Abstract/Background

1
José M. Cerrato and Andrea M. Dietrich
Department of Civil and Environmental
Engineering Joseph O. Falkinham III
Department of Biological
Sciences
Impact of Chemical and Microbiological Oxidation
and Reduction of Manganese in Drinking Water
Systems
418 Durham Hall
Environmental and Water Resources Engineering
Virginia Tech
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.

• 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.

Materials and Methods Findings/Results
2a
6b
6a
Figures 6a and 6b. PVC and Iron pipes collected
from the distribution system in Honduras.
2b

• 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 2a and 2b. Particulate manganese retained
in a 0.45 ?m membrane and in a water sample.
Table 1. Obtained concentrations of water quality
parameters in Honduras 1 B.D.L. Below Detection
Limit 2 N.A. Not Analyzed

• 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.

.. . .
Figure 4. Isolates recovered from the different
locations at the drinking water treatment and
distribution system.
Figure 3. Manganese cycle in the dinking water
system of Tegucigalpa, Honduras.
7b
7a
Figures 7a and 7b. Mn-oxidizing bacteria grown in
Mn-oxidizing selective agar and broth media.
Acknowledgements National Science Foundation
NSF Grant DMII0329474
5a
5b
Figures 5a and 5b. Assessment for Mn oxidation
and reduction of biofilm suspensions obtained
from Honduras.