Municipal gravity sewers: an unrecognised source of nitrous oxide

Journal article, 2014

Nitrous oxide (N 2 O) is a primary ozone-depleting substance and powerful greenhouse gas. N 2 O 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 N 2 O dynamics. Here we provide the first detailed assessment of N 2 O 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 N 2 O. Results from the monitoring program revealed hydraulic flow rate as a strong driver for N 2 O 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 N 2 O 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 N 2 O production in sewers elsewhere. © 2013 Elsevier B.V.