Desalination, 2nd Edition

Chapter 3Basic Terms and Definitions

Mark Wilf

European Desalination Society at the Genoa University, Italy and San Diego, CA, USA

Abstract

This chapter defines basic terms used in conjunction with RO systems. Also see Chapter 9 for additional information as to how these parameters affect the performance of an RO system.

3.1 Reverse Osmosis System Flow Rating

An RO system is rated based on product flow rate. An 800-gpm RO would yield 800 gpm of permeate. The influent and reject flows are typically not indicated except in the design details (they are usually calculated knowing the product flow rate and the percent recovery).

In some cases, the actual design permeate flow rate of the RO system may differ from the “name plate” flow rating. In most of these situations, the RO system is de-rated by design due to a poor feed water source or as a natural result of low feed water temperature.

3.2 Recovery

Recovery (sometime referred to as “conversion”) is a term used to describe what volume percentage of influent water is “recovered” as permeate. Generally, RO system recoveries range from about 50% to 85%, with the majority of systems designed for 75% recovery. (Individual spiral wound membrane module recoveries vary from about 10% to 15%—see Chapter 4.3). A system recovery of 75% means that for every 100 gpm influent, 75 gpm will become permeate and 25 gpm will be retained as concentrate.

Recovery is calculated using the following equation:

(3.1)

At 75% recovery, the concentrate ...