Sustainable Application of a Novel Water Cycle Using Seawater for Toilet Flushing

• Published in: Engineering (Beijing, China) Vol. 2; no. 4; pp. 460 - 469
• Main Authors: Liu, Xiaoming, Dai, Ji, Wu, Di, Jiang, Feng, Chen, Guanghao, Chui, Ho-Kwong, van Loosdrecht, Mark C.M.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.12.2016; Water Technology Center, The Hong Kong University of Science and Technology, Hong Kong, China; Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Hong Kong, China; Chinese National Engineering Research Center for Control and Treatment of Heavy Metal Pollution (Hong Kong Branch), The Hong Kong University of Science and Technology, Hong Kong, China%Department of Biotechnology, Delft University of Technology, Delft 2629 HZ, the Netherlands; Chinese National Engineering Research Center for Control and Treatment of Heavy Metal Pollution (Hong Kong Branch), The Hong Kong University of Science and Technology, Hong Kong, China%School of Chemistry and Environment, South China Normal University, Guangzhou 510006, China%Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Hong Kong, China; Elsevier
• Subjects: Alternative water resources; Life-cycle assessment; SANI; Seawater toilet flushing; Urban water system; 厕所; 可持续城市发展; 持续应用; 沿海城市; 海水循环; 淡水供应; 环境可持续性; 自养反硝化; Seawater toilet flushing; Alternative water resources; Life-cycle assessment; SANI; Urban water system
• ISSN: 2095-8099
• DOI: 10.1016/J.ENG.2016.04.013

Global water security is a severe issue that threatens human health and well-being. Finding sustainable alternative water resources has become a matter of great urgency. For coastal urban areas, desalinated seawater could serve as a freshwater supply. However, since 20%-30% of the water supply is used for flushing waste from the city, seawater with simple treatment could also partly replace the use of freshwater. In this work, the freshwater saving potential and environmental impacts of the urban water system （water-wastewater closed loop） adopting seawater desalination, seawater for toilet flushing （SWTF）, or reclaimed water for toilet flushing （RWTF） are compared with those of a conventional freshwater system, through a life-cycle assessment and sensitivity analysis. The potential applications of these processes are also assessed. The results support the environmental sustainability of the SWTF approach, but its potential application depends on the coastal distance and effective population density of a city. Developed coastal cities with an effective population density exceeding 3000 persons.km-2 and located less than 30 km from the seashore （for the main pipe supplying seawater to the city） would benefit from applying SWTF, regardless of other impact parameters. By further applying the sulfate reduction, autotrophic denitrification, and nitrification integrated （SANI） process for wastewater treatment, the maximum distance from the seashore can be extended to 60 km. Considering that most modern urbanized cities fulfill these criteria, the next generation of water supply systems could consist of a freshwater supply coupled with a seawater supply for sustainable urban development.