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VALIDATION OF ALKALINE DISINFECTION FOR RECYCLED WATER SCHEMES

Tilbury, A.L. Deere, D. Rodriguez, C. Vorster, F. Fox, N.J. Marunczyn, M. Piper, B.B.

Alcoa of Australia’s recycled water schemes use a single chemical treatment process of alkaline disinfection. Recycled water schemes are approved by the Department of Health and are based on the water quality being fit for purpose and are assessed using the Australian Guidelines for Water Recycling (AGWR) 2006 and Department of Health WA Guidelines for the Use of Recycled Water in Western Australia (2011). However, the guidelines refer to residential and municipal recycled water uses and exposures and guidance refers to conventional, not alkali, disinfection.

Disinfection with a chemical agent (e.g. chlorine, chloramine or, as in this case, caustic) requires some minimum effective concentration (often denoted C) and minimum contact time (often denoted T) to be effective. CT values are widely published for common disinfectants, but not for caustic. Therefore Alcoa completed microbial inactivation studies to establish a CT - equivalent for caustic and to determine whether the reference pathogens and microbial indicator organisms from the AGWR were relevant to the scheme.

Despite the presence of a reasonably applicable guideline, the tasks undertaken at the Alcoa site were specifically assessed to help better estimate exposure since those given in the national guidelines were not necessarily intended to cover industrial uses. The microbial log reduction requirements of the scheme were determined using the default values stated in the Australian Guidelines for Water Recycling, as well as from using actual measured volumes from personal exposure monitoring. Margins of safety between alkaline disinfection capability and health requirements were identified and assessed.