Phosphorus retention in filter materials for wastewater treatment and its subsequent suitability for plant production

Constructed sand filter beds are advantageous for the treatment of wastewater in areas with a low population density. Phosphorus-sorbing materials with additional beneficial characteristics may be used instead of sand. This study aimed at determining and comparing phosphorus (P) retention capacities of amorphous and crystalline blast furnace slags, limestone, opoka, Polonite® and sand, for filtering domestic wastewater through columns over a period of 67 weeks. The P-enriched filter materials were subsequently tested for their fertilizer effectiveness in a pot experiment where barley was cultivated. Polonite®, i.e. calcinated bedrock opoka, was most effective in removing P. This occurred at a relatively high hydraulic conductivity that reduced the risk of clogging. Barley grown in two types of slag, with a grain size of 0.25-4 mm, was most effective in dry matter production followed by Polonite®. Fine-grained slags and Polonite® were suggested as most suited of the investigated materials to recycle P back to agriculture.