Chloramination of Water Supplies

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

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Report No UWRAA 15

July 1990

SYNOPSIS

This report contains the results of a project ‘Chloramination of Water Supplies’ which commenced in 1987 under the auspices of the Urban Water Research Association of Australia.

The purpose of the project was to examine seventeen topics of interest to water authorities who are currently using or contemplating using the disinfection process of chloramination. Each of the seventeen sections of the report contains information about chloramination practices in Australia, a brief literature review and laboratory and/or field results. The sections include:

Chloramination in Australia
Formation of chloramines
Methods of control and residual measurements
Decay of monochloramine
By-products of chloramination
Removal of monochloramine by activated carbon
Effects of chloramination of potable water on the corrosion resistance of materials
Effect of changing from chlorination to chloramination on microbiological quality in water supplies
Effectiveness of monochloramine against Legionella spp
A comparison of MPN and MF techniques for the enumeration of coliform bacteria in chloraminated water
The effect of water quality on the efficiency of chloramination in selected South Australian waters
Bacterial nitrification in chloraminated water supplies
Effect of monochloramine on biofilms, particularly those associated with iron and manganese
The toxicity of chlorine and chloramines to algae
Effects of chloraminated water on plant growth
Design of a chloramination station
Cost – benefit analysis

The principal findings of the investigations are summarised below:

Use of chloramination in Australia has increased significantly during the 1980s. The survey undertaken in 1987 estimated that there were eleven stations operating in 1980 while a further thirty-two were commissioned during 1981-87.
In each system analysed, microbiological quality improved with the replacement of chlorination by chloramination. The frequency of isolation of Naegleria spp, n.fowleri, total coliforms, E.coli, Aeromonas spp, heterotrophic iron bacteria, plate count organisms and fungi were substantially reduced.
The decay of monochloramine is principally dependent on pH, temperature, dissolved organic carbon and bromide. An empirical decay rate expression was developed and has been successfully used to predict decay under field conditions.
Ammonia-selective membrane electrodes are an appropriate method to measure both excess and total ammonia in chloraminated systems.
Levels of adsorbable organic halogens (AOX) including trihalomethanes (THMs) are greatly reduced with chloramination compared to free chlorination. However, further formation in a distribution system can be significant and is probably related to bromide levels and detention time.
Monochloramine will control the growth of Legionella spp in water supply systems and internal systems in large buildings such as hospitals.
Inactivation of plate count organisms by chloramination in the field was influenced by pH (filtered water) and turbidity. The 99% inactivation times for plate count bacteria were generally less than 12 minutes.
Nitrification is probably the major problem facing operators of chloraminated systems. The numbers of nitrifying bacteria decreased as total chlorine residuals increased. However, they were still detected in 21% of samples that contained in excess of 5 mg/L combined chlorine.
Numbers of nitrifying bacteria increased markedly during periods of accelerated chloramine decay, however, in individual cases it was not clear whether this was a cause or effect of the accelerated decay. Increased levels of oxidised nitrogen, particularly nitrite, could be used as an indicator of bacterial nitrification.
Laboratory experiments indicate that chloramines are as effective as free chlorine for the removal of plate count organisms and heterotrophic iron precipitating bacteria associated with biofilms.
Field examinations confirmed that chloramines reduce the amount of biofilm material.
Five algal species tested in biocidal efficiency experiments were more resistant to chloramine than chlorine. The algal species were more resistant to the disinfectants tested than the common microbial indicator, E.coli, and the protozoan, N.fowleri.
Chlorophyll autofluorescence cannot be used as a reliable direct indicator of the viability of algal cells exposed to chlorine and chloramines.
It seems unlikely that the use of chloraminated water for irrigation of soil-grown plants would have adverse effects on growth whether the water is applied directly to the soil or as an aerial spray.
Concentrations of monochloramine normally found in chloraminated water are high enough to cause problems in hydroponic systems, particularly those that employ low volumes of water which are frequently replenished.

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