Blue Energy, a potential source of renewable and sustainable energy, is the energy released from the salination of water when freshwater mixes with saltwater. One process for capturing this energy is pressure-retarded osmosis (PRO). In PRO, a semi-permeable membrane separates a pressurized high-salinity solution from a low-salinity solution. Because the osmotic pressure across the membrane exceeds the hydraulic pressure of the high-salinity solution, water from the low-salinity solution permeates across the membrane through osmosis and dilutes the high-salinity solution. In this way, the chemical potential (osmotic pressure) is transformed into hydraulic potential and power is obtained by depressurizing the excess water through a hydroturbine.
One category of PRO systems is referred to as open-loop. Open-loop PRO systems take advantage of naturally occurring salinity gradients in “river-to-sea PRO” scenarios. In these systems, the solar energy that evaporates water from the sea is recovered by a PRO system in the estuary where the river water mixes with the seawater. Open-loop systems can also be used with engineered salinity gradients (e.g. in the disposal/dilution of the concentrate stream at reverse osmosis (RO) desalination facilities) in a “RO-PRO” scenario.
I have investigated PRO experimentally and theoretically in both river-to-sea and engineered configurations. Currently, I am exploring the potential of Humboldt Bay as a site for PRO through experimental investigations in my research lab in the Environmental Resources Engineering (ERE) department at HSU. I am also involving ERE seniors in the design of a PRO facility for the Humboldt Bay in their Capstone Design course this semester.
Results from the Capstone Design course will give insight into whether the available fresh water at Humboldt Bay will make it possible to locally house the first prototype river-to-sea PRO facility in the U.S. and to shorten time-to-market of PRO technology by attracting institutional and industry funds. Because of the exciting potential of PRO technology to provide large amounts of renewable energy, pressure retarded osmosis is an area of active and promising research. Stay tuned for future reports on this effort.
Read the Pro Power Brochure for additional information.