AMVD measurements

This project investigates the difficulties and solutions involved in the quantitative measurement of microbiological risks. In practice, the analyses required for pathogens in drinking water sources involve large sample volumes (max. 1,000 litres) that are concentrated to a few millilitres. In this process, recovery – which can be defined as the percentage of micro-organisms from the original sample that is recovered after the concentration of large volumes – is an important consideration. In addition, it is important to use the correct process indicator, including natural viruses, when quantifying purification processes.

This study contributes to the ongoing development of the reference document for AMVD (Analysis of Microbiological Safety of Drinking Water), which brings together all the available knowledge about the effectiveness of treatment processes.

Indicator organisms and pathogens

A correlation must be established between the reduction of indicator organisms by various treatment processes and the reduction of pathogens. However, during AMVD, it emerged that the same process indicator or indicator organism cannot be used for a pathogen in every process. Properties such as size and adhesion to filter material vary widely and there is therefore no exact correspondence between indicator organisms and pathogens. The correlation therefore has to be established in some cases. A major step can be taken in this direction using data from the literature.

The AMVD reference document was developed to bring this knowledge together and, ultimately, to establish the correct correlations. In addition, the reference document suggests ways of estimating reduction when measurement data are lacking. This project adds a number of processes that had not yet been covered. In addition, the data from processes that had already been covered will be updated and a number of improvements identified as desirable will be made to the associated web tool.

Quantitative risk analyses

The first step involves studying recovery – the percentage of microorganisms retrieved – from large sample volumes after concentration. In addition to looking at recovery, the project will obtain information that may be relevant for determining the causes of low recovery values. Examples may include location, sample volume, date/season and the analysis methods. Practical examples will be used to identify the minimum level of recovery that is adequate for a given sample volume. Experiments are being conducted with protozoa and enteroviruses.

The process indicators currently being used in the existing AMVDs will also be identified. This is primarily a literature study looking at the relationship between the reduction of indicator organisms and index pathogens in treatment processes. Risk calculations are used to evaluate current practice and alternative approaches are simulated, making it possible to study possible solutions for the future.

The knowledge from the literature study covers all the processes in the reference document AMVD. New knowledge and insights will be added to the document to allow the further adaptation of the processes in place.

Improving risk analysis in AMVD

In short, this project will produce the following results:

  • An understanding of the determinants of the recovery of Cryptosporidium, Giardia and future enteroviruses.
  • Where possible, recovery will be improved by adapting current methods.
  • The development of guidelines for the optimal measurement locations and sample volumes for obtaining the most valuable results for AMVD with the current, optimised, methods.
  • Overview of suitable indicator organisms for each treatment process, including the correlation with pathogen reduction for the relevant treatment processes in AMVD.
  • Update of the AMVD reference document for the processes already covered.
  • Extension of the AMVD reference document to include rapid filtration and active carbon filtration.
  • Improved AMVD web tool.
QMRA infographic e

Under the supervision of the Working Group on Infection Risk (WIR), the current Inspection Guideline for AMVD will be revised and published as the AMVD Guideline.