2.2. Phytoremediation of Tannery Effluent in Floating Wetlands with E. crassipes and S. auriculata

A primary effluent treated by coagulation–flocculation from a leather tanning company in the city of Asunción was used. Previous analyses of the effluent yielded values < 1 mg Cr(III)/L; therefore, the effluent was contaminated with 12.34 mg Cr(III)/L for the tests. The assays were conducted in triplicate with 40 L of the effluent in systems of 0.63 m length, 0.44 m width, and 0.15 m depth of liquid. The reactors were operated discontinuously for 72 h without aeration and with manual agitation every 6 h. The treatments were performed in triplicate for each plant, with a control without macrophytes. Samples of the effluent were taken from each replicate at the beginning and the end of the exposure period. The collected and filtered samples were kept in 10 mL falcon tubes and refrigerated until analysis. The samples obtained at the end of the study were used to determine chromium, in addition to the main physicochemical parameters, and the toxicity levels measured with D. magna and D. rerio.