What Are Chlorine Dioxide Generators?
Chlorine dioxide generators are widely available from many suppliers. They usually require on-site storage of relatively hazardous chemicals including concentrated acids and the attention of skilled operators to ensure their safe and efficient operation. Most require the use of a reaction chamber providing sufficient residence time for the chemicals to react fully. ClO2 is produced which is immediately dissolved in water to give a solution that can be dosed to the system to be treated.
Systems such as these operate most effectively where there is a constant demand for chlorine dioxide and they require little change in their operation. They do not easily respond to situations where demand is very variable as occurs in most industrial applications such as building services.
In many industrial applications a system is required that can respond immediately to changes in the flow of water to be treated, including plant start up and shut down.
In order for chlorine dioxide generators to meet the demands for a safe, reliable, easy-to-use dosing system it must:
• Produce chlorine dioxide instantaneously by mixing two solutions
• Activating solution should be non-hazardous dilute acid
• Dosing system controlled by flow of water to be treated (w/m signal)
• No strong starting materials or concentrated chlorine dioxide solutions
The availability of small self contained chlorine dioxide generators such as this utilising “dilute” chemicals that require little attention have allowed ClO2 to successfully compete with other oxidising biocides.
New systems for production have been introduced:
• Electrochemical - the use of a diaphragm cell to electrolyse a solution of sodium chlorite to produce ClO2 is claimed as a simple safe system. In practice this route has been found to suffer from fouling of the cell diaphragms and requiring their replacement and increasing the operational costs
• Ion exchange - passing a solution of sodium chlorite through an acid ion exchange resin can produce the conditions for the production of a solution of chlorine dioxide. Such systems are relatively new but have the potential to be simple to operate. Fouling of the ion exchange resin appears to be the main problem.
Products with a variety of names claiming to be solutions of “Stabilised chlorine dioxide” have been marketed for many years with the claim that they are a “safe” means of introducing it without the need for generators etc. These products DO NOT contain any of the chemical and they are no more than solutions of sodium chlorite buffered to a lower pH than commercial sodium chlorite. To obtain ClO2 these solutions have to be activated - usually by acidification with or without the addition of chlorine.