In order to achieve the carbon peak by 2030 and achieve the comprehensive goal of carbon neutrality by 2060, the research investigate the carbon emission performance of wastewater treatment plants (WWTPs) in China, and proposes suitable low-carbon strategies for WWTPs. The study utilized the operating data of 4346 WWTPs in China from 2014 to 2018, and calculated the carbon dioxide emissions and emission reductions. The carbon emissions include direct emissions (CH4 and N2O) during the treatment processes, and indirect carbon emissions embodied energy consumption. The carbon sinks comprise energy self-sufficient, energy saving by water reuse, and carbon emissions reduced by sludge composting. Research further simulated provincial carbon neutrality situation by meticulously giving each province a series of index determined by their per capita GDP, sunlight hours, per capita water sources, energy consumption of process design and agricultural land area. The results show that from 2014 to 2018, WWTPs in all provinces were still unable to achieve the target of carbon neutrality. Since the growth rate of carbon emissions is generally higher than that of carbon sequestration, the carbon neutrality efficiency has declined in the past five years. The direct carbon emissions of CH4 generally account for a relatively high proportion of all carbon emissions, and provinces with higher carbon neutrality level, such as Sichuan, Hubei and Shandong, also have a relatively low proportion of CH4 emissions. According to the simulating, we came up with the following results: nationwide, the net carbon emissions of WWTPs will reach its peak in 2027 and achieve carbon neutrality in 2052; provincially, the emissions of WWTPs will reach carbon neutrality in the time period between 2030-2060, and the timing of carbon neutrality is roughly the same as that of carbon peak; Except for Tibet with low carbon peak of WWTPs, carbon neutrality in other provinces can be achieved about 24 years after they reaching the peak of carbon emission respectively. Therefore, the study implicates more advanced emission reduction facilities of WWTPs are encouraged, such as the photovoltaic power generation devices, and suggest to increase the proportion of water reuse, and improve sludge utilization, in order to achieve the carbon neutrality goals.
Keywords Carbon emission, carbon sequestration, carbon neutrality, wastewater treatment plants