Alternatives to post-disinfection with chlorine dioxide

At present, low concentrations of chlorine dioxide are used for disinfection at a number of surface water treatment plants operated by Evides (in Berenplaat, Baanhoek, Braakman and Kralingen) and PWN Waterleidingbedrijf Noord-Holland (in Andijk).

Existing alternatives

The main purpose of applying chlorine dioxide is to kill off microorganisms originating from activated carbon filters. Chlorine dioxide is also particularly effective against viruses (adenoviruses in particular) and Campylobacter. In addition, it retards the later growth of microorganisms in water holding tanks.

However, there are also drawbacks. Undesirable by-products – chlorate and chlorite – are formed in low concentrations. In addition, organic compounds are also broken down, enriching the water in the mains network. Smaller organic compounds can then serve as nutrients for bacteria in the mains, encouraging growth and reducing biological stability.

The aim of the project is to investigate alternatives using current knowledge about post-disinfection with chlorine dioxide. The focus is on alternatives with similar disinfection capacity but with fewer by-products and problems with biological stability.

The main boundary conditions are:

• No formation, or very limited formation, of undesirable by-products.
• A sharp reduction in microorganisms from active carbon filters and limited growth in water holding tanks.
• No increase in the potential for later growth in the distribution network after the disinfection phase.
• The maintenance of adequate disinfection capacity for bacteria and viruses, in particular Campylobacter and adenoviruses.

Evaluation of alternative disinfection methods

The criteria for evaluating existing and new disinfection methods are:

• How effective are the alternative disinfection approaches in terms of reducing levels of microorganisms from active carbon filters?
• How effective are alternative disinfection techniques in terms of inactivating pathogenic microorganisms, and adenoviruses and Campylobacter in particular?
• Do the alternative technologies result in the formation of disinfection by-products?
• Do the alternative disinfection methods result in more or less growth later in the mains network compared with the current situation?

The project will determine the extent to which the costs, the impact on production capacity, sustainability, and the ease and safety of operational deployment of the most promising alternatives have to be taken into account. Subsequent steps can then be taken to roll out these alternative methods in practice.

Selection of potential disinfection methods

This study will teach us more about new, and possibly more appropriate, disinfection options to replace chlorine dioxide. It will therefore serve as a basis for subsequent research to determine the suitability of alternative methods in the field of pathogen reduction, the formation of by-products and the impact on later growth.