Change Alley

information, opinion, conversation

Posts Tagged ‘sustainable

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.

Advertisements

Written by Pete Smith

May 13, 2008 at 10:12 am

Cheap, abundant hydrogen?

leave a comment »

At the Los Angeles Auto Show, Honda unveiled its new model the FCX Clarity, powered by the Honda V Flow hydrogen fuel cell stack. American Honda plans to lease the FCX Clarity to a limited number of retail consumers in Southern California with the first deliveries taking place in summer 2008. This follows a recent announcement from General Motors that it will begin US consumer testing of its Equinox hydrogen fuel cell vehicles in early 2008, as part of ‘Project Driveway‘. Last week, the state of New York opened its first hydrogen vehicle refuelling facility, the first of six planned nationwide as part of the Department of Energy’s Infrastructure Demonstration and Validation Project.

It seems that the hydrogen-powered car just won’t go away. Appealing though the idea of a vehicle that emits nothing but water is, worries over where the hydrogen will come from continue to dog its progress. Most hydrogen today is generated either from non-renewable fossil fuels such as natural gas, or by water hydrolysis, which is only 50-70% efficient. The Holy Grail of cheap, plentiful sustainable hydrogen remains a mirage.

Researchers at Pennsylvania State University may have found an answer. In a paper published in ‘Proceedings of the National Academy of Sciences’, they describe a method of producing hydrogen gas from biodegradable organic material, using electron-generating bacteria and a small electrical charge in a microbial fuel cell. The process, known as electrohydrogenesis, has in the past shown low efficiency and yields, but reactor modifications have achieved hydrogen generation from a variety of organic substances at high yields. Lactic acid and acetic acid achieve 82%, cellulose 63%, glucose 64%.

“This process produces 288 percent more energy in hydrogen than the electrical energy that is added in the process,” said Bruce Logan, Professor of Environmental Engineering at Penn State.

Penn State press release

‘Sustainable and efficient biohydrogen production via electrohydrogenesis’