Performance Limiting Effects in Power Generation from Salinity Gradients by Pressure Retarded Osmosis

Yip, Ngai Yin; Elimelech, Menachem

Performance Limiting Effects in Power Generation from Salinity Gradients by Pressure Retarded Osmosis

Type

Article

Authors

Yip, Ngai Yin
Elimelech, Menachem

KAUST Grant Number

KUS-C1-018-02

Date

2011-12

Abstract

Pressure retarded osmosis has the potential to utilize the free energy of mixing when fresh river water flows into the sea for clean and renewable power generation. Here, we present a systematic investigation of the performance limiting phenomena in pressure retarded osmosis-external concentration polarization, internal concentration polarization, and reverse draw salt flux-and offer insights on the design criteria of a high performance pressure retarded osmosis power generation system. Thin-film composite polyamide membranes were chemically modified to produce a range of membrane transport properties, and the water and salt permeabilities were characterized to determine the underlying permeability-selectivity trade-off relationship. We show that power density is constrained by the trade-off between permeability and selectivity of the membrane active layer. This behavior is attributed to the opposing influence of the beneficial effect of membrane water permeability and the detrimental impact of reverse salt flux coupled with internal concentration polarization. Our analysis reveals the intricate influence of active and support layer properties on power density and demonstrates that membrane performance is maximized by tailoring the water and salt permeabilities to the structural parameters. An analytical parameter that quantifies the relative influence of each performance limiting phenomena is employed to identify the dominant effect restricting productivity. External concentration polarization is shown to be the main factor limiting performance at high power densities. Enhancement of the hydrodynamic flow conditions in the membrane feed channel reduces external concentration polarization and thus, yields improved power density. However, doing so will also incur additional operating costs due to the accompanying hydraulic pressure loss. This study demonstrates that by thoughtful selection of the membrane properties and hydrodynamic conditions, the detrimental effects that limit productivity in a pressure retarded osmosis power generation process can be methodically minimized to achieve high performance. © 2011 American Chemical Society.

Citation

Yip NY, Elimelech M (2011) Performance Limiting Effects in Power Generation from Salinity Gradients by Pressure Retarded Osmosis. Environ Sci Technol 45: 10273–10282. Available: http://dx.doi.org/10.1021/es203197e.

Acknowledgements

This publication is based on work supported in part by Award No. KUS-C1-018-02, made by King Abdullah University of Science and Technology (KAUST); the WaterCAMPWS, a Science and Technology Center of Advanced Materials for the Purification of Water with Systems under the National Science Foundation Grant CTS-0120978; and Oasys Water Inc. We also acknowledge the Graduate Fellowship (to Ngai Yin Yip) made by the Environment and Water Industrial Development Council of Singapore.