Bacteriology of granular activated carbon

Abstract

The goal of drinking water treatment has always been to provide microbiology safe water to the consumer. To accomplish this, especially when surface water is being treated, gravity filters containing sand and/or anthracite are typically used to remove particular matter. When filtration is followed by disinfection, pathogens should be removed and the microbial load of the water reduced to an acceptable level. As water quality regulations have become more restrictive, granular activated carbon (GAC) has been used to a greater extent as a filter medium because of its ability to adsorb regulated synthetic organic carbon compounds, materials that contribute to taste and odor in finished water, and organic matter that leads to the formation of disinfection by-products. GAC is known to become colonized with bacteria, and this trend has been exploited in treatment by using the organisms on biologically active carbon (BAC) to metabolize a fraction of the organic compound found in the water. However, there has been concern that indicator organisms and bacteria of public health interests may colonize and proliferate on GAC and BAC filters. For these bacteria to be found in finished water they must successfully colonize and compete with the indigenous organisms, be released from the filter and penetrate the disinfection barrier. This review describes these issues and the beneficial aspects of BAC filtration in water treatment.