Evaluation of detergent removal in artificial wetlands (biofilters)

A prototype artificial wetland was designed to treat greywaters from the community of El Carrizo in Durango, Mexico, to remove the surfactants derived from used detergents. For this study, 6″ PVC tubes with a water depth of 40 cm were used, in which the water was replaced after 3, 8 and 15 days. Tezontle, gravel and agave fibre were used as supports, and Schoenoplectus americanus, which is an emergent aquatic plant, was used as biological material. The different levels of the factors resulted in 24 treatments, whose differences were validated with a factorial ANOVA of 4 × 2 × 3 with three repetitions. At the beginning and end of each period, it was determined the removal of detergents, oils and grease, total solids, total volatile solids, total suspended solids, changes in pH and electrical conductivity and toxicity of the effluent through bioassays with lettuce seeds. The results show that the best percentage removal of detergents (surfactants linear alkylbenzene sulfonates, LAS) of 90% was obtained with the agave fibre, with or without S. americanus, at a hydraulic residence time of 15 days; however, the treated water showed low seed germination indexes. This was followed by the gravel-S. americanus system, which had a removal percentage of 78% and showed decreases in all of the measured parameters and the lowest toxicity value on germination and root growth of Lactuca sativa. These characteristics define the optimal parameters for the implementation of artificial wetlands in the community of El Carrizo, Durango, Dgo., Mexico.