"Solar umbrellas" could reduce the blight of evaporation ponds
Scientists at Berkeley Lab have developed a sort of “solar umbrella” which could radically reduce the amount of land needed for industrial evaporation ponds.
Evaporation ponds are a cheap way to deal with waste water contaminated by industrial processes in various industries, including power plants, desalination plants as well as the oil, gas and lithium industries. The idea behind evaporation ponds is to create shallow expanses of waste water which is naturally evaporated by sunlight, leaving behind solid waste which can be more easily disposed of.
The largest ponds can be the equivalent of hundreds of football fields in area, sometimes laid out one next to the other forming giant mosaics occupying vast areas of land.
As well as the direct impact they have on the natural environment, the high concentrations of salt and elements such as selenium can pose a direct risk to birds, which can mistake the ponds for natural wetlands.
An experimental prototype of the scientists’ umbrella has seen evaporation rates more than 100 percent greater than normal, which could mean that evaporation ponds can one day be significantly reduced in size.
The umbrella works on the principle that water is much better at absorbing solar radiation in infra-red wavelengths. Whereas normal sunlight will gradually heat the whole depth of the water, infra-red intensely heats only the surface, down to a depth of a mere 100 micrometers or so.
By building a canopy that sits a foot above the water, the incoming sunlight is converted from wavelengths of 400 to 1,500 nanometers to 3,000 nanometers or more, and the rate of evaporation increases.
This is not the first attempt to harness solar energy to improve evaporation ponds, but to date, most proposals have involved floating sunlight-absorbing materials in the ponds themselves. According to the Berkelely Lab researchers, these have the shortcoming of becoming clogged up with contaminants so that, as time passes, their performance drops off a cliff.
With more work, the researchers think their concept has the potential to increase overall evaporation by 160 percent. They intend to do economic analyses of the technology for both lithium extraction and desalination plants. They also hope to reduce costs by making the umbrella out of an inexpensive polymer.
The research was led by Akanksha Menon and Ravi Prasher of Berkeley Lab, and was published this week in the journal Nature Sustainability.
Source: Berkeley Lab