Characterisation of an attenuation system for the remediation of Mn(II) contaminated waters

Soluble manganese (Mn(II)) can be problematic in surface, ground waters and in domestic water supplies. Many mine drainage waters contain highly elevated concentrations of manganese (often > 100 mg l− 1). Current systems for remediating mine waters, although effective for other metals, are often inefficient at removing manganese. This paper describes the development of self-sustaining, low-cost bioreactors that can be used in situ for passive removal of manganese from contaminated water courses of pH > 4. A prototype bioreactor, set-up using Mn(IV)-coated pebbles from a fresh-water stream, was tested over one year and shown to be effective in removing Mn(II) from 10 to < 0.25 mg l− 1. Managanese-oxidising microorganisms isolated from the bioreactor included two species of fungi and one bacterial species. The fungi were identified as belonging to the order Pleosporales (Ascomycetes), and one was related (98% 18S rRNA gene sequence identity) to a known Mn(II)-oxidising fungus. The bacterial isolate was closely related to the α-proteobacterium Bosea thiooxidans. T-RFLP analysis showed that one or both of the fungal isolates were the dominant eukaryotes in the bioreactor community, while the Bosea isolate did not appear to be numerically important in the bacterial community.