Chloraminationof Water Supplies
ReportNo WSAA 15
July 1990
SYNOPSIS
Thisreport contains the results of a project ‘Chloramination of Water Supplies’which commenced in 1987 under the auspices of the Urban Water ResearchAssociation of Australia.
The purposeof the project was to examine seventeen topics of interest to water authoritieswho are currently using or contemplating using the disinfection process ofchloramination. Each of the seventeen sections of the report containsinformation about chloramination practices in Australia, a brief literaturereview 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 resistanceof materials
- Effect of changing from chlorination to chloramination onmicrobiological quality in water supplies
- Effectiveness of monochloramine against Legionella spp
- A comparison of MPN and MF techniques for the enumeration of coliformbacteria in chloraminated water
- The effect of water quality on the efficiency of chloramination inselected South Australian waters
- Bacterial nitrification in chloraminated water supplies
- Effect of monochloramine on biofilms, particularly those associatedwith 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
Theprincipal findings of the investigations are summarised below:
- Use of chloramination in Australia has increased significantly duringthe 1980s. The survey undertaken in 1987 estimated that there were eleven stationsoperating in 1980 while a further thirty-two were commissioned during 1981-87.
- In each system analysed, microbiological quality improved with thereplacement of chlorination by chloramination. The frequency of isolation of Naegleria spp, n.fowleri, total coliforms, E.coli,Aeromonas spp, heterotrophic ironbacteria, 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 rateexpression was developed and has been successfully used to predict decay underfield conditions.
- Ammonia-selective membrane electrodes are an appropriate method tomeasure 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 isprobably related to bromide levels and detention time.
- Monochloramine will control the growth of Legionella spp in water supply systems and internal systems inlarge buildings such as hospitals.
- Inactivation of plate count organisms by chloramination in the fieldwas influenced by pH (filtered water) and turbidity. The 99% inactivation timesfor plate count bacteria were generally less than 12 minutes.
- Nitrification is probably the major problem facing operators ofchloraminated systems. The numbers of nitrifying bacteria decreased as totalchlorine residuals increased. However, they were still detected in 21% ofsamples that contained in excess of 5 mg/L combined chlorine.
- Numbers of nitrifying bacteria increased markedly during periods ofaccelerated chloramine decay, however, in individual cases it was not clearwhether this was a cause or effect of the accelerated decay. Increased levelsof oxidised nitrogen, particularly nitrite, could be used as an indicator ofbacterial nitrification.
- Laboratory experiments indicate that chloramines are as effective asfree chlorine for the removal of plate count organisms and heterotrophic ironprecipitating bacteria associated with biofilms.
- Field examinations confirmed that chloramines reduce the amount ofbiofilm material.
- Five algal species tested in biocidal efficiency experiments were moreresistant to chloramine than chlorine. The algal species were more resistant tothe disinfectants tested than the common microbial indicator, E.coli, and the protozoan, N.fowleri.
- Chlorophyll autofluorescence cannot be used as a reliable directindicator of the viability of algal cells exposed to chlorine and chloramines.
- It seems unlikely that the use of chloraminated water for irrigation ofsoil-grown plants would have adverse effects on growth whether the water is applieddirectly to the soil or as an aerial spray.
- Concentrations of monochloramine normally found in chloraminated waterare high enough to cause problems in hydroponic systems, particularly thosethat employ low volumes of water which are frequently replenished.
Copiesof the Report are available from WSAA, price $A50. Orders may be placed throughthe Bookshop at www.wsaa.asn.au or by email to info@wsaa.asn.au.