Membrane crystallization for phosphorus recovery and ammonia stripping from reject water from sludge dewatering process

Membrane crystallization (MCr) have been applied on real wastewater to study the potential of recovering phosphorus as struvite (MgNH ₄PO ₄·H ₂O). The performance of MCr shows a stable flux at recovery factor of 70%. To facilitate struvite precipitation, magnesium has been added in the molar ratio of 1:1.3 of P:Mg. A recovery of 60% phosphorus have been obtained at pH of 8.3 and at recovery factor of 70%. Furthermore, the MCr process allows to produce an ammonia-rich stream on the permeate side, due to the hydrophobic nature of the membrane and the transport of volatile compounds through the membrane. This liquid stream can be considered to be used directly as a fertilizer product.