| During a visit to the Dry Creek Water Reclamation Facility in Cheyenne, Wyoming in 2011, distinct differences were noted in the color of the biofilm growing on the plastic media in adjacent parts of the Integrated Fixed-Film Activated Sludge (IFAS) units. On the influent side, the IFAS media had a typical grey/brown-colored biofilm; on the effluent side, the biofilm was notably black in color. Samples of media from both IFAS units were obtained and examined by a Field Emission Scanning Electron Microscope equipped with an electron dispersive spectrometer (FESEM-EDS). The "black biofilm" on the effluent side of the basins was found to contain Mn(IV) oxides. The main function of the IFAS process is BOD removal and microbial oxidation of ammonia; the media in the IFAS units are added to increase the surface area for microorganisms to colonize and so improve treatment efficiency. Although Mn is not a regulated constituent in wastewater effluents, if the Mn(IV) coatings on the media reduce the biofilm coverage or exert toxic effects on microorganisms in the biofilm, they may ultimately impact the treatment efficiency of the IFAS process. The Dry Creek facility is currently operating at about 60% of its design capacity. As the population of Cheyenne grows, however, and the IFAS units will need to run at full capacity, the impact of manganese oxide formation on the IFAS media may be problematic. The primary objective of this research was to determine what role Mn(IV) oxide deposition on IFAS media might play in biofilm formation. |
