Desalination Today and Tomorrow

20 Billions gallons a day!? Wow, that sounds like a lot.....Yet on a daily basis it is said we use 10 Billion tons of water....The US is said to use 3.9 Trillion gallons per month, with the average American using 100-175 gallons of fresh water per day...but agriculture uses the Lion's share of fresh water....and then there's the products we use that require fresh water to produce....it adds up...

http://www.theworldcounts.com/stories/average-daily-water-usage

When 70% of the earth is covered with people, then the vultures will take over.

Seriously, on a ship, at least the one I was on, you were made aware of just how precious potable water is.

I take it you weren't using 100-175 gallons of fresh water a day!

The Chief Petty Officers, who had a permanent coffee cup hook in their index finger, were concerned that coffee would have to be rationed. This resulted in the get wet, soap up, rinse off, turning the shower off between phases.

When I boarded the ship for the first cruse, I was ordered to make coffee by a shiny-panted Chief. I carried the 50 cup percolator around until I was finally directed to a deep sink in a mop locker by a helpful shipmate.

I filled the coffee maker with what I thought was unusually aromatic water, brought it back up the ladder into the AE shop and under expert direction (between poker hands) I loaded the coffee and plugged it in.

It wasn't until a couple of hands later, and a spray mist, that the job of making coffee went to someone else. Being a flat lander, I knew nothing of Seawater.

Prospects? You need a lot of Capital to build those plants. And then, you need a robust power grid to supply the juice to run those plants.

They're not cheap, period.

The sun coupled with a hurricane or two, puts those numbers to shame. The hurricane even transports it. A judicious use of cisterns could solve a number of problems. Using "grey" water for the commode can also go along way towards a solution. Nothing can be done of course when the one eared unicorn, needs twelve kilo tons of water/per day and its needs outweigh those of SoCal farmers. Of course pot growers take precedence over everything and everyone else. We have to keep our priorities in line.

Cisterns would be a good idea but the Federal Government owns all fresh water now and it is already illegal to save rain water!

Nestle Corp. is doing it's best to make it all their own.

https://www.youtube.com/watch?v=vWkA-uAPXCE

It's like Martin Borman has come back to haunt us.

Even if desal plants shift away from SWRO (for seawater) to FO using pyrolytic ammonium bicarbonate draw solution, there is still energy required to (1) pump the water across the membranes (far less than that for driving RO), (2)energy to pump the draw solution across the product side of membranes, (3) a low-grade thermal source to heat the water to ~50-60°C to break the ammonium bicarbonate down to ammonia and carbon dioxide, (4)energy to operate the gas compressors for these for re-injection, (5) energy as needed to re-cool the product water while pre-heating draw solution, and (6) energy required to move the brackish or seawater from its source to the FO plant. We won't count the energy to maintain the FO plant or that needed for membrane production, as those will seem small in comparison. In the final analysis, at some point more energy will be expended moving water to the places where it is needed than for purifying it. That will still require more power on the grid.

How efficient are the modern distillation systems, using concentrated solar heating? Turn the Tonapah plant into a water maker, rather than an energy source…Just asking ...

Certainly solar distillation using CSP will be a player, but why waste its potential to completely boil or heat water to temperatures near boiling? FO only needs a diffuse source of waste heat to operate, so use the CSP to produce the electricity to power the transfer pumps, or to pipeline the water where it is needed.

Reverse osmosis uses 3 times as much water as the amount of clean water it produces. The problem isn't how much they make, it's how much they destroy in the process.

Evap&recovery would be a good way to make clean water if you could keep the recovery process from getting contaminated.

that is simply not true, Mr. Rider. RO plants typically recover up to 90% of the feed water (HERO). True that there is some water lost to water softening regeneration, media filter backwash, etc., but these are a minimal % of the overall water balance.

FO has the potential to waste zero water, since the % recovery is not required to be high, the bulk of the water can be circulated in and back to the source (ocean), with some energy recovery over the slight increase in density of the water (but it has to be cooled to match or be cooler than the water temperature at depth of re-injection point), FO also works just fine with wastewater, even low-grade effluent, as it uses a very ROBUST membrane over 100 times the thickness of an RO membrane, at least that was the technology a few years ago. Oasys and other players have been keeping cards close to the chest (for a very extremely good reason).

FO sounds really good. I was reading this:

http://cdn.intechopen.com/pdfs-wm/20341.pdf

and noticed that pre-treatment is the secret to low by-product concentrations in RO plants. However, the article does mention that fouling of the filters is the biggest problem with high volume Osmosis plants and that particulates in the 0.45 micron diameter range are what really plugs up the filters.

This would mean that the location of desalinazation plants would be of critical importance to their efficiency. The cleaner the salt water going in, the faster the plant can produce fresh potable water.

However, if the salt is put back into the water, the higher resulting salt concentration makes the osmosis plant work harder as years go by.

This paper shows that by 2050, the salt level in the Arabian Gulf with it's 1500 desalinization plants, will be 5 times more than in 1996.

http://tvrl.se/ma/Documents/ESTIMATED%20FUTURE%20SALINITY%20IN%20THE%20ARABIAN%20GULF,.pdf

Furthermore, with higher atmospheric temperatures, evaporation from the oceans is steadily raising the salinity, too.

http://science1.nasa.gov/earth-science/oceanography/physical-ocean/salinity/

Since dead zones (no fish) have occurred in the Atlantic for the first time because of low salinity and low oxygen maybe de-salinization plants could be constructed there and the fresh water brought to land in tanker ships.

http://www.aol.com/article/2015/05/04/dead-zones-recorded-in-atlantic-ocean-for-first-time/21179392/