21. November 2021
The basket consists of a design based on standard leaf-collecting baskets, which is equipped with modular sieve pans. Six sieve pans with different pore sizes form a filter cascade. Following a rain shower, this device is removed completely with the basket and used for DIN-compliant fractioning of the particulate loads in a vibrator tower. When the project began, GKD had no preliminary data for the design of the basket and the filter cascade, which meant that conceivable flow behavior in the basket could only be calculated through simulation. Even mesh-specific flow rates dependent on the ponding depths had to be determined hypothetically. Based on these assumptions, GKD built an initial prototype of the basket at its in-house filter production site.
Over the next three years of the project, the sampling basket was developed and continuously optimized based on factual measurements from the test bench at the Technical University of Berlin and in subsequent practical tests at twelve different measuring points on roads in Berlin. This revealed that the finest sieve used to catch road runoff is critical to the entire flow. The breakthrough came in the form of the three-dimensional Porometric mesh from GKD. With a significantly greater dirt holding capacity and excellent flow characteristics, this mesh type enabled the smooth functioning that was required. Plus, the unbeaten cleanability demonstrated by Porometric mesh was critical to the success of the project, as the materials cleaned off are used as sampling material. The addition of a pleated mesh disc to each sieve, which functions as a preliminary filter to hold back larger particulate material such as leaves, supports blockage-free flow with the required mesh sequence and separation rates in the filter cascade. The filter cascade most frequently used in the tests consists of six sieve pans with mesh apertures of 1,000, 500, 250, 125, 63, and 20 micrometers. However, as experience has shown that the largest particulate load occurs in the range between 125 and 63 micrometers, the sieves with these pore sizes are sometimes doubled.
The conclusion drawn at the end of the research project is accordingly positive. The sampling basket performs as expected under all relevant conditions such as weather, flow rates, and separation rates down to 20 micrometers. It is the medium of choice for wet environmental samples and low-rainfall events in particular. While the systems previously used were only able to gather partial samples, the basket is able to sample rainfall events from the very first second. Because it is equipped with an additional integrated pump model that is able to take a representative partial sample of dissolved particulate matter in addition to the defined particulate sample, it gives samplers a full picture of the materials gathered.