Thursday, February 27, 2014

Chlorine Dioxide for Water Treatment

Now nearing its 200th birthday, the use of chlorine dioxide has been developed and honed over the years and it's widespread in water treatment industry. In industrial water treatment, it's main use is as a primary or secondary biocide in drinking water treatment. Where a water supply contains traces of organic contaminants, ClO2's selective oxidation of organics (without chlorination) reduces the taste and smell problems caused by disinfecting the water. By comparison, conventional chlorine treatment creates that classical swimming pool odour when it reacts with organic contaminants. An indication of the many potential uses of this widely used gas is gained from the US EPA list of approved use applications:

  • Industrial Cooling Water Treatment, Heat Transfer Systems (Evaporative Condensers, Dairy Sweetwater Systems, Hydrostatic Sterilizers and Retorts, Coolers, Warmers and Bottling Plants), Service Water, and Auxiliary Water Systems: For control of bacterial slime and algae in industrial recirculating and one-pass cooling systems.
  • Food Plant Process Water Treatment: For odor and microbial control in typical food processing water systems such as flume transport, chill water systems, and hydrocoolers.
  • Controlling Microbial Population In Poultry Processing Plant Waters in Federally Inspected Plants:
  • Public Water Systems: As both an oxidant and a disinfectant in drinking water treatment under 40CFR141.
  • Aqueous Systems For CIP Cleaning: As an antimicrobial agent in the recirculating cleaning solution.
  • Bacterial Slime Control in Paper Mills: In controlling microbiological growth in white water paper mill systems. to maintain control.
  • Mollusk Control in Water Systems: For mollusk control in commercial and industrial recirculating and one-pass cooling water systems.
  • Wastewater Treatment: As an oxidant in wastewater treatment.

Chlorine dioxide is particularly effective in controlling legionella bacteria, the cause of Legionnaires Disease.

  • It controls biofilm which can harbour legionella and protect them from the effects of other biocides.
  • It has a broad spectrum of activity against a wide range of micro-organisms in water at a pH between 4 and 10, whereas traditional biocides like chlorine and bromine start to lose effectiveness at pH >7.5 and >8.5 respectively.
  • It controls amoebae which have been shown to be a source of legionella.

The use of chlorine dioxide in these industrial water applications has been inhibited by the need to produce it "on site". Chlorine dioxide generators are often unreliable and difficult to control in applications where small quantities of chlorine dioxide are required intermittently such as a cooling tower or domestic building H&C system or a food washing line.