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Factors and mechanismsaffecting seasonal bioremediation of contaminated leachates in a natural wetland

Groudev Stoyan Nicolov, Spasova Irena, Komnitsas Konstantinos, Paspaliaris Ioannis, Georgiev Plamen , Nicolova Marina

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Summary

Acidic waters and leachates generated from abandoned mining works and waste dumps at the Curilo uranium deposuit in Western Bulgaria, due to the oxidation of several sulphide phases, were treated in a natural wetland located in the wider mining area. These acidic effluents contained a large number of contaminants (uranium, radium, iron, manganese, copper, zinc, cadmium, lead, nickel, cobalt, arsenic, sulphates) in concentrations usually much higher than the relevant permissible levels for discharge in receiving streams. The wetland occupies an area of about 500 square meters and its basin is located on very low permeability intrusive rocks. Effluents flow rare varied between 0.2 and 1.2 l/s corresponding to wetland residence time varying between 7o to 12 hours. The wetlnd is characterized by abundant water, emergent vegetation and diverse microflora. Typha latifolia and Typha angustifolia were the prevalent plant species but species of the genera Juncus, Eleocharis, Potamogeton, Carex and Poa as well as various algae were also present. The experimental study has shown that almost all pollutants were efficiently removed throughout the year, even during the cold winter months when the water temperature was extremely low. Removal was enabled due to a number of mechanisms but microbial dissimilatory sulphate reduction and the sorption of contaminants on organic matter (living, dead plant and microbial biomass) and clay minerals present in the wetland played the most important role.

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