Desalination, Recycled Water and the Yuk Factor

phred14

Tue Jul 25 06:33:09 -0700 2006

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Not quite drinking water, but in a lesser way, more environmentalsm (Last time was the 'electricity from cow manure.') from Vermont:. My wife and I stopped at the Sharon rest area yesterday, on our way home from New Hampshire.

http://www.nhpr.org/node/9217
http://petroleum.berkeley.edu/patzek/ce173/Materials/nyt_05_08_31b.htm

Desalination, Recycled Water and the Yuk Factor

bill_mcgonigle

Tue Jul 25 08:23:03 -0700 2006

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Cool, thanks for the links. I'm nearby and have been looking for a geothermal contractor - I'll have to check out who did this system.

Desalination, Recycled Water and the Yuk Factor

AB3A

Tue Jul 25 08:26:29 -0700 2006

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Despite the eww and yuk factors, wastewater that leaves our Tertiary and ENR (Enhanced Nutrient Removal) processes is cleaner in most ways than the water we put in the pipes from the water treatment plants.  The main reason why we don't reuse it is because it would cost too much to send back uphill to the beginning of the process. 

That said, if you continually recirculated water through the system, you'd have a problem as those contaminants the process doesn't remove well started building up.  At some point, fresh water, Reverse Osmosis or distillation would become necessary. 

 

 

Desalination, Recycled Water and the Yuk Factor

Doug Coulter

Tue Jul 25 19:24:16 -0700 2006

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AB3A is right (again).  And there IS this yuck factor some would have a tough time getting over.  I have also built solar distillers that worked fine, but as I don't need them anymore, I don't bother with it.  A solar distiller can be as simple as a tray of impure water at the bottom of a box, painted black, with a south facing sloped side covered in clear plastic, the other sides mirrored.  As the water heats, it condenses on the plastic (you want something like thin plastic with good thermal conductivity to the cooler outside air here, not glass) and runs down into a trough where it can be collected.  I copied that from an old design used on lifeboats IIRC.  It works fairly well if there aren't a lot of similar vapor pressure things in the impure water, but like all distillation processes is kind of slow.   Of course, the energy here is pretty cheap on sunny days, about half a kilowatt per square yard is realized.  A solar hot water heater I built from two sliding glass door panes, some wood framing, insulation on the back, and a copper flashing and pipe system painted black for the heat collection will easily boil quite a lot of water, and in that case it's troublesome as it fills the bathroom with steam.  Next one will be designed to drain fully when not in use!  I had at one time estimated that I could get nearly a horsepower out of this as mechanical energy along with the distilled water.  That's only on the rough order of 25% efficiency, but would have been just fine.  I plan to pursue that later on, after the electric car, as my PV system works just fine for my needs.  Maybe I'll build it to charge the car instead of using one of the main systems.

On the other hand, I used to live somewhere near the Blue Plains sewage plant, which was famous for allowing overflow to get into the Potomac river totally untreated (near National Airport), even unto creating, errmmm, "sh*t island" which we once got stuck in with our sailboat.  This was not fun to get out of as one might imagine.  Actually, it was great fun and makes a good and true story, but the smell...maybe they've improved in the 30 years since that happened?  Obviously you couldn't allow that sort of thing to happen if you were putting the water back into the supply system.  They were a pretty sloppy outfit.

Now, this country (USA) is very wasteful of water.  I myself have been pretty guilty.  Once when I got a huge water bill due it turned out not only to leaking toilets but to a leaking main after the water meter but before my house, I took the opportunity to go down into the sewage tunnels for my neighborhood with the guys who came out to help me troubleshoot it all.  They popped the lid to show me that indeed my house was guilty, and I could see the stream from each house in the immediate area.  I was surprised that A: it didn't smell too bad, and B: there were next to no solids in the water, it appeared to be mostly "rinse water", and C: the sheer volume of waste water produced by just a few houses on a cul-de-sac.  It would have been a good sized stream if found in nature. Once I got out into the country and had to provide myself with water I learned how not to waste so much as it was hard to get.

Desalination, Recycled Water and the Yuk Factor

pyro9

Tue Jul 25 21:02:16 -0700 2006

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The U.S. could greatly cut down on water waste with little if any impact on lifestyle. Currently I'm working on an adapter for the clothes washer to send the waste water to the lawn. As long as we use an appropriate detergent it will be a great way to keep it watered without further taxing our water supply (we routinely have watering restrictions in summer). I would redirect the bath tub as well but I'd have to rip out half of the bathroom to get to it.

I'd guess that in most households, toilets contribute only a small fraction of the water that goes down the drain. Most of it could be applied directly to to the lawn. Of course, grey water can also be used in toilets, but would require much more significant changes to the plumbing.

Desalination, Recycled Water and the Yuk Factor

danielwebb

Wed Jul 26 09:57:10 -0700 2006

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8I'd have to look it up to be sure, but 25% seems much, much too high for low-pressure steam if you mean light to mechanical energy efficiency.  I'd think more in the 5-10% range.  You're going to need some mighty big doors to get 5hp methinks; that's a lot of power.  That would be interesting to build even if it was 1 hp though.

Desalination, Recycled Water and the Yuk Factor

Doug Coulter

Fri Jul 28 07:58:51 -0700 2006

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You could well be right, 25% might be more than is easily achievable.  You only get so much temp rise in a simple collector, such that here in winter it becomes unusable to boil water, for example.  I tried using "better" glass, eg multiple panes, as in the better windows, but lost so much plain insolation that the improved insulation worked out to about an even trade.  Could be that the 2 pane system had extra IR transmission losses "by design", and something special was really needed, not just commercial insulating window parts.  A concentrating collector would surely be a lot better, but most designs need tracking to work.  I recall a design that showed up in Scientific American, not as an article but one of those "short blurbs" that had about 4-5::1 concentration, and if laid out E-W didn't need daily tracking.  It was a modified parabola when using a flat plate collector, or a couple of joined parabolas (like a W with the center shortened) for a tubing collector.  Then you'd have high enough temps to really run a heat engine.

Yeah, it'll be interesting to build.  I invested a bunch of my savings in a machine shop to do just this kind of thing.  I have two designs floating around in my mind at present.  One is a two stage turbine, first stage reactive, U shaped blades like a pelton wheel, second stage conventional "jet engine" blade shape, with multiple input jets controlled by steam pressure so it can handle a wide range of steam delivery.  The other is a piston engine made from hydraulic (air) cylinders, radial so it can be fully self starting.  Similar arrangements on the valve timing would allow this to handle wide steam supplies.  The generator either would drive can handle a wide range of RPM and torque.  Either would of course wear out, unlike PV panels.  Not sure what working fluid I'd want, but it'd want to be a closed system with a condenser to avoid scaling etc in the boiler.  After reading Babcock and Wilcox "Steam, its generation and uses" that seems to be a biggie.  And particles in the resulting steam wreak havoc on the mechanical parts, like sandblasting them.

Can anyone tell me why most working fluids (water, freon) seem to have this huge heat of vaporization and condensation?  I'd think an ideal fluid wouldn't make you waste those calories going both directions.  I know water is used mainly due to ubiquity and fortunate boiling temp, but when doing something special, why pick something that wastes a lot of energy to go through a phase change with no temp change?  According to the steam guys, the best thing they do runs water above the critical point anyway, where the distinction is moot and there's no heat of phase change (if I understand correctly).  Those temps and pressures are probably not going to happen in a solar-dynamic system at any rate!

I guess where you use the most water depends on where you live.  No one here waters lawns, and gardens only rarely.  We're lucky to be in a place where that's not needed, due to rainfall, and a lack of social pressures to have that golf green up front.  There's no way I could water my 30 acres of "lawn" even if I wanted to, the piping alone...even though I have a stream, springs, etc.  Would just make it harder to keep cut down to where one can walk through it at all.  I'm lucky to mow the whole place once yearly, due to terrain difficulties and sheer size.  Try mowing 30 acres of waist high grass, with pencil sized stalks sometime.

Don't underestimate a leaky toilet as a source of waste (or even a normal "low flush" toilet, none of which actually meet spec, I've bought and measured them all -- they take over 2 gal/flush unless extremely carefully used.  Couldn't afford the truly fancy types to test so far).  Some people flush a lot more than others as well.

Thing about a leaky toilet -- it goes comparatively unnoticed and unfixed, where a faucet leaking the same amount would be addressed quickly.  That 24 hour a day drip, or really flow in most of the ones I've seen can easily exceed all normal other usage.

Here, where there's just about no rules, zoning, building codes etc, grey water is believe it or not, illegal to put on the lawn, the garden, or just about anywhere.  A dual plumbing system to use it in toilets is banned.  I asked the friendly building inspector about that.  His comment was "you might have washed diapers in that water".  Of course, the rules may change when shortages hit, just like there are watering bans in some places and times.  Only a small part of the only small town in this county has "city water" at any rate, and the gov't has no input into how I use water I get myself.

Desalination, Recycled Water and the Yuk Factor

danielwebb

Fri Jul 28 22:15:21 -0700 2006

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998> Can anyone tell me why most working fluids (water, freon) seem to have this huge heat of vaporization and condensation?  I'd think an ideal fluid wouldn't make you waste those calories going both directions. 

For refrigeration, you *want* the heat of vaporization to be as large as possible.

> I know water is used mainly due to ubiquity and fortunate boiling temp, but when doing something special, why pick something that wastes a lot of energy to go through a phase change with no temp change?

And it's non-toxic and cheap.  All phase change of all kinds happens at constant temperature. 

> According to the steam guys, the best thing they do runs water above the critical point anyway, where the distinction is moot and there's no heat of phase change (if I understand correctly).  Those temps and pressures are probably not going to happen in a solar-dynamic system at any rate!

For something like you're describing, a phase change is preferable because it maximizes the heat transfer and minimizes losses.  If you tried to create a system like you're describing using a supercritical fluid I'd be surprised if it worked at all.  Heat transfer to a vapor sucks, heat transfer to a boiling liquid is great (you get terrific convective heat transfer due to the boiling itself).

Desalination, Recycled Water and the Yuk Factor

danielwebb

Fri Jul 28 22:25:02 -0700 2006

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98P.S. I'm interested in your project, email me if you want to discuss it privately.  I'm a chemical engineer, and although I'm a bit rusty on the thermo and fluids, I can help with basic stuff or point you in the right direction.  My email is public@danielwebb.us.  I think your efficiency will be poor, but that would still be a really cool project.  I'd love to have a shop to play with stuff like that someday.