Should heat and cool it with standing soundwaves. Salty water takes the heat, cools and falls (brine-fall) rest is less salty.add membranes at intersection points..
Why is desalination so difficult?
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Re: Why is desalination so difficult?
#62Can I shower in salt water? Then all I need to do is desalinate drinking water. “Distributed” home desalination for drinking water seems like the best approach in my mind, then people can pay as much or as little they need, but I have no real data to back this up.
No. Unless you want salt-caked hair. And body. Curious, have you ever been to a beach?
yeah but I usually feel quite refreshed after coming out of the waves, but keep in mind we don’t need clean feelings to survive, we do need fresh drinking water
Re: Why is desalination so difficult?
#63The energy costs are a bit of a red herring depending on local conditions. In California we currently "curtail" i.e. discard a huge amount of renewable energy in the spring season. If we can seasonally apply that energy to desalination, and store the fresh water for later, it is essentially a huge time-shifting battery that stores excess spring energy for the summer.
There's lots to unpack here why this isn't workable at scale.
1) Renewable energy product still has a cost associated with it, even if it is at times, excess.
2) That excess capacity, and the times when there's more energy produced than consumed might not match with water demand.
3) There definitely isn't, and won't be, enough excess renewable capacity to distill even a fraction of the fresh water consumed.
4) This means that you still have to calculate a per kWh cost for the energy consumed to distill salt water to fresh water. The average kWh might not be the same as the market average kWh price, since if you make your distillation plants oversized so you can utilize any spare energy production, but there will still be a price.
5) This price will most likely mean that the per gallon cost of distilled water will be higher than RO, or water pumped through a pipeline.
Desalination is still an extreme measure taken when all other forms of fresh water are cost prohibitive.
Re: Why is desalination so difficult?
#64The energy costs are a bit of a red herring depending on local conditions. In California we currently "curtail" i.e. discard a huge amount of renewable energy in the spring season. If we can seasonally apply that energy to desalination, and store the fresh water for later, it is essentially a huge time-shifting battery that stores excess spring energy for the summer.
I assume this isn't done due to the large cost of building a desalination plant, which isn't paying for itself when it's not running. The money could be invested in something else that runs 24/7.
Re: Why is desalination so difficult?
#65Googly eyes on the flow meter
Re: Why is desalination so difficult?
#66Is it just me, or did this article dance around the question? I am not a physicist but let me give it a stab: except for a few specialized steps like UV or oxidizing heavy metals, most filtration is mechanical. A series of filters with smaller and smaller pores capture more and more of the mess in the water like bacteria and particulates while UV breaks down viruses, the oxidizer precipitates out metals, and so on. N…
I think it's more a problem of entropy; You're taking a high-entropy mixture and trying to extract a pure substance. Think sorting red and blue lego.
Re: Why is desalination so difficult?
#67Stupid question time, why not expose the sea water over a larger area and expose to sunshine? There's plenty of room in the UAE for this, somebody is even building a wall that could hold the water which could be dual purpose and act as cooling via evaporation...
I mean basically you're describing a solar pond (https://en.wikipedia.org/wiki/Solar_pond) or salt evaporation pond (https://en.wikipedia.org/wiki/Salt_evaporation_pond). There isn't an easy way to recover the evaporated water from that process; you would effectively have to build an artificial enclosed environment and it wouldn't work as fast as exposure to the elements. Basically you would need a still (as in for alcohol) the size of 20 football fields. But sun power wouldn't be enough to power it fast enough to be practical. Maybe if you moved it into outer space...
Re: Why is desalination so difficult?
#68Because water is the universal solvent and NaCl is probably the most readily water-soluble salt. Reversing that state is going to take a lot of work
Re: Why is desalination so difficult?
#69Probably very dumb idea, but would it be feasible to just pump and sprinkle sea-water on hot, dry desert and let it naturally evaporate, and then collect it as fresh rainwater back? i.e. how much water would you need to evaporate to have a noticeable increase in rainfall?
i'd like to see the xkcd author tackle this as a "What If?"
He already has. https://what-if.xkcd.com/152/
Re: Why is desalination so difficult?
#70Relatively high energy cost since you’re undoing an endothermic reaction, you need to do a lot of it since we use water in large quantities… but most of all, the planet naturally does a lot of desalination for us already through various geological processes, so our “price point” for desalination is $0 per liter (infrastructure to capture rain, dam rivers, or tap groundwater isn’t literally free, but it’s pretty close…
In 2022, 85% of the country's drinkable water was produced through desalination of saltwater and brackish water. If there is a real need, and a will to address it, we have everything we need to to it. https://en.wikipedia.org/wiki/Water_supply_and_sanitation_in...
>In 2022, 85% of the country's drinkable water was produced through desalination of saltwater and brackish water.
Israel does this by burning massive quantities of fossil fuels: https://en.wikipedia.org/wiki/Energy_in_Israel#/media/File:E...
It's not even remotely economical without huge government subsidies. Completely untenable with current technology for poorer countries, or anyone that cares at all about carbon emissions.