Manganese (Mn) is still a troublesome problem for many water utilities,and its control and occurrence at the tap are not well understood, especially with regardsto the role of microorganisms. The possible influence of chemical and microbiologicalfactors on manganese oxidation and reduction in drinking water supply systems has beenstudied. Severe manganese contamination was reported in Tegucigalpa, Honduras and forthis reason the city was one of the selected locations for this research. Two watertreatment plants in the southeastern U.S. also perform Mn removal and were selectedlocations for this study.Water samples were collected from locations in the water treatment plant anddistribution system of Tegucigalpa. The results indicated that manganese in particulateform was easily dislodged from polyvinyl chloride (PVC) compared to iron pipes leading to severe "blackwater" problems. To demonstrate the possibility of microbial-catalyzed manganesecycling, Mn-oxidizing and Mn-reducing bacteria were recovered from biofilm samplescollected from particulates in the sedimentation and filtration basins of the three watertreatment plants studied. Mn -oxidizing and -reducing bacteria were also obtained fromwater samples collected in the distribution system of Tegucigalpa. Biofilms from PVCpipe, iron pipe, and sand filter media from Tegucigalpa were suspended and showncapable of both Mn-oxidation and reduction. Although Mn-oxidizing bacteria are aerobicand Mn-reducing bacteria are facultative anaerobic, the obtained results suggest thepossible coexistence of both types of bacteria in the same biofilm. Thus, it is likely thatbiofilms formed in the sedimentation basin, filtration basin and distribution systemcontribute to manganese release in drinking water.This study suggests that both chemical and microbiological factors affectmanganese cycling in drinking water distribution systems. Includes 10 references, figures.
