Quantitative microbial risk assessment

The concept of QMRA (quantitative microbial risk assessment) proposed by WHO shall be trialled in real waterworks in Germany. In this concept, compliance with defined health-based goals in water treatment is checked by determining the pathogens in raw water and characterising their removal via water treatment performance using indicators. 

In 2014, the German Environment Agency recommended a procedure to quantitatively assess the risk of microbiological results in raw water using an approach proposed by WHO (determination of pathogens in raw water and measurement the treatment results using indicators).

The aim of this project is to obtain practical experience using this approach for waterworks in Germany. The process shall be trialled using two to three selected waterworks. The waterworks should be plants with as high a microbial load as possible (river water as raw water). In these waterworks, the applicability of the method to calculate the effectiveness of treatment is tested.   

Three different surface waterworks were selected that each abstracted river water (Neckar or Ruhr), which is treated as part of preliminary treatment using rapid filtration and subsoil passage.

A measurement programme was implemented at these three waterworks over two years, during which extensive microbiological measurements were taken at least monthly in the raw water and following both particle-removal steps. These steps involved both indicators and pathogenic microorganisms.

After executing the measurement programme and obtaining a detailed database as part of sub-project B, evaluation programmes for risk assessment are tested and used to develop guidelines that enable water treatment plants to evaluate their performance from a hygienic perspective.