Project: Assessment of metaldehyde removal by GAC using
the RapStech® service
Client: Severn Trent Water Ltd.
When: Feb – Sept’ 08
Metaldehyde is a recently emerging problem and traces of the molluscicide have been detected in raw waters. Metaldehyde
is thought to be less easily adsorbed onto Granular Activated Carbon (GAC) which is used for treatment.
WatStech Ltd has conducted an assessment for metaldehyde removal using Rapid Small
Scale Column Tests (RSSCTs). This research was to give an indication of the approximate adsorption capacity of metaldehyde
onto Virgin GAC the profile of breakthrough, using site water and laboratory water spiked with metaldehyde.
Supplementary research was carried out by WatStech Ltd, which involved the determination
of the adsorption capacity of metaldehyde and mecoprop using single solute batch adsorption isotherms by various types of
media (spent, regenerated & virgin GACs and zeolite, which is a microporous alumino-silicate mineral).
The adsorption capacities were evaluated using the Freundlich model.
Isotherms can be a useful tool in comparing GAC treatment for
adsorption capacity for a particular chemical, but isotherm data is indicative only of the performance under
These GAC analysis techniques have been used to determine the adsorption of metaldehyde onto GAC and assist with
better understanding of the removal of this pesticide from drinking water.