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.

Figure1. Chemical and microbiological factors affecting manganese oxidation and reduction in drinking water systems.

Impact of Chemical and Microbiological Oxidation and Reduction of Manganese in Drinking Water SystemsJosé M. Cerrato and Andrea M. Dietrich:

Department of Civil and Environmental Engineering

Joseph O. Falkinham III: Department of Biological Sciences

418 Durham Hall Environmental and Water Resources Engineering

Virginia Tech

Objectives 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 There are no methods available for identification and separation of simultaneous chemical and microbial mediated redox reactions to determine their relative contributions.

Implications 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.

Materials and Methods

Findings/Results

Discussion

Chemical Factors 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.

Number of Isolates Recovered

0

5

10

15

20

25

30

Sedimentation Basin Filtration Basin Distribution System

Nu

mb

er o

f Is

ola

tes Oxidizers

Reducers

Chemical 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).

Microbiological Analyses 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).

Table 1. Obtained concentrations of water quality parameters in Honduras1 B.D.L. = Below Detection Limit 2 N.A. = Not Analyzed

Figure 4. Isolates recovered from the different locations at the drinking water treatment and distribution system.

8.10.310 0.061

0.021 0.006

0.036 0.012

Iron (Continuous)

10.50.610 0.038

0.068 0.025

0.821 1.469

PVC (Continuous)

7.10.375 0.007

0.018 0.004

0.743 0.471

Iron (First Flush )

8.20.550 0.014 0.009

15.732 10.323

PVC (First Flush )

9.31.250 0.06

0.254 0.034

0.261 0.036

Plant Effluent

N.A.2BDL10.259 0.011

0.282 0.012

Plant Influent

DissolvedTotal

Dissolved Oxygen

ChlorineManganeseSample

Concentration (mg/l)

8.10.310 0.061

0.021 0.006

0.036 0.012

Iron (Continuous)

10.50.610 0.038

0.068 0.025

0.821 1.469

PVC (Continuous)

7.10.375 0.007

0.018 0.004

0.743 0.471

Iron (First Flush )

8.20.550 0.014 0.009

15.732 10.323

PVC (First Flush )

9.31.250 0.06

0.254 0.034

0.261 0.036

Plant Effluent

N.A.2BDL10.259 0.011

0.282 0.012

Plant Influent

DissolvedTotal

Dissolved Oxygen

ChlorineManganeseSample

Concentration (mg/l)

Figures 5a and 5b. Assessment for Mn –oxidation and –reduction of biofilm suspensions obtained from Honduras.

Assessment for Mn Oxidation

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14

0 1 2 3 4

Time (week)

Mn

(mg/

l) / g

Dry

Wei

ght

Control

PVC Pipe

Iron Pipe

Sand Filter Media

Assessment for Mn Reduction

0

10

20

30

40

50

60

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0 1 2 3 4Time (weeks)

Mn

(mg/

l) / g

Dry

Wei

ght

Control

Iron Pipe

PVC Pipe

Sand Filter Media

Figures 6a and 6b. PVC and Iron pipes collected from the distribution system in Honduras.

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 Mn-reducing 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.

Figures 7a and 7b. Mn-oxidizing bacteria grown in Mn-oxidizing selective agar and broth media.

Acknowledgements National Science Foundation NSF Grant # DMII0329474

6b6a

Figure 3. Manganese cycle in the dinking water system of Tegucigalpa, Honduras.

PVC: High Mn, black

particles, low chlorine

Manganese

High Mn, black particles, low chlorine

W T P

Reservoir Water

Public InfrastructureMostly iron and concrete

Iron Pipes

Soluble Mn

IRON: lower Mn,, low chlorine

PVC Pipes

.. .… .

7a 7b

2a

2b

Figures 2a and 2b. Particulate manganese retained in a 0.45 m membrane and in a water sample.

Manganese Redox

Soluble Manganese,Mn+2

Insoluble Manganese,Mn+4, MnO2

Oxidation

Reduction

Chemical Oxidation

Oxidants: Oxygen (O2), Chlorine (Cl2), etc.

Mn -oxidizing bacteria

Mn -reducing bacteria

5a 5b