Why is desalination so difficult?

Post by soperj » Wed, Jul 05, 2023, 9:32 PM UTC

samstave wrote: post #39

zokier wrote: post #9

Probably 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?

You know this is how the Phoenecians became the dominant culture, its also where the term "salary" comes from and "worth his weight in salt" -- as salt was the only known preservative of the massive amounts of Tuna the phoenecians were catching and shipping throughout the mediterrainian - and made them a super-power - they had control of the preservance of food over shipping distances... Salt was used as money. EDIT:…

Post by schiffern » Wed, Jul 05, 2023, 9:32 PM UTC

Robotbeat wrote: post #200

jerf wrote: post #126

Earlier quoted context omitted.

There are several practical problems dumping the brine back in the sea. If you dump it on a living ecosystem you tend to kill it. Living ecosystems are, unfortunately, concentrated right where we are desalinating and is cheap to dump. Compounding this problem is that water mixes much more slowly than your intuition suggests. It can stay a coherent mass of high-salt water way longer than you'd think, killing as it goe…

> If you dump it on a living ecosystem you tend to kill it. This is false and somewhat dishonest. This is simply a choice of not diluting it enough. There is nothing about the discharge from reverse osmosis that is any more fundamentally toxic than the natural process of evaporation. Proper dilution is essential, and treating the discharge as fundamentally toxic actually undermines the engineering to do this proper d…

Post by eropple » Wed, Jul 05, 2023, 9:37 PM UTC

giantrobot wrote: post #220

suddenclarity wrote: post #145

Earlier quoted context omitted.

No reason to keep the 1:1 ratio. Use the salt to replace our current salt mines/outtakes and then use the water as an addition to our current freshwater usage.

The brine waste from RO is still mostly water. In order to extract the salt you'd need to evaporate the water which still takes a lot more energy. You could use evaporative ponds to let the Sun do the work but that takes a lot of space. In either case you're spending a lot more money per pound than just digging the salt out of a mine.

Post by flybrand » Wed, Jul 05, 2023, 9:40 PM UTC

Post by Hxnd » Wed, Jul 05, 2023, 9:41 PM UTC

Veserv wrote: post #132

iudqnolq wrote: post #120

Earlier quoted context omitted.

That equates to around 4,000 liters per person per day. Freshwater withdrawals is a very broad category, it also includes water released to turn hydropower turbines. But it's also unfair to compare across countries without taking into account water sent between countries in the form of produce and products.

You were quibbling about how 1,000 liters per day does not adequately account for all usage. Freshwater withdrawals is on average going to be a overestimate and the US is one of the worst outliers with significant agricultural exports which are one of the largest contributors to differential water withdrawals. Despite this, it would only be $2.00 per day for a fully desalinated water supply even if we safely overesti…