Use of concentrate water from seawater desalination plant as magnesium sources for struvite formation by using anaerobically digested effluent of swine wastewater

Although struvite crystallization has been proven an effective process to recover nutrients from wastewater, this method has not been used widely because of the cost of the raw chemicals, such as magnesium chloride, required as supplements. In this study, in view of the high cost of supplementing magnesium, reject water from a seawater reverse osmosis process was investigated as a potential source of magnesium. The magnesium was used in the nutrient recovery process, by which struvite crystallization was performed from the anaerobically digested effluent of swine wastewater. The results of all the experiments were positive, indicating that struvite formation was successfully performed from the effluent, using the concentrate water as a magnesium source. Removal efficiencies of up to 94.5% for phosphate and 12.7% for ammonium were achieved under normal operating conditions. Seed materials were successfully used as nucleation sites to enhance the purity of the struvite and the crystal size. The removal efficiencies of phosphate and ammonia could be improved up to 97 and 84%, respectively, by adding phosphate and seed materials.