[ricardobeat]

Someone correct me if I'm wrong (not the best at math), but the ocean is massive. The entire amount of brine they mention (31.5 million cubic meters) fits in one 300m square cube. Even if you drop it in an enclosed 1km-wide area of seawater, it will barely increase concentration by 0.01%. It would take millenia for us to increase sea salinity by this method, and all that treated water is eventually coming back.

Even if you took the total daily water consumption of the entire human race - 150l per person * 7 billion, or 1^12 liters, and made it extra salty, it is dwarfed by the total of 1.26^21 [mostly sea]water on earth.

This would be harmless assuming we are not adding anything to the byproduct, which unfortunately seems to be the case according to the other comments.

[SolaceQuantum]

The concern is not ocean-level damage through the salt directly but in localized ecological system destruction. The mangrove forest encompases a tiny portion of the ocean overall but removing this forest affects a large portion of sealife. The creation of 'deadzones' through salinity will have knockoff effects elsewhere that cannot necessarily be predicted.

[Retric]

At worst these dead zones would be tiny. They could dilute the waste stream by dumping it into the local sewage system, but I don’t think that’s going to change much.

It’s on the order of building a mall parking lot. Sure bad for the local ecosystem, but we have vastly larger issues.

[sp332]

It's going to be dumped near the shoreline, where sea life is very different from what is supported in the open ocean. If the shoreline is made uninhabitable, the marine life there might not have anywhere else to go.

[Retric]

Near in this case would need to basicly be directly into. Actual desalination plants don’t do this.

Further by parking lot I mean an actual parking lot. Dump it even 1000 feet from the shoreline and you would have trouble detecting the extra salt in the surf.

[WillPostForFood]

There are over 7500km of shoreline in Saudi Arabia, so marine life can move along the coast away from the salt water outlets.

[SolaceQuantum]

Shoreline is also highly variable and localized, and effects to the shoreline have staggering effects even if the region affected is small. I'd recommend looking at mangrove forests, coral reefs, and the mouths of rivers.

[philipkglass]

The local sewage systems can't deal with volumes this large. The sewage systems of the entire UK, population 66 million, deal with about 11 billion liters per day:

https://assets.publishing.service.gov.uk/government/uploads/...

Saudi Arabia, with a population of only 33 million, isn't going to have sewage systems sized to accommodate 31.5 billion liters of waste brine.

[Retric]

You would mix after the sewage treatment, simply placing the pipes next to each other would work.

As to impact the quality of brine is less important than the amount of surplus salt. Sea water is ~3.5% salt. You need 1:1 fresh water produced to get back to the default at discharge. While a significant fraction of the water produced would be lost as evaporation etc, desalination is not their only source of water.

Edit: Digging into the numbers it looks like Saudi Arabia is not limiting things to cities which have a closer relationship between water and sewage production.

[refurb]

Dissolution takes time. If we’re to dump the extra salty water off the coast, it would be hard to create an area of higher salinity.

Of course over time it would dissipate and barely change the salinity is the ocean.