Removal of alachlor in water by non-thermal plasma: Reactive species and pathways in batch and continuous process

• Published in: Water research (Oxford) 2019-09, Vol.161, p.549-559
• Main Authors: Wardenier, Niels, Gorbanev, Yury, Van Moer, Ineke, Nikiforov, Anton, Van Hulle, Stijn W.H., Surmont, Pieter, Lynen, Frederic, Leys, Christophe, Bogaerts, Annemie, Vanraes, Patrick
• Format: Article
• Language: English
• Subjects: Alachlor; By-products; Non-thermal plasma; Oxidative species; Pesticides
• ISSN: 0043-1354; 1879-2448
• DOI: 10.1016/j.watres.2019.06.022

Pesticides are emerging contaminants frequently detected in the aquatic environment. In this work, a novel approach combining activated carbon adsorption, oxygen plasma treatment and ozonation was studied for the removal of the persistent chlorinated pesticide alachlor. A comparison was made between the removal efficiency and energy consumption for two different reactor operation modes: batch-recirculation and single-pass mode. The kinetics study revealed that the insufficient removal of alachlor by adsorption was significantly improved in terms of degradation efficiency and energy consumption when combined with the plasma treatment. The best efficiency (ca. 80% removal with an energy cost of 19.4 kWh m−³) was found for the single-pass operational mode of the reactor. In the batch-recirculating process, a complete elimination of alachlor by plasma treatment was observed after 30 min of treatment. Analysis of the reactive species induced by plasma in aqueous solutions showed that the decomposition of alachlor mainly occurred through a radical oxidation mechanism, with a minor contribution of long-living oxidants (O3, H2O2). Investigation of the alachlor oxidation pathways revealed six different oxidation mechanisms, including the loss of aromaticity which was never before reported for plasma-assisted degradation of aromatic pesticides. It was revealed that the removal rate and energy cost could be further improved with more than 50% by additional O3 gas bubbling in the solution reservoir. •Decomposition of alachlor was evaluated in a dielectric barrier discharge reactor.•A comparison between batch and single-pass configuration was made.•Several oxidative species (O3, H2O2, 1O2, O) were produced in the treated liquid.•An alachlor decomposition pathway was proposed.