Exploring the role of granular activated carbon in drinking water production

Abstract: Safe and clean drinking water is recognised as a human right by the United Nations, but water sources world-wide are affected by the widespread use of synthetic chemicals, creating a challenge that drinking water producers must address. Many of these synthetic chemicals, here referred to as organic micropollutants (OMPs), are not well removed by conventional drinking water treatment, and thus additional treatment steps are needed. Granular activated carbon (GAC) is a commonly used sorption material in water treatment processes. This thesis explores different roles of GAC filters in drinking water production: as a chemical barrier, as a biofilter, as a post-treatment step after ozonation and as a waste management step after nanofiltration. In two pilot-scale experimental set-ups, different kinds of raw and process water were treated in processes involving GAC filtration. Removal rates of a broad range of OMPs (including per- and polyfluoroalkyl substances; PFAS) were studied, along with microbial abundance and several parameters characterising natural organic matter (NOM) content. The results showed that GAC filters were more efficient with pre-ozonation, but the efficiency of OMP removal decreased over time. Inclusion of ozone treatment also introduced new challenges, as it was shown to increase bioavailability of NOM, which GAC filters were not fully able to remove. However, the GAC filters inevitably transitioned into biofilters over time, and these biofilters were able to remove more NOM when pre-ozonated. The in-depth information provided by this thesis on GAC filter performance over time under different conditions provides new insights into water treatment options to protect human health.

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