Quantification of greenhouse gas emission from wastewater treatment plants

In this study, a new quantitative approach of greenhouse gas (GHG) emissions from wastewater treatment plants (WWTPs) is established. It is developed based on three categories of WWPTs: (1) energy and chemical consumption; (2) final disposal of biosolids; and direct GHG emission from treatment processes, which is helpful to better estimate the GHG emission pathways. The developed approach can provide actual results of GHG emission in terms of carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4) from wastewater treatment process. Then, this method is applied to a municipal WWPT, where the GHG emission from the processes of final treatment, biological treatment, and anaerobic digestion, at the southside of Guelph city in Canada. The results show that there are 6743.8 CO2 eq.kg/day of CO2 and 1924.48 CO2 eq.kg/day of N2O emissions from aeration tank/activated sludge system. The biological treatment and anaerobic digestion release 74177.58 CO 2eq.kg/day of CH4, 7258.5 CO2 eq.kg/day of CO2, and 59022.6 CO2 eq.kg/day of CH4, 3493.24 CO2eq.kg/day of CO2. If the methane, which discharged from biological treatment and anaerobic digestion, is captured and burned for energy regeneration, then it can produce 12937.9 CO2 eq.kg/day of CO2. The total amount of GHG indicates that about 80% GHG is emitted from the final disposal field while 9% and 11% GHG is emitted from biological treatment and anaerobic digestion, respectively. Therefore, based on the calculated results, engineers can put forward suggestions to optimize operation conditions to reduce greenhouse gas emissions. © 2022 Society of Chemical Industry and John Wiley & Sons, Ltd.