Taste Generation Associated with Chloramination

This report was produced for the Urban Water Research Association of Australia, a now discontinued research program.

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Report No UWRAA 3

November 1989

SYNOPSIS

This investigation was undertaken under the auspices of the Urban Water Research Association of Australia. The purpose of this investigation was to identify the cause of persistent taste problems associated with chloramination of waters from several major water supply reservoirs in Western Australia. This problem was seen to be of national significance as there has been increasing use throughout Australia of chloramination as a disinfection process in recent years.

A further objective of the investigation was to identify possible treatment strategies for the prevention of the taste formation in supplies where the problem arises.

A one year research program was undertaken which involved the following elements:

i Identification of active taste compounds using a combination of taste panel analysis and trace organic analysis.

ii Evaluation of the role of chloramination process variables and alternative treatment options in suppressing taste formation.

iii Studies of the role of water chemistry in generating tastes on samples collected from schemes where chloramination is currently being used (or proposed to be used)throughout Australia.

The key findings of the investigation are summarised below:

1. Nature of the taste problem generated on chloramination

Tastes described as chemical and drying were found to develop on chloramination of water collected from a number of water supply reservoirs throughout Australia. In particular tastes were consistently generated with water from Harding Reservoir (WA) and on occasions with water from Wellington Reservoir (WA).Similar but less intense tastes were generated on chloramination of untreated waters from North Pine Reservoir (Queensland) and Upper Avon (New South Wales).There was no apparent correlation between major water quality parameters and taste formation.

In general taste development was not affected by the order of addition of chlorine and ammonia. Similarly altering the time interval between additions did not affect taste development. The tastes were not due to the chloramines themselves.

2. Nature of the organic by products identified in chloraminated waters

Several nitrile compounds were identified in chloraminated waters. Persistent drying tastes were demonstrated to occur with dilute solutions of aliphatic nitriles, and therefore nitriles may have contributed to the drying taste.

Iodoform and other trihalomethanes were detected in chloraminated waters during this study, but iodoform was not considered to contribute to the chemical taste described above. It was considered that the various trihalomethanes identified were partly responsible for medicinal and chlorinous tastes observed.

Some compounds previously shown to possess musty flavours were identified in chloraminated waters. These were C2 and C3 alkyl substituted benzenes and2-ethylhexanol.

3. Effectiveness of Alternative Treatment Options on Taste Generation

Effective treatment strategies for prevention of chemical tastes on chloramination were found to be:

The use of a strong oxidant such as hydrogen peroxide, ozone or chlorine dioxide prior to chloramination.

The use of activated carbon in combination with coagulation/filtration prior to chloramination.

Prechlorination (> 10 mg L-1 Cl2) with or without added chlorination step using sodium sulphite prior to chloramination.

Further research recommended.

In water supplies where taste problems arise due to chloramination further studies to optimize the process performance of the various treatment options identified in this investigation would be necessary to avoid taste generation. Such studies should an examination of the types of organic compounds produced under each treatment regime since each process could produce organic by products that could be of concern for health reasons or lead to the creation of new taste problems.

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