• Membrane Journal
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• v.25 no.4
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• pp.367-372
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• 2015

In pressure-retarded osmosis (PRO) and forward osmosis (FO) processes, solvent (permeate) flux depends on which surface the draw solution faces. There are two operation modes. PRO mode indicates that the active layer faces the draw solution, and FO mode means that the porous substrate fronts the draw stream. It is often observed that the PRO mode produces higher flux than that of FO under the same operating conditions. The current work uses the method of proof by contradiction, and mathematically proves the intrinsic flux inequality between the two modes.

• Journal of Korean Society of Environmental Engineers
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• v.36 no.11
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• pp.791-802
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• 2014

Energy shortage is being exacerbated due to the increase of energy consumption and depletion of fossil fuels. In order to release the energy crisis, new types of energy resources such as small hydropower, solar power, wind power and biomass have been already developed or actively researched. Recently, osmotic power, which harvests energy from salinity gradient between seawater and fresh water, is considered as a feasible candidate. Among the osmotic power processes, pressure retarded osmosis (PRO) is widely gaining attention because of no emission of carbon dioxide and less sensitivity to the external environmental conditions. However, PRO process is facing difficulties such as the lack of specialized PRO membrane and optimization technologies. Therefore, PRO was reviewed in this paper in terms of theoretical background, membrane development, process development and fouling mechanism to provide insights and suggest the future direction of PRO research.

• Journal of Korean Society of Environmental Engineers
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• v.38 no.9
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• pp.476-481
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• 2016

Pressure retarded osmosis (PRO) is a quite new technique for power generation using an osmotically driven membrane process. In the PRO process, water permeates through a semipermeable membrane from a low concentration feed solution to a high concentration draw solution due to osmotic pressure. This study carried out to evaluate the performance of the 8 in spiral wound membrane module using reverse osmosis concentrate for a draw solution and reverse osmosis permeate for a feed solution. Three different flowrates of draw and feed solution, such as 2.4 L/min, 5.0 L/min, and 10.0 L/min were used to estimate the power density and water flux under various range of hydraulic pressure differences between 5 bar and 30 bar. In addition, the effects of feed and draw solution concentration, flowrate, and mixing ratio on 8 in spiral wound PRO membrane module performance were investigated in this study. As major results, increases of the draw solution concentration lead to the improvement of power denstiy, and water flux. Also, increase of flowrate resulted in the improvement of power density and water flux. In addition, optimal mixing ratio of draw and feed solution inlet flowrate was found to be 1:1 to attain a maximum power denstiy.

• Journal of Korean Society of Water and Wastewater
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• v.30 no.3
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• pp.321-325
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• 2016

The Pressure Retarded Osmosis (PRO) is the next generation desalination technique and is considered as a eco-friendly energy. This was conducted to evaluate the effect of the temperature and pressure on the PRO performance. The flux of the permeation was measured under different operating conditions and estimated the power density. An improvement of PRO performance is depend on increasing solution temperature and optimum pressure. The effect of increasing feed solution temperature has stronger impact on the PRO performance comparing to the draw solution temperature. The reason of the results was due to the change of osmotic power, viscosity, water permeability and structure parameter(s).

• Journal of Korean Society of Water and Wastewater
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• v.30 no.3
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• pp.299-312
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• 2016

The main objective of this paper is to develop computer simulation program for performance evaluation and cost estimation of a reverse osmosis (RO) and pressure-retarded osmosis (PRO) hybrid process to propose guidelines for its economic competitiveness use in the field. A solution-diffusion model modified with film theory and a simple cost model was applied to the simulation program. Using the simulation program, the effects of various factors, including the Operating conditions, membrane properties, and cost parameters on the RO and RO-PRO hybrid process performance and cost were examined. The simulation results showed that the RO-PRO hybrid process can be economically competitive with the RO process when electricity cost is more than 0.2 $/kWh, the PRO membrane cost is same as RO membrane cost, the power density is more than $8W/m^2$ and PRO recovery is same as 1/(1-RO recovery).

• Journal of Korean Society of Water and Wastewater
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• v.30 no.3
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• pp.271-278
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• 2016

Recently, reverse osmosis (RO) is the most common process for seawater desalination. A common problem in both RO and thermal processes is the high energy requirements for seawater desalination. The one energy saving method when utilizing the osmotic power is utilizing pressure retarded osmosis (PRO) process. The PRO process can be used to operate hydro turbines for electrical power production or can be used directly to supplement the energy required for RO desalination system. This study was carried out to evaluate the performance of both single-stage PRO process and two-stage PRO process using RO concentrate for a draw solution and RO permeate for a feed solution. The major results, were found that increase of the draw and feed solution flowrate lead to increase of the production of power density and water permeate. Also, comparison between CDCF and CDDF configuration showed that the CDDF was better than CDCF for stable operation of PRO process. In addition, power density of two-stage PRO was lower than the one of single-stage. However, net power of two-stage PRO was higher than the one of single-stage PRO.

• Membrane Journal
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• v.31 no.4
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• pp.253-261
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• 2021

Solutions to water pollution, global warming, and climate change have been currently discussed. Pressure retarded osmosis (PRO) using a difference in salt concentration between two fluids is proposed to meet the demand for clean water and produce eco-friendly energy. Although PRO has been researched continuously, it has not been commercialized yet due to limitations such as lack of technology and the high price of membranes. Meanwhile, the membrane is one of the most significant parts of the PRO engine and salinity gradient power (SGP) technology. Research continues to technologically develop graphene oxide membranes and nanocomposite membranes used in salinity gradient power generation. Studies on efficient membranes, solvents, and solutes are active to enable high energy efficiency of the osmotic heat engine even at low temperatures of waste. Studies have been conducted on reducing internal concentration polarization and increasing power density by using membranes with balanced permeability and selectivity. In this review, dealing with these studies, we discuss the types of PRO membranes, theoretical modeling of technologies through efficient membranes, and other technologies to develop the process efficiency.

• Water for future
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• v.51 no.4
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• pp.59-65
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• 2018

• Korean Chemical Engineering Research
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• v.52 no.1
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• pp.68-74
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• 2014

In the spiral wound module of the pressure-retarded osmosis (PRO) system for the salinity gradient power generation, effects of the inlet pressure differences between feed-channel and draw-channel were studied. Fluxes of water and solute through membrane and power were estimated. The water flux through membrane decreased along the x-direction and increased along the y-direction with the increase of inlet pressure differences between two channels. On the other hand, the solute flux through membrane showed the opposite trend. The concentration of flow in the feed-channel increased a lot along the y-direction and that in the draw-channel decreased along the x-direction. In our system, for the inlet pressure differences of 1~11 atm, the flow rate in the feed-channel decreased about 8~13% and that in the draw-channel increased by the same amount. The power density increased and then decreased with the increasing inlet pressure difference.

• Journal of Korean Society of Water and Wastewater
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• v.29 no.1
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• pp.133-138
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• 2015

Pressure retarded osmosis (PRO) process is one of membrane processes for harvesting renewable energy by using salinity difference between feed and draw solutions. Power is generated by permeation flux multiplied by hydraulic pressure in draw side. Membrane fouling phenomena in PRO process is presumed to be less sever, but it is inevitable. Membrane fouling in PRO process decreases water permeation through membrane, resulting in significant power production decline. This study intended to investigate the effect of hydraulic pressure in PRO process on alginate induced organic fouling as high and low hydraulic pressures (6.5 bar and 12 bar) were applied for 24 h under the same initial water flux. In addition, organic fouling in draw side from the presence of foulant (sodium alginate) in draw solution was examined. As major results, hydraulic pressure was found to be not a significant factor affecting in PRO organic fouling as long as the same initial water flux is maintained, inidicating that operating PRO process with high hydraulic pressure for efficient energy harvesting will not cause severe organic fouling. In addition, flux decline was negligible from the presence of organic foulant in draw side.