TrojanUVTorrentECT reactors; H2 O2 dosing system
The UK and the European Union have strict regulations controlling levels of pesticides in drinking water. Drinking water treatment facilities are required to produce potable tap water with less than 0.1 μg/L of any pesticide. In the UK, metaldehyde, a “molluscicide” used to control the spread of slugs and snails, has received particular attention given its widespread use.
The traditional barrier used in the UK for the removal of micropollutants such as pesticides is granular or powdered activated carbon, sometimes in combination with ozone or UV. Early pilot testing demonstrated that the physical and chemical properties of metaldehyde made adsorption onto carbon limited when compared to the other commonly-found pesticides. As a result, longer contact times would be required as well as more frequent replacement of spent carbon. Collectively, this would result in higher capital and operating expenses and made carbon on its own a non-viable option for metaldehyde treatment.
Another observation was that metaldehyde would desorb (release) from GAC back into the water supply during times when concentrations of metaldehyde dropped.
As an alternative to ozone, Anglian decided to install a TrojanUVTorrent™ECT UV-oxidation system as part of a multi-barrier approach to ensure it produced a potable water supply that matched the high standards required by the regulators and customers. UV-oxidation uses the combined application of UV light and hydrogen peroxide (H2O2) to destroy chemical contaminants through a combination of UV-based photolysis and chemical oxidation.
TrojanUV along with Anglian and its various partners, worked closely for nearly 10 years to develop suitable treatment for a range of micropollutants including pesticides. This extensive research and co-operation gave confidence that the final solution of using UV technology and H2 O2 was the most cost-effective approach to providing the advanced oxidation required to significantly reduce metaldehyde and other known contaminants in the River Trent.
In addition to using UV-oxidation for pesticide treatment, the TrojanUVTorrentECT will also enhance the simultaneous disinfection of micro-organisms as part of a multi-barrier approach to disinfection.
The system at Hall WTW was originally designed to consist of three TrojanUVTorrentECT reactors and an H2 O2 dosing system. However, the decision was made to install a fourth reactor in response to rising metaldehyde concentrations in the River Trent. Each UV reactor installed at Hall WTW will contain 96 lamps using TrojanUV Solo Lamp™ Technology. The Solo Lamp is a revolutionary low-pressure high-output (LPHO) lamp designed for high UV output while maintaining the high electrical efficiency commonly associated with LPHO lamps. The result is a smaller and more energy-efficient UV system using far fewer lamps than an equivalent UV installation designed using standard LPHO technology.
The system complements the UV-oxidation system located at the Drift WTW located in Cornwall, South-West England currently treating various pesticides, including metaldehyde.