Biological denitrification process configurations

1. BIOLOGICAL DENITRIFICATION PROCESS
CONFIGURATIONS
By
Dadebo Derrick
Department of Civil Engineering
Uganda Technical College - Kyema
Email: d.dadebo@utckyema.ac.ug
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2. INTRODUCTION
• Denitrification occurs when heterotrophic bacteria consume
a carbon source under anoxic conditions in the presence of
nitrate.
• An anoxic environment is one in which there is very little to
no free dissolved oxygen but where oxygen is present in
combination with other molecules (like nitrate).
• Denitrifiers require reduced carbon source for energy and
cell synthesis.
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(Redox reaction)

3. DENITRIFICATION PROCESS CONFIGURATIONS
 The dissimilative reduction of nitrate in wastewater to
molecular nitrogen (N2) can be accomplished using a
variety of different suspended growth reactor
configurations.
a) Post-denitrification Systems
b) Pre-denitrification Systems
c) Four-stage Bardenpho systems
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4. POST-DENITRIFICATION SYSTEM
 Also called Wuhrmann process -1964
 BOD removal and nitrification occur first in an aerobic
environment, followed by denitrification in an anoxic
environment.
a) Single Sludge
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5. b) Separate Sludge arrangement
 There are separate sludge recycle and waste streams for
the nitrification/BOD removal and denitrification stages.
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6. o Aerobic and anoxic conditions are controlled by the
placement of aeration devices.
o For example, diffused aerators can be placed along the
aerobic zone and no aerators placed in the anoxic zone.
 Denitrification consumes 2.86mg CBOD in the anoxic
zone.
 However, Organic substances are oxidized in the
aerobic tank and a denitrification rate in the anoxic tank
will be decreased.
 This requires the addition carbon source as an electron
donor of the denitrification into an anoxic tank.
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7.  Denitrifying bacteria require a carbon-to-nitrogen ratio
of about 3:1 to 4:1
 A low ratio of BOD to TKN is a constraint to
denitrification thus supplementary carbon source is
required
 External carbon sources for post-denitrification include;
 Methanol
 Ethanol
 Acetate
 Glucose
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8. o The RAS is to maintain the F:M Ratio and ensuring the
desired MLSS concentration in the aerobic/aeration tank
for optimum system operation.
o The increase in mixed liquor recirculation highly improves
the denitrification performance.
o N-elimination of 96 % in post-denitrification and effluent
of 2.5 mgN per litre can be achieved.
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9. PRE-DENITRIFICATION SYSTEM
 Also called modified Ludzack-Ettinger process after
Ludzack and Ettinger -1962
 Pre-denitrification in activated sludge systems, where an
anoxic stage is located upstream of an aerobic stage.

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10. o Primary effluent first passes through an anoxic denitrification
zone and then proceeds to an aerobic combined
nitrification/BOD removal zone.
 External carbon source is not typically required.
 Nitrate generated from the aerobic zone is recycled to the
anoxic zone, where it is converted to nitrogen gas.
 The nitrogen gas generated in the anoxic zone is removed by
stripping.
 Not all the nitrates formed from the aerobic reactor are
recycled to anoxic reactor.
 Part of it exits the system with the effluent.
 Thus, complete nitrate removal cannot be achieved.
 Pre-denitrification can achieve up to 84 % of N removal.
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11. FOUR-STAGE BARDENPHO PROCESS CONFIGURATION
 This system has additional anoxic and aerobic zones in
addition to those of the pre-denitrification (Barnard, 1973)
 This follows the initial aerobic zone to remove the nitrate
that is not recycled back to the anoxic zone.
 In order to overcome the deficiency of incomplete nitrate
removal in the Modified Ludzack–Ettinger
(MLE) system.
 This configuration can achieve N-Total removal up to 3-4
mg/L
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12.  Low concentration nitrate from the aerobic reactor to the
secondary anoxic reactor will be denitrified to produce a
relatively nitrate-free effluent.
 Re-aeration reactor strips the nitrogen gas and nitrify the
ammonia released during the denitrification. 12

13. REFERENCES
 Capodaglio, A., Hlavínek, P., & Raboni, M. (2016). Advances in Wastewater
nitrogen removal by biological processes: State of the art review. Revista
Ambiente e Agua, 9(3), 445–458. https://doi.org/10.4136/ambi-agua.1772
 Curtin, K., Duerre, S., Fitzpatrick, B., & Meyer, P. (2011). Biological Nutrient
Removal. In Minnesota Pollution Control Agency (Vol. 4, Issue August).
https://doi.org/10.1016/B978-0-444-53199-5.00094-4
 Hamada, K., Kuba, T., Torrico, V., Okazaki, M., & Kusuda, T. (2006). Comparison
of nutrient removal efficiency between pre- and post-denitrification wastewater
treatments. Water Science and Technology, 53(9), 169–175.
https://doi.org/10.2166/wst.2006.272
 Kraume, M., Bracklow, U., Vocks, M., & Drews, A. (2005). Nutrients removal in
MBRs for municipal wastewater treatment. Water Science and Technology,
51(6–7), 391–402. https://doi.org/10.2166/wst.2005.0661
 Vocks, M., Adam, C., Lesjean, B., Gnirss, R., & Kraume, M. (2005). Enhanced
post-denitrification without addition of an external carbon source in membrane
bioreactors. Water Research, 39(14), 3360–3368.
https://doi.org/10.1016/j.watres.2005.05.049
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14. THE END
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