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"Water shoots into the cylinders at a pressure of 70 atmospheres and is pushed through the membranes, while the remaining brine is returned to the sea."

I've heard this brine can have a pretty negative ecological impact, I wonder how that could be mitigated.

They conveniently have an already briny place to dump it all:

"The brine discharge from the plant will be piped 100 miles north through Jordan to replenish the Dead Sea"

Huh. That's pretty cool and very convenient.

That's for the new plant they're building, not the currently active ones.

Explain why?

The ocean is say 99 parts water and 1 part stuff. We take out 1 part water and .01 parts stuff, keep the water, then put the .01 parts stuff back. Doesn't seem to really change the ocean concentration? I guess maybe if dumped too close to shore it could make a brine slick?

https://en.wikipedia.org/wiki/Desalination#Outflow gives an overview of the environmental problems in desal outflow:

> Desalination processes produce large quantities of brine, possibly at above ambient temperature, and contain residues of pretreatment and cleaning chemicals, their reaction byproducts and heavy metals due to corrosion.[45] Chemical pretreatment and cleaning are a necessity in most desalination plants, which typically includes prevention of biofouling, scaling, foaming and corrosion in thermal plants, and of biofouling, suspended solids and scale deposits in membrane plants.[46]

> To limit the environmental impact of returning the brine to the ocean, ...

> Brine is denser than seawater and therefore sinks to the ocean bottom and can damage the ecosystem. Careful reintroduction can minimize this problem. Typical ocean conditions allow for rapid dilution, thereby minimizing harm.

What's an example of not typical?

Here's an article which points out that the Arabian Gulf is shallow, with low circulation rates and high evaporation rates which make it naturally saltier. That, combined with the damming of freshwater and increasing number of desal plants places a limit on to how much it can be use as a water source: http://www.thenational.ae/news/uae-news/environment/desalina...

From the article, "chemical-free method." [1] I'm sure the salt concentration isn't great, but it's a lot easier to spread salt around than remove heavy metals and cleaning chemicals.

[1] https://www.researchgate.net/profile/Ilana_Berman-Frank/publ...

More details at http://www.filtsep.com/view/44376/success-behind-advanced-sw... :

> Minimizing the plant's environmental impact: Pipe jacking .... Other measures: the potential impacts of the Sorek Plant's operation on the environment were thoroughly assessed, and appropriate measures were taken to prevent, minimize and mitigate these. The following are some highlights of these measures:

> – The feed water pumping station is located far (2,400 meters) from the coastline, and feed water flows by gravity to the on-site pumping station.

> – Entrainment and impingement effects at the intake system are minimized, thus minimizing the consumption of electricity and chemicals (especially CO2) and reducing the emission of related greenhouse gases, air pollutants and noise.

> – Environmentally-friendly antiscalants, and inorganic and treatable cleaning solutions, are used.

> – Brine is discharged back to the sea approximately 2 kilometers offshore, and at a depth of 20 meters through a specially designed outfall system (diffusers) that enhances quick brine dilution to the seawater body. The critical parameters of the brine disposal are monitored online, 24/7.

> – The plant is equipped with a special sludge treatment system to treat any effluents generated in the process. This system removes all suspended matter and only clear water is discharged to the sea.

Why don't they create a huge "sea" using concrete and just dump the brine there? I'd imagine if they built it large enough, they could dump all the brine they needed to and it would evaporate faster than they could pour it in (leaving behind the salts/chemicals).

The evaporation rate is too low.

From http://www.ide-tech.com/blog/b_case_study/sorek-project/ assume 26,000 m³/hour of brine outflow.

According to http://www.engineeringtoolbox.com/evaporation-water-surface-... , 1000 sq. meters of water surface evaporates under 500 kg/hour.

26,000 m³ = 26,000,000 kg => 52,000,000 sq. meters are needed or 52 sq. km.

However, as the salinity increases, the evaporation rate decreases. If I read http://www.actis.com.au/evaporation_rate_of_brines.pdf correctly, a saturated saline needs almost 50% more area for the same evaporation rate.

So, call it 75 sq. km. for your evaporation pan/sea.

Oh, and double it because night-time. And add more safety factor because of rain. Perhaps 200 sq. km will do?

That's a huge area.

As a quick check, some of the storm waves in the eastern Med. can be 5 meters high - http://www.sciencedirect.com/science/article/pii/03783839859... . So you're talking about some massive walls. To say nothing of redundancy, since you don't want the sea to breach a nearly full basin of salt.

That's not how desalination works in practice, you don't end up with 100% salt as a result, even so that would be problematic. Typically you end up with about half of the inflow salt water being converted to fresh water and the other half being converted to higher salinity salt water.

Note that the salt in seawater is actually about 3.5%. So what happens is you suck up a bunch of seawater, which is pretty easy to mitigate negative effects from, and then you have an outflow of 7% salinity seawater, which you have to be somewhat careful with. Ignoring power usage, the US draws something like ten thousand cubic meters per second of water for its use. So a single plant that is supplying water for, say, only a million people might be expected to discharge a volume of water brine that was on the order of 1 million cubic meters a day. The ocean is big, but it would be extremely costly to discharge that amount of brine into the ocean in a way that wouldn't create a very large persistently briny volume near the discharge point. Also, that discharge point is almost certainly going to be near to the shore, which means that it will impact ocean life.

You are correct. The new plant in San Diego dumps out a ~20% brine IIRC that is supposed to be not as bad as the 50% brine that creates dead spots in the ocean. Not sure about the Israeli brine, but they did help develop the San Diego facility.

High local concentrations could certainly be a problem, but it seems pretty easy to solve.

Just setup a pump to pull a ton of sea water into the plant and deposit back out off shore. Slowly inject the brine into the stream and it would be instantly diluted.

Not easy. You have to consider the energy cost of pumping tons of sea water around.

Still easy, just expensive.

My understanding is that the brine you get from desalination is only slightly more salty than sea water. It might take 20 gals of sea water to prosuce one gallon of desalinated water.

Gravity? Make a 3 mile pipe with a small angle down.

You still have to pump the water uphill.

Might be able to use the density differences to get some passive effect?

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