Jul 22 2014

Desalination: reconclining fresh water needs with energy demand

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The Water-Energy Nexus has become an increasingly nascent consideration for innovating solutions to environmental problems and managing natural resources. The term simply explains the inextricable connection between water and energy, meaning sources of one are often required by the presence of the other (Gliek 1994.) Fresh water resources is now considered one scarcest natural resources on earth. Particularly in coastal areas, the decreasing availability of fresh water opposes growing resource demands with an increasing population. As a result, water utility companies have chartered the exploration of desalination technologies. However, coinciding with the reality of the Water-Energy nexus, many desalination processes are scrutinized for having both water and energy intensive technologies. Thus, evaluations of coastal desalination projects are crucial for assessing both the environmental and economic feasibility for employing desalination as an effective method of water resource management.

Schematic of the Water-Energy Nexus (Vox Global)

Schematic of the Water-energy Nexus (Vox Global)

Desalination Processes               

While desalination accounts for only 2% of the world’s fresh water consumption, it has seen a tremendous growth rate of 15% per year (Tal, 2011.) Desalination occurs through two primary technologies: distillation and reverse osmosis. The primary distillation technology is known as multiple effect distillation (MED) in which salt water is condensed and evaporated through multiple cells at low pressures (Martin-Lagardette, 2001.) Although this technology is seemingly simple when translated to large installations, the energy benefits are largely negligible with increasing scale (Martin-Lagardette, 2001.) Consequently, reverse osmosis (RO) technologies are widely utilized in large scale operations. RO technologies use several consecutive permeable membranes to manipulate the movement of salts in opposite directions under conditions of tremendous pressure, which creates fresh water and concentrated wastewater  (Tal, 2011.) Thus, one potential environmental impact from RO plants is found in the high salt concentrations of brine (wastewater) accrued in production. In some cases, the high salinity of brine is much greater than that of seawater, which could pose a threat for the dynamics of benthic communities and marine organisms (Tal, 2011.) However, impacts on both economic and energy costs posit greater threats to environmental prosperity.

Desalination in Israel

The arid conditions of the Mediterranean in collusion with ubiquitous proximity to large bodies of saltwater present ideal geographical and climatic conditions for desalination technology. For Israel, its controversial foreign policy track record validates its candidacy for desalination, such that with by domestic fresh water resources, political vulnerability is minimized. Israel uses reverse osmosis technology in their three largest desalination plants, which produced 300 million cubic meters of fresh water per day in 2011 and are arguably the most efficiency facilities in the world (Tal, 2011) Moreover, Ashkelon, Israel’s largest desalination facility, is a self-sufficient energy generation plant (Tal, 2011.) Conversely, the other dominant facilities in Israel rely on electricity from the coal-dominated grid system (Tal, 2011.) To put this in perspective, one of these grid reliant systems requires 60 megawatts per hour of electricity, which can generate greenhouse gases comparable to a city of 45,000 people (Tal, 2011.)

 

http://www.ide-tech.com/case-study/ashkelon-project/

Aerial view of the Ashkelon Desalination Facility (IDE Technology)

Additionally, private financiers of Israeli projects often retain contractual ownership rights in exchange for covering capital costs (Tal, 2011) As a consequence, the costs of desalinized water often reflect energy prices used to power the facilities, creating highly variable water costs dependent on rising energy prices (Tal, 2011.) Therefore, the exorbitant energy demands of and subsequent impacts on climate change call into question the economic and environmental sustainability of widespread desalination in Israel.

The Australian Strategy: Renewable Desalination Generation

The Australian climate historically oscillates between periods of drought and flooding. However, the severity and duration of either extreme is increasingly exacerbated by climate change, creating great stress on fresh water supplies. In 2005, amidst the country’s worst drought in history, the government declared its intentions to build a $2 billion desalination facility in the capital Sydney (Tal, 2011.) Australia was the first nation to power its desalination plants exclusively through renewable energy technologies, which accounted for the great increases in construction costs. Consequently, estimations during construction predicted that the cost of desalinized water would reach $2 per cubic meter of water when including costs of mitigating greenhouse gas emissions (Tal, 2011.) In reality, consumers only saw an increase of approximately $110 per year over a five year period. (Tal, 2011.)

Despite the positive outcomes from reducing carbon emissions, critics of the project claim that employing supply-side solutions to water scarcity problems encourages the continuation of wasteful consumption, rather than promoting adaptive behaviors within technical and social spheres (Tal, 2011.) This argument comes back to a central paradox of desalination, such that it is a solution utilized by developed countries to extend water-inefficient consumption patterns rather than reducing demand through widespread social initiatives. In other words, desalination adds economic and philosophical complexity to the cycle of water-energy interdependence, even in efforts to reduce the impacts of climate change.

Conclusions

The different experiences and results of desalination provide variable evidence when assessing long term viability of desalination. In many cases, initial environmental impact assessments have not translated into having any significant impact on marine ecosystems. Thus, questions of energy demands bring about the most poignant concerns for environmental feasibility. The advent of renewable energy innovation complicit with advances in desalination technologies could alleviate reliance on fossil energy demand, but conversely stands to increase water costs in the long term.

 

Citations

Tal, A. (2011). The Desalination Debate: Lessons Learned Thus Far. Environment: Science and Policy for Sustainable Development, 53(5), 34–48. Retrieved from http://scholar.google.com.libproxy.lib.unc.edu/scholar?q=the%20desalination%20debate%20lessons%20learned%20thus%20far

 

Martin-Lagardette, J. L. (2001). Desalination of Seawater . Water and Energy Management , 18–20. Retrieved from http://www.wqpmag.com/sites/default/files/Desalination_4_01.pdf

 

Gleick, P. H. (1994). Water and Energy  . Annual Review of Energy and Environment, 19(1), 267–299. Retrieved from http://www.annualreviews.org.libproxy.lib.unc.edu/doi/pdf/10.1146/annurev.eg.19.110194.001411

Images:

http://voxglobal.com/2011/03/the-energy-water-nexus-an-emerging-risk/

IDE Technology . (n.d.). Retrieved from http://www.ide-tech.com/case-study/ashkelon-project/

 
Vox Global . (n.d.). Retrieved from http://voxglobal.com/wp-content/uploads/Energy-Water-blog.gif

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