(718b) Parametric Sensitivity of Reverse Electrodialysis for Electricity Production Using Salinity Gradient

Global population growth has led to increased energy demand and stress on energy supplies. Concerns over the stability, sustainability, and environmental impact of global energy consumption have generated renewed interest in alternative energy sources. The ideal source would be locally distributed and renewable with minimal economic and environmental impact on our current lifestyle.

The sun is the source of virtually all energy. Solar energy can be utilized in the form of fossil fuels, wind energy, photovoltaic or thermal solar, and hydroelectric. Growing interest exists in using the salinity difference between fresh water and sea water to produce power from mixing the two streams. Membrane processes such as Reverse Electrodialysis (RED) and Pressure Retarded Osmosis (PRO) can be used to produce electricity [1, 2]. Literature reports the effects of membrane type, membrane and gasket thickness, electrode systems and flow rates on power production [3].

In the current study, we demonstrate the optimization of power output using RED. The effects of operating parameters such as current density, concentration of process streams and the concentration and composition of electrode rinse are investigated. We also examined the relationship between electrons generated (current) and ion transfer between the solutions. The efficiency of RED can be determined from the ratio of current to ion transfer. We examined possible sources of energy loss and inefficiency. Shunt currents and membrane area occupied by spacer mesh are believed to be significant contributors. The origin and reduction of these factors to increase the efficiency is discussed as well as the effect of other cell design variables.

References:

1. Post, J. et. al., Salinity-gradient power: Evaluation of pressure-retarded osmosis and reverse electrodialysis, Journal of Membrane Science 288 (2007) 218–230.
2. Dlugolecki, P. et. al., Practical Potential of Reverse Electrodialysis As Process for Sustainable Energy Generation, Environmental Science and Technology 43 (2009) 6888–6894.
3. Veerman, J. et. al., Reverse electrodialysis: evaluation of suitable electrode systems, Journal of Applied Electrochemistry 40 (2010) 1461–1474.