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Not necessarily a “large scale” problem but the increased salinity means you create a enormous dead zone near your output system unless you spend a ton of energ
by mikeyouse 5y ago
Not necessarily a “large scale” problem but the increased salinity means you create a enormous dead zone near your output system unless you spend a ton of energy to mitigate it.
We had Bechtel design us a desalination/RO system for a biofuel startup I worked with and to prevent the dead zone, you need a massive system of buried pipes in the ocean. Iirc, it was the most expensive part of the entire design since you need to output it over something like a square kilometer and you need to mix in fresh seawater at several points to dilute the effluent before you release it. So in addition to the CapEx of a construction project in a horribly hostile environment, you have permanent energy consumption even past the filters.
And of course, since it’s coastal, there are tons of regulations and government bodies interested in making sure you don’t cut corners.
- hasmanean 5y agoWow, most people never consider the dead-zone around desalination plants. Us landlubbers just think of it as manna from heaven, “free freshwater.” The way we discuss technical solutions is woefully inadequate. Everything is still presented as a miracle-cure for our problems. We should have a more mature understanding of how these things are constructed and maintained.
- goldenkey 5y agoThe ocean is pretty big. That's why fish poop and pee in it. Not much of a problem. And if you weren't already aware, did you know plants also excrete waste through their roots? I only found out recently. But yes, all waste needs to be spread out and able to diffuse into the large atmosphere or it causes dead zones.
- pl-94 5y agoPlant wastes are a part of an eco system. They are cunsomed and transformed into other wastes. Actually, only human beings see wastes as a definitive lost. For every sustainable cycles, a waste is going to be transformed into you will consume again.
- hasmanean 5y agoYes. One piece of poop in the forest—nature. A sewer pipe discharging a river of poop from an entire city into a forest—a toxic waste dump. The entire surface of the sea is evaporating fresh water and the resulting brine is slinging constantly. It’s not creating a dead zone because it’s distributed. A river of brine in the oceans would be like a toxic cloud of ammonia that kills anything it touches…until it mixes sufficiently.
- goldenkey 5y agoWhich was my point. As long as the outtake is distributed, it would be fine. I think everyone is aware of that..even the landlubbers.. We kind of figured it out 150+ years ago: https://en.wikipedia.org/wiki/Great_Stink https://en.wikipedia.org/wiki/Great_Stink
- mrfusion 5y agoThere must be some creative solutions to the brine problem. At the end of the day we’re really not processing much seawater compared to the size of the ocean.
- mikeyouse 5y agoRight but the size of the ocean is the wrong metric - it’s really only the coastal region adjacent to the desal plant that you have to work with, and the chemistry and power realities mean that you just have a ton of very salty water to pump through pipes.
- highenergystar 5y agoPut the lithium plant on a barge and tug it around without lingering too long in any one spot.
- mrfusion 5y agoAwesome idea! Or even build on a platform and locate in a major current like the Gulf Stream. That could mix it pretty fast.
- choeger 5y agoI wonder if one could not simply pump it into some old oil reservoirs. The nations that need to do seawater refining should have some nearly empty oilfields lying around.
- AYBABTME 5y agoInteresting answer and thanks for providing it. Do you think the geography of the coast changes how expensive this gets? I'd think a coast that goes deep quickly or has strong currents wouldn't need as much spread out disposal infrastructure as one in a shallow area.
- mikeyouse 5y agoYeah it 100% does - mixing rate is a big design driver. We actually had decided that is was better for our primary effluent pipe to be several KM longer to reach the “coast” vs the smaller bay that we were immediately adjacent to. But even then, if the ends of your system are in 50’ deep ocean, the water column is such that the top ~10% sees really good mixing and exchange due to wind and wave action but the rest really doesn’t. It’s rare that there are strong currents near enough coastlines to take advantage of.