Basic Oxygen Furnace steel slag and apatite for sustainable phosphorus removal at small wastewater treatment plants

Recent developments in phosphorus (P) removal have focused on P reactive materials to use within constructed wetlands (CW), as a sustainable alternative to chemical dosing. In this study, different fractions of Basic Oxygen Furnace (BOF) steel slag and apatite media have been tested in full-scale CWs, being the first trial of its kind in the United Kingdom evaluating the P removal capacity of both these media. Column experiments have also been carried out to confirm the effect of hydraulic retention time (HRT) on effluent pH. The results show that both materials can efficiently and consistently remove P. Smaller slag fractions are more efficient in P removal than larger fractions, but produce slightly higher effluent pH. Apatite shows a similar P removal as the smallest slag fraction, but produces lower effluent pH. The pH of all CW effluents is high at the start but decreases with time. HRT is a key operational parameter in controlling the effluent pH in this type of CW.