Every few years, you hear about some new revolution in the process, but nothing much after. Why is that? Is it very hard to scale up or…?
Also, is it going to become more viable as fresh water is becoming more scarce?
Thank you in advance.
Thank you all. So it was basically what I thought. It’s not hard to do, but it is not really feasible due to many factors.
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Desalination itself is super easy. Take salt water, evaporate and recondense it to separate the salt and other minerals/etc from the water. You can do it yourself on a stovetop or a campfire.
The problem is that there’s no way to scale it easy for the massive demands of human use (personal, industrial, and agriculture). It takes a decent amount of energy to heat up water, and you need to do something with all of the salt you’ve got left over – no matter where you dump it, you’re going to cause environmental problems. Salt is also corrosive so there’s longevity problems with equipment/piping/etc but those are relatively minor problems with partial solutions. You can’t ignore physics, or just make giant piles of salt disappear.
Desalination isn’t particularly hard at a small scale.
The issues with desalination – the area around the plant gets saltier than the rest of the ocean (you have to dump that excess salt somewhere,) which kills all the marine life in the vicinity of the plant. Also, humans need a ton of water, so the plants need to be very large to fulfill all the domestic demand. And since the plants are at sea level, you need large pumps to get all that desalinated water into pressurized pipes – which means you need a lot of power.
It’s not hard, in the sense that it’s not difficult to do in principle. It’s just energy-intensive and therefore expensive, and it requires facilities that are themselves expensive.
It isn’t so much that it’s hard to do, but it’s hard to do cheaply enough to make it economically feasible. Most methods take a lot of energy, others are relatively slow.
In every case though, desalination on a large scale leaves you with all the salt and minerals that you remove from the water. It’s difficult to find somewhere inexpensive to dump those without it screwing up the local ecosystem.
I wouldn’t say it is hard more than it’s energy intensive.
Even using the Sun’s heat–a solar still– which is free, takes quite a bit of energy: I guess it depends on scale as well.
To provide potable water for a medium sized city needs a lot of energy. Then, what to do with the salty sludge leftover.
Do you return this to the ocean? It will make the dump site toxic. Do you store all of it somewhere on land? Again, it’ll make that area toxic to plants and you don’t want rain bringing that salt to the water table, contaminating it.
It takes a lot of pressure and therefore energy to pump salt water through salt-removal membranes.
I operate in the climate space but am not an engineer or expert in water resources. So remember that as I give my understanding. It is *very* expensive. It uses a lot of energy. And it changes the salivation of ocean water around it which probably is not a good thing. The salt must go somewhere. And it can mess with groundwater. It is a solution of last resort.
The primary and least sexy way to begin the fix is conservation in a serious way. No more golf courses. No more home lawns bigger than x. Make wicked sure agriculture is using water in a sensible way. This is very hard but crucial – tackle the water rights monster and make it realistic and sensible. And a culture change. If your clothes aren’t dirty you wear them multiple days before washing. No washing hair everyday. Maybe a shower every few days with quick ‘army’ cleanups everyday. I know this sounds weird or far fetched but it is these type of mind shift that will help us manage in days ahead.
Desalination is primarily done through high pressure filtration, no by phase change. It is more energy efficient, but still extremely demanding.
Also, the super salty brine needs to be disposed of, and can’t just be dumped into one spot in the ocean or it creates a dead spot. You gotta pump it out into the open water in a current…
Basically, it’s expensive. So you don’t do it unless you absolutely must.
It is not hard, it is just very expensive because of how energy intensive it is. When it comes to anything, but especially water, cost is king, in regards to mass adiption.
If the water cost is double to irrigate crops, that is a big problem.
Right now, in most parts of the world, there isn’t an actual shortage of fresh water. The problem is managing and distributing the water that *is* available there, and managing the usage. So it’s generally cheaper to buy & transport water, or reduce usage, than to build and operate a desalination plant. There are some exceptions, like some newly built cities in the Middle East.
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