The specification of two different guideline values that are not related stoichiometrically is confusing and it is not clear why two values are needed. We suggest using a single monochloramine guideline value reported as 5 mg/L as Cl2. It is proposed that the guideline should read: Based on health considerations, the concentration of monochloramine in drinking water should not exceed 5 mg as Cl22/L.
It is suggested that amperometric titration be acknowledged as an alternative measurement option for chlorine residual, given its high accuracy, and that the text be modified to: The concentration of monochloramine in drinking water can be determined by the DPD ferrous titrimetric method (APHA Method 4500-Cl Part F 2012) or by amperometric titration.
We recommend that the taste and odour threshold not appear in the ‘guideline’ section of the fact sheet. The taste and odour threshold should not be used as the aesthetic guideline value independently from the Taste and Odour Fact Sheet (see the discussion in Appendix 1, below, prepared by [NHMRC has removed third party information], one of our organisation's members). [NHMRC has removed third party information] has observed different taste and odour thresholds for different source waters and believes that it is up to the individual authority to determine the appropriate taste & odour threshold levels for their own supplies, taking into consideration consumer complaints and maintaining disinfection.
The following wording is suggested for the ‘general discussion’:
Monochloramine is used as a disinfectant for drinking water supplies. It is increasingly being used in conjunction with chlorine, or in its own right, to provide primary disinfection of drinking water entering the distribution system and/or maintain a disinfectant residual through the distribution network. Although it is not as strong an oxidant as chlorine, monochloramine can be quite useful and effective in distribution systems with long water ages as it persists for longer. Where monochloramine is used overseas concentrations typically range from 1.5 to 2.5 mg/L (as Cl2).
Use of monochloramine for primary disinfection at the treatment facility needs to be considered carefully in terms of the range of Ct values achievable prior to the first customer.
Use of monochloramine can significantly reduce the level of disinfection by-products compared to that produced by similar levels of chlorine. If not managed proactively, however, use of chloramine can lead to nitrification in the distribution system resulting in a reduction of its effectiveness.
Monochloramine is formed by the addition of ammonia and chlorine in drinking water. This reaction can also result in the formation of dichloramine and trichloramine, both of which have lower taste and odour thresholds than monochloramine, and which should be minimised. The preferential formation of monochloramine is affected by the pH and the physical arrangements of adding the two chemicals.
Monochloramine has an odour threshold of 0.5mg/L
For additional information refer to the Disinfection Information Sheet for Chloramines.
APPENDIX 1: Previous Review Comment from [NHMRC has removed third party information] on the Taste & Odour Threshold for Monochloramine
Taste and odour threshold values discussed in the Taste and Odour, Chlorine and Monochloramine fact sheets (FS 26, 46 &59).
Issue:
The odour threshold values for chlorine and monochloramine residuals discussed in the two corresponding fact sheets are being interpreted by many as the “Aesthetic Guideline Value". Although mentioning odour thresholds in the discussion, the fact sheets for chlorine and monochloramine do not state any aesthetic guideline value. However the Summary of Guidelines section (Pages GL 1-20) lists the odour threshold values as “aesthetic guideline values”. [NHMRC has removed third party information] would suggest the odour threshold should not automatically be assumed to be an aesthetic guideline value but should be dealt with systematically under the taste and odour fact sheet along with any other taste and odour issue.
If the stated odour thresholds are to be treated as aesthetic guidelines based on taste and odour then this assumes that water with chlorine residuals higher than these threshold values is “not acceptable to most people” as defined in the Taste and Odour Fact Sheet. Based on complaint data and internal testing [NHMRC has removed third party information] experience is noticeably different for monochloramine. Typically the sensitivity in [NHMRC has removed third party information] systems appears to be around 0.5 - 0.6 mg/L for free chlorine and well over 1.0 mg/L for monochloramine.
In examining the cause of the taste and odour from chlorine/monochloramine residuals there has been little attempt to differentiate the taste and odour component due to chlorination of organic compounds present in various waters from that due to the actual hypochlorous acid or monochloramine concentrations present. The level and type of chlorinated organic compounds (and their aroma) may vary considerably from source water to source water. That is, what is commonly thought to be chlorine odour may in reality be due to other compounds.
As an example it is suggested that the odour threshold attributed to chlorine residuals in a given raw water, and in the same water after filtration may be measurably different. There may be grounds to argue for different stated thresholds for raw and filtered water supplies.
Thus, based on the variability of organic compounds between source waters across Australia, and the need to allow for filtered and chlorinated only drinking supplies, [NHMRC has removed third party information] would suggest that an “average” Australia wide taste and odour threshold is questionable and may not be the best approach.
One model that could be considered is to specify a common approach for water authorities to follow in determining the residual level corresponding to the taste and odour threshold for a given water supply. Another model would be to deal with this issue totally under the taste and odour fact sheet, as at the moment there appear to be three direct taste and odour targets in the guidelines, one driven by local customers and two imposed independent of the local customers.
Should regulators consider requiring complete compliance with the 1996 NHMRC Guidelines then the ability of water authorities to protect public health from microbiological risks and to also meet the current aesthetic taste and odour thresholds for chlorine and monochloramine may be virtually impossible in many areas.
As a separate discussion point the value of using both taste and odour (ie two tests) for acceptance rather than one has some disadvantages. Some recent papers have suggested the use of a single test of “flavour”. [NHMRC has removed third party information] would like to ask if the NHMRC has considered this type of proposal in the past? If this is not the case then [NHMRC has removed third party information] would suggest that it could be included in any review of the Taste and Odour Fact Sheet in order to more fully examine the implications of such.
Proposal:
(a) [NHMRC has removed third party information] would like the NHMRC to clarify the original intent of the ‘odour threshold value’ in relation to the aesthetic guideline values for chlorine and monochloramine, and to make this clear in the Guideline documents. [NHMRC has removed third party information] believes that the odour threshold value for chlorine or monochloramine residual does not necessarily constitute the point at which the taste and odour of the water becomes “unacceptable to most people” which is the definition used in the taste and odour fact sheet.
(b) A general statement should be made as to which is the primary document, the Fact Sheets or the Summary section. [NHMRC has removed third party information] auditors appear to have selected the summary section as the defining requirement. [NHMRC has removed third party information] would suggest the Fact Sheet be the primary document should the perception of any inconsistency arise.
(c) [NHMRC has removed third party information] believes that a ‘national’ odour threshold value is inappropriate and suggests that the threshold should be determined on a case by case basis for each water source using a standardised methodology. In particular closer examination should be given to differentiating the impact of chlorinated organics from that of the free chlorine and monochloramine residual compounds.
(d) [NHMRC has removed third party information] recommends that the issue of acceptability of taste and odour from chlorine and monochloramine residuals is better dealt with only under the taste and odour fact sheet. This way all taste and odour issues are driven in the same manner by local customers rather than by a national average.
(e) That NHMRC/ARMCANZ includes examination of the use of the “flavour” concept discussed in some recent published papers in any review of the taste and odour fact sheet.
