Department of Civil and Environmental Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, Norway.
Department of Civil and Environmental Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, Norway.
Water Res. 2020 Apr 15;173:115572. doi: 10.1016/j.watres.2020.115572. Epub 2020 Jan 31.
Seawater, as an alternative magnesium source, has the potential to improve the overall economics and environmental footprint of struvite production compared to the use of pure magnesium salts. However, the dilution effect and the presence of other ions in seawater can reduce the phosphorus recovery potential and the simultaneous precipitation of other compounds may reduce the quality of the produced struvite. This work presents a comparative study of seawater and MgCl by performing a series of thermodynamic equilibrium modeling and crystallization experiments. The results revealed that acceptable phosphorus recovery (80-90%) is achievable by using seawater as the magnesium source for struvite precipitation. Further, the simultaneous precipitation of calcium phosphates was successfully controlled and minimized by optimum selection of reaction pH and seawater volume (i.e. Mg:P and Mg:Ca molar ratios). The increase of temperature from 20 °C to 30 °C reduced the phosphorus recovery by 15-20% while it increased the particle size by 30-35%. The presence of suspended solids in reject water did not have significant effects on phosphorus recovery but it made the struvite separation difficult as the obtained struvite was mixed with suspended solids. The experimental results and economic evaluation showed that the use of seawater can reduce the chemical costs (30-50%) and the CO-footprint (8-40%) of struvite production. It was concluded that seawater is a potential alternative to pure magnesium sources in struvite production, while studies in larger scale and continuous mode are needed for further verification before full-scale applications.
海水作为一种替代镁源，与使用纯硫酸镁相比，具有提高鸟粪石生产的整体经济性和环境足迹的潜力。然而，海水的稀释效应和其他离子的存在可能会降低磷的回收潜力，同时其他化合物的共沉淀可能会降低所生产的鸟粪石的质量。本工作通过进行一系列热力学平衡模拟和结晶实验，对海水和 MgCl 进行了比较研究。结果表明，使用海水作为镁源沉淀鸟粪石可以实现可接受的磷回收（80-90%）。此外，通过优化反应 pH 值和海水体积（即 Mg:P 和 Mg:Ca 摩尔比）的选择，可以成功控制和最小化同时沉淀的磷酸钙。温度从 20°C 升高到 30°C 会使磷的回收降低 15-20%，同时使颗粒尺寸增加 30-35%。废水中悬浮固体的存在对磷的回收没有显著影响，但由于获得的鸟粪石与悬浮固体混合，使鸟粪石的分离变得困难。实验结果和经济评估表明，使用海水可以降低鸟粪石生产的化学成本（30-50%）和 CO 足迹（8-40%）。结论是，海水是鸟粪石生产中替代纯镁源的一种潜在选择，但在大规模和连续模式下进行进一步验证之前，需要进行全面应用。
