Comparison of the removal of chlorpyrifos and dissolved organic carbon in horizontal sub-surface and surface flow wetlands.

Chlorpyrifos is an organophosphorus pesticide widely used in Colombia for agricultural and domestic pest control. It is also commonly found in water sources in rural areas. Constructed wetlands are being used as viable alternatives for the treatment of domestic wastewater with large organic loads. For this research, three pilot-scale subsurface horizontal flow constructed wetlands and three horizontal surface flow wetlands were used for the treatment of synthetic wastewater with different concentrations of chlorpyrifos (0.0 μg L(-1), 478 μg L(-1), 589 μg L(-1) and 788 μg L(-1)), 100 mg L(-1) of dissolved organic carbon and nutrients. The wetlands were constructed in equal dimensions and in the same size range as the gravel bed (3.18-6.35 mm) and planted with Phragmites australis. The efficiencies of the removal of the pesticide and dissolved organic carbon were then determined. Additionally, other physicochemical parameters, as well as 3,5,6-trichloro-2-pyridinol, the main breakdown product of chlorpyrifos, were measured. The average removals of this agrochemical and dissolved organic carbon in the subsurface horizontal flow constructed wetlands were 93% and 92%, respectively, and in the horizontal surface flow wetlands, the average removal was 95% for both compounds. The removal is the result of the joint action of microorganisms and the adsorption and absorption of roots and rhizomes of plants found in wetlands. Both types of wetlands are very efficient at treating the domestic wastewater contaminated with pesticides and dissolved organic carbon, although the results were slightly better in the surface flow wetlands.