PhosphoReduc filter system is a“closed loop” gravity fed passive filtration system for P harvesting/removal, re-use and recovery. The technology was developed as an outcome of a decade (1999 – 2009) of research by Drizo and co-workers on the use of steel slag aggregates (SSA) for P removal from wastewaters (Weber et al, 2007; Drizo et al, 2008; Bird and Drizo, 2009; Bird and Drizo, 2010; Drizo, 2012).