The light source provides eight hours of electricity per dose of saline water, and the lantern comes with a dedicated water bag for mixing the solution.

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Sapphire Energy's answer is a form of "green crude oil" made from algae, which can be grown on non-agricultural land in shallow paddies full of undrinkable saline water.

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If the demonstration plant works as well as hoped, the plan will be to build combined electricity and hydrogen generating stations in locations where there are geological formations containing saline water overlain by a thick caprock serving as a seal.

ECONOMIST: Tech.view

Algae at least can be grown, with sufficient engineering, on a large scale that does not require prime crop land in competition with growing food crops (as rules out conventional biofuel strategies beyond grants from governments and the European Union), and there is no demand for freshwater since saline water does even better to promote the growth of certain highly oil-yielding strains.

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The alternatives to silicone include saline -salt water - filled pads, or soya-based implants.

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In Colorado's San Juan basin, for example, the water is saline and must be reinjected into wells a safe distance away from any aquifer.

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The cyclists could also drink large amounts of water, or inject themselves with saline solution, in order to accelerate the fading of the glow.

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She said they could not survive long in fresh water and tended to stay nearer the estuary, where the saline level was higher.

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