In drinking water supplies there are oftentimes different types of contaminants varying from algae to domestic waste. These can cause bad tastes and odors. Two contaminants commonly smelled and tasted are 2-methylisoborneol, MIB, and geosmin. Activated carbon is a cost-effective measure to remove these contaminants and bring the drinking water back up to the highest of quality and standards. Both powdered and granular activated carbon are used to treat the drinking water supplies. We will discuss them both below.
Powdered activated carbon has the advantage that it can be used when and as needed as the taste and odors are typically a seasonal occurrence. This helps in reducing operating and maintenance costs. The disadvantage of using PAC is that it will accumulate at the bottom of the tanks or reservoirs and occasionally leach the contaminants back into the drinking water supply.
Unlike powdered activated carbon feed systems, granular activated carbon filters run around the clock all year long. This will cause a high operating cost. GAC is more effective which combats the higher costs associated with its use. There are also ways in which you can lengthen GAC’s life. For example, with empty bed contact time it is noted, “GAC filters with EBCTs of 6.5 and 13 min effectively reduced MIB and geosmin levels to below their respective [odor threshold concentrations] for about 10 months (of continuous operation). In contrast, a GAC filter with an EBCT of 20 min achieved that same level of performance for nearly 18 months.”1 Extending the life of a bed of carbon and reducing the amount of times a changeout must occur will decrease the cost of a GAC system in the long run.
The Cudahy Water Utility in Wisconsin has GAC filters for MIB and geosmin which they have seasonal outbreaks in the end of summer and fall seasons. They changeout the carbon each year and find this method very successful. Gainesville Georgia have installed a PAC system to treat their contaminants. Plano Texas also uses activated carbon for their taste and odor issues.
1 – Activated Carbon: Solutions for Improving Water Quality by Zaid K. Chowdhury, R. Scott Summers, Garret P. Westerhoff, Brian J. Leto, Kirk O. Nowack and Christopher J. Corwin
2 https://www.tpomag.com/online_exclusives/2015/08/how_to_eliminate_algae_taste_and_odor_ with_activated_carbon by the Treatment Plant Operator