Ferric chloride extends GAC bed life and prevents calcium buildup. Granular activated carbon (GAC) treatment is one method that water utilities can use to increase removal of natural organic matter and comply with the recently promulgated Disinfectants/ Disinfection By‐products Rule. The cost of GAC depends on its useful service life and its capacity for reuse. The research reported here used minicolumns to investigate how ferric chloride coagulation influenced the total organic carbon (TOC) subsequently removed by GAC. Ferric chloride pretreatment lengthened GAC bed life by lowering influent TOC and by rendering the TOC that remained more adsorbable. Jar tests showed that at pH < 6.0, ferric chloride was superior to aluminum salts, on an equimolar basis, for removing TOC.
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Nowack et al. (1999) studied this question.