Seawater desalination for sustainable water supply

Contents I. Introduction 2 II. Seawater desalination and its advantages and disadvantages 2 III. Environmental impacts 3 IV. Policy for desalination plant 3 V. Conclusion 4

Student ID: z5084901
Student name: Boheng Zhu
School of Chemical Engineering
The University of New South Wales
April 2016
Introduction
Australia has uncertain rainfall and most parts of it have droughts, and has increasing population in large cities in recent years (Legislative Council Secretariat 2015). These conditions pose a threat to water supply. In addition, it is more and more limited and improper to build water pipes to draw water from dams and reservoirs. Due to these facts, seawater desalination plants have been constructed to ensure the water supply in Australia’s large population urban centers. Seawater desalination mainly uses membrane process to desalinate seawater rather than thermal process, because reverse-osmosis (RO) in membrane process consumes less energy, and in the RO desalination, seawater is divided into two streams: one with very high dissolved salts and the other one with less salts (Gary Crisp, E.A. (Bob) Swinton and Neil Palmer* 2010).
However, seawater desalination has its drawbacks: energy intensive, generation of greenhouse gases, impacts of desalination discharge on marine environment and its high operating costs. These issues are associated with Australia’s environment and economy (Reza Dashtpour and Sarim N. Al-Zubaidy 2012), therefore it is necessary to cope with these problems with the development and improvement of the membrane process technology.
This essay will introduce RO seawater desalination, discuss both advantages and disadvantages, some environmental issues and give policies about how government should regulate seawater desalination plant in Australia.
Seawater desalination and its advantages and disadvantages a. Seawater desalination
Seawater desalination is a process separating solids from seawater with semi-permeable membrane. It mainly has two different processes or techniques: membrane processes and thermal processes. In the membrane processes, semi-permeable membrane and reverse osmosis technology are used to remove salts from seawater. In the thermal processes, it uses the various forms of evaporation methods to remove salts from the sea water (M. Mulder, 1996, p.297).
In today’s Australia, membrane processes to desalinate seawater are mainly used to get potable water, for thermal processes consume more energy. In the process of membrane process desalination, first, the seawater will go through a pre-treatment filter to remove the larger particles. Next, under very high pressure, seawater is forced to go through a semi-permeable membrane removing its salts and impurities and this process is called ‘reverse osmosis’ (G, Crisp, & K, Athanasiadis & C Hertle, 2015). At this stage the seawater desalination concentrate is returned to the sea and the seawater desalination permeate is for potable water supply. b. Advantages of seawater desalination
Seawater desalination advantages include sustainability, using infinite seawater, less harm to environment and climate proof. First, seawater is infinite resource and could be used all the time to produce drinkable water. Next, desalination plant does less harm to environment which means its negligible impacts can be controlled and be more environment friendly. For example, the Sydney Desalination Plant uses the renewable energy from a wind farm equivalent to the energy consumed in the desalination plant resulting in no net greenhouse gas emissions as a result of its operation (Sydney Desalination Plant 2010). In addition, it can continuously produce drinkable water regardless of the climate changes as well as greatly meet the water demand for people, industries and agriculture (Ben, R. & Don, G & Alberto, T. 2012). c. Disadvantages of seawater desalination
Seawater desalination has its drawbacks about high energy cost, affecting marine system and health concerns. First, seawater desalination is still energy intensive which means using more fossil fuel or other renewable energy (solar energy and wind power) to generate electricity power. When desalination plant uses more fossil fuel to provide energy, there will be more greenhouse gases having negligible impacts on the environment. What is more, the desalination discharge with high salts could affect the marine flora and fauna. And some people have concerns about the health which could be affected by drinking the desalination water.
Environmental impacts a. Desalination discharge affect marine ecosystem
Desalination discharge return to the sea could bring negligible impacts on the marine environment. For example, waste concentration rich in salt, toxic metals and chemicals from desalination’s equipment de-fouling and water pretreatment will contaminate the sea (Smyth, Chris 2007). As a result of this, the local water salinity, circulation, oxygen levels and temperature could be changed, resulting in dead wildlife and vegetation, and some wildlife will move away from the changed water area. It will cause the loss of fish and tourism industries near the water area being discharged desalination concentrate (API Management Pty Ltd, 2010). b. Seawater intake affect marine ecosystem
Seawater intake for desalination is to collect enough water from the sea. However in this process, impingement and entrainment could cause the wildlife trapped against intake screens by forcing lots of water to desalination plant. This could cause marine system imbalance as well as the loss of marine wildlife (Rashad, D 2007). c. Greenhouse gas emissions
The energy for desalination plant operating usually comes from fossil-fuel generation and it is the main reason why desalination plants may cause greenhouse emissions, therefore desalination could worsen the climate change by adding greenhouse gases.
Policy for desalination plant a. Budget for desalination plant
Before constructing seawater desalination plant, it is necessary to know the overall cost. There are two main costs: capital and operation and maintenance (O&M) cost. These two key costs includes the main component cost about source water collection, pretreatment, desalination, posttreatment, storage and distribution, and disposal of concentrate and other residuals. It is important to know the budget and to know the feasibility of the desalination plant. b. Selecting proper location for desalination plant
It is important to choose a proper site to build seawater desalination plant. Some proper locations near the sea have social and environmental values, thus other locations should be considered. A proper location will make seawater desalination as soon as possible to deliver potable water and cause less negligible impacts on local life and environment. c. Improving technology of seawater desalination
Government should support the development of desalination technology, therefore seawater desalination plant will be more likely to consume less energy cost and cause less environmental issues. Renewable energy such as wind power and solar power should be encouraged to provide the energy for desalination plant. d. Community consultation
Government should consider community’s suggestions and elaborate the detail of the seawater desalination plant construction. By this means, government could make a more reasonable decision about the selection of a location or the overall cost and the designed life. e. Reducing negligible impacts on environment
In order to reduce negligible impacts form fossil fuel generations on environment, renewable energy should be encouraged to reduce the fossil fuel consumption. And it is necessary to monitor the water area (Australian Research Council 2012) which is being discharged desalination concentrate to protect the marine system.
Conclusion
To summarize, seawater desalination could help reduce the pressure of water supply in Australia’s large urban centers and is a sustainable way to secure water resources. Also it has been widely used to produce potable water in recent years. In addition, seawater desalination plant can continue providing drinkable water even if reduction of rainfall causes the poor storage of water in dams and dwindling rivers and shrinking aquifers (Gary Jon Crisp 2012). As a result of that, seawater desalination meet the high demand water and reduce the overuse of reservoir water.
However, there are some environmental issues which need to be carefully taken into consideration. Concentrate of discharge will affect the marine environment and greenhouse gas emissions will cause a series of environment issues. Government should attach importance to improving and regulating the desalination plant as well as taking care of the negligible impacts of the desalination plants by using different policies.
Reference：
1. Ben, R. & Don, G & Alberto, T. (2012), “Potential role of renewable energy in water desalination in Australia”, Journal of Renewable and Sustainable Energy，AIP Publishing, pp. 3-10 2. Legislative Council Secretariat, (2015), “Seawater desalination in Australia”, Facts Sheet, p.1-5 3. Gary Crisp, E.A. (Bob) Swinton and Neil Palmer* , (2010), “A brief review of desalination in Australia in 2010”, Int. J. Nuclear Desalination, Vol. 4, No. 1, pp.66-75 4. M. Mulder, 1996, Basic Principles of Membrane Technology, 2nd Ed., Dordrecht, Kluwer Academic Publishers, pp. 295-300 5. Reza Dashtpour and Sarim N. Al-Zubaidy, (2012), “Energy Efficient Reverse Osmosis Desalination Process”, International Journal of Environmental Science and Development, Vol. 3, No. 4, pp. 349-345. 6. Smyth, Chris. (2007), “Seawater desalination: what it means to our marine ecosystems”. Habitat Australia, Vol. 35, No. 4, pp. 4 7. Gary Jon Crisp, (2012), “Desalination and water reuse—sustainably drought proofing Australia”, Desalination and Water Treatment 42, pp. 323–332. 8. Rashad, D, (2007)， “Desalination Plants: Potential impacts of brine discharge on marine life”, the ocean technology group, final project, Sydney. 9. “API West Pilbara Iron Ore Project - Stage 1 Desalination Discharge Management Plan”, API Management Pty Ltd, (2010), Oceanica 10. G, Crisp, & K, Athanasiadis & C Hertle, (2015), “Desalination for Industry and Resources: Australia’s Success Story for World Application”, Technical Paper, pp.130-134 11. Sydney Desalination Plant, 2016, accessed 10/04/2016, http://www.sydneydesal.com.au/what-we-do/water-supply/