Insight into greenhouse gases emissions from the two popular treatment technologies in municipal wastewater treatment processes

Highlights: • Aerated zones significantly contribute to GHGEs in both AAO and SBR. • Higher emission was found in SBR than in AAO in terms of CO₂, CH₄ and N₂O. • To quantify direct emissions with low uncertainty is essential for GHG controlling. • GHGEs impact factors help in establishing the rational control strategies. -- Abstract: Due to the impact of methane, carbon dioxide and nitrous oxide on global warming, the quantity of these greenhouse gases (GHG) emissions from municipal wastewater treatment plants (WWTPs) has attracted more and more attention. Consequently, GHG emissions from the two popular treatment technologies: anaerobic/anoxic/oxic (AAO) process and sequencing batch reactor (SBR) should be properly identified and discussed toward the current situation in developing countries. Direct and indirect carbon dioxide (with and/or without including in Intergovernmental Panel on Climate Change (IPCC) report) are all discussed in this article. This literature study observed that a quantity of total carbon dioxide emissions from SBR (374 g/m³ of wastewater) was double that of AAO whilst 10% of these was direct carbon dioxide. Methane emitted from an SBR was 0.50 g/m³ wastewater while 0.18 g CH₄/m³ wastewater was released from an AAO. The level of nitrous oxide from AAO and SBR accounted for 0.97 g/m³ wastewater and 4.20 g/m³ wastewater, respectively. Although these results were collected from different WWTPs and where influent was in various states, GHGs emitted from both biological units and other treatment units in various processes are significant. The results also revealed that aerated zone is the major contributing factor in a wastewater treatment plant to the large amount of GHG emissions.