Flow-Electrode capacitive deionization for enhanced selective separation of Ammonia, Phosphorus, and caproate from sewage sludge fermentation: Performance and mechanistic insights

Huimin Sun; Pengyao Wang; Xuedong Zhang; Bo Wu; Minhua Cui; Hongbo Liu; Mustafa Evren Ersahin; Hale Ozgun; He Liu

doi:10.1016/j.biortech.2025.132048

Flow-Electrode capacitive deionization for enhanced selective separation of Ammonia, Phosphorus, and caproate from sewage sludge fermentation: Performance and mechanistic insights

Bioresour Technol. 2025 Jan 8:132048. doi: 10.1016/j.biortech.2025.132048. Online ahead of print.

Authors

Huimin Sun¹, Pengyao Wang², Xuedong Zhang³, Bo Wu², Minhua Cui⁴, Hongbo Liu¹, Mustafa Evren Ersahin⁵, Hale Ozgun⁵, He Liu⁶

Affiliations

¹ School of Environment and Ecology, Jiangnan University, Wuxi 214122 China.
² Pen Yao Environmental Protection Company, Yixin 214214 China.
³ School of Environment and Ecology, Jiangnan University, Wuxi 214122 China; Pen Yao Environmental Protection Company, Yixin 214214 China. Electronic address: [email protected].
⁴ School of Environment and Ecology, Jiangnan University, Wuxi 214122 China; Jiangsu Collaborative Innovation Center of Water Treatment Technology and Material, Suzhou University of Science and Technology, Suzhou 215011 China.
⁵ Istanbul Technical University, Civil Engineering Faculty, Environmental Engineering Department, Ayazaga Campus, Maslak 34469 Istanbul, Turkey; National Research Center on Membrane Technologies, Istanbul Technical University, Ayazaga Campus, Maslak 34469 Istanbul, Turkey.
⁶ School of Environment and Ecology, Jiangnan University, Wuxi 214122 China; Jiangsu Collaborative Innovation Center of Water Treatment Technology and Material, Suzhou University of Science and Technology, Suzhou 215011 China. Electronic address: [email protected].

PMID: 39793672
DOI: 10.1016/j.biortech.2025.132048

Abstract

Caproic acid has broad applications and can be produced from activated sludge via fermentation, but its quality is hindered by ammonia (NH₄⁺-N) and reactive phosphorus (RP) in the fermentation broth. However, flow-electrode capacitive deionization (FCDI), a novel ion separation technology that operates continuously without secondary pollution seems to be an efficient process that separates the ions. The results showed that at pH 5.0, the majority of N and P presented as NH₄⁺ and H₂PO₄^-, with removal efficiencies of 59.5 % for NH₄⁺-N, 49.5 % for RP, and 17.4 % for caproate. Higher caproate concentrations increased boundary layer thickness, thereby promoting caproate transport to compensate for the ions consumed. The anion exchange membrane exhibited stronger rejection of divalent phosphate than acetate and caproate, resulting in lower HPO₄^2- selectivity. The FCDI holds potential as a viable technology for resource recovery from fermentation broth, offering an alternative method in bioprocessing applications.

Keywords: CFD simulation; Caproate concentration; Continuous operation; Electrochemical process; Ionic competition.