An integrated approach to vivianite recovery from waste activated sludge

[Display omitted] •The sludge anaerobic fermentation process efficiently reduces Fe3+ to Fe2+.•The acid-elutriation solubilizes Fe and P from the solid phase to the liquid phase.•The acid-elutriation significantly enhances the liquid–solid separation.•High-quality vivianite is harvested via neutralizing sludge eluate. The waste activated sludge (WAS) of wastewater treatment system is often rich in phosphorus (P), which is a basic element of human life and could use up in the near future. This study proposed an integrated approach to efficiently recover P as vivianite from WAS and simultaneously enhance the sludge dewaterability. The raw WAS was first acidified using FeCl3, which was then fed to anaerobic fermenter for Fe3+ reduction. After fermentation, a technology named acid-elutriation was introduced to convert Fe and P from solid phase to liquid phase and concomitantly enhance the liquor-solid separation. Finally, vivianite was obtained via sludge eluate neutralization. The enhanced sludge dewaterability not only increases the recovery efficiency of Fe and P but also decreases the cost of sludge disposal.