Taste Generation Associatedwith Chloramination
Report No WSAA 3
Thisinvestigation was undertaken under the auspices of the Urban Water ResearchAssociation of Australia. The purpose of this investigation was to identify thecause of persistent taste problems associated with chloramination of watersfrom several major water supply reservoirs in Western Australia. This problemwas seen to be of national significance as there has been increasing usethroughout Australia of chloramination as a disinfection process in recentyears.
A furtherobjective of the investigation was to identify possible treatment strategiesfor the prevention of the taste formation in supplies where the problem arises.
A one yearresearch program was undertaken which involved the following elements:
Thekey findings of the investigation are summarised below:
Tastesdescribed as chemical and drying were found to develop on chloramination ofwater collected from a number of water supply reservoirs throughout Australia.In particular tastes were consistently generated with water from HardingReservoir (WA) and on occasions with water from Wellington Reservoir (WA).Similar but less intense tastes were generated on chloramination of untreatedwaters from North Pine Reservoir (Queensland) and Upper Avon (New South Wales).There was no apparent correlation between major water quality parameters andtaste formation.
Ingeneral taste development was not affected by the order of addition of chlorineand ammonia. Similarly altering the time interval between additions did notaffect taste development. The tastes were not due to the chloraminesthemselves.
Severalnitrile compounds were identified in chloraminated waters. Persistent dryingtastes were demonstrated to occur with dilute solutions of aliphatic nitriles,and therefore nitriles may have contributed to the drying taste.
Iodoformand other trihalomethanes were detected in chloraminated waters during thisstudy, but iodoform was not considered to contribute to the chemical tastedescribed above. It was considered that the various trihalomethanes identifiedwere partly responsible for medicinal and chlorinous tastes observed.
Somecompounds previously shown to possess musty flavours were identified inchloraminated waters. These were C2 and C3 alkyl substituted benzenes and2-ethylhexanol.
Effectivetreatment strategies for prevention of chemical tastes on chloramination werefound to be:
Theuse of a strong oxidant such as hydrogen peroxide, ozone or chlorine dioxideprior to chloramination.
Theuse of activated carbon in combination with coagulation/filtration prior tochloramination.
Prechlorination(> 10 mg L-1 Cl2) with or without adechlorination step using sodium sulphite prior to chloramination.
Inwater supplies where taste problems arise due to chloramination further studiesto optimize the process performance of the various treatment options identifiedin this investigation would be necessary to avoid taste generation. Suchstudies should an examination of the types of organic compounds produced undereach treatment regime since each process could produce organic byproducts thatcould be of concern for health reasons or lead to the creation of new tasteproblems.
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