Experimental validation of a test to estimate the remaining adsorption capacity of granular activated carbon for taste and odour compounds

Abstract

In drinking water treatment, there is a need to be able to measure the present-day adsorptive capacity of an existing bed of granular activated carbon (GAC) for compounds that occur only periodically, such as some taste and odour compounds, to ensure that the bed would be effective if those compounds were to appear. This work expanded a previously proposed laboratory-scale “minicolumn” test by pilot-scale validation, using grab samples from GAC contactors comprising 16 GACs from 4 different drinking water treatment plants. The minicolumns showed close agreement in terms of geosmin and MIB removal (about 10–20%) compared to the pilot-scale columns. The minicolumn test also closely matched geosmin and MIB removal (to within 10%) across two full-scale GAC beds during a taste and odour event. This study discusses the optimization of the minicolumn test duration, GAC sieving method, particle size, column diameter, and temperature control. Importantly, results from the sites where GAC was harvested suggest that the MIB and geosmin mass transfer zones across the GAC bed are very broad, which is a condition that is necessary for the accuracy of this test, and for which information from the field had not been previously reported.