Brendan Van Wyk, Global Pulp and Paper Manager at Air Products SA, tackles the myths associated with ozone by highlighting its very real significance.
While the conventional applications of ozone as a powerful disinfector and oxidant are well documented, industry is starting to open its eyes to a myriad of new possibilities for ozone and ozone technology, all of which point to a healthier and cleaner physical world.
Ozone’s fall from favour and return to grace
Since its discovery in 1840, ozone has been the centre of debate in scientific circles, making the gas difficult to explain, isolate and classify. However, its usefulness was quickly recognised, and ozone was soon adopted as a means of treating water to drinking standards.
But ozone lost its position at centre stage in the water purification industry during the First World War when the cheap manufacture of chlorine gas lead to a decline in interest in ozone. Chlorine disinfection lasted longer, was easier to transport and cheaper to manufacture. This was despite the fact that the by-products of chlorination were already known to be harmful to both people and the environment.
Now, ozone has re-emerged, demanding fresh attention as a viable, mainstream water and air treatment option.
The reasons for ozone's coming full circle are varied, and include: improvements in ozone production technologies; the advances in ozone chemistry; the tightening on environmental legislations, and deteriorating water supplies.
A Fresh Look at Ozone
Industry is starting to take a fresh look at ozone in terms of potential applications and possibilities that have not yet been fully explored. This list of potential applications of ozone technology is growing by the day, and ranges from organic synthesis reactions in the pharmaceutical industry, to the disinfection of chicken's eggs in the hatchery business.
Going for Gold
One of the technologies coming to the fore, and very much applicable in the South African context, is the destruction through ozone of cyanide in goldmine tailing streams.
Air Products South Africa Pty Ltd., in partnership with ITT, global specialists in water and wastewater management, have successfully demonstrated a system that will destroy cyanide from tailings levels as high as 120ppm down to less than 5pmm. Ozonation results in a very rapid and complete decomposition of cyanides, cyanates and thiocyanates; ultimately, given enough contact time, to carbon dioxide and nitrogen. This allows the tailings to be sent back underground as backfill without further treatment.
Changing Water Treatment Options
A further application of ozone technology, and one with increasing applicability to the South African market, is ozone treatment of cooling tower water. With the increases expected in the cost of water, as well as the degradation of our water sources, conservation and re-use of water are becoming very important.
By switching from conventional water treatment options in a cooling tower to using just ozone, companies cannot only save water but reduce the cost of treating effluent. Ozone treatment allows for a far higher recycle rate (cycles of concentration) of water within the cooling circuit before any water is blown down (if at all). Ozone is completely effective in the control of bacteria like Legionnaires' disease. Ozone treatment also eliminates the handling and dosing of a variety of different chemicals to the tower.
Advanced Oxidation Process (AOP)
And then there is Advanced Oxidation Process (AOP), a system which greatly enhances the conventional application of ozone in drinking water. The combination of ozone and hydrogen peroxide forms the hydroxyl radical, an aggressive oxidant which reacts chemically with common taste and odour (T&O) compounds, a wide range of volatile organic compounds (VOCs) and various other micro contaminants. This makes it ideal for drinking water and water re-use applications. Applications for AOP systems include:
. Control of taste/odour and colour of drinking water
. Destruction of volatile organic compounds in effluents and drinking water
. Disinfection for water reuse
. Removal of microcontaminants, such as endocrine disrupters
. Removal of a host of recalcitrant compounds
Environmentally-Friendly and Useful Ozone
Because ozone oxidizes cell walls, it reacts up to 3,500 times faster than chlorine, rapidly destroying all bacteria, endotoxins, mould and yeast spores, and even viruses. Moreover, micro-organisms cannot build up an immunity to ozone.
The short lifespan of an ozone molecule means that it quickly reverts back to oxygen, leaving behind no chemical residues or harmful by-products.
In an age where environmental concerns top the priority list in both government and industry, ozone is poised to come into its own as an environmentally-friendly and versatile industrial gas.