(533h) Bench-Scale Testing of Electrochemical Recovery of Phosphorus from Post-Digester Municipal Wastewater Driven By Magnesium Salt

Phosphorus is an irreplaceable macronutrient necessary for plant growth and other industrial processes, whereas when in excess in water bodies can lead to eutrophication which causes algal blooms, reduced water clarity, and toxicity to aquatic life due to lack of oxygen. Through human excrements, dishwashing agents, and other unspecific sources, approximately 1.8 g phosphorus per capita per day reaches the wastewater treatment plants [1]. This wastewater, low in phosphorus concentration, passes through a primary clarifier and then a digestion process. The typical digestion process results in a phosphorus-rich supernatant in the digester effluent. In addition, as demand for fertilizers increases globally and the supply of non-renewable rock phosphate steadily decreases, the costs of phosphate-based fertilizers will increase, significantly impacting the affordability of food products [2, 3]. Recovery of phosphorus from waste, as struvite (MgNH₄PO₄·6H₂O): a slow-release fertilizer, is a potential pathway to solving these problems. Therefore, it is imperative to develop a technology to optimize phosphorus recovery from post-digester wastewater as this could lead towards environmental sustainability and create economic value.

This research study focuses on recovering phosphorus as struvite (or a mixed-phase solid) from post-digester municipal wastewater using an electrochemical technology. The electrochemical technique adopted provides localized pH control which is necessary for struvite formation through oxygen reduction at the cathode. This approach also aims to achieve a process that enables easy automation with little or no human intervention. Belarbi et al. investigated the impact of the presence of other dissolved species specifically Ca²⁺ in wastewater and how it can alter the chemistry of struvite precipitation [4]. This provided insight into negating the effect of this competing ion by increasing the concentration of magnesium in the wastewater in addition to other major ions in this stream including Na⁺, K⁺, SO₄^2- and Cl^-. In a bid to potentially recover phosphorus as struvite in this study, magnesium will be supplemented by the introduction of magnesium salt.

The effect of the available surface area of the working electrode, flow turbulence, applied potential, and dissolved oxygen present will be investigated. Also, the percentage recovery of phosphorus as struvite will be determined while analyzing it using various characterization techniques such as scanning electron microscope, Energy-dispersive X-ray spectroscopy, Raman spectroscopy, and X-Ray Diffraction.

References:

1. Cornel, P., & Schaum, C., “Phosphorus recovery from wastewater: needs, technologies and costs” Water Science and Technology, 59(6), 1069–1076, 2009.
2. László Kékedy-Nagy, Leah English, Zahra Anari, Mojtaba Abolhassani, Bruno G. Pollet, Jennie Popp, Lauren F. Greenlee, “Electrochemical nutrient removal from natural wastewater sources and its impact on water quality” Water Research, 210, 2022.
3. Arseto Yekti Bagastyo, Anita Dwi Anggrainy, Khoiruddin Khoiruddin, Riang Ursada, IDAA Warmadewanthi, I Gede Wenten, “Electrochemically-driven struvite recovery: Prospect and challenges for the application of magnesium sacrificial anode” Separation and Purification Technology, vol. 288, 2022.
4. Z. Belarbi, D. Daramola and J. P. Trembly, “Bench-Scale Demonstration and Thermodynamic Simulations of Electrochemical Nutrient Reduction in Wastewater via Recovery as Struvite” J. Electrochem. Soc., vol. 167, no. 4, Nov. 2020.