Graduation Date

Fall 2022

Document Type



Master of Science degree with a major in Environmental Systems, option Environmental Resources Engineering

Committee Chair Name

Dr. Margaret Lang

Committee Chair Affiliation

HSU Faculty or Staff

Second Committee Member Name

Dr. Andrea Achilli

Second Committee Member Affiliation

Community Member or Outside Professional

Third Committee Member Name

Dr. Tesfayohanes Yacob

Third Committee Member Affiliation

HSU Faculty or Staff

Subject Categories

Environmental Resources Engineering


Pressure retarded osmosis (PRO) is an emerging osmotic power technology that could mitigate the major challenges faced by seawater reverse osmosis desalination (RO): brine disposal and high energy consumption. The primary focus of this paper is process optimization for a linked seawater reverse osmosis (RO) and pressure retarded osmosis (PRO) water purification system. PRO generates power by using osmosis to “pump” water through a membrane from low pressure and low concentration to high pressure and high concentration (RO brine). This commercial-scale pilot effort explores process optimization for pressure retarded osmosis as an industrial process rather than theoretical or experimental process. To achieve this purpose, a linked seawater desalination and pressure-retarded osmosis system was built on Humboldt Bay, CA, with assistance from Cal Poly Humboldt, CA DWR, and the Humboldt Bay Harbor Commission.

This study explored the lowest net specific energy consumption (SECnet) for producing freshwater from seawater in the first U.S. RO-PRO pilot-scale facility employing commercially-available components. The lowest SECnet was found by adjusting and testing six operating variables: RO yield rate, PRO operating pressure, PRO dilution rate, PRO feed solution flow rate, and PRO draw solution flow rate. Each variable was tested independently to narrow the range of optimal values. Findings conclude that energy losses in the RO-PRO system approximately equal the amount of potential energy that can be gained using PRO membranes available in 2017. Increasing membrane performance and optimizing module membrane spacers for PRO could significantly increase potential energy recovered by PRO in an RO-PRO system.


Data and construction details available upon request.

Citation Style



Thesis/Project Location