Carbon Emission Accounting and the Carbon Neutralization Model for a Typical Wastewater Treatment Plant in China

To reduce carbon emissions and achieve carbon neutrality in China, it is pivotal to explore low-carbon wastewater treatment processes and carbon-neutral wastewater treatment plants (WWTPs). This study investigated the Beijing Gaobeidian WWTP to explore the current energy consumption and carbon emission status of representative WWTPs in China. Furthermore, it explored a possible low-carbon operating model. Results show that the current total energy consumption of Gaobeidian WWTP is 280,717 MWh/y, while its energy recovery is 268,788 MWh/y. As a result, the energy neutralization ratio is 95.8%, and the plant is close to reaching energy neutrality. The carbon emission of this plant is 446,468 t/y. However, it reduced its carbon emissions by 252,994 t/y and reached only 56.7% of carbon neutrality. Although the plant almost reached energy neutrality, it has a long way to go before reaching carbon neutrality. It was found that a subsequent increase in the recovery of residual heat from secondary effluent can increase the energy and carbon neutralization ratio to 523.1% and 219.0%, respectively, meaning that the WWTP can become a power production unit and a carbon sink. This study can provide a reference for exploring efficient energy use and reaching carbon neutrality for domestic WWTPs.