Using subsurface flow wetlands with Phragmites australis as a bioremediation alternative for surface sources affected by acid drainage from coal mines

Abstract

Mining generates environmental impacts such as Acid Mine Drainage (AMD). The Cali River is one of the main water resources in the city of Santiago de Cali, Colombia and it is affected by drainage from abandoned mines, which reach the Cali River through the Las Minas brook. As bioremediation alternatives, the use of subsurface flow wetlands coupled with a limestone-based pretreatment was assessed in this study. The research methodology was structured in two stages: a) physicochemical monitoring of Las Minas brook waters, and b) treatment system operations. For these purposes, four systems were evaluated: 1) Wetlands with plants (WL1), 2) Limestone + WL1 (LS + WL1), 3) Wetlands without plants (WL2) and 4) Limestone + WL2 (LS + WL2). The results revealed that the water from the Las Minas brook presents characteristics similar to AMD (pH: 2.4-4.0; acidity: 1 303.2 mg/l ± 139.2; iron: 715.3 mg/50 ± 70.6; sulfate: 1 134.5 mg/l ± 314.6) and affects the Cali River mainly owing to the increase in iron, aluminum, and the presence of ferric hydroxide precipitates. In addition, limestone-based treatment systems achieved greater efficiencies, and the LS + WL1 configuration is recommended. All systems were able to reduce the affluent acidity from 31 to 52 %. Furthermore, the average iron removal efficiencies achieved were between 54 and 67 %; sulfates between 16 and 35 %, nickel between 25 and 50 %, and aluminum between 0 and 73 %. However, manganese could not be removed.