Electrodialysis (ED) based processes for resource recovery

• Main Author: Yang, Dingchang
• Other Authors: She Qianhong
• Format: Thesis-Master by Research
• Language: English
• Published: Nanyang Technological University 2022
• Subjects: Engineering::Environmental engineering
• Online Access: https://hdl.handle.net/10356/163202
• Institution: Nanyang Technological University

Driven by sustainable development and circular economy, wastewater treatment has shifted from the simple removal of pollutants to the simultaneous recovery of valuable resources. Among various technologies, electrodialysis (ED) and its related processes are regarded as promising perspectives for wastewater treatment and resource recovery. In this thesis work, two studies were conducted: (1) ED for ammonium concentration, and (2) bipolar membrane electrodialysis (BPED) for acid and base production from pre-treated seawater desalination brine. Firstly, to obtain a high concentration ammonium solution for subsequent more effective recovery, ED was used to concentrate ammonium from low concentration domestic wastewater. In this process, various operating parameters, including current density, the volume ratio between dilute and concentrate solution, and the ion exchange membrane (IEM) arrangement in ED stacks, were investigated. In addition, the transport number and selectivity of cations (i.e., Na+, K+, Ca2+, or Mg2+) over NH4+ into concentrate chambers were studied to elucidate the mechanism of competitive ion transport in ED. Results show that a higher applied current density (2 mA/cm2), a greater volume ratio between dilute and concentrate (20:1), and the configuration with anion exchange membranes (AEMs) adjacent to electrode chambers could achieve better ammonium concentration efficiency. In the second part of using BPED for acid and base production, the BPED performance was experimentally evaluated using different commercial anion exchange membranes (AEMs) and cation exchange membranes (CEMs). The results revealed that acid production is mainly influenced by the properties of AEMs rather than the CEMs, while base production is mainly influenced by the properties of CEMs rather than the AEMs. Specifically, both IEMs with higher permselectivity and lower electrical resistance could achieve better performance, i.e., higher acid and base production, lower energy consumption, and higher current efficiency. A long-term BPED batch-test up to 26 h was conducted, which produces 0.97 M HCl and 0.80 M NaOH with high purity for both products (around 95%) and low energy consumption. This research demonstrates the high promise of ED-based ion exchange membrane processes for resource recovery and waste valorization.