Pressure Retarded Osmosis (PRO) utilizes osmosis through a semi-permeable membrane to generate osmotic energy. In PRO, water spontaneous flows from a low-salinity feed solution to a high-salinity draw solution against an applied pressure, driven by the osmotic pressure difference between the feed and draw solutions. The permeation water flow is immediately pressurized to the applied pressure on the draw solution side, which can be further utilized for power generation via a turbine or an energy recovery device. The research groups in Singapore are the only ones utilizing two waste streams (i.e. seawater RO brine and NEWater RO reject) for the harnessing of osmotic energy. This extracts additional value (i.e. energy recovery) from the two waste streams before they are discharged into the ocean. The power density of the PRO membrane is 6-fold higher than the commercial requirement of 5 W/m2 in the lab condition, and 2-fold higher when tested with the waste streams. The PRO membrane has demonstrated stable power generation under extensive pilot tests. More importantly, PRO dilutes the seawater RO brine with the NEWater RO reject and therefore mitigate the problems associated with discharge of concentrated seawater RO brine.
This invention offers a series of novel thin film composite (TFC) membranes with high water permeabilities, high salt rejections, strong mechanical strengths and small structural parameters for osmotic power generation by pressure retarded osmosis. The membranes have been scaled up to 4-inch modules and pilot-tested. In addition, the invention offers how to design an effective and efficient process to harvest the osmotic energy from seawater reverse osmosis brine to supplement the energy consumption of seawater desalination.
1. Pressure retarded osmosis (PRO) can be used for direct power generation, utilizing seawater or its brine as the draw solution and freshwater or wastewater or its concentration as the feed solution.
2. PRO can be easily integrated with existing seawater reverse osmosis systems to use osmotic energy to supplement the energy consumption of seawater desalination.
3. Surplus of power supply from the national grid can be stored as osmotic energy in the form of seawater brine and freshwater, and later regenerated through PRO.
The customer can directly apply pressure retarded osmosis (PRO) for osmotic power generation. This invention offers PRO hollow fiber membranes with the world highest mechanical strength and power density. The new membrane is easy to fabricate and scale. Furthermore, PRO can be readily integrated with seawater reverse osmosis to (1) dilute and potentially recycle the seawater brine, (2) generate a higher power density, (3) reduce the energy cost of seawater desalination and (4) mitigate the problems associated with seawater brine discharge.