Why Is Desalination So Difficult?

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I've drank literally thousands of gallons of desalinated water over 20 years while I was in the US Navy. First ship used 7 stage evaporators and the last two used reverse osmosis. You couldn't tell the difference between them since it was pure water that came out of them and the engineers added minerals back into them to make them drinkable.

I'm a Navy veteran and I served on a Nuclear Aircraft Carrier. We had a desalination system built into the Reactor system using the excess heat from the steam powerd turbines. It was actually very efficient.

As a water treatment specialist it feels good to be seen. The RO segment was dead on. TDS and scaling are constant challenges.

I grow salicornia (sea asperagas) at home and it does surprisingly well turning salt water into usable water and a snack thats pretty dang salty and not bad tasting in my opinion. Not sure if its great for every purpose but here in florida it works pretty well.

It is SO extremely important how you put things in perspective in these videos. “It took X kilowatt-hours to do this process.” You could end there and compare numbers at the end, but then people wouldn’t understand what that actually means. It’s great.

Here in Uruguay we are facing a drought right now, and the government decided to mix treated salt water in the normal fresh water supply, so now we are getting water on our taps with a salt concentration about 10x of what it used to be. This video turned out to be very well timed for us.

Having companies privatize desal water like you mentioned is incredibly scary. Water, Electricity, and Internet should all be public utilities.

Really great explanations and comparisons. Thank you for taking the effort to set up the bench top examples. I believe that desalination won't come into popular view until it is the only choice left for larger regions of the world outside of the middle east. As mentioned, water is plentiful but the amount of energy it takes to transport it and prepare it is key.

Lived in Saudi Arabia for a while and dad worked at the desalination plant there. Interesting bit was steam generated by the boilers were split into two pressure points. High pressure steam was used to turn the turbines to produce electricity while low pressure steam was used to make fresh water. Interesting when I heard about it the first time.

Here in Tampa they tried to build a RO desal plant near the Apollo Beach Power Plant. The biggest issue was not any of what you outlined here. The problem was zebra mussels. They are a non native invasive species that would collect on the intake pipes for the desal plant and they were spending 100's of thousands of dollars each month just to keep the pipes clean, and that is what killed the project in the long run.

Love this channel. As a trained EE I wish my education had this kind of practical experiments and thought-experiments.

I lived in the desert for 25 years. In that period I build very simple solar distillers that delivered less than 1 mg/l total dissolved solids. The feed for my stills were about 2500 TDS. All the water I drank at my home (that really is almost all) came from these stills. There were a few technical improvements in building them but it is possible to produce drinking water (and even water for laboratory use). The problem is that people need to use saline water for a number of purposes rather than purified water because solar distillation gives really pure water but great enough in quantity not in fire fighting or irrigation. When I see this, I realize how primitive our society's understanding of water chemistry is.

On our 470' research vessel housed 130 people, we had two distillers plus a reverse osmosis. The distillery was pretty brilliant as we pulled a vacuum on the container and we used heat from our diesel electric engines. When the vacuum was applied the water would vaporize at 165°F rather than 212° F pretty clever. The units on our ship produced 1200 gallons per day. Some of that water was additional purified by R.O. So the waste heat from the engines was not an additional cost only the energy used by the pumps was energy negligible.

Well thank you Grady! My late father was a widely-acclaimed reverse osmosis water chemist but I never understood exactly what was special about RO, and the difference it could make. He travelled extensively in the UK and the Middle East, solving RO problems encountered by water utilities at local and even national levels, eg Namibia in Southern Africa. This video has resolved for me what had been a fog of comprehension, so I can’t thank you enough for facilitating a new enlightenment for me! 🙌 High five to you Grady!

One issue missed by most people who promote desalination for urban use is that the sea water near the coast is too polluted to desalinate and drink. The ship I worked on required us to be 25 miles offshore to make potable water.

love that you did an experiment demo and didnt just talk about it. the scientist in me loved it.

Spoken like a true engineer... "The instructions didn't say to not run salt water through the pump"

I worked in a power plamt that used a multistage RO to clean up produced water from an oilfield. The oil was separated, and the water was run through softeners, but it was still in the part per thousand range. We ran the RO at 75% permeate and 25% reject in the winter. We had to run it at only 70% permeate in the summer due to the water being much hotter. Input temperature and pressure have a high effect on the process. We got <1 ppm hardness, and around 16 ppm total dissolved solids. This was necessary because the next step was deionization, yeilding 17.8 mmho water. Theoretically pure water (which doesn’t exist) is 18 mmho. Water that clean will actually make you sick with extended use. It basically reverses the osmosis in your intestines, pulling nutrients out of your blood instead of vise versa. As far as seawater desalination, I took a contract in Saudi Arabia in the mid eighties. Theentire eastern half of the country was supplied freshwater by a huge RO plant just south of Al Jubail on the Persian Gulf coast.

Thanks for covering the renewable energy part, I've been grumbling about using that for years. Now I have a clue of the continuing drawbacks.