Mitigating Nitrous Oxide Emission – How to Achieve?

Environmental Seminar 08/03/2009Cheng-Yao TsaiUniversity of California, Irvine

Motivation

• Green house gas emission concern

• N2O is reported as a green house gas with radiative efficiency about 300 times as high as that of CO2. (IPCC, 2005)

• Indicator for nitrification failure

• N2O increases (from 16.5 to 186.3 ppm) before the failure of nitrification. (NH3 increases from 3.4 to 41.2 mg/L)

(Butler et al., 2008)

Nitrogen Cycle

1. Nitrogen fixation

2. Aerobic ammonium oxidation

3. Aerobic nitrite oxidation

4. Denitrification

5. Anaerobic ammonium oxidation

6. Anaerobic dissimilatory nitrate and nitrite reduction

Enzymes Required for Nitrification

Oxidation of NH3 to NO3-

NH3 NH2OH NO2- NO3

-HAOAMO NXR

AMO : Ammonia monooxygenase

HAO : Hydroxylamine oxidoreductase

NXR : Nitrite oxidoreductase (NOR in old papers!)

-120kJ mol-1 -114kJ mol-1 -74kJ mol-1

Enzymes Required for Denitrification

Reduction of NO3- to N2

NO3- NO2

- NO N2O N2

NAR NIR NOR NOS

NAR : Nitrate reductase NIR : Nitrite reductase

NOR : Nitric oxide reductase NOS : Nitrous oxide reductase

2 types 3 types 1 or ???

Anammox

Anammox : Anaerobic Ammonium Oxidation NH4

+ + NO2- N2 + H2O

Species: Brocadia anammoxidans Kuenenia stuttgartiensis “Candidatus” Scalindua brodae “Candidatus” Scalindua wagneri “Candidatus” Scalindua sorokinii

???

Mechanisms of Anammox

HH: Hydrazine hydrolase HAO: Hydrazine oxidoreductase

HD: Hydrazine dehydrogenase Q: Quinone

bc1: cytochrome bc1 complex (Kuenen, 2008)

Source of Nitrous Oxide

Nitrification Byproducts of hydroxylamine oxidation

or ammonia to hydroxylamine pathway

Denitrification Obligatory intermediates

NH3 NH2OH NO2-

HAOAMO

N2O

NO N2ONOR

Respiratory of Nitrous Oxide

Nitrous Oxide Reductase (NOS)

Environmental Factors on NOS Adequate supply of copper.

1µM copper is required at least for N2O reduction. (Matsubara et al., 1982)

1.6mM to 2.0mM will poison pseudomonas syringae. (Trevors and Cotter, 1990)

NOS is sensitive to pH. pH<7 is soils drives the reduction of NO3

- to N2O rather than to N2. (Liu et al., 2008)

Operations to Affect N2O Emission

Oxygen concentration C/N ratio Ammonia loading rate Hydraulic retention

time

(Hwang et al., 2006)

Bacterial Community

Aerobic Nitrification Autotroph: Ammonia oxidizing bacteria

(AOB) and nitrite oxidizing bacteria (NOB) e.g. Nitrosomonas, Nitrosospira (AOB), Nitrobactor (NOB).

Heterotroph: Paracoccus denitrificans, Alcaligenes faecalis, Pseudomonas putida

Anaerobic Nitrification (Anammox) Anammox bacteria

Bacterial Community

Denitrification Autotroph: AOB (cell maintenance-no growth) Heterotroph: Bacillus, Pseudomonas, Sprillum,

Alcaligenes, Agrobacterium… and so on. Some are aerobic denitrifiers!

Pseudomonas putida can tolerate 5-6 mg/L O2 and perform nitrate removal rate as high as 95.9%. (254.6 mg/L hour) (Kim et al., 2008)

Paracoccus denitrificans reduced added nitrate in an atmosphere of 92% O2 by 27%.

(Su et al., 2004)Not all bacterial species are capable to produce nitrous oxide

reductase (NOS) !

Conclusion

In order to mitigate N2O production from wastewater treatment process, pH>7 Longer HRT (above 2 days) Adequate ammonia loading rate Carbon and copper supply Oxygen condition in anoxic zone

(<80µM) New operation system?

Thanks for your listening!

Questions?