Why Not Reverse Osmosis?
In our early exploration of this project, the decision to use reverse osmosis was settled on due to our initial calculations of production costs and rates based on comparisons to other desalination plants currently being installed. Reverse osmosis has a significantly lower production cost and higher rates of production than distillation. The difference in the scale of this challenge compared to any existing desalination plants is tremendous which is why we later chose to change our method to distillation. We used a regression curve to determine the cost savings in plant construction as the size of the plant is increased. Unfortunately, construction costs are just one piece of this complicated puzzle. We found that a reverse osmosis plant of this size was unrealistic in terms of cost and energy requirements. [20][10][22]
Currently reverse osmosis desalination is the predominant desalination technology grossing $15.48 billion in desalination investments from 2011-2015, while multi-effect desalination secured $4.04 billion in investments during the same period of time. Reverse osmosis is the most favored technology because of advances in membrane technology and its large-scale reliability. However, the energy needed to create an efficient RO desalination plant large enough to support this project would require a significant amount of energy, and the cost to run the entire operation would be unfavorable [5]. Previous studies have calculated the cost of water per cubic meter of multi-effect distillation is between $0.55 and $0.7 [19], and $0.5 to $1.20 for reverse osmosis [5]. This cost per cubic meter of water from multi-effect distillation equates to $1.50 to $2.00 per Ccf. However, our calculations have concluded that the cost of our project will average $14.00 per Ccf. The investment cost of a SWRO plant is also higher, averaging at $1600/m^3/day [5]. The lower investment cost of $1,100/m^3/day makes MED and more attractive option for desalination [25].
A disadvantage of using the RO method includes membrane replacement requirements. These are not needed for MED. Chlorine is a chemical often used in the RO process to clean and disinfect water and wastewater. However, chlorine causes the membranes to degrade at a faster rate, which requires the membranes to be replaced regularly, and therefore increases operating cost. [8] Another advantage of MED includes the ability to process water of almost any salinity with little pre-treatment, while the costs listed above for a SWRO plant do not include the pre-treatment process. [5]
Negative Social Impacts of the Reverse Osmosis Plan
1) There would be jobs created for the Mexican population – while this is great, it creates more problems in the form of legislation, transportation, environment and education.
2) Mexico does not have as much legislation in place as the United States does and that was a concern for our Capstone class.
3) There is an estuary in the bay of Rocky Point that would be contaminated and/or damaged from the output of brine waste through underwater release points.
4) It was simply too expensive/resource intensive to transport the volume of water we needed to move to Arizona.
5) Rocky Point is subject to geological faults such as earthquakes, hurricanes and even the possible tsunami which would destroy the R/O plant and allow brine waste to contaminate the surrounding area.
6) The tourism sector in Rocky Point alone would never allow a desalination plant to be built.
7) Fishermen and women earn their livelihood from the Puerto Peñasco bay. The ecological effects that would ensue would be devastating for the fisherman’s way of life.
Why not intake seawater closer to shore?
Seawater intake is one of the main environmental concerns involved with desalination and can potentially be extremely harmful to marine life for two reasons:
Impingement– the trapping large organisms against the intake screens due to high seawater intake speeds [4].
Entrainment– occurs when small organisms like algae or plankton enter into the piping system [4].
What are we doing to minimize these processes?
First, the intake pipes will be sited in an area of low biodiversity (see figure 9.2a) [9] where impingement will be minimal . The intake area is also 40 kilometers offshore and deep in the Gulf of California basin, which has a mean depth of over 800 meters [15], meaning that larval populations will be small and entrainment will be minimized [4]. Impingement and entrainment will also be curtailed using inexpensive barrier nets as recommended by the Pacific Institute [18]. Unfortunately, some commercially important organisms like shrimp call this area home and would be vulnerable to entrainment in its larval form [1] [4]. The only way to completely eliminate these negative impacts of seawater intake is by building a subsurface intake system [4] [18], but this was ruled out for this project due to the debilitating cost [18]. |
Why not direct discharge?
The North American Marine Protected Areas Network [2] represents a tri-national network of natural resource agencies, marine protected areas (MPA) managers, and other relevant experts. Its goal is to enhance and strengthen the conservation and protection of biodiversity in critical marine habitats and to help foster a comprehensive network of MPAs in North America. The Gulf of California contains five marine priority conservation areas (PCAs). These regions are the Corridor of Los Cabos/Loreto, Alto Golfo de California, Grandes Islas del Golfo de California/Bahía de Los Ángeles, Humedales de Sonora, Sinaloa y Nayarit/Bahía de Banderas, and Islas Marías. These PCAs are part of one of the most productive marine ecosystems on Earth [2].
Titles I and II of the Marine Protection, Research, and Sanctuaries Act (MPRSA) [6], also referred to as the Ocean Dumping Act, generally prohibits the following: transportation of material from the United States for the purpose of ocean dumping; transportation of material from anywhere for the purpose of ocean dumping by U.S. agencies or U.S. flagged vessels; and the disposal of material transported from outside the United States into the U.S. territorial sea. In order to deviate from these prohibitions a permit must be obtained. Under the MPRSA, the standard for permit issuance is determined based upon whether the dumping of the material will "unreasonably degrade or endanger" human health, welfare, or the marine environment [6].
The areas in which this project will occur are ecologically rich. Our project spans two ecologically sensitive areas that are part of the North American Marine Protected Areas Network, the Upper Gulf of California and the Colorado River Delta [16]. The Gulf of California is an area rich in ecological heritage. Not only is the area famous for John Steinbeck’s poetic descriptions of its flora and fauna in The Log of the Sea of Cortez [21], but it also has immense natural capital. The area is home to one third of the world’s whale and dolphin species and contains 39% of the world’s marine mammal species [23]. The project also runs, via pipeline, through the Sonoran Desert, which is one of the most ecologically rich and unique desert ecosystems on the planet [1]. The ecological impact on this desert ecosystem will be low, because the piping will follow the World Health Organization’s safe piping guidelines [26], and only relatively small portions of desert habitat will be used for the piping and plant operations in order to minimize ecological impacts.
The proposed pipeline also runs through the densely vegetated Estero la Pinta and Estero Almejas estuaries. A keystone species of these estuaries is the coastal mangrove. These mangroves are not only primary producers in this ecosystem and great carbon sinks, but provide the physical habitat that most of the invertebrates in this coastal region call home [1]. It will be necessary to remove large portions of mangrove forest to run the saltwater intake pipes through Sonora; this will effectively upend these coastal ecosystems from the bottom up, potentially causing localized extinctions of small organisms [1]. The initial proposal for this plan involved reverse osmosis desalination, which produces massive amounts of brine waste that would likely have to be discharged into these estuaries, potentially causing great ecological damage [1]. Fortunately, we have chosen to use the multi-effect distillation method which creates a solid waste that will not have to be put into these estuarine ecosystems.
Species of Concern
The dense entanglement of the ecological communities of both the Gulf of California and the Sonoran Desert will cause cascading, negative effects that will be widely spread throughout the areas that surround the desalination plant. Economic value, endangerment, cultural significance, and ecological importance have distinguished certain native species to be of special concern when considering the ecological implications of building the plant:
“Each of them in his own tempo and with his own voice discovered and reaffirmed with astonishment the knowledge that all things are one thing and that one thing is all things—plankton, a shimmering phosphorescence on the sea and the spinning planets and an expanding universe, all bound together by the elastic string of time. It is advisable to look from the tide pool to the stars and then back to the tide pool again.” -John Steinbeck, The Sea of Cortez [16]
Below is a slideshow highlighting important species of concern as related to this proposed project [3] [11] [12] [13] [16] [19].
References
[2] Commission for Environmental Cooperation, North American Marine Protected Areas Network: Gulf of California 2011. Available at:
[3] Convention on International Trade in Endangered Species of Wild Fauna and Flora. (2013). [online] United Nations Environment Programme. Available at: http://www.cites.org/eng/app/appendices.php [Accessed Feb. 2015].
[4] Desalination Plant Intakes: Impingement and Entrainment Impacts and Solutions. (2011). [online] WateReuse Association. Available at: https://www.watereuse.org/sites/default/files/u8/IE_White_Paper.pdf [Accessed 2 Apr. 2015].
[5] Einav, R, Harussi, K & Perry, D, 2002, "The footprint of the desalination processes on the environment", Desalination, Vol. 152, No. 1-3, pp. 141-154. .
[7] Ghaffour, N., Missimer, T. and Amy, G. (2013). Technical review and evaluation of the economics of water desalination: Current and future challenges for better water supply sustainability. Desalination, 309, pp.197-207.
[8] Greenlee, L., Lawler, D., Freeman, B., Marrot, B. and Moulin, P. (2009). Reverse osmosis desalination: Water sources, technology, and today's challenges. Water Research, 43(9), pp.2317-2348 .
[9] Hendrickx, M., Brusca, R. and Findley, L. (2005). A distributional checklist of the Macrofauna of the Gulf of California, Mexico =. [Arizona]: Arizona-Sonora Desert Museum.
[10- Hernández-Escobedo, Q., Saldaña-Flores, R., Rodríguez-García, E. and Manzano-Agugliaro, F. (2014). Wind energy resource in Northern Mexico. Renewable and Sustainable Energy Reviews, 32, pp.890-914.
[11] International Union for Conservation of Nature, (2014). The IUCN Red List of Threatened Species. [online] Available at: http://www.iucnredlist.org [Accessed Feb. 2015].
[12] Morgan, L., Maxwell, S., Tsao, F., Wilkinson, T. and Etnoyer, P. (2005). Marine Priority Conservation Areas. Baja California to the Bering Sea. Montreal, Canada: Commission for Environmental Cooperation.
[13] National Oceanic and Atmospheric Administration, (2000). Annual Report: Administration of the Marine Mammal Protection Act of 1972. Washington, D.C.
[14] National Research Council, (2008). Desalination: A National Perspective. [online] Washington, D.C.: The National Academies Press. Available at: http://waterwebster.org/documents/NRCDesalinationreport_000.pdf [Accessed 8 Feb. 2015].
[15] Nix, R. (2013). The Gulf of California: A Physical, Geological, & Biological Study [online] University of Texas, Dallas. Available at: https://www.utdallas.edu/~rnix/MAT-SE_Units/gulf_cal.pdf [Accessed 1 Feb. 2015].
[16] North American Marine Protected Areas Network. (2015). [online] Available at: http://www2.cec.org/nampan/ [Accessed Feb. 2015].
[17] Pacific Americas Flyway. (2011). [online] Birdlife International. Available at: http://www.birdlife.org/datazone/userfiles/file/sowb/flyways/1_Pacific_Americas_Factsheet.pdf [Accessed Mar. 2015].
[18] Pacific Institute, (2013). Key Issues in Seawater Desalination in California: Marine Impacts. [online] Oakland, California. Available at: http://pacinst.org/wp-content/uploads/2013/12/desal-marine-imapcts-full-report.pdf [Accessed 1 Mar. 2015].
[19] Reddy, K. and Ghaffour, N. (2007). Overview of the cost of desalinated water and costing methodologies. Desalination, 205(1-3), pp.340-353.
[20-] 2011, Seawater Desalination Costs, Water Reuse Association Desalination Committee.
[21] Steinbeck, J. and Ricketts, E. (1958). The log from the Sea of Cortez. London: Heinemann.
[22] Tabassum-Abbasi, Premalatha, M., Abbasi, T. and Abbasi, S. (2014). Wind energy: Increasing deployment, rising environmental concerns. Renewable and Sustainable Energy Reviews, 31, pp.270-288.
[23] The Gulf of California. [online] United Nations Educational, Scientific, and Cultural Organization. Available at: http://whc.unesco.org/en/list/1182/ [Accessed Feb. 2015].
[24] United Nations Educational, Scientific, and Cultural Organization. Islands and Protected Areas of the Gulf of California, 2011. Available from http://whc.unesco.org/document/116264 [9 April 2015]
[25] Wade, N. (1993). Technical and economic evaluation of distillation and reverse osmosis desalination processes. Desalination, 93(1-3), pp.343-363.
[26] World Health Organization, (2004). Safe Piped Water: Managing Microbial Water Quality in Piped Distribution Systems. IWA Publishing.
[27] Zhang, HL Baeyens, J & Caceres, G 2013, ‘Concentrated solar power plants: Review and design methodology’, Renewable and Sustainable Energy Review, vol. 22, pp. 466-481. Available from: Elsevier. [4 April 2015]