kindalike pumping the salty brine into the last mile of a sweetwater river before it enters the sea … (conceptually speaking)
of course you (generic you) can do the math and figure out how much brine can be accepted to not disturb the ecosystem …
and a more relevant problem: if you have a sweetwater river nearby - no need for desalination …
in terms of wastwater runoff: I just stumbled on a vid that explains that out of 100L saltwater, 45 L sweetwater was won and 55 L will run back … so to make math easy, call it 50:50 … so you have 50L of water running back with twice the salt concentration …
doesn’t sound unsurmountable … but as so often - the devil is in the details … e.g. making the mini-geographics work …
Gotta thought: AFAICT, container ship ballast usually takes the form of salt water. Maybe they could load up in port with desalination-concentrate brine instead, and gradually swap it out with regular-salinity seawater while en route? Even concentrated brine seems likely to be much more effectively diluted if dumped across miles of deepwater ocean.
The waste product from the desalination process, referred to as brine, is about twice as salty as normal seawater . The brine is blended with the City’s treated wastewater and is discharged into the ocean over a mile and a half offshore.
You gotta get the brine to the port. That would be expensive unless the desal plant is next to the port (not likely).
Also not sure the ship’s ballast tanks would be enough to put a dent in the amount of brine they need to dispose of…but it could be a part of a larger system (maybe…I don’t know the math on this).
Here in the north of Chile, there are huge mining operations in the atacama-desert - up at 4000+ m. above sea … which use substantial amounts of water, but are only 50 or so km from the sea.
What they did is: come to an agreement with local communities and use the meltwater from above (pretty much where they are) and supply the lower lying communities with desal. water (probably at a 1:2 ratio or so to sweeten de deal).
so they do not have to pump up obscene amouts of water 4km high … (which they do anyway to a certain degree) …
Thinking about Santa Barbara’s desal system that can produce about 10,000 acre-feet of fresh water, and seeing figures of approx 1.5x brine produced, I get about 5 billion gallons of brine per year at max production.
Google suggests that the largest container ships carry 2 to 3 million gallons of water in ballast at max capacity. So there I figure we’d need to load up 2,000 container ships with our brine if they showed up dead empty, which of course is unlikely. I would guess that least half of a ships ballast is relatively “permanent” water, taking my guesstimate to 4,000 ships a year.
Couple problems. Santa Barbara is a very small city with only one desal plant so scale gets quickly even more out of hand for a more populous area. Also, somewhat inconveniently, no container ships dock here. But even so, the port of LA only saw several hundred container ships last year and that’s one of the busiest ports in the world.
Instead of a single desalination plant with pipelines to distribute the brine back into the ocean, I wonder if the reverse would work. Have multiple, smaller desal plants and pipelines to collect/distribute the fresh water to where it’s needed. It would depend on whether this new tech would be viable in small installations as well as large ones.
Are we figuring in salt used for livestock, de-icing of roads, and such? There’d probably still be some salt left over, but this would get us a little closer.
Of course, where is it written that all human fresh water needs would come from desalination? If the brine does become a usable byproduct of desalination, maybe we’ll see desal plants built in the most economically favorable areas, while everywhere else gets their fresh water from the same sources they do now. Rather than build enough plants to meet all our water needs, we may only build enough to meet the demand for brine.
I know treating to the level of gray water is done a lot and that water can be used for many things…just not consumption. My sense of it is that last step to potable water is a big and expensive step.
My biggest question is scalability. It’s easy to make a desalination system that needs no energy input other than sunlight: Take any old desalination system, and attach it to as many solar panels as are needed to power it. But that many solar panels take up a lot of space.
How much area would a system like this need to supply, say, Los Angeles with drinking water?
