Eco Rehabilitation at Real Scale of a Water Stream with Acid Mine Drainage Traits

The Água Forte (AF) stream located in the Southern Alentejo region (Portugal), is a tributary of the Roxo river. The AF stream has acid mining drainage (AMD) traits, which contributes to the degradation of the river’s water quality and the adjacent soils. The use of ecological floating beds (EFBs) is an eco-rehabilitation strategy for polluted waters. This work aimed to evaluate the application of EFBs at real-scale as a water treatment system for the AF stream. Thus, three EFB, planted with Vetiveria zizanioides (3.3 m2·unit−1; density 40.5 plants·m−2), were placed on the stream. The water quality was monitored monthly, upstream (Inlet) and downstream (Outlet) of EFBs, from May 2020 to November 2021. With the use of the EFBs, the pH remained acidic, and the other main parameters showed average removal rates of around: 8% organic matter; 7% sulphates; 4% chlorides; 18% nitrogen, 30% copper, 29% zinc, 53% iron, and 10% manganese. Inlet and Outlet mass loads correlations showed high removal diversity. For the parameters under analysis, during the treatment period, the removal efficiency showed high variability due to the hydraulic conditions. The higher removal efficiencies were obtained for low-hydraulic retention times, except for heavy metals. Overall, EFBs showed some potential, but their efficiency was variable, highlighting the need for optimization under variable hydraulic conditions.