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Potential optimisation and improvement of the mean dissolved oxygen difference (MDOD) test to assess the ability of non-metallic materials of construction to enhance microbial growth. - WT1252

The objectives of the research are:

First Phase – optimising the current MDOD method

Based upon research findings already available and summarised at Annex 1, work will be undertaken on several areas –

1) Dissolved oxygen measurement – new probes based upon photoluminescence are now available, more stable and easier to calibrate. An investigation of these probes to be undertaken, and, if possible, their use included in one or more aspects of the research.

2) Test vessel headspace – investigate the impact of reducing this to the minimum possible for practical undertaking of the test – to be run alongside current commercial testing of materials to evaluate the impact of the change.

3) Periodicity of water changes – the Dutch ATP method uses a weekly water change. Investigate the effect, if any, of changing the test water only once a week (a longer period between changes could lead to the development of anaerobic conditions for some test materials at the end of each period of stagnation) - to be run alongside current commercial testing of materials to evaluate the impact of the change.

4) Duration of the test – the Dutch ATP method is a 12 week test, with measurements of ATP taken at weeks 4, 8 and 12. Investigate whether extending the current MDOD test to 12 weeks, with once weekly water changes and dissolved oxygen readings at weeks 4, 8 and 12 only, would increase the sensitivity of the test - to be run alongside current commercial testing of materials to evaluate the impact of the change.

5) Effect of the test sample S/V ratio – investigate whether there is a correlation between the S/V test ratio and the MDOD values, and whether an increase in the S/V could lead to enhanced sensitivity and reproducibility of the test. It would be wise to undertake this work on samples of materials already tested, using three to four different increased S/V ratios, in addition to a re-test using the standard S/V ratio of 15000mm2/litre.

On the basis of the test results evaluate whether it would be possible to express the dissolved oxygen uptake on the basis of a unit surface area of the test material rather than uptake from the test water in the test container, and how this might be related to the existing pass/fail criteria.

Second phase – possible revision of the test

On the basis of the test results from the First Phase, evaluate whether the result justifies any change(s) to the existing test method. If this is found to be the case, undertake an inter-laboratory trial using a minimum of six diverse test materials, plus the standard control/reference systems, to determine how reproducibility and repeatability compares with the existing method, and by comparison with results obtained for these materials in the existing test, determine whether changes are required to the pass/fail criteria.

Collaborating laboratories are expected to provide written comments and reports to the co-ordinator in an agreed format.

The objectives of the co-ordinating role are:

1. To supervise the laboratory collaborative research, to provide guidance and advise as necessary and provide a report on the final outcome.

2. To liaise with the Department’s contract Manager or nominated Deputy.

3. To ensure that the collaborating laboratories adhere to agreed timetables for conduct of the study and the reporting of results.
Project Documents
• FRP - Final Report : DWI70-2-259   (724k)
• EXE - Executive Summary : DWI70-2-259exsum   (24k)
Time-Scale and Cost
From: 2010

To: 2011

Cost: £73,092
Contractor / Funded Organisations
WRc-NSF Ltd, Intertek, WRc plc, The Water Quality Centre
Drinking Water              
Fields of Study
Water Quality