Cr(III) and Cr(VI) removal in floating treatment wetlands (FTWs) using Typha domingensis

Floating treatment wetlands with Canna indica for the removal of Cr(III) and Cr(VI) from water: A comprehensive study

The efficiency in Cr (III) and Cr (VI) removal by Floating Treatment Wetlands (FTWs) vegetated with Canna indica, metal accumulation in sediment and plants were determined. Plant tolerance and its morphological response to metal were studied. Treatments were 5 and 10 mg L-1 of Cr(III) (5Cr(III) and 10Cr(III), respectively), and 5 and 10 mg L-1 of Cr(VI) (5Cr(VI) and 10Cr(VI), respectively), with and without FTWs, and a biological control (BC: with FTW without Cr addition). After 35 days, Total-Cr removals in treatments with FTW were 99.6 %, 96.9 %, 96.9 % and 81.7 % in 5Cr(III), 10Cr(III), 5Cr(VI) and 10Cr(VI), respectively. In Cr (III) treatments, the sediment from the reactors without FTW accumulated significantly more metal than the sediments with FTW, while the opposite occurred in the Cr(VI) treatments. Chromium in sediment was accumulated mainly bound to organic matter in all treatments (38-64 %). Roots of C. indica were the main Cr accumulator organ in all treatments (76-88 %). In 10Cr(VI) treatment, Cr was translocated to aerial parts resulting in a decrease in plant biomass and Chlorophyll a concentration. C. indica modified its internal and external root morphology as a mechanism to tolerate Cr toxicity, without affecting removal efficiencies. FTWs vegetated with C. indica were efficient in the remediation of water bodies contaminated with Cr. In addition, these systems have an aesthetic value because they use an ornamental species.

Chromium (III) removal by perennial emerging macrophytes in floating treatment wetlands

Floating treatment wetlands (FTWs) are a sustainable solution to treat polluted water, but their role in chromium (Cr(III)) removal under neutral pH conditions remains poorly understood. This study evaluated the potential of FTWs planted with two perennial emergent macrophytes, Phragmites australis and Iris pseudacorus, to remove Cr(III) and nutrients (N and PO4-P) from water containing 7.5 mg/L TN, 1.8 mg/L PO4-P, and Cr(III) (500, 1000, and 2000 µg/L). Within 1 h of exposure, up to 96-99% of Cr was removed from the solution, indicating rapid precipitation. After 50 days, Phragmites bound 9-19% of added Cr, while Iris bound 5-22%. Both species accumulated Cr primarily in the roots (BCF > 1). Biomass production and growth development were inhibited in Cr treatments, but microscopic examination of plant roots revealed no histological changes at 500 and 1000 µg/L Cr, suggesting high resistance of the tested species. At 2000 µg/L Cr, both species exhibited disruptions in the arrangement of vessel elements in the stele and increased aerenchyma spaces in Phragmites. At the end of the experiment, 70-86% of TN and 54-90% of PO4-P were removed.