INTRODUCTION

Ion exchange processes are widely used in water and wastewater treatment to remove objectionable ionic contaminants. The nature of ion exchange, as used by industry, has changed dramatically over the last 80 years. The first ion exchange processes used inorganic zeolites mined from natural deposits as a cation exchanger for water softening. Modern synthetic polymer-based exchange media are today used as cation and anion exchangers. They have largely displaced the natural zeolites, primarily due to higher capacities, except in specialized applications. By the mid-1990s, in response to more stringent discharge limits and pending implementation of tighter potable water guidelines, there was increased development activity of ion exchanges with high selectivities for specific substances. Some of these are organic-based and others are inorganic-based.

Ion exchange processes primarily treat waters with low mineral content, to reduce undesirable ionic contaminants. By far, the largest single application of ion exchange is in softening. Softening is the process of removing calcium and magnesium ions from water. Ion exchange is widely used in the power and utility industries to produce softened or demineralized water and in-home water softeners. The use of ion exchange in these applications has been widely practiced for several decades and is well defined.

Since September 11, 2001, a greater awareness of possible terrorist threats to potable water systems has created new challenges for water treatment operators. So-called dirty bombs, made from conventional explosives and packed with radioactive substances, are of concern because they...