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# Mobile large scale desalination

extra water in drought conditions
 (+5) [vote for, against]

In extreme drought, agricultural land is basically going to waste. If one could convert an acre or two into a giant solar still, it would greatly reduce hardship.

The stills could be fed with brackish/or otherwise questionable groundwater, or seawater if some is close enough. Perhaps the seawater will need to be trucked in.

An acre of low tech solar stills will provide about 4,000 gallons a day, in optimal conditions.(1 gallon/square meter, 4000 square meters/acre)

The question is, how to make it mobile? I think you need:

1 black tub 1 "brackish" water tube 1 clear domed top 2 "clean" water tubes

Times 4000X, or, 3844, since that actually makes a square.

A square meter is a perfectly good size for a square tub. The tubs would have to be a somewhat durable, stacking plastic, with 2 holes in them. Some special tubs might come with extra holes to be more flexible in use. Caps will be provided for the holes that won't be used

With each tub will have tubes for the holes connecting it two other tubs, except for the start tub and the end tub.

The start tub is where brackish water enters the system. It has a tub in the bottom that runs to the next tub. The entry point for the second tub is about 2/3 up the side. The exit point for tub is on the bottom, and so on. I am hoping this will be enough mixing for the system.

The tubs are lined up in nice neat little rows, on level ground. On a square plot, you can fit 62*62 tubs(maybe 64, but it has to be an even number). In one row on the south end, the water would run west. Then it would run north up a column and south in the next column over, then north and south, again 30 or so more times . If you connected the end tub and the start tub, it would complete a circuit.

A crude example, 8 by 8, is shown below:

>v>v>v>v
^v^v^v^v
^v^v^v^v
^v^v^v^v
^v^v^v^v
^v^v^v^v
^>^>^>^v
SE<<<<<<

This can be scaled up to any size, as long as the number of columns is even.

Next comes the clear domed tops. They stack too, but not as good as the tubs, because the tops are ringed with a water collector Water will condense on thes domes, and run down the sides. the clear domed tops will fit snugly over the black tubs. The sides of all the tops will be completely connected to each other. Caps to plug the tops at the edges of the system will be provided. The clean water can have a outlet on one side of the system, that connects to larger pipe whichs leads to a trough for watering animals, or a pump for storage, etc.

The tubs will hold slightly less than a cubic meter of water. Let's say they hold 180 gallons. At the 120 gallon markwater will spill into the next tub. Let's say a truckload of tubs is 40 tubs, so you'll need a truckload of water for every truckload of tubs during setup. Assuming you can get 10 truckloads each of water and tubs a day delivered to a setup site, you could have a system going in 10 days. Then you will need a truckload or two of brackish water each day to sustain the system, and occaisionally flush the system. Hopefully the water can be piped in, but either way should work.

Teardown will be just as tedious, but simple as well. plug the first tub's connection to the second tub, and then pump the water into the second tub. Then repeat, again and again.

It'd probably take 10 days, again, to disassemble.

I imagine an acre-sized system would be rented out for 2 years, minimum. In winter, depending on how harsh the winter gets the system will have to be either drained, or kept warm. The greenhouse effect going on inside the tubs, plus the fact the water will be salty, might make the system able to handle a mild winter without freezing. Perhaps a winter freeze desalination unit can be used to continue to milk the system for fresh water, and warm it with waste heat.

Getting rid of the brine will be a hassle but it will be a small hassle compared to having no water available.

*edit*

On second thought, getting rid of the brine won't be as difficult after all. Notice how the end of the tub layout is a straight line. If you always poor new water into the start point, you'll get a salt gradient through the system. Salt would be concentrated in the last few tubs. You can decide: do we let the brine concentrate till salt layer grow, or remove the brine before then?

If this is further inland, and taking on salt from a brackish aquifer, returning the salt to the sea might not be practical, and if think returning that salt to the groundwater might be counterproductive. But, it can be delivered to a saltworks for purification, iodization, whatever.

How high a chimney are you thinking? I bet you could design a reasonably mobile chimney. Store it in hemicircles. have slats on the inside to mount "shelves" for the water to drip onto.

From there, the water can be directed to a more premanent storage. I can imagine a water tower with "stories", that you can plug right into the cooling chimney. The water tower would be modular, but more permanent. I imagine that anyone who will use the MLSD system will want to build themselves a water tower or two so that when they stop renting the MLSD they have leftover clean water to allow them to handle one year of drought before needing to rent it again.

(??) Brackish Aquifers http://dmc.utep.edu.../water/aquifers.htm

nice vid of problem and a portable product [popbottle, Mar 24 2014]

 why go with hard plastic units? with a small blower you can blow nice little structures like tunnel 'glass'houses. That could be set up in a day and be transported on the back of a truck. But the main problem would be getting rid of the brine. Maybe if you are pumping up salt water, you can pump the extra salt water down again.

An extra addition could be a 'solar tower' The heat in the glasshouses is used to drive airflow into a very high chimney. As the humid air rises up, it cools due to adiabatic expansion. The water will condense on the walls of the chimney. Collect and store it high enough and you have instant solar powered water pressure. (but the chimney will not be too transportable)
 — nietsch, Sep 20 2005

A grand idea. I love the improvement by "nietsch". The double sided inflated tube could literally be as long as you want it to be and very easy to and inexpensive to build on a large scale. If sea water were readily available, I suggest a "flow through" system where by the water is in constant flow from and to the sea, thus washing out the water with "higher" salt concentration and leaving behind almost no solids. The water from the sea would be inexhaustible and need not be completely evaporated. There is a need for a flat or slightly inclined area, but that could easily be arranged with land leveling machines over large areas. In essence, these desalination plants could be numerous and the water collected would only be limited by how many square miles you have of land that is suitable for them. Oh, there would be some need for pumps and such...but that could be done with either wind or wave generators supplying the power or mechanical pumping action. I love this idea.
 — Blisterbob, Sep 20 2005

Get more water by digging a bunch of holes in the ground, tossing cactus in them, covering them with a tarp, letting dew form and drip into buckets. Water farming perhaps.
 — Antegrity, Sep 20 2005

 Antegrity, yes, that would get water, but we want to have only one unprocessed water entry point, one clean water exit, and one brine/waste exit. It's worth spending ten days of setup to avoid a whole season of bending over to get water from the buckets and changing the chopped up cactus parts.

Plus I don't want to sacrifice so many cactus. There's plenty of brackish water aquifers in the western US. Or other wells with water that is undrinkable for other reasons.