Hidden greenhouse gas emissions for water utilities in China's cities

Drinking water supply and wastewater treatment require significant energy inputs, and considerable greenhouse gas (GHG) emissions. Developing countries such as China are investing significantly in the construction of additional water infrastructure at the cost of increased GHG emissions. To understand the complexities of the inclusive impacts of GHG emissions from urban water systems, this study aims to examine both direct and indirect GHG emissions for water utilities in China's cities. A practical hybrid framework was proposed to reveal hidden GHG emissions via a combination of Intergovernmental Panel on Climate Change (IPCC) guidelines (bottom-up) and an Environmental Input-Output model (top-down). The study found that average annual GHG emissions between 2006 and 2012 from urban water utility operation in China accounted for 41 Mt CO2-eq, 58% came from energy use, 40% from treatment processes, and 2% from chemical use. Based on the proposed framework, Scope 3 emissions (indirect emissions other than electricity and heat purchase) for the operation of water utilities were estimated to be 8 Mt CO2-eq, which is significant to the total emission inventory; this corrected the bottom-up estimation in which 90% of Scope 3 emissions were not captured. The main hidden emission sources were upstream emissions of electricity and heat generation (21%), management of water conservancy (9%), manufacture of metal products (15%) and plastics (6%), and other chemical inputs (4%).Embodied emissions from cement and lime production (27%) and steel rolling of (22%) were the main sources of Scope 3 emissions for the construction of water infrastructure. Future variations of GHG emissions from water utilities were determined to be largely a result of the growth of wastewater treatment. This study demonstrates the feasibility of a hybrid approach to supporting low-carbon planning of water utilities from the viewpoint of water-energy-GHG nexus, and suggests that reduction of non-CO2 emissions in wastewater treatment and emissions of electricity consumption across supply chains has a significant potential to mitigate total GHG emissions from China's water sector.