Tidally influenced surface water sources that are being treated or being considered for treatment include the Taunton River in the Massachusetts, the Hudson River in New York, the Chesapeake Bay, Tampa Bay, and the San Francisco Bay. These raw water sources can experience changes in salinity as great as 10,000 mg/l and changes in temperature of over 25 deg C. This wide range of design conditions can create significant challenges for the design of a reverse osmosis system. This paper investigates the design considerations for a reverse system treating tidally influenced surface water that experiences a similar wide range in quality. In this specific example the design must consider tidal fluctuations in salinity of over 7500 mg/l and a temperature range of over 26 deg C in the Hudson River. Because the higher salinity range of operation for this project approaches the crossover range between typical brackish RO and seawater RO operation, an evaluation was performed to determine the relative advantages and disadvantages of an all brackish RO membrane array versus a hybrid brackish/seawater design. Membrane performance projections were generated for both an all brackish RO design and a hybrid design to determine which membrane configuration offered the greatest benefits for this project. Energy recovery devices were also evaluated for this application. Designing a membrane plant for a surface water with a wide range of feed quality and physical parameters presents a challenge to the process designer. The membrane array cannot be designed without consideration of the pumping requirements to make the process sustainable over the range of feed conditions. Particular attention should be paid to the hydraulics of the membrane array and maintaining the cross-flow velocities in the tail-end elements to reduce the fouling potential. Using the appropriate energy recovery devices should be part of the design practice in order to reduce the power required and reduce or eliminate the need for permeate backpressure to keep the hydraulic profile through the membrane array within the design limits of the membrane manufacturer.
This presentation is available to AMTA Members only.
- Kurt Kiefer, P.E., BCEE
- CDM Smith Inc.
- AMTA Annual Meeting, San Diego, CA
- San Diego Biennial
- Tidal influence, reverse osmosis,