The majority of sewage treatment plants in Europe utilize chemical phosphorus removal (CPR) by dosing iron salts(Korving et al., 2019). With CPR, phosphorus precipitates as iron phosphate and is immobilized in the produced sludge. This sludge is then often anaerobically digested for hygienisation and energy recovery by methane production. Iron can also be added in the treatment process as a coagulant to enhance primary sedimentation and thus biogas production, or to prevent hydrogen sulfide emissions.

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Research at Wetsus has shown that vivianite (Fe3(PO4)2·8(H2O)) is the main iron phosphate mineral that forms  during digestion of sewage sludge, provided that enough iron is present (Wilfert, 2018). Vivianite is paramagnetic and can be recovered from the sludge after digestion using a magnetic separator designed for the mining industry. This has been demonstrated on lab-scale (Prot et al., to be published) and more recently at bench-scale and pilot-scale.The ViviMag project offers a separation process to recover vivianite from digested sludge by using magnetic separation. ViviMag will fit into existing treatment processes without major adjustments.