The Role of Macrophytes in Constructed Surface-flow Wetlands for Mine Water Treatment: A Review

• Published in: Mine water and the environment 2021-09, Vol.40 (3), p.587-605
• Main Authors: Opitz, Joscha, Alte, Matthias, Bauer, Martin, Peiffer, Stefan
• Format: Article
• Language: English
• Subjects: Alkalinity; Aquatic plants; Artificial wetlands; Clean technology; Colloids; Design; Drainage; Earth and Environmental Science; Earth Sciences; Ecotoxicology; Efficiency; Environmental conditions; Exposure; Filtration; Geology; Heavy metals; Hydrodynamics; Hydrogeology; Industrial Pollution Prevention; Kinetics; Macrophytes; Metals; Mine drainage; Mine waters; Mineral Resources; Optimization; Organic matter; Oxidation; Oxides; Plants; Ponds; Precipitation; Removal; Review; Reviews; Scavenging; Settling; Wastewater; Wastewater treatment; Water quality; Water Quality/Water Pollution; Water treatment; Wetlands
• ISSN: 1025-9112; 1616-1068
• DOI: 10.1007/s10230-021-00779-x

Constructed wetlands are a standard sustainable technology in waste and mine water treatment. Whereas macrophytes actively contribute to decomposition and/or removal of wastewater’s organic pollutants, removal of hydrolysable metals from mine water is not attributable to direct metabolic, but rather various indirect macrophyte-related mechanisms. These mechanisms result in higher treatment efficiency of (vegetated) wetlands relative to (unvegetated) settling ponds. Contribution of macrophytes to treatment predominantly includes: enhanced biogeochemical oxidation and precipitation of hydrolysable metals due to catalytic reactions and bacterial activity, particularly on immersed macrophyte surfaces; physical filtration of suspended hydrous ferric oxides by dense wetland vegetation down to colloids that are unlikely to gravitationally settle efficiently; scavenging and heteroaggregation of dissolved and colloidal iron, respectively, by plant-derived natural organic matter; and improved hydrodynamics and hydraulic efficiency, considerably augmenting retention and exposure time. The review shows that constructed surface-flow wetlands have considerable advantages that are often underestimated. In addition to treatment enhancement, there are socio-environmental benefits such as aesthetic appearance, biotope/habitat value, and landscape diversity that need to be considered. However, there is currently no quantitative, transferrable approach to adequately describe the effect and magnitude of macrophyte-related benefits on mine water amelioration, let alone clearly assign optimal operational deployment of either settling ponds or wetlands. A better (quantitative) understanding of underlying processes and kinetics is needed to optimise assembly and sizing of settling ponds and wetlands in composite passive mine water treatment systems.