Why cant Water Desalination Plants store excess Salt on land somewhere?


Brine, salt water, things that come out of Desalination plants are normally put back in the ocean at an environmental cost. Why cant the brine be pumped somewhere safe, or have the salt removed and put somewhere safe? Arent there plenty of places on land to put all of that salt? Why cant the brine be pumped into the desert to evaporate?

In: 4

Cuz dumping ocean salt back to the water will not make ocean more salty, there is too much water in ocean to make a difference, but having that much salt on land will kill everything that lives there and nearby

It’s circular. If you desalinate sea water, the desalinated water will eventually end up back in the sea. So if you took the salt out and stored it on land, the salinity of the sea would slowly go down.

The scale of it is completely off the charts. Storage is infeasible. A desalination plant produces around 1-1.5 the amount of brine for every amount of fresh water. A desalination plant produces hundreds of thousands of m^3 of fresh water a day meaning at least that amount of brine daily. For reference, an olympic sized swimming pool has around 2000-2500 m^3 capacity – so the amount of storage for 1 day’s worth of brine (every day) would be around 100 swimming pools.

Even though desalination is expensive, water is still (relatively) inexpensive and is impractical at high costs. Pumping water or brine anywhere is expensive. Unless the desert is within a few tens of miles (at the most!) of the plant, the cost of pumping the water would be financially infeasible, not to mention having a huge carbon footprint from using all that energy.

The effects of brine isn’t huge, all things considered. With any sort of wave activity at the sea or ocean, the brine mixes and becomes insignificant within a fairly short distance. Of course, it needs to be discharged responsibly (ie not near sensitive marine ecosystems or fisheries etc). But remember the evaporation off the ocean removes far more water (like millions of times more) from the ocean a day than any amount of desalination plants could ever hope to do although it doesn’t do it in a concentrated area.

Simple answer: space, contamination, and money. Any waste product will require large amounts of land to store. It also takes a lot of money to build something to hold or store and monitor the waste product.

Even if it’s a hole in the ground (just like a landfill) it would be required to provide an barrier to protect contamination to a ground water source.

Also, think about the cost to transport millions of gallons of brine water to a desert or wherever. Even if you say you can pump it, it would cost a ridiculous amount to pump it.

Source: Professional Engineer that designs water and wastewater plants

Fun fact: Gulf Coast countries that heavily rely on desalination tend to primarily desalinate ground water, not sea water. – Reject brine is still fed back into the original source, but that unfortunately aggravates the issue further, because with no precipitation, ground water does not see enough dilution to not be salty.

Because of the global cycle of evaporation and precipitation, the only source of “real” fresh water is rainfall (or snow, hail, pick your precipitate). So temperate or tropical areas with a lot of precipitation have fresh water stores underground that are constantly fed by water trickling through the many layers of the Earth’s crust until it “pools” in those underground aquifers. Arid desert areas that don’t see a lot of fresh water coming in often have ground water that is quite salty. Oasis are where the occasional aquifer feeds a spring, but aquifers are more common in some areas (e.g. Saudi Arabia) than others (e.g. the UAE).

Because of this dynamic, evaporating reject brine on the surface doesn’t actually remove salt from the system, it just creates an entirely unpredictable reservoir of salt that might trickle back into the ground water at any point, while also removing more water (which would have been returned in the reject brine, but has now been evaporated to late turn into precipitation that will not actually happen in place, but condense somewhere else on the planet).

So you might be thinking “why not just take the salt OUT of the water entirely?” – well, the short answer is: it’s just too hard. Desalination is essentially a progressive filtering process, which is very hard to get perfect if you are missing the liquid phase. So the salt water can be concentrated down, but not really split into its components. And while there are small-scale desalination plants capable of full removal, they are currently not feasible or / and cost-effective at the scale needed.