As　a　novel　phosphorus　recovery　product,　vivianite　(Fe-3(PO4)(2)center　dot　8H(2)O)　has　attracted　much　attention　due　to　its　enormous　recycling　potential　and　foreseeable　economic　value.　Taking　sponge　iron　as　seed　material,　the　effect　of　different　reaction　conditions　on　the　recovery　of　phosphorus　in　waste　activated　sludge　by　vivianite　crystallization　was　studied.　Through　single　factor　tests,　the　optimal　conditions　for　vivianite　formation　were　in　the　pH　range　of　5.5-6.0　with　Fe/P　molar　ratio　of　1.5.　Scanning　electron　microscopy　(SEM),　powder　X-ray　diffraction　(XRD),　and　energy　dispersive　spectroscopy　(EDS)　were　used　to　analyze　the　components　of　the　crystals.　The　results　showed　that　the　vivianite　produced　by　sponge　iron　as　the　seed　crystal　were　larger　and　thicker　(300-700　mu　m)　than　other　seed　(200-300　mu　m)　and　without　seed　(50-100　mu　m).　Moreover,　vivianite,　which　was　synthesized　with　sponge　iron　as　seed,　was　obviously　magnetic　and　could　be　separated　from　the　sludge　by　rubidium　magnet.　The　Box-Behnken　design　of　the　response　surface　methodology　was　used　to　optimize　the　phosphorus-recovery　process　with　sponge　iron　(maximum　phosphorus　recovery　rate　was　83.17%),　and　the　interaction　effect　of　parameters　was　also　examined,　pH　had　a　significant　effect　on　the　formation　of　vivianite.　In　summary,　this　research　verifies　the　feasibility　of　using　sponge　iron　as　the　seed　crystal　to　recover　phosphorus　in　the　form　of　vivianite　from　waste　activated　sludge,　which　is　conducive　to　the　subsequent　separation　and　utilization　of　vivianite.