Evaluation of GAC for Removal of Precursors to Chlorine Disinfection By-Products

A series of Rapid, Small-Scale Column Tests, or RSSCTs, was conducted to investigate the removal of NOM (Natural Organic Matter) from a drinking water supply for Fayetteville, North Carolina, and the subsequent formation of disinfection by-products. Disinfection by-products, in particular, trihalomethanes (THMs) and haloacetic acids (HAAs), are of concern due to the Stage 1 of the USEPA D/DBP (Disinfection/Disinfection By-Product Rule) rule which reduced the maximum contaminant level (MCL) for THMs from 100 μg/L to 80 μg/L and set the MCL for HAAs at 60 μg/L. For the sample water tested, it was found that THMs were produced in higher concentrations than HAAs. For the feed water used, the HAA5 concentration never reached the current MCL of 60 μg/L. For the RSSCTs conducted, 70% breakthrough times for TOC (Total Organic Carbon) ranged from approximately 70 days to 150 days for a 10 minute EBCT and 125 days to 200 days for a 20 minute EBCT. In addition to the RSSCT, adsorption isotherms were conducted for each seasonal sample of water. The adsorption isotherm was used to assess the variability of NOM adsorption between seasons. Also, the isotherm results were used in the logistic function model to describe the breakthrough curves of NOM from the RSSCT. These isotherm data were used estimate service times for a GAC (Granular Activated Carbon) bed to reach the regulatory limit for TTHM. Using this method, service times until TTHM breakthrough ranged from 73 days to 117 days for a 10 minute EBCT and 151 days to 159 days for a 20 minute column.Master of Science in Environmental Engineerin