Greenhouse gas emissions from membrane bioreactors

Nowadays, it is widely accepted that wastewater treatment plants (WWTPs) are significant sources of greenhouse gas (GHG) emission, significantly contributing to anthropogenic sources of GHG emission. Among the GHG emitted from WWTPs, nitrous oxide (N2O) has been identified as the potentially major component, since its high global warming potential (GWP) is 298 times higher than that of Carbon dioxide (CO2) and also to its capability to react with stratospheric ozone, causing the ozone layer depletion. Up to now, most of the experimental investigations aimed at assessing the key mechanisms of N2O formation, as well as the operational conditions that can enhance its emission, have been carried out on conventional activated sludge (CAS) processes, while the knowledge of N2O emission from advanced technologies such membrane bioreactors (MBRs) is still very limited. Moreover, the specific peculiarities of MBRs might hamper the direct transferability of data achieved on CAS systems. Therefore, there is an imperative need to increase the knowledge about N2O emission from MBRs, through experimental and mathematical modelling activities. The present chapter aims to provide a non-exhaustive picture of the GHG emissions from MBR systems, referring in particular to N2O, reporting some experimental data carried out on pilot plant systems, characterized by different configuration. The effect of specific wastewater features and operational conditions on N2O production/emission from MBRs are highlighted