for water tests on watercourses
CEPA – custom-built systems
High-speed tubular centrifuges from CEPA can be extended variably and individually equipped in a variety of versions. A miniature laboratory in a car trailer is fitted out as a mobile system, for the sampling of water bodies. It is fully equipped with centrifuge, generator, pumps, workbench, hoses and light. It can also be installed in a truck, the solution adopted by the Lower Saxony Water Management, Coastal Protection and Nature Conservation Agency.
“Suspended matter tests are an increasingly important part of water body monitoring”.
While water body testing for pollutants have hitherto been conducted exclusively within the matrix of “water”, “solids” tests are increasingly becoming the priority, explains Dr. Dieter Steffen from the Lower Saxony Water Management, Coastal Protection and Nature Conservation Agency in this interview.
Where do the challenges lie in water body testing?
The problem when testing water samples, above all for organic pollutants, is that these often fall below the limits of determination. Obtaining interpretable measurements – which are in the range of tenths of a nanogram per litre for PCB – involves a large amount of analytical work. And remember that in the case of water tests, you are usually analysing bulk samples with the suspended matter present in a water sample. As a result, water samples may exhibit sharp fluctuations in concentrations over a short period of time, depending on the levels of suspended matter, which in turn vary according to the hydrological conditions of a water body such as flooding. These make the results very difficult to evaluate.
So what is the solution?
Suspended matter tests are a useful way of obtaining results that can be reliably evaluated. A high-speed centrifuge is used to separate the phases, and the solid samples are then analysed. Because certain pollutants are enriched or accumulate predominantly on particles of solids, when these are tested the levels of determination, which are a matter of milligrams per kilogram for heavy metals and nanograms per kilogram for organic matter, are passed much less frequently; that makes the analysis results more meaningful.
How do CEPA tubular centrifuges help?
Suspended matter samples can be obtained by filtration, using settling tanks or continuous centrifuges. The advantage of continuous centrifuges is that the fine-grained particles are captured in full, so separation is performed almost quantitatively. The temporal resolution of the suspended matter sample obtained can be varied over a range of a few hours to a few days in the centrifuge. If the volumetric flow is also measured and the quantity of suspended matter obtained is determined, the exact pollutant loads can also be calculated. Running at 17,000 revolutions per minute and with a throughput of around 1,000 litres per hour, CEPA high-speed centrifuges are very high-performance. Based on our many years of working with CEPA centrifuges, they are also very reliable and durable.
The Lower Saxony Water Management, Coastal Protection and Nature Conservation Agency (NLWKN) uses four CEPA high-speed centrifuges (Z61) in total. Three are permanently installed at quality measurement stations, and one is in mobile use in the lab vehicle. The first CEPA centrifuge was purchased in 1992 and has been in operation ever since. Applications of note include heavy metal tests in resin, PAH tests and the use of the mobile CEPA high-speed centrifuge during flooding along the river Elbe in June 2013.