Fig. 1. Theoretical framework of research on carbon emissions of urban wastewater treatment system based on “water-energy-carbon” nexus

Fig. 2. Process flow diagram of the first phase of a wastewater treatment plant (WWTP) in Zhengzhou City

Fig. 3. Process flow diagram of the second phase of a wastewater treatment plant (WWTP) in Zhengzhou City

Fig. 4. Variations of total carbon emissions of the wastewater treatment plant (WWTP) in Zhengzhou City

Fig. 5. Proportion of carbon emissions of the wastewater treatment plant (WWTP) in Zhengzhou City

Fig. 6. Variations of carbon emissions per unit volume of wastewater treatment of the wastewater treatment plant (WWTP) in Zhengzhou City

Fig. 7. Variations of direct carbon emissions of the wastewater treatment plant (WWTP) in Zhengzhou City

Fig. 8. Variations of indirect carbon emissions of the wastewater treatment plant (WWTP) in Zhengzhou City