Minicolumn Test of Remaining GAC Performance for Taste and Odor Removal: Theoretical Analysis

Micropollutant Mass Transfer Zones in Granular Activated Carbon Contactors

“…There are therefore more pore blockages in the bottom GAC, resulting in a lower MIB and geosmin adsorption rate (i.e., adsorption kinetics). Thus, although the bottom GAC is less affected by small size NOM and shows a greater MIB/gesomin equilibrium adsorption capacity (as shown in Figure ), a lower MIB/geosmin adsorption rate in the bottom GAC would lead to a lower overall MIB/geosmin removal because the adsorption efficiency of the two compounds has been found to be mainly controlled by adsorption kinetics. , This may explain the lower adsorption kinetic parameter values observed in the bottom GAC (Figure S7). Later, due to the low adsorption energy required, more small size NOM could deposit on the previously adsorbed small size NOM on the top GAC to increase the NOM fouling layer thickness and subsequently decrease the MIB/geosmin film diffusion rate (i.e., adsorption kinetics).…”

“…The glass minicolumn for this study (Figure S2) had an internal diameter of 2.5 cm and a length of 30 cm, which contained 10 cm of GAC positioned between two 10 cm layers of glass beads (1 mm in diameter) to ensure plug flow hydraulics. More detailed descriptions of the minicolumn design and test protocol are given in ref and were recently validated. , The target compounds were purchased in a dry powder form from Sigma-Aldrich Inc. (Oakville, ON) and dissolved in Milli-Q water to prepare concentrated spiking solutions. The feedwater was prepared by injecting the spiking solutions into filter influent water collected at each drinking water treatment plant, with the spiked water pumped through the minicolumns at the same empty bed contact time (EBCT) as that of the full-scale GAC beds, with several exceptions (noted below) in which a 1 min EBCT was used.…”

“…Details about the minicolumn test approach, including the test protocol, theoretical justification, and experimental validation, have been fully described in several recent publications. 2,3 For this study, the GAC age ranged from 1 to 17 years of service time. Six different micropollutants [2-methylisoborneol (MIB), sucralose, carbamazepine, geosmin, caffeine, and acetaminophen] were selected, representing a range of predicted adsorbabilities.…”

“…When drinking water treatment plants use granular activated carbon (GAC) to remove micropollutants, the GAC gradually becomes saturated due to the loading of both micropollutants and natural organic matter (NOM), eventually requiring replacement. A minicolumn test method for monitoring the saturation of GAC beds was developed. − This test is needed when contamination is intermittent, such as removing taste and odor compounds from seasonal algal blooms, preventing full-scale GAC performance from being directly monitored when the contaminants are not present. The method is conducted by harvesting the whole depth of a GAC core sample from the full-scale contactor and sieving it to select the median grain size, which is then challenged with the contaminant of interest.…”

“…Therefore, the primary objective of this study was to identify the shape of the MTZs in full-scale GAC contactors by harvesting GAC from 10 GAC contactors at four drinking water treatment plants and to record the GAC performance at three different depths (top, middle, and bottom) in each filter using minicolumn tests. Details about the minicolumn test approach, including the test protocol, theoretical justification, and experimental validation, have been fully described in several recent publications. , For this study, the GAC age ranged from 1 to 17 years of service time. Six different micropollutants [2-methylisoborneol (MIB), sucralose, carbamazepine, geosmin, caffeine, and acetaminophen] were selected, representing a range of predicted adsorbabilities.…”