Optimal conditions for chlorpyrifos and dissolved organic carbon removal in subsurface flow constructed wetlands

摘要

This work used subsurface flow constructed wetlands, planted with Phragmites australis, using 2 water depths and 2 sizes of granular material, in order to find the optimal conditions for the removal of chlorpyrifos and dissolved organic carbon (DOC) from synthetic wastewater. In addition, some bacterial groups were identified which formed the biofilm present in subsurface flow constructed wetlands used in the removal of chlorpyrifos. In samples taken from influents and effluents of the wetlands, chlorpyrifos was quantified by gas chromatography (GC μ-ECD), DOC by an organic carbon analyser and bacterial groups using conventional microbiology, according to Standard Methods. The highest values of chlorpyrifos (97.9%) and DOC (80.1%) removal were found with granular material having diameters within 3.18-6.35 mm and according to water column depth (0.4m) were 97.8% and 79.7%, respectively. The bacterial groups quantified in the biofilm were total heterotrophic, revivable heterotrophic, total coliforms, facultative sporulated, Pseudomonads, denitrifying bacteria and sulphate-reducing bacteria. Some bacteria showed little development, probably due to the pesticide and/or the anaerobic conditions of the systems (negative redox potential and dissolved oxygen (DO) concentrations approaching zero). It was proven that subsurface flow constructed wetlands, in adequate conditions, are able to eliminate organic matter and chlorpyrifos.