In terms of power generation its not a ton. 100kw capacity?

But I think the idea is that it's performing 2 functions that already needed to happen, and getting power as a byproduct. The two functions being: diluting desalination brine back down to normal levels for discharge, and discharging treated wastewater (this is the key that the article doesn't make very clear, but this one lays it out better: "In Fukuoka’s system, a generator is attached to a local desalination plant located near a sewage treatment facility. It draws in highly saline wastewater from the desalination plant and receives treated sewage.".

Plus it's a proof of concept/research facility for larger scale implementations elsewhere (gulf states maybe?)

I didn't realize there were parts of japan so dry that they needed desalination to have reliable water supply so I was also initially confused tbh.