Ecotoxicological evaluation of effluents treated by constructed wetlands

ABSTRACT

The research objective was to evaluate the performance of wetlands constructed with vertical sub-surface flow cultivated with Eleocharis sp. (Junco) and Typha sp. (Taboa). For this, ecotoxicological tests were used with the microcrustacean Daphnia similis, with the dicotyledon Lactuca sativa (alface), the monocotyledon Sorghum vulgare (sorgo) and the aquatic macrophytes Lemna sp. (Duckweed) and Azolla sp. The domestic effluent was toxic to Daphnia similis with a mean EC₅₀ of 1.3%. Macrophyte treatments significantly reduced effluent toxicity with EC₅₀ averages of 73% for junco treatment, EC₅₀ 53.17% for taboa treatment, and EC₅₀ 78.25% for taboa + junco treatment. The control (without macrophytes) also significantly reduced toxicity, with a mean EC₅₀ of 63.13%. In the phytotoxicity tests, lettuce and sorgo were not sensitive to the analyzed effluent, although they were for other types of effluents. The macrophyte Lemna sp. was also not sensitive to the effluent studied. However, it was possible to identify the eutrophic potential of the effluent with this species, since it was better developed in the raw effluent than in treated ones. With the macrophyte Azolla sp., it was possible to verify that the raw effluent has greater eutrophic potential when compared to the treatments with junco, taboa and control, where nitrogen and phosphorus removal was observed. However, toxic effect was observed for Azolla sp. in treated effluents.

Keywords: ecotoxicology; constructed wetlands; domestic wastewater; water macrophytes