Dessì Emma, Company Emma, Pous Narcís, Milia Stefano, Colprim Jesús, Magrí Albert
Laboratory of Chemical and Environmental Engineering (LEQUIA), Institute of the Environment, University of Girona, Girona, Spain.
University of Cagliari, Department of Civil-Environmental Engineering and Architecture (DICAAR), Cagliari, Italy.
Heliyon. 2024 Aug 23;10(17):e36766. doi: 10.1016/j.heliyon.2024.e36766. eCollection 2024 Sep 15.
There is high interest in the recovery of phosphorus (P) from wastewater through crystallization processes. However, the addition of chemical reagents (e.g., sodium hydroxide) to raise the pH may result in high treatment costs and increased concentrations of undesired metal ions (e.g., sodium). As an alternative, in this research we considered electrochemical mediated precipitation at low current densities (0.4-1.2 A m) without using chemical reagents. For that purpose, a two-chamber electrochemical system was operated in batch for treating denitrified swine effluent (48 mg P L). By applying current at 1.2 A m, and targeting pH 11.5, a maximum P removal rate of 33.4 mmol P (L·d) was obtained while the P removal efficiency was above 90 %. New solids that formed mostly remained suspended in the catholyte. Before discharge, the catholyte effluent was recirculated to the anodic compartment to neutralize the pH, achieving a final pH of 6.4 ± 0.1. Chlorine (Cl) production in the anodic compartment was favored by a small anode surface and a high initial pH of the catholyte. Although the production of chlorine achieved was limited (the highest concentration was 8.6 ± 0.1 mg Cl L) these findings represent a new opportunity for the recovery and onsite use of this side-product. Electrochemical impedance spectroscopy tests confirmed that the deposition of solids inside the cathodic compartment during the experimental period was limited. Membrane analysis revealed significant scaling of carbonate compounds. The electrochemical treatment described above was shown as a promising alternative to sodium hydroxide and sulfuric acid dosage for pH adjustment when crystallizing phosphate salts.
通过结晶工艺从废水中回收磷（P）备受关注。然而，添加化学试剂（如氢氧化钠）来提高pH值可能会导致高昂的处理成本，并增加不需要的金属离子（如钠）的浓度。作为一种替代方法，在本研究中，我们考虑在不使用化学试剂的情况下，以低电流密度（0.4 - 1.2 A m）进行电化学介导沉淀。为此，一个双室电化学系统以分批方式运行，用于处理脱氮猪废水（48 mg P L）。通过施加1.2 A m的电流，并将pH值设定为11.5，获得了最大磷去除率33.4 mmol P（L·d），同时磷去除效率高于90%。形成的新固体大多仍悬浮在阴极电解液中。在排放前，将阴极电解液流出物再循环到阳极室以中和pH值，最终pH值达到6.4 ± 0.1。阳极室中氯气（Cl）的产生受到小阳极表面和阴极电解液高初始pH值的促进。尽管产生的氯气量有限（最高浓度为8.6 ± 0.1 mg Cl L），但这些发现为回收和现场利用这种副产物提供了新机会。电化学阻抗谱测试证实，在实验期间阴极室内固体的沉积是有限的。膜分析显示碳酸盐化合物有明显的结垢现象。上述电化学处理方法被证明是在结晶磷酸盐时替代使用氢氧化钠和硫酸调节pH值的一种有前景的方法。
