IPR removes dissolved phosphate (PO₄³⁻) from water by converting it into a solid form through a reaction with iron. By injecting FeCl₃ into the influent pipe, hydro ferric oxide (HFO) is formed and coats the media surface inside the reactor. This HFO reacts with phosphate in the water to form solid FeHPO₄, which is then removed from the system. This process can reduce total phosphorus to as low as 0.03 mg/L. It requires a minimal amount of chemicals and generates little sludge.