PTs for rapid tests in waste water treatment plants
Recommended procedures for quality controlled self-control to support the official surveillance of municipal waste water treatment plants (WWTPs)
The Ministry of the Environment, Nature Conservation and Transport Baden-Württemberg has published in the above mentioned
recommendations a system that enables the operators of waste water treatment plants to grade up their self-control in a way to minimize
the official surveillance.
To achieve this quality control control of the self-control analyses according to ATV A704 is necessary. This is checked during a third-party surveillance visit. In addition successful participation in the related proficiency testing scheme oif AQS Baden-Württemberg is necessary.
More details can be taken form the recommendation available from the Ministry of the Environment, Nature Conservation and Transport Baden-Württemberg (in German only).
Once per year AQS Baden-Württemberg provides a proficiency test for rapid tests in waste water treatment plants. The following parameters have to be analysed in this PT round:
- Total nitrogen
- Nitrate nitrogen
- Ammonium nitrogen
- Total phosphorous
- TOC (optional)
As a general rule the analyses have to be made using rapid tests.
Up to now the PT scheme for WWTPs is in German only.
Evaluation and assessment
Evaluation and assessment are done according to DIN 38402 - A45 (ISO/TS 20612) and the LAWA lefalet A-3 (Proficiency testing for the external quality control
of laboratories; published in: LAWA - AQS-Merkblätter zur Wasser-, Abwasser- und Schlammuntersuchung, Erich Schmidt Verlag).
determintaion of assigned value usually is done based on the robust mean of the results of all participants. In certain circumstances the PT coordinator may also calculate the assigned value from the formulation of the spiked sample. To do that the content of analyte in the matrix used must be known with high accuracy. This value can be derived from the results of the participants and the weighings from the spiking process in standard addition-like procedure. The standard addition for proficiency assessment used to calculate the ZU-Scores also is derived from the results of the participants. Whenever possible the variance function described in DIN 38402 - A45 (and ISO/TS 20612) is used for the determination of the standard deviation for proficiency assessment.
Before the start of the PT round the PT coordinator defines upper and lower limits for the standard deviation in order to prevent too stringent or too slack quality requirements in the PT.
After finalization of the evaluation and assessemnt procedure all participating laboratories receive a data evaluation sheet that shows the assessment of all values as "+" or "-". In addition for all parameters it is shown whether they were analysed "successfully" or "not successfully". Classification as "successful" means that more than 50% of the values were inside the tolerance limits. Parameters where no results were reported are marked as "not participated"
If at least 80% of the reported results and 80% of the parameters were "successful", the participation in total ia assessed as "successful". This is also stated on the data evaluation sheet. The "successful" participants receive a certificate stating this.
Of course all participants get a comprehensive evaluation report, that anonymously contains the results of all participants in tabels and diagrams. These reports are also available on this website.