CASE STUDY: FROSTBURG, MD – A STUDY OF GRANULAR ACTIVATED CARBON VS. ANTHRACITE FOR REMOVAL OF DBP'S, THM'S AND HAA5'S.

Granular Activated Carbon (GAC) and anthracite filter media are commonly used to meet today's water quality standards. GAC has been traditionally associated with replacing anthracite for problems such as Taste and Odor, Organics and Color removal. However, new regulations will require many plants to review their filter media make up and consider how to meet the demands for removal of DBP's, THM's and HAA5.This case study specifically focuses on the city of Frostburg, Maryland as an example of replacing anthracite with GAC to handle DBP issues. The current water treatment plant at Frostburg began treating water in 1997, and treats a flow rate of 3 MGD to serve the city and surrounding communities. The original plant design utilized anthracite for physical filtration of their drinking water supply. However, with impending EPA regulations limiting the allowable discharge of disinfection byproducts such as total trihalomethanes (TTHM's — limit of 80 ppb) and the group of five haloacetic acids (HAA5's — limit of 60 ppb), the city began evaluating changes to its treatment process.One option considered was to replace the existing anthracite filter media with GAC. To evaluate this option, a pilot study was conducted in the summer of 2003 to compare GAC made via two different manufacturing processes (reagglomeration and direct activation) and anthracite filter media for removal of DBP, THM, TOC and HAA5 as well as finished water quality (taste and odor and color).The results of the pilot study were as follows:Both activated carbon products far outperformed the anthracite for all of the water quality parameters tested.The reagglomerated and direct activated carbons both exhibited similar breakthrough characteristics for TOC and UV254, with the reagglomerated GAC removing approximately 10% more total TOC and UV254 Absorbance over the life of the study.Both products effectively reduced the HAA5 levels to below 5 ppb throughout the trial.The most dramatic difference in performance was with TTHM removal; the reagglomerated product treated double the water volume before reaching saturation for TTHM's, and the direct activated GAC exhibited what is known as “rollover” - the desorption of TTHM (probably due to adsorption of other, more highly adsorbable species) that approached the TTHM limit of 80 ppb.Based on the results of this trial, Frostburg decided to replace their anthracite with GAC, with their product choice being domestically produced reagglomerated GAC. Full-scale replacement of the anthracite with GAC occurred in 2005.