Japan has opened its first osmotic power plant

So let me get this straight:

1. I take a shower and produce non-salty waste water

2. That waste water and brine from a desalinization plant can be used in this plant.

3. The result is concentrated waste water and less salty brine and some power

4. The power can be used to (partially) power the desalinization plant produces fresh water from sea water and brine.

5. I get fresh water for my shower.

And the diluted brine from step 3 goes to the sea? Or can it be run through the desalinization plant again? Does concentrating the waste water in step 3 also help with the eventual treatment of it

The article mentions "partially treated wastewater", which I take to mean "water that we're ok with dumping into the ocean, but not ok with drinking". I think you can generally read this as a way of gaining some utility out of this partially-treated wastewater before you dump it into the ocean by mixing it with the extra-salty brine from the desalinization plant. The utility you get is: - a bit of energy that would have just been wasted - a more environmentally friendly product to dump in the ocean than just straight brine

I imagine someone out there does a cost-benefit analysis to compare this system to just fully treating and reusing the wastewater and thus needing to desalinate less saltwater.

The diluted brine goes out to sea. It's less harmful than dumping the concentrated brine you had before, with the bonus that you got some power out of it.

The concentrated waste probably gets disposed of rather than trying to get the remaining water. You treat it like the results of a waste treatment plant. You might dehydrate it a bit, just so you don't have to ship the water, but you probably won't try to recover any more water than you already have.