The removal of chlorophenoxy herbicides from drinking water by activated carbon adsorption and liquid core microcapsule perstraction
Engels, Nora (2012) The removal of chlorophenoxy herbicides from drinking water by activated carbon adsorption and liquid core microcapsule perstraction. Master of Science thesis, Dublin City University.
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Drinking water quality reports have highlighted a persistent trend in pesticide detection in the Republic of Ireland. One of the main concerns of the drinking water industry is that consistent pesticide removal rates do not occur despite the existence of activated carbon (AC) treatment regimes in most plants. The present work examines the removal of three chlorophenoxy herbicides (MCPA, 2,4-D and dichlorprop) from aqueous solutions by AC adsorption and a novel liquid-core microcapsule perstraction system. Herbicide adsorption to three ACs used in the drinking water industry was dependant on the pH of the water.
As pH increased, adsorption decreased. Herbicide adsorption to AC was further decreased when humic acid (HA) was added to the contacting system. HA uptake by AC was minimal,
possibly due to the large molecular weight associated with HA. Herbicide adsorption to AC was hindered by the presence of HA in the sample solutions and by HA pre-saturated
to the AC. The possible interaction between herbicides and HA was investigated by UV Visible and fluorescence spectroscopy to evaluate any potential interactions occurring during site competition. Weak spectral changes were observed and the florescence intensity was quenched by HA addition, suggesting that some form of interaction occurs. Capsular perstraction of MCPA, 2,4-D and dichlorprop by dibutyl sebacate liquid-core microcapsules
(LCMs) was demonstrated. The use of LCMs results in between 9 and 18 % of the herbicides being extracted within 60 minutes of capsule addition. The quantity of LCMs added
was equal to 1 g of oil core and could be increased to achieve higher levels of extraction. The results were compared to adsorption by 1 g of activated carbon (AquaSorb 2000) over the same time period of 100 minutes. Although the remediation of herbicides was more effective, AC equilibrium had not been reached after 100 minutes. The results demonstrate the time efficiency incurred by using LCMs compared to AC.
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