Change Alley

information, opinion, conversation

Green Light For London Desalination

with 5 comments

Boris Johnson paddling a coracleLondon’s new Mayor, Boris Johnson, has dropped a legal challenge to Thames Water’s proposed £200 million desalination plant in Beckton, East London. The High Court challenge was initiated by his predecessor, Ken Livingstone, on the grounds that the project was inefficient and bad for the environment.

Mr Livingstone said cleaner, cheaper and less wasteful alternatives should be found to avoid the “energy-guzzling and carbon-intensive” way the plant was run. According to Times Online, Boris Johnson withdrew the case after Thames Water “promised to introduce a series of environmentally-friendly measures”.

The plant will use reverse osmosis to remove salt from river water. Osmosis occurs between two solutions of different concentrations or strengths. A very fine membrane separating the solutions allows liquid (but not the dissolved solids) to pass from the weak solution to the strong solution.

Over time, the concentration of the two liquids will balance out but pressurising the stronger solution can stop the flow. If the pressure on the stronger solution is increased further the osmotic process is reversed and the liquid passes from the stronger solution making it more concentrated. This reverse osmosis process can be used to remove water from a saline solution (i.e. brackish water) thus providing a desalination technology.

The first reverse osmosis water treatment plant was built in California and started working in 1965. The nice thing about this technology is that it’s highly scalable, suitable for large projects like Beckton, producing enough water for 400,000 homes, right down to small-scale devices like Red Button Design’s ROSS (‘Innovate or Die‘)

According to Thames Water’s FAQ page, the process will be timed to extract water during the three hours leading up to low tide, minimising the salt content to less than one-third that of seawater. This means that the plant will use approximately half the energy required to treat pure sea water, and around 15% of that used by the most energy-intensive thermal desalination plants.

The plant “will use around 6.3MW a year over a 25-year lifespan”. Hmmm, not sure what that means, someone doesn’t know the difference between a megawatt and a megawatt-hour it seems. More work needed, must try harder. Thames Water have “given a legally binding commitment that 100% of the plant’s energy needs will be met from renewable energy”. Options being considered are wind power, and used cooking fat and oil. Initially, however, the plant will be powered by biodiesel, which raises the old questions, where will the biodiesel come from, and what environmental damage will be caused in producing it? I bet it’ll have some palm oil in it.

Interesting how the word ‘sustainable’ doesn’t show up in Thames Water’s information on the plant, it’s all about ‘renewable’ energy, which is more difficult for the green lobby to take exception to. They’re learning.

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Written by Pete Smith

May 13, 2008 at 10:12 am

5 Responses

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  1. Very interesting. ‘Renewable’ indeed. Perhaps Thames Water could buy Shell’s share of the London Array.

    Matt

    May 13, 2008 at 2:52 pm

  2. Clare (Perth, WA) writes about her city’s new desalination plant;

    http://elsewear.wordpress.com/2008/05/13/desalination3/

    Matt

    May 14, 2008 at 7:52 am

  3. The desal plant in Perth seems to have overcome it’s environmental concerns. Although the main “good” thing about it is that it runs on windpower and if the plant wasn’t there, this windpower could be used to replace current coal-generated electricity – governments don’t think of things like that. The tides of the Thames would mix the hypersaline discharge well so that shouldn’t be a problem as it was thought to be in Perth. Used cooking fat and oil can be used as biodiesel -recycling. Although we’d all be better off if the fast food places who crank out the used cooking fat and oil closed down.

    The main problem I have with desal plants is the enormous cost of construction. Perth’s 1st cost $A387 million and the 2nd is expected to cost $A1 billion. This money could be better used in recycling water, etc. Sydney is getting in on the action too with a desal plant in the planning stages.

    Re: The plant “will use around 6.3MW a year over a 25-year lifespan”
    I’ve been reading about electricity generation for a blog post i wrote http://elsewear.wordpress.com/2008/04/25/cheap-coal/ and most things I read used the abbreviation MW to mean megawatt-hour.

    ClareSnow

    May 14, 2008 at 9:13 am

  4. Hi Clare,
    “most things I read used the abbreviation MW to mean megawatt-hour”
    That’s a pity, because that’s not correct usage and can only cause confusion. A megawatt-hour is a MWh, and always will be in my book 🙂
    Quite right to be oncerned about the high capital costs of such projects. They do love their big schemes, don’t they? It’s all about control. The bean counters are scared of decentralised initiatives such as domestic water recycling because it’s much harder to measure success and value for money.

    Pete Smith

    May 14, 2008 at 9:26 am

  5. This is quite a up-to-date info. I’ll share it on Twitter.

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    April 15, 2009 at 6:41 pm


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