Sunlight Helps Turn Salty Water Fresh 58
MTorrice writes "With energy-efficient desalination techniques, water-starved communities could produce fresh water from salty sources such as seawater and industrial wastewater. But common methods like reverse osmosis require pumping the water, which uses a substantial amount of energy. So some researchers have turned to forward osmosis, because in theory it should use less energy. Now a team has demonstrated a forward osmosis system that desalinates salty water with the help of sunlight. The method uses a pair of hydrogels to absorb and squeeze out freshwater."
Re:Am I missing something? (Score:5, Informative)
How is this distinctly more efficient than simply using sunlight to warm water, which evaporates, and collecting the fresh water that condenses? Desalination plants work like this, except they tend to use energy from some other source to boil the incoming seawater.
Efficiency isn't one of the claims being made here. In fact TFA indicates that at the lease an order of magnitude improvement is required to get this anywhere near competitive.
But they do mention that the highest temperature required is 30C, with is well withing what you can collect with nothing more than greenhouse, and a heck of a lot lest than evaporator processes need.
However, the summary jumped to conclusions about the seawater bit.
The device also struggles with desalinating seawater, which has a salt concentration about 17 times greater than the team’s test solution, As a result, he says the current method would be most useful for purifying industrial wastewater streams that have a lower salt concentration.
.
So, not really practical at this time.
Re:Am I missing something? (Score:2, Informative)
Evaporation takes a great deal of energy: about 2 MJ/kg.
If the solar flux is 500 W/m^2 and the system is otherwise perfectly efficient, that would permit evaporating at most 0.9 L/m^2-hr.
The system in the article can produce 10 L/m^2-hr with unconcentrated sunlight of that intensity, or 25 L/m^2-hr if concentrated to 2 kW/m^2. So it's at least 10 times more efficient than evaporation, and in practice quite a lot more than that.
Concentrating the sunlight is less energy-efficent, but allows a given area of their fancy stuff to produce water faster.