Phosphate adsorption capacity testing of natural and industrial substrates in view of application in swimming and fish pond water treatment systems

Several substrates have been examined on their phosphate sorption capacity. Wollastonite powder exhibited the highest removal capacity. At all phosphate concentrations (0.1-20mgP/l) the removal was above 82%, with a maximum of almost 96%. The uptake rate was high in the first hour of the batch test and increased with increasing concentration. The wollastonite granules did not take up phosphate at concentrations below 2mgP/l. At higher concentrations the removal fluctuated between 82 and 96%. Slag exhibited a high absorbing capacity (up to 86%) at concentrations starting from 2mgP/l. Other materials (ceramic cylinders with active micro-organisms, porphyry and scoria) that were studied did not exhibit phosphate uptake. From this study it is concluded that, of all the substrates studied, wollastonite powder has the highest phosphate removing capacity. The slag has a lower removal capacity, but is a more coarse material and is thus less prone to clogging. As such it can be concluded that combining both materials, wollastonite powder and slag would be ideally suited for application in a skimmer as the material, provided that the material can easily be replaced.