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Denitrification as a Source of Nitrous Oxide

Denitrification as a Source of Nitrous Oxide. Paracoccus denitrificans. Drew Meyers. Nitrous Oxide (N 2 O), Why Does it Matter?.

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Denitrification as a Source of Nitrous Oxide

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  1. Denitrification as a Source of Nitrous Oxide Paracoccusdenitrificans Drew Meyers

  2. Nitrous Oxide (N2O), Why Does it Matter? • “N2O is now the most significant ozone-depleting substance emission and 3rd most important greenhouse gas released into the atmosphere.” – United Nations Environment Program (UNEP), N2O Report 2013

  3. Emissions of N2O • How much do we emit? • 5.3 Teragrams of N2O – N per year • What are the sources of N2O emission? Agriculture: 73%, 17% from Nitrate runoff Wastewater: 3% UNEP 2013 N2O Report

  4. Denver’s Largest Wastewater Treatment Site

  5. Labile Carbon and NO3- from treated wastewater

  6. Labile Carbon and NO3- from treated wastewater NO3- from agricultural runoff

  7. Labile Carbon and NO3- from treated wastewater NO3- from agricultural runoff Aerobic Respiration: Labile Carbon + Oxygen  CO2 +H2O + energy

  8. Labile Carbon and NO3- from treated wastewater NO3- from agricultural runoff Aerobic Respiration: Labile Carbon + Oxygen  CO2 +H2O + energy Anaerobic Respiration: Some bacteria use Nitrate as an electron acceptor. This is the process of Denitrification.

  9. Labile Carbon and NO3- from treated wastewater NO3- from agricultural runoff Complete Denitrification Process, <0.5mg Oxygen/L:NO3- NO2-  NO + N2O  N2 Redox Rxn: 2 NO3− + 10 e− + 12 H+ → N2 + 6 H2O

  10. Labile Carbon and NO3- from treated wastewater NO3- from agricultural runoff Incomplete Denitrification Process: Conditions are not completely anoxicNO3- NO2-  N2O

  11. N2O leaves water, enters atmosphere Labile Carbon and NO3- from treated wastewater NO3- from agricultural runoff Incomplete Denitrification Process: Conditions are not completely anoxicNO3- NO2-  N2O

  12. O3 +hv O2 + O(1D) N2O + hv  N2 + O(1D) N2O + O(1D)  N2 + O2 or 2NO 3 – 4% of N2O loss in stratosphere results in Nitric Oxide (NO)

  13. O3 +hv O2 + O(1D) N2O + hv  N2 + O(1D) N2O + O(1D)  N2 + O2 or 2NO 3 – 4% of N2O loss in stratosphere results in Nitric Oxide (NO) NO + O3 NO2 + O2 NO2 + O  NO +O2

  14. O3 +hv O2 + O(1D) N2O + hv  N2 + O(1D) N2O + O(1D)  N2 + O2 or 2NO NO + O3 NO2 + O2 NO2 + O  NO +O2 Net Rxn: O3 + O  2O2

  15. How can we reduce N2O emissions from Denitrification? • More efficient use of fertilizer on crops • Release effluent at times when anoxic conditions dominate the stream/hyporheic zone • At night?

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