The increasing demand for energy in the world has raised the interest in salinity gradient power as a realistic source of renewable energy. Salinity gradient power, which is the energy from mixing seawater and river water, can be captured by reverse electrodialysis (RED) using ion exchange membranes. Now, after several years of research in laboratory and at pilot conditions, the first full-scale RED plant has been constructed at the Afsluitdijk, where the water from the IJsselmeer and the Wadden Sea meet each other. However, the use of natural feeds has brought new challenges to the on-going research. Fouling and the effect of multivalent ions present in natural feed waters can reduce the obtainable power density by more than 40% .
Figure 1. Principle of reverse electrodialysis (RED). The salt water and fresh water flow alternately along cation exchange membranes (CEM) and anion exchange membranes (AEM). In this case, a(reversible) redox reaction converts the ionic current into an electrical current.
Fouling (Figure 2) and the presence of multivalent ions in natural feeds introduce significant problems to RED as it reduces power outputs. In standard membrane-spacer systems the power output was reduced more than 40% compared to the theoretical power output obtainable. In order to make RED a viable technology for power generation, this loss in power output needs to be reduced and fouling control is essential. The understanding of fouling behaviour, interactions between foulants and the membranes, feed water compositions, type of membranes and spacers, and hydrodynamic effects in the stack is essential to increase the power output.
Figure 2. SEM visualization of fouling occurring on the ion exchange membranes in a RED stack using natural feed waters.
The aim of this project is to investigate both in the full-scale RED installation and under laboratory conditions:
- The occurrence and reasons for fouling in RED using real feed waters.
- Effective fouling management strategies for RED.
- The RED stack design and improvements in hydrodynamics as a way to reduce fouling.
Figure 3. Full-scale RED plant at the Afsluitdijk
 Vermaas et al (2013) Water Research 47 (3), 1289-1298