BOD and Total Nitrogen Removal from Wastewater Using Microbial Fuel Cells

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BOD and Total Nitrogen Removal from Wastewater
Using Microbial Fuel Cells
Caitlyn Shea and Robert NerenbergDepartment of
Civil Engineering and Geological Sciences,
University of Notre Dame, Notre Dame, IN
46556cshea1_at_nd.edu, rnerenbe_at_nd.edu
PLUG FLOW MFC FOR TOTAL NITROGEN REMOVAL
INTRODUCTION

• As treatment objectives become increasingly
  stringent, especially for nutrient removal,
  wastewater treatment energy requirements will
  continue to rise. Microbial fuel cells (MFCs) are
  a novel technology that produces electricity
  during the oxidation of BOD, and may provide more
  energy efficient treatment. Recently, it has been
  shown that an MFC cathode can serve as an
  electron donor for denitrifying bacteria
  (Clauwaert et al. 2007), yielding nitrogen gas as
  its terminal product (Park et al. 2005). We
  evaluated two microbial fuel cell (MFC)
  configurations that potentially can be used to
  remove BOD and total nitrogen from wastewater.
  The first was a two-chamber MFC with a
  denitrifying biocathode, where exoelectrogenic
  bacteria used the cathode as an electron donor
  and nitrate as the electron acceptor. The second
  was a plug flow configuration, where influent
  wastewater is first passed through an anode
  compartment and then through a cathode
  compartment.

The anode supported an electrochemically active
biofilm that removed BOD below detection. In the
cathode compartment, nitrifying biofilms growing
on air-filled hollow-fiber membranes (HFMs) were
alternated with denitrifying biocathodes. The
nitrification fluxes were up to 1.1g NH4 - N/m2
HFM/d, which is comparable to other hollow fiber
membrane based processes, and denitrification
fluxes were up to 0.5 g NO3- - N/m2 cathode/d.
This configuration achieved a power density of
0.7 W/m3 (11 mW/m2 cathode). The results suggest
that these MFC configurations may be suitable for
removing BOD and TN from wastewater, concurrent
with electricity production.
Hollow Fiber Membranes
TWO CHAMBER DENITRIFYING MFC
Figure 4. A schematic of the MFC for Total
Nitrogen Removal design. the MFC was fed with a
single stream containing 100mg/L acetate and 16
mg NH4-N/L at an increased flow rate of 2
mL/min, for a nitrogen loading rate of 1.7 g N/
m2 cathode d. The racks of hollow fiber
membranes (HFMs) were supplied with 2 psi of air.
The external resistance of the MFC was 50 O. The
HRT was 2.7 hours.
Current (A)
Current (A)
Current (A)

Figure 1. A schematic of the two-chamber MFC. The
MFCs were constructed from rectangular plexiglas
frames and filled graphite granules, as described
in Clauwaert et al. (2007). Each electrode
compartment had a 400-mL total volume and, after
the granular electrode material was added, there
was a 200-mL liquid volume. An Ultrex PEM
separated the two chambers. The HRT was 22 hours.
The external resistance of the MFC was 10 O.
Time (days)
Time (days)
Time (days)
Figure 2. Theoretical current and measured
current in the denitrifying biocathode. The anode
was inoculated with a consortium of bacteria from
activated sludge and existing MFC anodes, and
continuously fed 200 mg/L of acetate as an
organic electron donor in a 16 mM phosphate
buffered minimal growth media. The cathode
compartment was inoculated with microbial
communities from a denitrifying MFC cathode, and
activated sludge. The cathode chamber was
continuously fed 20 mg-N/L of nitrate in a
modified 16 mM phosphate buffered minimal growth
media.
Ammonium, Nitrate, Total Nitrogen mg N/L
Acetate mg/L
Sustained Power Production and Nitrate
Reduction The MFC achieved a sustained current of
3 - 3.5 mA (Figure 2), and power production of
0.23 0.31 W/m3 cathode liquid volume (reactor
and recirculation vessel) Nitrate was removed
below detection and denitrification rates
obtained in this system were 26 gN/m3-day, based
on the cathode liquid volume, or 4.6 gN/m2-day,
based on the estimated surface area of graphite
granules in the cathode compartment. BOD was
completely removed.

Figure 5. Polarization curves of the Plug Flow
MFC show an improvement in electrochemical
performance with time. Phase 1 was in the
start-up configuration where the anode and
cathode are partitioned and the HFMs are in a
separate batch chamber. Phase 2 was in the
start-up where the HFMs were included in the
cathode chamber, but the anode and cathode were
still partition by a PEM. Phase 3 is configured
with a single feed stream and no partition
between the anode and the cathode.
Distance (cm)
Figure 6. Concentrations of substrates along the
length of the Plug Flow MFC vessel obtained
during Phase 3 of MFC operation, where there was
a single influent and effluent.
CONCLUSIONS
This work demonstrates that there are
opportunities for nitrogen removal using MFCs,
with an added advantage of energy production.
Microbial Ecology of Anode and Cathode
Biofilms The dominant genus within the anode
compartment was Geobacter. Geobacter species
have previously been described as an
exoelectrogens (Bond and Lovley 2003). Instead of
common denitrifying species, the cathode
community was dominated by sequences most closely
affiliated to mesophilic, neutrophilic
Fe(II)-oxidizing genera, such as Siderooxidans
and Ferritrophicum. Iron-oxidizing bacteria have
previously been coupled with nitrate reduction
(Weber, 2006).

• Two-chamber MFC
• Revealed a unique microbial community associated
  with the biocathode
• High specific surface area of the cathode may be
  more appropriate for concentrated waste streams
• May have applications in industrial wastewater
  treatment

• Plug flow MFC
• Demonstrated total nitrogen removal in a MFC
  system
• Possess some limitations in reactor conditions
  such as pH and oxygen inhibition on
• electrochemically-active communities
• May be retrofitted into activated sludge tanks
  for BOD and TN removal.

Figure 3. Phylogenetic tree of 16S rRNA gene
sequences recovered from denitrifying biocathode
and bioanode. Key taxa are shown, and clusters of
sequences have been compressed for presentation
purposes. Clusters of sequences associated
primarily with cathode have been highlighted in
orange and those associated primarily with anode
have been highlighted in purple. The bacterial
lineages Betaproteobacteria (?),
Alphaproteobacteria (?), Deltaproteobacteria (?)
and Bacteroidetes (Ba) are indicated in gray
circles. The scale bar represents 10 sequence
divergence.
Acknowledgements The Bayer Predoctoral Research
Fellowship from the Center for Environmental
Science and Technology and the Nerenberg
Research group
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