A Comparative Study of Greenhouse Gases Produced by Membrane Bioreactors, Submerged Membrane Electro Bioreactors and Lagoons During Wastewater Treatment Process

Climate change is without a doubt the most important environmental issues of our age. Numerous studies have indicated the climate change and its effects are attributed to anthropogenic activities emitting CO2, CH4, N2O and other greenhouse gases. Wastewater treatment plants and their discharge account for 7.6% of the total emissions. The main objective of this study was to investigate greenhouse gases generated by two advanced wastewater treatment methods: conventional membrane bioreactor (MBR) and novel submerged membrane electro bioreactor (SMEBR). Subsequently, outcomes from both systems in lab scale were compared to the most popular wastewater treatment method, the lagoon systems, which account for 80% in Canada. This study comprises four phases. In phase 1, the 7 L MBR system was set up and run based on synthetic wastewater, simulating discharge to lagoons in in a municipality in Quebec. Subsequently, gas emissions were collected and analyzed. In phase 2, a submerged membrane electro-bioreactor, with identical technological parameters as MBR in phase 1, was submitted to investigations, where its emitted gases were also analyzed. In phase 3, a larger MBR was exposed to biogas measurements. Then, it was transformed to SMEBR while gas measurements continued. In phase 4, gas emissions from lagoons were estimated and compared to the outcomes from phases 1, 2 and 3. Results showed that the MBR produced around 22 g of CO2 equivalent per litre of wastewater per day, while the SMEBR generated around 12 g CO2 eq/L per day. In phase 3, the MBR transformation to SMEBR permitted to decrease the gas production while improving the ammonia removal efficiency. Phase 4 showed that the SMEBR reactor generated less N2O when compared to other investigated systems. It was concluded that the SMEBR system produced the lowest amounts of N2O per litre of wastewater, while showing superiority in nutrient removal. It is an important information from the point of view of sustainability and climate change prevention.