Control of calcium buildup in GAC: Effect of iron coagulation Original Research Article

In response to proposed EPA regulations governing disinfection by-products the water treatment industry may need to remove natural organic matter (NOM) more extensively prior to chlorination. Unit processes such as granular activated carbon (GAC) adsorption and enhanced coagulation can be used to achieve conformance with these proposed regulations; and the water treatment industry actively seeks means to reduce the cost of these unit processes. One of the cost-saving steps in GAC use pertains to its reactivation; however the buildup of calcium within GAC pores can deleteriously alter the micropores of the GAC during thermal reactivation and affect its performance. Thus, it is proposed that by reducing the buildup of calcium within GAC during water treatment service, a utility could improve its reactivation effectiveness. The purpose of this paper is to explore how iron coagulation and competitive complexation with NOM can limit calcium accumulation within GAC, and therefore contribute to favorable reactivation.