ABSTRACT
The present paper summarises the design and operation results of a pilot scale anaerobic wetland for the treatment of acidic drainage in the Stratonion lead-zinc sulphide mines. Pilot design parameters such as type and volume of organic substrates, metal removal capacity, and retention time were determined based on extensive laboratory test work. The pilot application consisted of a constructed anaerobic cell with an operating capacity of 7.5 m3; the cell was filled with organic substrate consisting of cow manure and chestnut wood chips (weight ratio 2:1) and was covered to maintain anaerobic conditions. The inflow of the cell was acidic mine water (pH 2.8) with increased levels of Fe, Zn, Mn, Pb draining from mined out areas. The flow rate was adjusted to 1 lit/min and the retention time was 7 days. Pilot plant performance was evaluated by daily measurement of field parameters, i.e. pH, EMF, conductivity and temperature and weekly chemical analysis of inflow and over flow water samples for Fe, Zn, Mn, Pb, SO4= and BOD. Pilot plant results after six months of operation showed efficient removal of dissolved metals averaging 85–95% for Zn, 80–95% for Fe, 50–55% Mn and 100% for Pb. The pH of the outflow was 6,0 and the EMF remained consistently at reducing values, −60mV. Based on these data the calculated metal removal efficiency of the specific substrate in terms of mg metal/g substrate were; 6.48 for Fe, 6.86 for Zn and 8.41 for Mn. Sulphate reduction was 30–40% indicating that precipitation of metals as sulphides is a major removal mechanism in anaerobic wetlands.
