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| Fig. 1: World Water Day 2010 Informational Graphic. (Source: Wikimedia Commons) |
Access to clean water is a fundamental human right. However, as of 2017, 2.1 billion people still do not have access to water that is considered fully safe to drink, and there has been little improvement in the last decade, as seen in Fig. 1. If humanity is to move steadily towards the United Nations Sustainable Development Goal of clean drinking water for all by 2030, all promising techniques must be explored. [1] The volume of water supplied by overexploitation of the world's natural groundwater is estimated between 110 and 200 km3/year. [2] Also, evidence suggests that wastewater recycling is not high enough to sustain rising demand. [3] For these reasons, oceanwater desalination is a competitive option to pursue.
The vast majority of desalination plants in operation are specifically designed for desalination only. The most popular desalination techniques are either driven by the vaporization of water, namely multieffect distillation (MSD) and multistage flash (MSF), or by pressure gradient flow through a semipermeable membrane, namely reverse osmosis (RO). [4] One factor that drives the continual depletion of natural groundwater is that these desalination technologies can only compete with natural groundwater economically in very particular settings, generally extremely arid regions. This is due to the large amount of energy input required, nearly 1kWh for 100 gallons of freshwater. [3] Not only would nuclear power produce fresh water without nearly the environmental footprint of fossil fuel power, it is also believed to be more cost effective.
Proponents of nuclear desalination argue that nuclear plants would run most efficiently as cogeneration plants. The average nuclear power plant operates at a thermal efficiency of roughly 35%, and the energy remaining is released as waste heat. [5] This substantial amount of waste heat in cooling water would be used to heat up the salt water feed, making thermal desalination processes require less outside energy input and allowing membrane process to have higher product yields. [4] This would be especially advantageous for low temperature hybrid desalination methods, such as membrane distillation, which are driven by a vapor pressure gradient across a hydrophobic membrane. [6] Table 1 shows the relative costs of desalination techniques, including both direct and cogeneration energy sources. [7] Nuclear cogeneration seems to be the most viable economic option currently.
China is the best candidate in the world to adopt nuclear desalination. Nuclear energy is a contentious issue among the public in Western countries, and nuclear plant growth has slowed considerably there. Regardless, China's economic growth rate is roughly three times that of any advanced economy in the world, and China sees the urgency of expanding energy output as much more important than the fears raised by nuclear power critics. [8] Furthermore, China's political style allows it to quickly and efficiently plan infrastructure advances.
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| Table 1: Techno-Economic Assessment of Desalination Processes. [7] |
China currently has a nuclear energy capacity of 32.4GWe from 36 reactors at 11 different sites, but to meet electricity needs, China is constructing a staggering 58 additional reactors at 21 new sites, to be finished by 2030. [9] Of those 94, 69 are deemed to be new enough, large enough, and close enough to the coast to warrant cogeneration with desalination. Studies show that desalination at these sites would cause a total supply cost ranging from $0.87/m3 to $1.96/m3, which is among the lowest costs for desalination in the world. This range is only due to water transportation. Fortunately, 30% of China's population live on the coast, and 60% live within 200 mi of the coast. [10] In cities located relatively near to the coast such as Nanjing, Tianjin, Shanghai, Jinan, Hefei, Beijing, and Shijiazhuang, this cost is at or below $1/m3. [9]
Fortunately for proponents of nuclear desalination, China has already identified water as a paramount issue warranting dramatic infrastructural changes. In 2014, China opened an extension to the South-to-North Water Transport Project (SNWTP) canal, which diverts water 895 miles to Beijing. That is equivalent to the distance between New York City and Orlando, Florida. Two thirds of Beijing's tap water and a third of its total supply come from this massive canal. The continuation of these water diversion projects is the biggest competitor to the prospect of widespread nuclear desalination. This is because canal water from the SNWTP costs roughly $0.51/m3 currently. [9]
Experts argue that, since the sources of the SNTWP are in the middle of the country, future water diversion projects would be better directed towards cities in more remote provinces, and nuclear desalination should be the focus of coastal regions. This is due to many reasons. First, canal water that has traveled hundreds of miles is too impure for many industrial processes, even if it is deemed potable, and requires additional purification costs. Second, there are many coastal water scarce places that are geographically unreachable by the SNWTP. Third, canals provide water much more surface area to be affected by evaporation and environmental disturbances, such as climate change and seasonal droughts. Fourth, the Beijing addition of the SNWTP required 15 million m3 of cement and 0.7 million tons of steel, while the construction of the 69 desalination plants will use 0.3 million m3 of cement and 0.02 million tons of steel. Fifth, every new canal project is met with scrutiny by the populations that it displaces. The Beijing addition forced 300,000 people to resettle. Finally, diversion simply doesn't create more potable water like desalination. [9]
© Brandon Clark. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] S. Parkinson et al., "Balancing Clean Water-Climate Change Mitigation Trade-Offs," Environ. Res. Lett. 14, 014009 (2019).
[2] M. Besbes, J. Chahed, and A. Hamdane, National Water Security: Case Study of an Arid Country: Tunisia (Springer International Publishing, 2019), Ch. 1.
[3] A. Jahansouz, "Nuclear Plus Desalination," Physics 241, Winter 2017, Stanford University.
[4] S. Dincer and I. Dincer, "Comparative Evaluation of Possible Desalination Options With Various Nuclear Power Plants," in Exergetic, Energetic and Environmental Dimensions, eds. I. Dincer, C. O. Colpan and O. Kizilkan (Academic Press, 2018), Ch. 2.20.
[5] N. Fathi et al., "Efficiency Enhancement of Solar Chimney Power Plant by Use of Waste Heat from Nuclear Power Plant," J. Clean Prod. 180, 407 (2018).
[6] A. Deshmukh et al., "Membrane Distillation at the Water-Energy Nexus: Limits, Opportunities, and Challenges," Energ. Environ. Sci. 11, 1177 (2018).
[7] S. U. D. Khan et al., "Nuclear Energy Powered Seawater Desalination," in Renewable Energy Powered Desalination Handbook: Application and Thermodynamics, ed. V. G. Gude (Butterworth-Heinemann, 2018), Ch. 6.
[8] J. W. Lee and W. J. McKibbin, "Service Sector Productivity and Economic Growth in Asia," Econ. Model. 74, 247 (2018).
[9] A. P. Avrin, G. He, and D. M. Kammen, "Relevance of Nuclear Desalination as an Alternative to Water Transfer Geoengineering Projects: Example of China," in Renewable Energy Powered Desalination Handbook: Application and Thermodynamics, ed. V. G. Gude (Butterworth-Heinemann, 2018), Ch. 7.
[10] B. Cicin-Sain, R. W. Knecht and N. Foster, eds., "Trends and and Future Challenges for U.S. National Ocean and Coastal Policy," U.S. National Oceanic and Atmospheric Administration, January 1999.
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