IVL Swedish Environmental Research Institute

To evaluate direct greenhouse gas emissions from Membrane Biological Reactor (MBR), measurements of nitrous oxide (N2O) and methane (CH4) were made at a pilot-scale MBR treating municipal wastewater Measurements were conducted during two campaigns with some changes in processes, i.e. introducing a pre-aeration tank in the second measurement, different distributions of aeration in the treatment line, not the same wastewater inflow rate, two types of ultrafiltration membrane. It was found that about 0.004% and 0.07% of the total ammonium loads were emitted as N2O, CH4 emissions were 0.026% and 0.12% of incoming TOC (0.008% and 0.04% of incoming COD) in 2014 and 2018. The obtained N2O emission values were relatively low.

The study suggested that a high aeration at the beginning of the treatment line may result in significantly high emissions of both N2O and CH4. A significant change in aeration in the membrane ultrafiltration tank did not have the same impact. The MBR process is known for high quality effluent but have been questioned due to its higher carbon footprint due to energy consumption. This study gave a reference case about direct GHG emissions from MBR process and provide information for the further evaluation of MBR processes.