Abstract
A membrane-based technique for production of pressure-retarded osmosis (PRO) is salinity gradient energy. This sustainable energy is formed by combining salt and fresh waters. The membrane of the PRO process has a significant effect on controlling the salinity gradient energy or osmotic energy generation. Membrane fouling and operating conditions such as temperature have an extreme influence on the efficiency of the PRO processes because of their roles in salt and water transportation through the PRO membranes. In this study, the temperature impact on the power density and the fouling of two industrial semi-permeable membranes in the PRO system was investigated using river and synthetic sea water. Based on the findings, the power densities were 17.1 and 14.2 W/m2 at 5 °C for flat sheet and hollow fiber membranes, respectively. This is the first time that research indicates that power density at low temperature is feasible for generating electricity using PRO processes. These results can be promising for regions with high PRO potential that experience low temperatures most of the year.
Highlights
Osmotic power, known as salinity gradient energy, has recently received a lot of interest as a sustainable energy source due to greenhouse gas emissions and resource depletion
Based on the fouling results, the produced power density decreased over time, but the amount of the power density after three hours was still much higher compared to the minimum required power density in pressure-retarded osmosis (PRO) processes for both membrane modules at low temperature
It was interesting to observe that the permeate flux and produced power density declined by decreasing the temperature, the amount of produced power density at the lowest temperature used in this research (5 ◦C) was still higher than the minimum required power density
Summary
Known as salinity gradient energy, has recently received a lot of interest as a sustainable energy source due to greenhouse gas emissions and resource depletion. For the generation of electric power based on salinity gradient energy, many technologies such as pressure-retarded osmosis (PRO), reversed electrodialysis (RED), electrical double-layer capacitor (EDLC), and power generation via vapor pressure difference (VPD) are being developed. A difference in osmotic pressure between the two sides of the membrane (∆π) causes this and as a result, water with less salinity from the feed solution is driven to a pressurized draw solution with higher salinity [10]. This energy can be harvested wherever surface/clean water from rivers encounters salt water from a sea, bay or saline lake [8]. Hydraulic pressure (∆P) is nearly zero and water passes through the membrane from the fresh side to the concentrated salt side in FO, and in RO water passes through the membrane from the concentrated salt side to the fresh side by applying hydraulic pressure (∆P > ∆π) [1]
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