Effectiveness of Differently Designed Small-Scale Constructed Wetlands to Decrease the Acidity of Acid Mine Drainage under Field Conditions

Constructed wetlands are a near‐natural method for the treatment of acid mine drainages (AMD). Because of the different site‐specific wastewater qualities and the variability of the used constructed wetlands regarding design, it is difficult to compare their efficiencies on the basis of literature data (often specific removal rates are missing). The AMD treatment efficiencies (pH, acidity) of differently designed planted and unplanted small‐scale constructed wetlands (subsurface flow – SSF, surface flow – SF, and hydroponic – HP systems with an area of 0.55 m2 each) were compared under long‐term field conditions. The planted SF was found to be most effective, reaching mean acidity removal in the range of 80–90 %, and most resistant in view of external influences (i.e., heavy rain events). The planted SSF also showed high efficiency (50–90 %), but much more sensitivity to rain events. In both systems, the pH increased from 3.3 (mean of the inflows) to above 4.5 in the outflows. The efficiencies of the unplanted SF were insufficient and in the range of the (planted and unplanted) HP, i.e., smaller than 40 %. In general, the importance of plants for the success of the neutralization processes could be concluded. The efficiency of constructed wetlands for mine water treatment is difficult to compare because of different site‐specific wastewater qualities and the variability of sizing and design. Here, the efficiencies of six different designed constructed wetlands to change the pH and to remove the acidity of acid mine drainage under comparable long‐term field conditions are presented.