Sydney Water's Woronora Delivery System periodically trialed chloramination over the last three years, with initial trials resulting in nitrification and bacteriological counts. A more planned and structured approach was used in June 2000 to reintroduce chloramination. The aim of the study was to assess the feasibility of chloramination as the preferred method of disinfection for the Woronora system, considering the impact on issues such as trihalomethane (THM) formation, nitrification, compliance performance and residual chlorine management. The implementation of chloramination and the optimisation of system hydraulics have resulted in significant improvements in water quality performance in terms of chlorine residuals, heterotrophic plate counts (HPC20), total and faecal coliforms and disinfection by-products. Higher chlorine residuals were seen throughout the system, taste and odour complaints were reduced to negligible levels, THM levels declined by two-thirds and nitrification was not evident at any stage throughout the trial. A critical control matrix was developed as a vital management tool to address the issues that could impact on chloramination/nitrification in the system. Managing the nitrification balance in terms of the available ammonia and maintaining the chlorine to ammonia ratio close to 4:1 (as Cl2:NH3) within the total system and the maintenance of a higher residual chlorine level (>1.00 mg/L) were found to be the most critical factors in managing a chloraminated system.

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