Enhancing phosphorus recovery by a new internal recycle seeding MAP reactor

Phosphorus is a depleting resource that needs recovery from wastewater streams. The magnesium ammonium phosphate (MAP) crystallization process could simultaneously recover ammonium nitrogen and phosphorus at equal molar basis to yield slow-release MAP fertilizer. However, the present MAP processes are not efficient in recovering phosphorus at low P concentrations. This work presented and tested the performance of a newly proposed MAP reactor, the internal recycle seeding reactor (IRSR) that comprised of a reaction zone and a settling zone connecting with an internal recirculation loop. Owing to the enhanced secondary nucleation rates of MAP crystals in reaction zone under controlled circumstance, the proposed IRSR recovered 78% of phosphorus from wastewater at a low level of 21.7 mg-PL(-1). The optimal operation parameters for the IRSR were investigated with synthetic wastewater and determined as that the Mg/PO(4)(3-)-P molar ratio was 1.3-1.5:1, THRT was up to or longer than 1.14 h, the seed concentration of reaction zone was 0.40-1.0 gL(-1). Further needs for the proposed IRSR strategies were also discussed.