Nitrous Oxide Measurements on a Pilot Scale MABR

Kevan Brian (Watercare Services Limited)

Nitrous Oxide is a potent greenhouse gas with a global warming potential of nearly 300 times that of carbon dioxide. Emissions of nitrous oxide from Watercare’s wastewater treatment plants account for about 70% of our operational emissions based on IPCC 2016 emission factors. Understanding how much nitrous oxide is emitted from our treatment plants and how it might be mitigated are keys aspects of meeting our commitments of 50% reduction in emissions by 2030 and net zero by 2050.

Membrane Aerated Biofilm Reactors or MABR’s are a new technology for the treatment of wastewater. The process is energy efficient and ideal for process intensification where total nitrogen removal or nitrification is required. The MABR process is claimed to have lower nitrous oxide emissions than processes such as activated sludge. Therefore, the technology has the potential to reduce emissions on both existing and new wastewater treatment plants. 

Both MABR technology and the quantification of N2O emissions are relatively new areas of focus in wastewater treatment, and there are few studies that have been conducted that quantify emissions from MABR. Most have looked at MABR as a standalone unit and there are very few studies in the literature that have looked at a complete system (MABR with activated sludge reactors).

This paper presents monitoring undertaken on a pilot scale hybrid Membrane Aerated Biofilm Reactor, using a combination of gas and liquid phase measurements. The paper presents some lessons learned that can be applied to monitoring N2O in general. Some key differences in monitoring approaches for reporting of emissions and determining cause and effect are presented as well as a proposed emissions factor for the MABR process.