[Systematic Evaluation of Low-carbon Operation of Typical A²O Processes in Municipal Sewage Plant]

Under the "Carbon Peak, Carbon Neutral" goal, the systematic evaluation of the carbon emission equivalent (CO₂eq) and its compositions of the typical A²O process has important guiding significance for the low-carbon operation of most municipal sewage plants in China. Based on the operational data on the first municipal sewage plant of Jiaozuo in 2020 and the methods presented in "2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories, " a systematic evaluation of the CO₂eq of the typical A²O process was established, including direct emissions that were built on the Arrhenius model introducing the water temperature factor and indirect emissions from the three aspects of electricity consumption, agent addition, and sludge transportation. The results showed that the daily emission intensities of CH₄ and N₂O were (115±56) kg·d^-1 and (30±18) kg·d^-1, respectively. Additionally, indirect carbon emissions from electricity consumption and agent addition accounted for 48.4% and 51.3% in the biochemical treatment section, respectively. In 2020, CO₂eq amounts of total research plant and per unit sewage were 2.17×10⁴ t and (0.63±0.07) kg·m^-3, respectively. The magnitude of the proportion of different carbon emission compositions was as follows:sewage electricity (36.5%)>sewage agent (26.6%)>N₂O direct (15.4%)>sludge agent (9.6%)>sludge electricity (6.7%)>CH₄ direct (4.9%)>sludge transportation (0.3%). System import/export fluxes of carbon and nitrogen elements were calculated, followed by the carbon to nitrogen mass ratio in the sewage plant. Direct carbon emission characteristics of CH₄ and N₂O and their influencing factors were discussed, respectively. Based on the balance theory of carbon and nitrogen elements in the system, it is proposed that the selective introduction of industrial wastewater may become an important reference measure for the low-carbon operation of municipal sewage plants in the future.