Manganese removal and occurrence of manganese oxidizing bacteria in full-scale biofilters

Biological treatment of drinking water to remove manganese (Mn) is becoming more and more common. However, details as to how the technology works remain poorly understood. Some previous studies have focused on bacteria of the genus Leptothrix, identifying them as one of the predominant organisms in Mn oxidizing biofilms. This research took media from inside the filters of four Mn biofiltration plants in the province of New Brunswick, Canada. The water was characterized for all four sites and it was found that Mn removal from all plants is virtually 100%. Biofilm was detached from the sand and tested for presence of Leptothrix using real-tme polymerase chain reaction (RT-PCR) DNA amplification. Less specific testing for Mn oxidizing bacteria was done simultaneously using indicative agar plates. Results showed that only one plant contained Leptothrix in its filters while three of the four plants tested positive for manganese oxidizing bacteria (MOB) through plating. These results, along with other evidence, suggest that while the mechanism of oxidation observed is likely biological, Leptothrix is not necessarily the predominant organism carrying out biooxidation.