Basket anode filled with CaCO3 particles: A membrane-free electrochemical system for boosting phosphate recovery and product purity

Zhengshuo Zhan; Runhua Wang; Michel Saakes; Renata D van der Weijden; Cees J N Buisman; Yang Lei

doi:10.1016/j.watres.2023.119604

Basket anode filled with CaCO₃ particles: A membrane-free electrochemical system for boosting phosphate recovery and product purity

Water Res. 2023 Mar 1:231:119604. doi: 10.1016/j.watres.2023.119604. Epub 2023 Jan 12.

Authors

Zhengshuo Zhan¹, Runhua Wang¹, Michel Saakes², Renata D van der Weijden³, Cees J N Buisman³, Yang Lei⁴

Affiliations

¹ School of Environmental Science and Engineering, Southern University of Science and Technology (SUSTech), Shenzhen 518055, China.
² Wetsus, Centre of Excellence for Sustainable Water Technology, P.O. Box 1113, 8900CC Leeuwarden, The Netherlands.
³ Wetsus, Centre of Excellence for Sustainable Water Technology, P.O. Box 1113, 8900CC Leeuwarden, The Netherlands; Department of Environmental Technology, Wageningen University and Research, P.O. Box 17, 6700AA Wageningen, The Netherlands.
⁴ School of Environmental Science and Engineering, Southern University of Science and Technology (SUSTech), Shenzhen 518055, China. Electronic address: leiy3@sustech.edu.cn.

PMID: 36669305
DOI: 10.1016/j.watres.2023.119604

Abstract

Phosphorus (P) is often regarded as the primary stimulant for eutrophication, while its importance as a crucial life element is also well acknowledged. Given its future scarcity, P recycling from waste streams is suggested and practiced. Electrochemically mediated precipitation (EMP) is a robust and chemical-free process for P removal and recovery, yet it requires further developments. The first generation of the CaCO₃-packed electrochemical precipitation column successfully solved the problem of H⁺-OH^- recombination, achieving enhanced P removal efficiency with less energy consumption but suffering from low Ca-phosphate purity in recovered products. Herein, a new concept of a basket-anode electrochemical system is proposed and validated to prevent direct H⁺-OH^- recombination and enhance product purity. The CaCO₃ pellets packed basket anode alleviates the OH^- depletion by CaCO₃-H⁺ interaction and provides extra Ca²⁺ for enhanced P removal. The novel structure of the basket anode, by its derived acidic anode region and alkaline cathode region, completely avoids the precipitation of Ca-phosphate on the packed CaCO₃ and greatly facilitates the collection of high-quality Ca-phosphate product. Our results suggest that almost 100% of the removed P was in high-purity, highly crystalline Ca-phosphate on the cathode. The recovered products contained significantly more P (13.5 wt%) than in the previous study (0.1 wt%) at similar energy consumptions (29.8 kWh/kg P). The applied current density, pellets size, and influent P concentration were critical for P removal performance, product purity, and power consumption. We further demonstrated the long-term stability of this novel system and its technical and economic feasibility in treating real stored urine. Our study provides new cell architectural designs to enhance the performance of EMP systems and may inspire innovations and developments in other electrochemical water treatment processes.

Keywords: Basket anode; High-purity products; Local pH; Long-term application; Phosphate recovery.

MeSH terms

Chemical Precipitation
Electrodes
Phosphates*
Phosphorus*
Recycling

Substances

Phosphates
Phosphorus