Carbon emission analysis of municipal wastewater treatment plants and discussion on synergistic path of pollution and carbon reduction

The wastewater treatment industry is one of the top ten CO₂ emission industries, the carbon emissions of which account for 2%-3% of the total global carbon emissions, and its carbon emissions show an increasing trend year by year. So, carrying out carbon emission reduction in the wastewater treatment industry and achieving the synergistic effect of pollution reduction and carbon reduction is the necessary path to promote the realization of the "double carbon" goal in China. The carbon emission situation of the wastewater treatment plants (WWTPs) of China was systematically analyzed. The result showed that direct CO₂ emissions produced by the biochemical treatment process occupied a large proportion of that in the whole processing section, and among them, the direct CO₂ emission in the aerobic area was the largest. Meanwhile, the indirect carbon emissions resulting from power and drug consumption accounted for a large proportion of whole direct and indirect carbon emissions, which was the key link of carbon emission reduction of WWTPs. Additionally, the way of anaerobic digestion + biogas power generation was the recommended low-carbon treatment of sludge. The problems of carbon emission reduction in WWTPs mainly included inaccurate carbon emission accounting, the lack of development and application regarding the low-carbon wastewater treatment technology, and inadequate top-level design and management. Based on this, the possible pathways suitable for the synergistic reduction of pollution and carbon of WWTPs in China were put forward, which needed multiple efforts. These efforts included accounting the carbon emission accurately, strengthening the development and application of energy-saving, carbon reduction, carbon replacement and carbon sequestration technology, and designing a multi-dimensional carbon control scheme. Moreover, an overall framework for carbon reduction driven by technological innovation and policy support should be built, thus forming a closed-loop system for carbon reduction in WWTPs, and assisting the low-carbon development of WWTPs of China.