high current cell to create hydrogen and ozone. It is also possible to make ozone using the oxygen in the air. Early systems for doing this often resulted in an ozone that was less pure and was not as soluble in water. 'Nowadays we have very good systems for filtering the oxygen from air to feed the ozone systems so that we make ozone with pure oxygen,' stressed Fielder. 'That gives us a more powerful and a much more soluble product that will stay in the water better.'

Ironically, one of ozone's strengths - its short half-life - is also one of its disadvantages. Because it will remain active in water for only around 20 minutes, it cannot be stored and must be made in situ as required. However, chilling the water can increase the half-life by slowing down the reaction time.

Ozone's oxidation power can also have drawbacks as it can damage some materials with which it comes into contact, particularly some of the softer plastics such as nylon. Material selection for components such as seals and gaskets is therefore crucial.

dramatic growth

There are also limits on human exposure: the maximum permissible continuous exposure limit to ozone in air is 0.1 ppm averaged over an eight-hour work shift. However, ozone has a pungent odour and is detectable by smell at levels as low as 0.01 ppm. All Waterwise ozone systems are operated under a vacuum, eliminating the risk of leakage of high concentrations of ozone.

Although only 15-17% of Waterwise's business is in the pharma sector, Fielder sees great potential. 'We can see ozone's use in pharmaceuticals growing dramatically in areas such as washing of containers and general rinse-down, as well as in body contact areas such as purified water,' he says. Even in the high purity areas less than 50% of plants currently have ozone, but this is likely to rise as plants are refurbished and ozone systems are incorporated.