Abstract
Metaldehyde, an organic pesticide widely used in the UK, has been detected in drinking water in the UK with a low concentration (<1 μg L−1) which is still above the European and UK standard requirements. This paper investigates the efficiency of four materials: powdered activated carbon (PAC) and carbon-doped titanium dioxide nanocatalyst with different concentrations of carbon (C-1.5, C-40, and C-80) for metaldehyde removal from aqueous solutions by adsorption and oxidation via photocatalysis. PAC was found to be the most effective material which showed almost over 90% removal. Adsorption data were well fitted to the Langmuir isotherm model, giving a qm (maximum/saturation adsorption capacity) value of 32.258 mg g−1 and a KL (Langmuir constant) value of 2.013 L mg−1. In terms of kinetic study, adsorption of metaldehyde by PAC fitted well with a pseudo-second-order equation, giving the adsorption rate constant k2 value of 0.023 g mg−1 min−1, implying rapid adsorption. The nanocatalysts were much less effective in oxidising metaldehyde than PAC with the same metaldehyde concentration and 0.2 g L−1 loading concentration of materials under UV light; the maximum removal achieved by carbon-doped titanium dioxide (C-1.5) nanocatalyst was around 15% for a 7.5 ppm metaldehyde solution.Graphical abstractᅟ
Highlights
Metaldehyde, which has been reported by the UK Environment Agency, is an organic compound used as pesticide targeting slugs, snails, and other molluscs and is widely used in agriculture (UK Environment Agency 2009)
This study investigated the effectiveness of using three novel nanocatalysts, i.e., C-doped TiO2 with a carbon content of 1.5, 40, and 80% under UV-C light to remove metaldehyde from aqueous solution
The isotherm shows that as contact time (Ce) increases, the adsorption capacity increases until it reaches maximum capacity which corresponded to the highest removal of metaldehyde at loading concentration of 0.2 g L−1 showed more significant removal of metaldehyde at low concentrations than higher concentrations
Summary
Metaldehyde, which has been reported by the UK Environment Agency, is an organic compound used as pesticide targeting slugs, snails, and other molluscs and is widely used in agriculture (UK Environment Agency 2009). There are growing concerns that relatively high levels of metaldehyde have been detected in surface water. It is reported that trace amounts of metaldehyde have been found in treated drinking water in the UK with concentrations as high as 1 μg L−1 which is above the European and UK standards of 0.1 μg L−1 (Water UK 2013). The common treatment designed to remove pesticides from water by adsorption onto granular activated carbon (GAC) or by other processes involving chlorine or ozone was proven to be ineffective in removing metaldehyde (Water UK 2013). There are a number of studies investigating new methods to remove metaldehyde from water. Using ultraviolet (UV) irradiation to activate a number of different chemicals such
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