Quantification of nitrous oxide emissions during biological nitrogen removal from waste water: a systems comparison

O. Pahl, T. Calvert, Jim Baird, J. Baird

Research output: Contribution to conferencePoster

Abstract

There is strong evidence that the biological removal of nitrogen from waste water emits considerable amounts of nitrous oxide (N2O) gas. Up to 80% of removed nitrogen is emitted in the form of N2O, which is a strong greenhouse gas and ozone depletant. This fact is well reported for treatment of agricultural wastes but not for the treatment of communal/industrial waste water. This difference may be due to the fact that, conventionally, the emission of nitrous oxide is seen to be caused by denitrifying bacteria involved in the water treatment process. Inventories of gaseous emissions from commercial treatment works thus may have missed out a potentially significant source of this gas, namely nitrification.

The project investigated, under controlled conditions in a laboratory, whether the treatment of communal/ industrial waste water for nitrogen removal can principally lead to significant releases of nitrous oxide and showed that this was not the case. Nitrogen and COD removal rates during all experiments were high, indicating that the systems were operated in a way that provided appropriate conditions for biological nutrient removal. Emission rates of nitrous oxide during the various treatment schemes were negligible; they accounted for less than 0.5‰ of nitrogen removed from the wastewater, at maximum, and for a tenth of that on average. Emissions at this rate contribute only marginally to the overall anthropogenic N2O production: the results of this project can be extrapolated to represents 0.063% of the UK’s total anthropogenic N2O production of 128kta-1 in 2005.

As such, the project showed that the treatment of industrial or communal waste waters does not lead to significant emissions of nitrous oxide. However, it does not provide an explanation as to why high emissions can occur in an agricultural context; this aspect still merits further investigation. Furthermore, comparison with evolving "nitrite short-cut" treatment schemes for nitrogen rich waste waters shows close parallels to agricultural waste water treatment and this particular aspect of industrial waste water treatment may benefit from closer inspection for its N2O release potential.
Original languageEnglish
Pages179
Number of pages1
Publication statusPublished - Sep 2008

Keywords

  • waste water treatment
  • nitrous oxide
  • greenhouse gases

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