Emissions of nitrous oxide (N2O) from wastewater treatment processes are gaining increased recognition as the collective action on the reduction of anthropogenic greenhouse gas (GHG) emissions has been globally recognized.Studies on domestic wastewater reported a contribution of 1.6% of the total worldwide N2O emissions in 2010 and over 20 years those emissions increased by 1.6 Tg CO2 Eq. (46%). N2O is a potent GHG (300 times more than CO2 over a 100 year lifespan) and ozone depleting substance. The real picutre related to N2O emissions is likely more complex as our recent studies have shown.Nitrous oxide is produced during biological nitrogen removal (BNR) in wastewater treament plants (WWTPs) as result of nitrification and denitrification. BNR processes have been widely implemented to address increasing regulations concerning greater nutrient removal from WWTPs effluents in developed countries, however it has in turn potentially contribute to N2O emissions due to intrinsic characteristics of the treatment, such as anoxic-oxic cycling. Based on the knowledge gained over the past five years or so, it has been shown that water quality from BNR plants and gaseous emissions from them are directly proportional.  Therefore water quality and air quality are in concert and not in conflict.Potential solutions to concurrently achieving adequate water quality, while at the same time minimizing emissions include the following.Adequate design and operation of BNR plants to minimize effluent reactive nitrogenAvoid transient nitrification plants or nitrification only plants.  In other words, either avoid nitrification completely, or else couple nitrification with denitrification or with energy efficient options such as anaerobic ammonia oxidationMinimize transients in influent loading by providing equalization if possibleMinimize spatial gradients in nitrogen concentrations (and thereby microbial N-turnover activity) by providing adequate mixing or re-circulationIn addition to these options, an entirely novel paradigm could also involved completely arresting nitrogen redox transformations in sewage processing and re-orienting efforts towards nutrient recovery.

Mitigation options for nitrogenous greenhouse gas emissions from wastewater treatment plants

248th National Meeting (2014)

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