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418 Durham Hall Impact of Chemical Environmental and Water Resources Engineering Virginia Tech and Microbiological Oxidation and Reduction of Manganese in Drinking Abstract/Background Worldwide, corrosion of drinking water pipes and build-up of scales on the interior pipe wall impacts both the quality and quantity of water delivered to consumers. This research investigated the role of chemical and microbiological factors on pipe corrosion and manganese oxidation and reduction in drinking water supply systems. Severe manganese contamination was reported in Tegucigalpa, Honduras. Consumers constantly complain of receiving “black water” at their taps and for this reason the city was selected for this research. Two water plants from Virginia that perform Mn removal were also selected for this study. Results of this study indicate that control of both microbial and chemical processes are important to limiting corrosion and that pipe type (PVC vs. iron) will influence scaling, biofilm growth, and water quality. Chemical Analyses Microbiological Analyses Measured pH, chlorine, and dissolved oxygen concentrations in situ using portable instrumentation. Determined total and dissolved manganese concentrations via inductively coupled plasma (ICP-MS). Statistical analyses performed using SAS (α=0.05). Detection and enumeration of Mn-oxidizing and reducing microorganisms using selective agar and broth media. Oxidation was assessed via spectrophotometry at 620nm. Mn-reduction was assessed via atomic adsorption by measuring dissolved Mn (filtered through 0.22m membrane). Concentration (mg/l) Sample 2a Mn -oxidizing bacteria 2b Insoluble Manganese, Mn+4, MnO2 Oxidants: Oxygen (O2), Chlorine (Cl2), etc. Chemical Factors Findings/Results Oxidation Soluble Manganese, Mn+2 Discussion Materials and Methods Manganese Redox Chemical Oxidation Figures 2a and 2b. Particulate manganese retained in a 0.45 m membrane and in a water sample. Manganese Chlorine Dissolved Oxygen Total Dissolved Plant Influent 0.282 0.012 0.259 0.011 BDL1 N.A.2 Plant Effluent 0.261 0.036 0.254 0.034 1.250 0.06 9.3 PVC (First Flush ) 15.732 10.323 0.014 0.009 0.550 8.2 Iron (First Flush ) 0.743 0.471 0.018 0.004 0.375 0.007 7.1 PVC (Continuous) 0.821 1.469 0.068 0.025 0.610 0.038 10.5 Iron (Continuous) 0.036 0.012 0.021 0.006 0.310 0.061 8.1 B.D.L. = Below Detection Limit 2 Reduction Microbiological Factors The fact that Mn-oxidizing and –reducing bacteria have a natural tendency to form a biofilm when attaching to solid surfaces is important because such environment could potentially harbor pathogenic bacteria. Although Mn-oxidizing bacteria are aerobic and Mnreducing bacteria are facultative anaerobic, the obtained results suggest the possible coexistence of both types of bacteria in the same biofilm. It is likely that biofilms formed in the sedimentation basin, filtration basin and distribution system contribute to manganese release in drinking water. N.A. = Not Analyzed Number of Isolates Recovered Manganese Figure1. Chemical and microbiological factors affecting manganese oxidation and reduction in drinking water systems. Identify microbiological and chemical factors involved in deposition, cycling, and removal of manganese in biofilms of drinking water systems. Investigate the effect of piping materials -PVC and iron- on drinking water quality for a water supply system constantly fed by Mn(II). Limitations 30 Soluble Mn PVC Pipes WTP Public Infrastructure Mostly iron and concrete High Mn, black particles, low chlorine Mn, black h ig H : C V P w chlorine particles, lo Iron Pipes IRON: lo wer Mn, , low ch lori .. . …. Number of Isolates Reservoir Water 6b Figures 6a and 6b. PVC and Iron pipes collected from the distribution system in Honduras. Table 1. Obtained concentrations of water quality parameters in Honduras 1 Manganese “pipe scales” were easily dislodged from PVC pipes leading to severe “black water” problems. Less particulate manganese was released from iron pipes because it was incorporated into biofilms and iron pipes where it contributed to corrosion. Residual chlorine concentrations of water samples collected in the distribution system were approximately 70% less than those at the treatment plant, suggesting that manganese increased the chlorine demand and possibly reduces disinfection. 6a Mn -reducing bacteria Objectives José M. Cerrato and Andrea M. Dietrich: Water Systems Department of Civil and Environmental Engineering Joseph O. Falkinham III: Department of Biological Sciences 25 Oxidizers 20 Reducers 15 10 5 0 ne Sedimentation Basin Figure 3. Manganese cycle in the dinking water system of Tegucigalpa, Honduras. Filtration Basin Distribution System Figure 4. Isolates recovered from the different locations at the drinking water treatment and distribution system. There are no methods available for identification and Control Control 12 Mn (mg/l) / g Dry Weight As an essential element, manganese is necessary for health but excessive concentrations cause illness. Control and occurrence of manganese at the tap is still a troublesome problem for many water utilities, especially with regards to the role of microorganisms. This research represents a great opportunity for interdisciplinary collaborations in microbiology, chemistry, and engineering to uncover new fundamental science that can be immediately applied to drinking water treatment and supply practices. 70 14 Mn (mg/l) / g Dry Weight Implications Assessment for Mn Reduction Assessment for Mn Oxidation separation of simultaneous chemical and microbial mediated redox reactions to determine their relative contributions. PVC Pipe 10 Iron Pipe Sand Filter Media 8 6 4 2 0 7a Iron Pipe 1 2 Time (w eek) 3 4 5b 7b PVC Pipe 50 Figures 7a and 7b. Mn-oxidizing bacteria grown in Mn-oxidizing selective agar and broth media. Sand Filter Media 40 30 Acknowledgements National Science Foundation NSF Grant # DMII0329474 20 10 0 0 5a 60 0 1 2 Time (w eeks) 3 Figures 5a and 5b. Assessment for Mn –oxidation and –reduction of biofilm suspensions obtained from Honduras. 4