Overview

It's tough to make predictions, especially about the future .

Yogi Berra

Ultrafiltration (UF) and microfiltration (MF) membrane processes were traditionally used as stand-alone separation processes with nominal pre-treatment, for example ultrafiltration (UF) processing of industrial wastewater or dairy products. In the case of desalination and water purification by reverse osmosis (RO), however, it was always a hybrid process integrated with other unit operations as discussed in Chapter 2. The term hybrid or integrated membrane processes refers to the integration of one or more membrane processes with or without conventional unit operations to increase performance depending on the type of feed and product quality required. ^[1]- ^[3] The main goal of these systems is to increase purity, for example in the case of water and gas purification, and productivity and yield of the product, for example in the case of fermentation processing. Similarly, pervapora-tion (PV)-based hybrid processes can be more economical than traditional separation processes for the removal of volatile organic compounds from industrial, municipal water, or groundwater contaminated with carcinogenic halogenated hydrocarbons instead of catalytic combustion. ^[4], ^[5] Hybrid membrane systems also reduce operating costs and environmental pollution, and make the overall process more efficient. For a perspective on membrane system design and operation, the reader should review Chapter 4 and the relevant portions in Chapter 2.

Hybrid membrane systems for several applications are illustrated in this chapter followed by a discussion of a few case studies specific to water treatment. All examples highlight the...