Practical application of tested systems according to EN 12566 Part 7
Why do prefabricated small sewage treatment plants designed for a tertiary treatment step (EN 12566-7) require special attention in practice?
Plant modules used for the third treatment stage are usually not generic treatment systems and are typically tailored to perform a certain function, such as the additional reduction of phosphorus or nitrogen. It is important to bear this fact in mind when interpreting test results from initial type tests according to Part 7 of the standard, such as reports or declarations of performance. This is possible only if their function and mode of operation are clearly understood and the conditions during the test are taken into account.
Depending on the process type, two test schedules are possible for testing the treatment performance according to the standard. The test sequence of seven weeks for systems with chemical and electrical processes or 16 weeks for systems with biological and physical processes is a comparatively short test period which does not always allow to draw conclusions about the performance in long-term operation. For the test, the manufacturer specifies the daily hydraulic inflow and daily inflow concentration for COD, BOD, SS and the parameters that are in the focus for the system. The inlet dynamics are also relevant. They are usually based on either the flow diagram of an SBR system or a gravity flow system and thus specify the later area of application. In general, it is not possible to transfer the results of the tested system to other inlet conditions. In order to reach a reasonable application of modules for the tertiary treatment stage in practice, it is thus necessary to also specify the results, the specifically focused treatment objective and the inlet conditions during the test.