Removal of organic micropollutants in a drinking water treatment plant by powdered activated carbon followed by rapid sand filtration

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Powdered activated carbon (PAC) is a promising technology to reduce organic micropollutants (OMPs) in drinking water treatment plants and combined with biological treatment processes such as rapid sand filters (RSFs), has the potential to remove a broad range of OMPs during water treatment. However, the removal of OMPs by a combination of two treatments (PAC-RSF) is not fully understood. 49 OMPs were spiked in PAC followed by RSF pilot plant treatment and the effluent was measured after 1, 4 and 7 day(s). Also, in a separate experiment 29 OMPs (out of 49) were dosed into the RSF column to assess the removal of OMPs by just RSF. Statistical analyses were performed and the OMPs were classified according to their charge and hydrophobicity. The results showed that OMPs were removed at the highest percentage after the first 24 h of dosing. The highest removal was observed for the neutral and hydrophobic compounds (80.0%–99.5%). The removal of neutral and hydrophilic compounds varied (0.14%–98.5%) depending on the possibility of forming π-π interactions and hydrogen bonds. Electrostatic repulsion between anionic OMPs and negatively charged PAC led to a decrease in the removal of anionic compounds. In contrast, electrostatic attraction led to an increase in the removal of cationic OMPs. Regarding OMPs removal by RSF, some compounds were removed by the sand filter depending partly on their physical-chemical properties and more dominantly on their functional groups. By comparing the OMPs removal by PAC-RSF with RSF, it was possible to determine the contribution of biological processes in the sand filter in the removal of some OMPs.