Struvite recovery from wastewater having low phosphate concentration

Liquid-solid two-phase fluidized bed type reactor was operated for struvite recovery for the purpose of developing the reactor that can be applied to wastewater having low PO4-P concentrations. In area-wide sewage sludge treatment plant, the reactor was examined to recover struvite from thickener effluent, whose PO4-P concentration was around 40 mg/L. When the thickener effluent was treated by the reactor without the addition of Mg2+, Ca2+ affected struvite recovery and the Ca contents of the recovery particles increased. In batch tests, it was confirmed that the condition where struvite precipitates prior to calcium phosphate in wastewater requires the condition of [Ca2+]/[Mg2+] < 0.25 in the influent. The inorganic SS flowing into the reactor was also found to affect the recovery in column tests. To prevent this effect by the inorganic SS, the reactor was operated without the influent of fine suspended solids in the wastewater from the melting furnace. The only influent processed was the thickener effluent, and MgCl2 aq. was added using a magnesium resource. Consequently, the recovery rate improved to 62%. In the case that struvite is recovered from wastewater including low PO4-P concentration, the recovery rate of struvite was affected by the coexistent substances in the influent. But if this effect was controlled, this reactor could recover struvite particles passably.