Monday, November 17, 2014

Securing Our Future Water Needs

Last night, CBS 60 minutes had a story about the loss of water the Western US is experiencing due to a drought we've experienced over the last 9 years or thereabouts. The story centered around a study that came about in part thanks to the NASA GRACE Satellite Mission. GRACE stands for Gravity Recovery And Climate Experiment, and has used the Earth's local gravitational pull on the satellite to determine such things as the loss of water mass in the ground below the satellite. The researchers have determined that 75% of the water lost over the last 9 years in the Colorado River Basin has been from underground water sources. In other words, the aquifers are being pumped dry to compensate for the lack of surface water due to the drought, and there is some concern that we may run out of underground water and thus water in general to grow crops out in the West. If you were thinking that losing the west's crops would be no big deal, you would be very wrong. California alone produces a surprising amount of the US's fruits and vegetables. The list is extensive.

There is some research which suggests that the California drought is linked to climate change. In particular, due to the formation of a permanent high-pressure system next to California which is diverting rain away from the state. So this drought condition may be with us for the long term. If so, we need to start coming up with alternative fresh water sources to keep ourselves afloat.

I want to suggest areas of research that may help with the water supply problem. They may not solve the problem, so much as alleviate the symptoms. My interest is in desalinization of sea-water using minimal energy techniques, and with minimal cost. It isn't entirely obvious that both of these techniques would be low-energy or low-cost, but the thought experiment is at least worthwhile. Here they are, at any rate:

Dig a Well in the middle of the Ocean

This idea may have no validity at all. It's so simple, I have no idea why it hasn't already been tried. The most likely reason is because it wouldn't work, but here goes anyway... Reverse Osmosis (RO) works by driving Sea Water through a membrane that separates the salt in the sea-water from the fresh water. If you put Sea Water at 400 PSI on one side of the membrane, fresh water will leak out the other side. Generally sea water is pumped across one side of the membrane, becoming more saline as it passes along, and fresh water is yielded on the other side. You need at least 391 PSI of water pressure to overcome the "osmotic pressure" of the salt in sea water. Anything less than that won't yield fresh water. With these bits of data in mind, here's the first solution: A submersible well pump is placed in the middle of a membrane wrapped container that is dropped into 1000 foot deep water off the California coast (we have water that deep, close to the shore all along the Monterey Bay).

Most well pumps can't move water that far up a pipe in one go, so likely there will be a need for several pumps along the total length of the pipe. One of these units might produce 1500 gallons per day (this is a REALLY rough guess, based on the data for one reverse osmosis filter specification), so you'd need several of these units to supply a community, and there is the consideration of maintaining the RO membranes, which might kill the overall efficiency of the system. Still, I find there is a certain attraction to the idea of drilling a hole in the middle of the ocean and pulling fresh water out of it.

Wave Powered Water Distiller

The second notion honestly came to me when considering how a country could extract fresh water from the Red Sea. In that case, I was thinking about Jordan. Later on, I adapted the idea as a method of supplying water to the people of the Gaza Strip, such that they could supply themselves with an uninterruptible supply of water, preferably using a low maintenance, low cost device. Essentially the idea is simply to create a heated chamber for near-vacuum distillation of sea water. A tallish-chamber is located on a pier. It is heated by the sun. The bottom of the chamber is open and is stuck in the sea water below the pier. A wave powered pump sucks air out of the chamber, causing the sea water to be sucked in through the chamber's bottom opening. If the chamber is a bit over 32 feet tall, the water will never be able to reach the top of the chamber, due to there being a total vacuum above the water. The water in the top of the chamber will just about be boiling due to the vacuum.

As the pump continues to maintain the vacuum in the chamber, the pump outlet will be driven into a pipe, which drops into a cooling tank, located below the surface of the sea water, below the pier. With the increase in pressure and the drop in temperature, the steam collected from the boiling water of the evacuated chamber will condense into water. While this solution might have efficiency problems, at least it wins for using free energy for driving the process.


These are two ideas that I think would be worthwhile checking out. One of my concerns for traditional desalinization plants is they are energy intensive and destructive to any creatures which get sucked into them. Supplying loads of energy to a desalinization plant seems counter-productive, as you use a fair amount of fossil fuels and potentially water, to supply that energy. The thought with both of my solutions is that they are relatively economical, energy-wise and have low impact on the surrounding marine environment. Even the distillation unit, with it's open ocean access, gives creatures the option of swimming back out of chamber rather than facing vacuum and higher salinity, and even a simple screen would prevent most aquatic tragedies. It is my hope that people figure out how to get their water without further straining our environment. These ideas are my attempt to facilitate that hope.


Blogger Marcel F. Williams said...

You could also use off-peak electricity from nuclear power plants (Diablo Canyon) to produce desalinated water through mechanical vapor compression, putting this unused electricity to good use.


November 18, 2014 11:44 AM  
Blogger bill said...

Not a bad idea Marcel.

November 18, 2014 1:21 PM  
Anonymous yamini said...

Thanks for your details and explanations..I want more information from your side..I Am working in Bisleri Authorised Distributor In Chennai.

February 23, 2016 4:15 AM  

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