SustainableEngineering@Edinburgh Group 7: DESALINATION - A SUSTAINABLE

OPTION? By: Matthew Harvey (0679153); Richard Lea (0569383.); Callum Kerr (0561778); Gary Britton (0789271)

IMS3/MSFM3 Sustainability Module, March 2008

Desalination has been a source of fresh water since the 1950’s in the Middle East. But is desalination a sustainable option for countries around the globe as water scarcity becomes a bigger problem?

INTRODUCTIONSince the 1950’s the world’s population has doubled but at the same time the amount of fresh water hasn’t changed. This problem is only set to worsen as population continues to rise and climate change affects the amount of fresh water available each year. Regions of the world will no longer be able to rely solely on fresh water sources to provide drinking water.

DESALINATION METHODS

R.O uses 4kWh/m3 (site specific) compared to 13kWh/m3 for MSF (distillation). R.O has a unit cost of $0.5/m3 making it close to matching cheaper water recycling and re-use alternatives. R.O is becoming the leading desalination method due to it’s lower energy use making it the more sustainable method.

SUSTAINABILITY PROBLEMS Impingement and entrainment of organisms at the sea water intake of large volume plants. High energy use required for plants, especially plants using thermal methods. Energy usually comes from fossil fuels which is a finite source. Disposal of high concentrate brine solution, post-process. Brine is double salinity of normal sea conditions. Which can seriously affect the marine environment.

FUTURE DEVELOPMENT

Australia – 2 year drought has forced Government to consider desalination. Projects in Perth and Sydney combine plants with renewable energy sources.

America – Florida, Texas and California all implementing desalination. Florida has the Tampa Bay plant with a 25mgd capacity.

Spain - Looking to double its already large desalination capacity within the next year.

CONCLUSIONS

1. Desalination is on the rise around the world.

2. Need proper measures for planning and running of large scale desalination plants

3. Process still requires high energy input, so often relies on fossil fuels.

4. New desalination plants will need to incorporate sustainable energy sources.

5. Research is needed into the impact of brine disposal on the marine environment.

INSTITUTE’S POLICYHave a large influence on industrial and public support. The EU: Recognise the need for alternative water sources Have a weak stance on fresh water as a basic human right. Has expensive safety checks for intake water preventing large scale desalination.

Influence from WWF, who sway public opinion by taking a stance against desalination. Institute support would allow greater research into desalination as a sustainable water source.

REFERENCESS. Lattemann, T. Höpner (2008) “Environmental impact and impact assessment of seawater desalination” Desalination 220 1-15.American Water Works Association(2006) Desalination of Seawater and Brackish Water, Denver

Rachel Einav, Kobi Harussi, Dan Perry (2002) “The footprint of the desalination processes on the environment”, Desalination 141-154

Distillation.Involves evaporating saline water to obtain pure water by condensing the vapour.

Reverse Osmosis.Uses semi-permeable membranesto separate fresh water in one chamber from brine. Applying pressure in excess of the osmotic pressure to the brine, fresh water will pass in the reverse direction, i.e. out of the brine.

“While seawater desalination is already a well-established water source in these regions [Middle East], the era of large-scale desalination projects is only about to start in other parts of the world.”

ENERGY PROBLEMS

All desalination methods require a large energy input, historically coming from fossil fuels. With sources diminishing across the globe future plants will need to look at sustainable alternatives. Possible sources are:

Wind power

Photovoltaic

Nuclear (good for large scale plants)

Tidal

SUSTAINABLE SOLUTIONS

Co-location with power plants.

Desalination Plant located by power plant

Uses existing water intake infrastructure of power plant

Brine discharged into power plant outflow, diluted due to large volume of water flowing through out-take.

Other solutions are using long pipes to discharge brine into deep sea areas away from the coast.