Wetsus, Centre of Excellence for Sustainable Water Technology, P.O. Box 1113, 8900CC Leeuwarden, The Netherlands.
Sub-department Environmental Technology, Wageningen University and Research , P.O. Box 17, 6700AA Wageningen, The Netherlands.
Environ Sci Technol. 2017 Oct 3;51(19):11156-11164. doi: 10.1021/acs.est.7b03909. Epub 2017 Sep 20.
Phosphorus (P) is an essential nutrient for living organisms and cannot be replaced or substituted. In this paper, we present a simple yet efficient membrane free electrochemical system for P removal and recovery as calcium phosphate (CaP). This method relies on in situ formation of hydroxide ions by electro mediated water reduction at a titanium cathode surface. The in situ raised pH at the cathode provides a local environment where CaP will become highly supersaturated. Therefore, homogeneous and heterogeneous nucleation of CaP occurs near and at the cathode surface. Because of the local high pH, the P removal behavior is not sensitive to bulk solution pH and therefore, efficient P removal was observed in three studied bulk solutions with pH of 4.0 (56.1%), 8.2 (57.4%), and 10.0 (48.4%) after 24 h of reaction time. While P removal efficiencies are not generally affected by bulk solution pH, the chemical-physical properties of CaP solids collected on the cathode are still related to bulk solution pH, as confirmed by structure characterizations. High initial solution pH promotes the formation of more crystalline products with relatively high Ca/P molar ratio. The Ca/P molar ratio increases from 1.30 (pH 4.0) to 1.38 (pH 8.2) and further increases to 1.55 (pH 10.0). The formation of CaP precipitates was a typical crystallization process, with an amorphous phase formed at the initial stage which then transforms to the most stable crystal phase, hydroxyapatite, which is inferred from the increased Ca/P molar ratio from 1.38 (day 1) to the theoretical 1.76 (day 11) and by the formation of needle-like crystals. Finally, we demonstrated the efficiency of this system for real wastewater. This, together with the fact that the electrochemical method can work at low bulk pH, without dosing chemicals and a need for a separation process, highlights the potential application of the electrochemical method for P removal and recovery.
磷（P）是生物体必需的营养物质，不能被替代或取代。在本文中，我们提出了一种简单而高效的无膜电化学系统，用于将磷作为磷酸钙（CaP）去除和回收。该方法依赖于在钛阴极表面通过电介导的水还原原位形成氢氧根离子。阴极处原位升高的 pH 值为 CaP 高度过饱和提供了局部环境。因此，CaP 的均相和异相成核发生在阴极表面附近和表面。由于局部高 pH 值，磷去除行为对本体溶液 pH 值不敏感，因此，在三种研究的本体溶液中（pH 值分别为 4.0（56.1%）、8.2（57.4%）和 10.0（48.4%）），反应 24 小时后观察到有效的磷去除。虽然磷去除效率一般不受本体溶液 pH 值的影响，但在阴极上收集的 CaP 固体的物理化学性质仍与本体溶液 pH 值有关，这一点通过结构表征得到了证实。初始溶液 pH 值较高时，有利于形成具有相对较高 Ca/P 摩尔比的更结晶的产物。Ca/P 摩尔比从 1.30（pH 值 4.0）增加到 1.38（pH 值 8.2），进一步增加到 1.55（pH 值 10.0）。CaP 沉淀物的形成是一个典型的结晶过程，在初始阶段形成无定形相，然后转化为最稳定的晶体相羟基磷灰石，这可以从 Ca/P 摩尔比从 1.38（第 1 天）增加到理论值 1.76（第 11 天）以及针状晶体的形成推断出来。最后，我们展示了该系统对实际废水的处理效率。这一事实以及电化学方法可以在低本体 pH 值下运行、无需投加化学物质且无需分离过程的事实，突出了电化学方法在磷去除和回收方面的潜在应用。
