Many treatment facilities remove soluble Mn by an autocatalytic adsorption-oxidation process involving manganese oxide (MnOx(s))-coated filter media and a free chlorine residual known as the natural greensand effect (NGE). In recent years, significant amounts of aluminum (Al) have been found integrated into MnOx(s) coatings on media from drinking water treatment facilities worldwide. The primary objective of this study was to characterize MnOx(s) coatings developed in the presence and absence of Al, and to further define the role played by Al in the coatings' initiation and development. A secondary objective of the study was to examine the potential for pre-filter oxidation of Mn and formation of nano-size MnOx(s) particles, which would be destabilized by Al(OH)3(s) and captured in the filter. This material could act as a seed for coating formation and help explain the integration of Al into MnOx(s) coatings. Bench-scale column tests were conducted to examine Mn removal and backwash composition, while centrifugation and ultrafiltration were utilized to examine the potential for rapid Mn oxidation. Results indicate that the presence of Al augments the initiation and development of MnOx(s) coatings. The backwash solids of columns loaded with Al were composed of a mixture of Mn and Al, suggesting that active adsorption-oxidation sites were present in the Al(OH)3(s) floc captured by the filter. These results suggest at least a small amount of pre-filter MnOx(s) formation by contact with free chlorine; further, that Al(OH)3(s) solids present may destabilize these negatively charged solids into a form that is important to MnOx(s) coating formation. / Master of Science

The Mn oxide (MnOx(s)) surfaces of water treatment filtration media are known to aid in the capture of dissolved Mn species, but the discovery of significant deposits of Al within these coatings raised several questions about the MnOx(s) surface. A series of experiments and analyses were performed to examine the presence of Al within MnOx(s) coatings formed on water treatment filtration media. It was hypothesized that the presence of Al within the MnOx(s) coatings might have an impact on the capture of Mn by the MnOx(s) surface. A 2008 study of oxide coated filtration media found that Mn and Al are present in nearly equimolar quantities within the oxide coatings. This led to questions of how and why the Al became incorporated into the surface. This phenomenon was analyzed by conducting a series of bench-scale column studies, treatment plant data collection, and analysis of the MnOx(s) surface utilizing an electron microscope. The results confirm that Al deposits onto the MnOx(s) media surface by two separate mechanisms; adsorption of dissolved Al species and the deposition of colloidal and particulate Al(OH)3(s) precipitate species onto the surface. Analysis of the MnOx(s) coating with by electron microscopy shows a heterogeneous surface composed of a mix of crystalline Mn oxides existing alongside amorphous Al(OH)3(s) species. The deposition of Al onto the media surface does not have any significant effect on the removal of soluble Mn, but the potential impact that Al might have on the capture of other dissolved species should be explored further. / Master of Science

Soluble manganese (Mn) is a common water contaminant which can cause discoloration of water and staining if not treated properly in a water treatment plant. The "natural greensand effect" is one of the proven methods for efficient removal of Mn from water. Therefore, research is ongoing to develop different ways to effectively create the natural greensand effect in a post-filtration sorptive contactor for application at water treatment facilities. The research reported by Zuravnsky (2007) focused on the use of oxide-coated media in a post-filtration contactor and served as a starting point for the research reported in this thesis. As a part of the work conducted by Zuravnsky (2007), a preliminary model was formulated to predict soluble Mn removal via adsorption and oxidation onto large-size MnOx(s)-coated media. A major part of the current research was to calibrate the proposed model in predicting the soluble Mn removal performance by incorporating a statistical non-linear regression method to estimate a best-fit value for the fitting parameter kr, the rate constant associated with Mn oxidation by free chlorine. The research work included an 18-week pilot-plant study conducted at a water treatment facility in Newport News, VA. A contactor column loaded with 27â of pyrolucite media was operated at varying applied water conditions. Hydraulic loading rate (HLR), temperature, pH and influent free chlorine concentration were the operational parameters that were varied and their effect on the Mn removal performance evaluated. The resulting data were then used in the model to aid in its calibration and to obtain the best-fit kr values corresponding to effective Mn removal for the various operating conditions. Soluble Mn removal in the contactor column was directly dependent on solution pH and initial free chlorine concentration. The applied water temperature and HLR also had a small impact on the Mn removal profiles observed. On analyzing the results obtained from the model, it was noted that the best-fit kr values for the pilot plant data increased with increasing solution pH (When temperature = 200C and the initial Cl levels were below 1.5mg/L). Also, the Mn uptake capacity of the pyrolucite media increased with both an increase in initial Mn concentration and solution temperature. Long-term operation of the contactor also resulted in significant head loss accumulation in the upper portion of the contactor column, most probably due to MnOx(s) deposition on the media and partial blockage of contactor void spaces. Media fluidization was necessary to address this operational issue. / Master of Science