Recovery of nitrogen as struvite from swine wastewater: Comparison study of batch and continuous fluidized-bed crystallization process

The recovery of valuable compounds from waste supports the idea of a circular economy. Two systems were introduced in this study to recover nitrogen as struvite from swine wastewater, including batch stirred and fluidized-bed homogeneous crystallization (FBHC) systems. MgCl2 and NaH2PO4 were applied as precipitants to form struvite. In the batch stirred system, the removal efficiency of NH4+, Mg2+, and PO43- reached the optimum condition of 92.1 %, 75.6 %, and 91.1 %, respectively, under the operating conditions of pH 9 and an Mg/P molar ratio of 1.2. In the same operating conditions, the Crystallization ratio (CR) and Total Removal (TR) of the FBHC system reached 83.2 % and 89.1 %; 86.7 % and 90.6 %; 71.2 % and 76.1 % for NH4+, Mg2+, and PO43-, respectively. The XRD and FT-IR analyses confirmed the high purity and quality of the struvite solid product. However, the water content of the FBHC product is much lower than that of the batch-stirred system (5.8 % and 95.3 %, respectively). The great potential of swine wastewater as a nitrogen source for fertilizer production is evidenced by the high purity struvite product (>85.0 %).