Predicting Pesticide Removal
There is a wide range of pesticides of increasing concern to water supply, in relation to meeting the regulatory standard of 0.1 µg/l for individual pesticides and 0.5 µg/l for total pesticides.
Granular activated carbon (GAC), sometimes in conjunction with ozonation, is the most effective means of removing most pesticides. The key factors which determine the effectiveness of this treatment process are competitive adsorption from background natural organic matter, GAC type, adsorber design (empty bed contact time) and the GAC regeneration regime.
The increasing costs of virgin GAC and regeneration of GAC, and the wider range of GAC types available have made it even more important to procure the most appropriate GAC for the application. Furthermore, optimised regeneration has become a key factor for cost savings on already tight operational budgets.
Selection of the most effective GAC for a specific situation can require costly long term trials at full scale or pilot scale. WRc has developed a range of services based on our expertise in water treatment, including laboratory tests and associated treatment simulation software for ozonation and GAC, generating design data in weeks rather than months, at relatively low cost. WRc provides:
- Impartial information on the most effective GAC and operating conditions for the pesticides of concern.
- Residual capacity of part-used GAC for single or multiple pesticide scenarios at realistic influent concentrations.
- Estimates of operating costs for alternative process designs.
- Benefits of ozonation prior to GAC, in terms of increased bed life and overall operating costs.
Because the tests are carried out with water from the works of interest, with spiking of pesticide if needed, the results can be used in a site-specific way with a greater degree of confidence. The treatment simulation modelling also allows alternative designs to be compared, for example in relation to number of adsorbers and empty bed contact times, as well as type of GAC.
Work has been carried out for both individual and consortia of water utilities (e.g. Anglian Water, Thames Water) to evaluate removal of pesticides of long-standing concern, such as isoprotron, and “emerging” pesticides of more recent concern, such as metaldehyde and clopyralid.