PERFORMANCE OF CONSTRUCTED WETLANDS TREATING MINE DRAINAGE IN KOREA

Passive mine drainage treatment system such as wetlands have been recognized as low cost, minimal maintenance systems that could lessen the impact of mine drainage on downstream. As of 2002, over 20 wetlands had been built in Korea to treat mine drainage. Most of the wetland system constructed in Korea, consist of oxidation pond, successive alkalinity producing system (SAPS) and oxic wetland. However, maintenance costs for the passive treatment systems currently installed at the abandoned mines are steadily increasing due to some problems such as low metal removal efficiencies, overflows and accumulation of sludge. Moreover, present passive treatment systems will be constructed at many closed mines, and similar problems are likely to be encountered in the future. Thus, a study to improve the treatment system is highly required. An experimental program was undertaken to improve the efficiency of the passive treatment system. The passive treatment system in the Gapjung coal mine, which consists of a oxidation pond, SAPS and oxic wetland, was selected for this study. The area of the whole treatment systems is about 4,000 m², and the flow rate of influent is 2,100 ton/day. Hydraulic loading rate (HLR) in pond, SAPS, oxic wetland was 2.1m/d, 3.0m/d, and 0.05m/d, respectively. Loading rate of the metallic constituents, such as Fe, Al and Mn, is about 45.236 g/day. The pH of the influent and outflow was 5.5 and 6.6. Chemical analysis showed that 98% of Fe was removed by the treatment systems. In case of Al, removal efficiency was 97%, and Mn was removed up to 93% by the treatment system. The removal rates for the Fe constituent were found as 5g/m²/d by the pond, 7g/m²/d by SAPS, and 1g/m²/d by the oxic wetland. It was observed that lots of sludge resulted from the removal of metals accumulated in the bottom of the pond and on the substrate in SAPS. Thus, this means that sludge reduce the retention time of mine drainage and impede down flow in SAPS.