Empty bed contact time: The key for micropollutant removal in activated carbon filters

The removal of micropollutants from wastewater is an emerging issue that currently concerns the wastewater sector the most. Granular Activated Carbon (GAC) has gained recognition as a suitable technology for dealing with this problem. This study assesses the performance of six GAC-filters for the removal of micropollutants installed as final treatment step at a municipal wastewater treatment plant. The influence of the GAC-type and the Empty Bed Contact Time (EBCT) on the filter performance was evaluated. The breakthrough behaviour of 13 selected micropollutants as well as the removal of the Dissolved Organic Carbon (DOC) and UV absorption at 254 nm were investigated. Besides, the adsorbed DOC (q_DOC) was introduced as assessment parameter (adsorbed and biodegraded DOC), instead of the commonly used treated bed volume. Finally, Size Exclusion Chromatography (SEC) with online DOC and UV_254nm detection was applied for a better understanding of the influent and effluent characteristics. The results showed that the pore size distribution is a crucial feature of the activated carbon. A balanced proportion of macro-, meso‑ and micropores may play a role in the better removal of micropollutants in presence of DOC. Regardless of the GAC-type, a minimum EBCT between 20 - 30 min was necessary. We proved that a short EBCT would not fully use the sorption capacity, whereas a long EBCT would increase the carbon demand without improving of the removal. Lastly, according to the SEC results, after a short operation time no difference between the influent and effluent chromatographable fractions (DOC and UV_254nm) was observed.