Microbe-assisted phytoremediation of domestic and tannery wastewater: in vitro application of a macrophyte mixture for contaminant removal

The discharge of inadequately treated domestic and tannery wastewater has a severe impact on the environment. Different legislations are seeking to reduce this impact by requiring full treatment prior to discharge. An environmentally friendly, non-invasive, and cost-effective alternative to achieve this is microbe-assisted phytoremediation with native macrophytes. In this work, a mixture of free-floating macrophytes was used to remove pollutants from domestic and tannery wastewater. The plants, identified as Lemna gibba, Lemna minuta, and Wolffia columbiana, were collected from a wetland that receives domestic wastewater. The mixture was tolerant to pure domestic wastewater and a 1/20 dilution of tannery wastewater. Different variables were determined at the start and at the end of the treatment to evaluate the remediating ability of the plant system. In domestic wastewater, significant removal efficiency was observed for organic matter and nutrients, with a total nitrogen reduction of 80%. Sulfates and chlorides decreased by around 71% and 20%, respectively. In tannery wastewater (1/20 dilution), the reduction values for organic matter, nutrients, and chlorides were lower, between 5 and 50%. A higher removal was detected for sulfates, total chromium and phenols. Total mesophilic aerobic bacteria and total coliforms were almost completely eliminated (> 95%) in both wastewaters. The treatment also improved turbidity, suspended solids, odor and color. The findings show that these plant species are highly able to eliminate or reduce contaminants, organic matter, and microorganisms that pose sanitary risks in wastewater, thus making it much more apt for discharge than before treatment.