Double the salinity? Other comments suggest it’s only slightly more salty than sea water.
Only a very small fraction of water is isolated from a very amount of sea water.
The article states
> Modern desalination plants generally recover about half of the intake flow, which means their brine stream is about twice the concentration of normal seawater.
I imagine this heavily depends on the actual plant design though. Also because of the above mentioned issues you generally don't discharge it like that but blend it with other water.
To solve that you can just dilute it more, either mixing with some other waste water stream or by releasing it over a larger area rather than a single outlet.