Influence of Fe+2 ions on the process of biological removal of manganese in rock filter.

An efficient removal of manganese from polluted waters was achieved by means of a laboratory-scale rock filter. The rock filter consisted of three cells connected in a series with a total volume of about 12 l. The cells were filled with mix of limestone and gravel with a particle size of about 20-50 mm. Experiments for treatment of synthetic Mn-containing waters have been carried out using laboratory installation, containing biofilms of Mn-oxidizing bacteria. The oxidation of manganese was connected with the bacterial production of hydrogen peroxide and enzyme catalase. The Mn 2+ was then precipitated as MnO2. The concentration of dissolved manganese in the filter effluents was less than 0.8 mg/l and this was achieved within residence times of about 72 hours. It was determined that the higher concentrations of Fe 2+ , lead to negative effects in the rock filter related to reduction of Mn 4+ to Mn 2+ and its reversible mobilization in the water.