Abstract: A waste dump formed during the exploitation of quartzite deposit in Sobov mine (Slovakia) produces large quantity of acid mine drainage (AMD) which is mainly a product of pyrite oxidation. Sulphuric acid--the most aggressive oxidation product--attacks gangue minerals, mainly clays, as well. This process lead to a sharp decrease of the pH values (2-2.5) and increase of Fe, Al and SO (super 2-) (sub 4) contents (TDS = 20-30 mg/1). Passive treatment system was designed to remediate AMD. Chemical redox reactions along with microbial activity cause a precipitation of mobile contamination into a more stable forms. The sulphides are formed in the anaerobic cell, under reducing conditions. Fe-, Al- oxyhydroxides are precipitated in the aerobic part of the system. Precipitation decreases the Fe and Al contents along with immobilization of some heavy metal closely related to oxyhydroxides. Besides oxidation, the wetland vegetation is an active part of on aerobic cell. The system has been working effectively since September 1999. The pH values of outflowing water are apparently higher (6.2-6.8) and contents of dissolved elements (Fe from 2.260 to 4.1; Al from 900 to 0.18; Mn from 51 to 23; Cu from 4.95 to 0.03 mg/l) is significantly lowers.

Abstract: The effectiveness of wetland treatment of acid mine drainage (AMD) was assessed using three measures of performance: treatment efficiency, area-adjusted removal, and first-order removal. Mathematical relationships between these measures were derived from simple kinetic equations. Area-adjusted removal is independent of pollutant concentration (zero-order reaction kinetics), while first-order removal is dependent on concentration. Treatment efficiency is linearly related to area-adjusted removal and exponentially related to first-order removal at constant hydraulic loading rates (flow/area). Examination of previously published data from 35 natural AMD wetlands revealed that statistically significant correlations exist between several of the performance measures for both iron and manganese removal, but these correlations are potentially spurious because these measures are derived from, and are mathematical rearrangements of, the same operating data. The use of treatment efficiency as a measure of performance between wetlands is not recommended because it is a relative measure that does not account for influent concentration differences. Area-adjusted removal accounts for mass loading effects, but it fails to separate the flow and concentration components, which is necessary if removal is first-order. Available empirical evidence suggests that AMD pollutant removal is better described by first-order kinetics. If removal is first-order, the use of area-adjusted rates for determining the wetland area required for treating relatively low pollutant concentrations will result in undersized wetlands. The effects of concentration and flow rate on wetland area predictions for constant influent loading rates also depend on the kinetics of pollutant removal. If removal is zero-order, the wetland area required to treat a discharge to meet some target effluent concentration is a decreasing linear function of influent concentration (and an inverse function of flow rate). However, if removal is first-order, the required wetland area is a non-linear function of the relative influent concentration. Further research is needed for developing accurate first-order rate constants as a function of influent water chemistry and ecosystem characteristics in order to successfully apply the first-order removal model to the design of more effective AMD wetland treatment systems.