Large quantities of filter substrate accumulate in retention ground filters (Fig.). Within the scope of the granulate research, development engineers of the FLW AG came across mineral granulates produced by ROTEC GmbH & Co. KG. After several months of column experiments at the University of Applied Science in Münster, it could be proven that the filter substrate HygroRet that is based on mineral granulates from Rotec purified significantly better with a 20 % lower fill height than typical sand carbonate mixtures. The adsorption capacity for ammonium compared to carbonate sands improved by a factor of 175, so that the ammonia that is toxic to fish was converted to nitrate by almost 100 %, even during winter months. The higher overall pore volume improves the water retention capacity and the air supply, which positively affects the biological processes, such as biofilm formation, and increases process stability.
ROTEC GmbH & Co. KG, Urmitz (D),
Tel.: +49 2630 95574-0, www.rotocell.de