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Engineering    2016, Vol. 2 Issue (4) : 460 -469     DOI: 10.1016/J.ENG.2016.04.013
Research |
Sustainable Application of a Novel Water Cycle Using Seawater for Toilet Flushing
Xiaoming Liu1,2,3,Ji Dai1,2,3,Di Wu1,2,3,Feng Jiang4,Guanghao Chen1,2,3,Ho-Kwong Chui1,3,Mark C. M. van Loosdrecht5,()
1. Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Hong Kong, China
2. Water Technology Center, The Hong Kong University of Science and Technology, Hong Kong, China
3. 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
4. School of Chemistry and Environment, South China Normal University, Guangzhou 510006, China
5. Department of Biotechnology, Delft University of Technology, Delft 2629 HZ, the Netherlands

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.

Keywords Alternative water resources      Seawater toilet flushing      SANI      Urban water system      Life-cycle assessment     
Corresponding Authors: Mark C. M. van Loosdrecht   
Just Accepted Date: 21 December 2016   Online First Date: 23 December 2016    Issue Date: 28 December 2016
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Xiaoming Liu
Ji Dai
Di Wu
Feng Jiang
Guanghao Chen
Ho-Kwong Chui
Mark C. M. van Loosdrecht
Cite this article:   
Xiaoming Liu,Ji Dai,Di Wu, et al. Sustainable Application of a Novel Water Cycle Using Seawater for Toilet Flushing[J]. Engineering, 2016, 2(4): 460 -469 .
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