Comment by rdtsc | Hacker News Reader

Comment by rdtsc | Hacker News Reader

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> They really fail to explain a key point here. The reason you colocate this with a desalination plant is because you use the super-salty wastewater from desalination as the salty side of the osmosis power plant. Then you find some wastewater which is low in salt (such as semi-treated sewage), and use that as the fresh side of the osmosis power plant.

They do hint at it at end:

> “It is also noteworthy that the Japanese plant uses concentrated seawater, the brine left after removal of fresh water in a desalination plant, as the feed, which increases the difference in salt concentrations and thus the energy available.”

And the "fresh" water is also "treated wastewater". That could mean a bunch of things but in most cases it's water that's released into the environment by the water treatment plant. Its quality can be as good as clean water, but most municipalities wouldn't feed that right back to the consumer, they dump in a river or lake instead.

Aren't there better uses for the treated water than this? Can't you use it instead of desalinating salt water? Or just run this treated water through the same RO and you won't produce any brine and the result will be just as pure.

Yeah I think that's the difficulty here, the technology needs just the right kind of placement and the right surrounding setup. There is a desalinization plant nearby, they feed the water into the city, the city uses the water, the sewage comes to the water treatment plant, they clean it up to environmental release standards and instead of dumping it back into a river or the ocean, they use it together with stronger brine from the desalinization plant to produce some electrical power.

From what I understand most municipalities do not directly feed sewage treated water right back to the consumer, normally they dump it into a lake or river first. A lot of that may just be an informal "yuk" factor not necessarily not having the technology.

It's cool but everything sort of has to be aligned for it to work well.

Usually you loop the treated waste water through nature for dilution (and more filtering if you use ground water) in case there is some problem with the treatment process.

Also it is kinda hard to sell to people the concept of “you are drinking literal shit/piss” even though if you stop and think about it all lake/river/reservoir water is full of fish, bird, etc shit.

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