Articles & Case Studies

Are desalination plants the solution to the water crisis?

Posted: Monday 5th June 2006

With the recent hosepipe bans substantiating the seriousness of the UK’s 17 month drought, now is past the time to think about future solutions and prevention so that we are more prepared for climate change-related alterations in weather patterns. Much has been made of the water lost through leaky pipes – particularly in the south east which is the worst hit area, but while more is now being done to repair and replace ageing pipes, it will take a lot more than this to stop a recurrence of the present problem.

With so many factors to take into account: cost effectiveness, reliability, timescales, space, energy efficiency and so on, it’s a subject that provokes raging debate. Thames Water believes the most viable solution for London now is a desalination plant. With 97% of the world’s water contained in the sea, it seems an entirely sensible solution to convert this into drinking water, provided the technology is available – which it is. In the past, desalination has been rejected due to high costs and energy use, but due to further research, costs have been reduced and this is becoming an increasingly viable option.

Thames Water is sure their proposed plant in the London Borough of Newham would offer a best-case-scenario for London’s water shortage, having considered all the possible options. Although their proposals were initially approved by the London Borough of Newham, London’s Mayor Ken Livingstone then directed Newham to refuse the planning application. The project had already passed through Ofwat’s review of the company’s business plan, and the case for building the plant is recognised by the Environment Agency and CCWater

One very dry year on and it is clear that actions such as educating the public on water saving methods like running taps for less time and using buckets to wash the car are not going to be enough to prevent serious drought. An appeal has been lodged against the Mayor’s ruling but it could be several months before a decision is made.

“The capital’s water resources face huge pressures from faster than expected population growth and rising personal consumption of water. All of London’s fresh water resources are already being used, and the plant is the only viable option that can provide the city with the extra water it needs,” explains Chris Shipway, senior press officer at Thames Water.

Alternatives that have been considered include greywater recycling, further work to store winter rainfall underground and piping additional supplies into the region from parts of the UK with surplus water. But none of the options could reliably provide the necessary water quickly enough and at an acceptable cost. Other conventional options like treating water from boreholes and rivers are not possible because there isn’t enough freshwater.

“Surface and ground water resources offer a finite volume of water. We are limited in the amount of water we can take from rivers and underground sources, and placing them under further strain would be environmentally unsustainable, reducing the flow of water through streams and rivers at the cost of the local environment. This is why we have to look at more innovative solutions, which tend to have higher energy costs,” says Shipway.

Energy consumption is one of Ken Livingstone’s central objections to the desalination plant. “The plant would treat water less than one third as salty as seawater, so the energy consumption is not comparable to traditional desalination – and is less than other options we’ve considered,” says Shipway.

The method used for the Newham plant would be a four stage reverse osmosis process to purify water (this is much more energy efficient than the alternative method of distillation). This utilises the passing of highly pressurised feed water through a semi-permeable membrane so that water molecules can pass through, but molecule impurities (including salt) are unable to pass through and are separated as a concentrate. Reverse osmosis doesn’t need energy to heat water, so this keeps levels down - but pumping water at high pressures does use more energy than conventional water treatment.

Energy recovery devices are being used to improve the efficiency of the desalination plant. Although the highly saline wastewater (concentrate) from reverse osmosis will not have the same pressurisation that was initially applied to the intake water, the residual pressure will be harnessed with a turbine so the energy can be fed back into the process

Thames Water says it would offset some of the energy used for the plant by meeting the Mayor’s policy for 10% of the power to be generated through renewable energy They have also considered a gasification plant (fuelled either by energy crops or waste wood) and wind generated power and are looking to improve the energy efficiency of the sewage sludge powered generators at Beckton – already one of London’s biggest sources of renewable energy.

“We already have excellent credentials in exploiting opportunities for renewable energy including generating 10.5% of our energy needs as a business from renewable sources – a figure in excess of the Mayor’s standards for new developments”, confirms Shipway.

Thames Water also has the greatest capacity to generate renewable power within the M25, aside from power companies. And they are considered industry leaders in the field, using combined heat and power plants at sewage treatment works throughout their region to minimise their carbon footprint.

Desalination uses a lot less energy than many of the other possibilities examined. “There are no viable alternatives that would provide the necessary amount of water in the short time that is available,” says Shipway. And when you put it like that what option do we have?

The current drought will end when it rains enough to replenish our resources, but the scenario has brought the issues to the forefront of our minds. Could this reduced rainfall be part of a permanent change in our climate, and if so, how best can we manage it?

Andrew Boyd

RWE Thames Water plc

Clearwater Court

Vastern Road

Reading

RG1 8DB

andrew.boyd@thameswater.co.uk

Tel: 0118 373 8921




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