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Sci Total Environ. 2014 Jan 15;468-469:211-8. doi: 10.1016/j.scitotenv.2013.08.051. Epub 2013 Sep 10.

Municipal gravity sewers: an unrecognised source of nitrous oxide.

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  • 1UNSW Water Research Centre, School of Civil and Environmental Engineering, University of New South Wales, Sydney, New South Wales 2052, Australia; SA Water Centre for Water Management and Reuse, School of Natural and Built Environments, University of South Australia, Adelaide, South Australia 5095, Australia. Electronic address:


Nitrous oxide (N2O) is a primary ozone-depleting substance and powerful greenhouse gas. N2O emissions from secondary-level wastewater treatment processes are relatively well understood as a result of intensive international research effort in recent times, yet little information exists to date on the role of sewers in wastewater management chain N2O dynamics. Here we provide the first detailed assessment of N2O levels in the untreated influent (i.e. sewer network effluent) of three large Australian metropolitan wastewater treatment plants. Contrary to current international (IPCC) guidance, results show gravity sewers to be a likely source of N2O. Results from the monitoring program revealed hydraulic flow rate as a strong driver for N2O generation in gravity sewers, with microbial processes (nitrification and possibly denitrification) implicated as the main processes responsible for its production. Results were also used to develop a presumptive emission factor for N2O in the context of municipal gravity sewers. Considering the discrepancy with current IPCC Guidelines, further work is warranted to assess the scale and dynamics of N2O production in sewers elsewhere.

© 2013.


Gravity sewer networks; Greenhouse gas emissions; Municipal wastewater; Nitrification–denitrification; Nitrous oxide; Urban water sector

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