Emergy analysis of urban domestic water metabolism: A case study in Beijing (China)

his work elaborated an analysis of urban water metabolic system. The system's flows and processes were modeled and accounted on the basis of the ecosystem cumulative energy availability, also known as emergy. In detail, both the urban domestic water supplying process metabolism model and accounting framework were defined. Then, the whole process of the supplying of domestic water was analyzed, considering Beijing (China) as a case study. In particular, the existing water sources were included: surface water, underground water, water of the South-to-North Water Transfer Project; potential desalinated water from Tianjin. The results showed that, for the supply of 1 m3 of tap water, the total emergy input from the above-mentioned four sources are 3.22E+12, 3.34E+12, 4.55E+12, and 12.55E+12 sej. These values reflect the different energy costs of the existing supply systems, that are related to water transportation, treatment and distribution, Moreover, the emergy cost of desalinated water is about 4 times higher than the one of surface water. Conversely, the value of South-to-North Water Transfer Project is not much higher than that of surface water. Finally, the higher costs are related to the water treatment phase. Consequently, some policy recommendations and future research directions are identified for improving the sustainability for Beijing domestic water supply