Towards a better tinyhouse

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Quick and easy Chlorinator

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The diagram above shows a handy chlorinator device.  Much cheaper than the usual method of using $400 dosing pumps, typically used in well water treatment.  I would point out that this should work perfectly for well water, too.  Basically, Sodium hypochlorite solution is added to the reservoir container, which is sealed airtight except for the 2 tubes that come away from it.  One tube siphons out solution from chamber 1 to chamber 2, when the other tube is not submerged in water, e.g. air can get in.   So, when the water level drops, more air enters chamber 1 and the solution is allowed to enter chamber 2 until the air tube is again submerged.  The air tube is mostly ends up filled with water too, though, btw.

So basically you have 2 mechanisms at work in parallel here: one, the mechanism mentioned above, which regulates the water (solution) level in the second chamber, transferring solution from the first when needed, and the other one, which transfers solution out from 2 into chamber 3, as the level in the water storage chamber rises.

In case it’s not apparent, the way the latter mechanism works is by taking advantage of the rise in water level inside the “feedback tube,” this rise causes air to be forced into chamber 2, forcing solution out of the output tube.

The height between the lower end of the output tube and the water level in chamber 2, and the diameter of the hole in the bottom of the output tube is critical – looking at the diagram, it might look like water should just siphon out of the output tube.  But, if the output hole is the right size and the water level height is right, the water will be held in by the capillary forces.  If you try to fill a pipette or eyedropper with water after removing the rubber bulb thing, you can fill it to some height before water escapes from the other end, because of this same capillary force.  The smaller the opening at the bottom is, the higher you can fill it (the height should be inversely proportional to the diameter of the tube.)

Now, when the air starts to come into chamber 2 (i.e. when the water level rises in the storage tank), water starts to go up the liquid check valve, and pressure builds in chamber 2 until it is enough to force the solution out of that hole.   When the water level in the storage tank drops again, air must enter the chamber through the liquid check valve, then go into the feedback tube so the water level within the feedback tube can drop.  There is a small amount of pressure needed to start this happening, because the bottom of the check valve is submerged a bit, and that water has to be pushed out of the tube before air from the surrounding atmosphere can get into chamber 2, if you see what I mean.

So there is a small amount of hysteresis here, when it comes to the rise and fall in the water level in the storage tank, and when solution starts to escape from the storage tank, and when air starts to enter chamber 2.  That is, suppose the water starts flowing through the apparatus, and accumulating in the storage tank, the water level starts to rise…. Before any chlorine starts to come out of the output tube, some water needs to be put into the storage tank.   Likewise for when the water level starts to drop.  Some negative pressure is required before the device starts to operate (because of the slight submergence of the liquid check valve tube.)

These hysteresis should be minimized, of course, but at some point when the liquid check valve is not sufficiently submerged, for instance, the device will start to become sensitive to malfunction slightly when being tilted or jolted.  So there’s a compromise there.  However, chamber 3 can help to even out the concentration of chlorine that the water flowing through the device ends up with, of course, the bigger that tank is, the more even the concentration will be.  I figure, take the amount of water that is involved in the hysteresis mentioned above, and make the take bigger than that, anyway.

About the “contact tank” thing.  Well, to kill bacteria and inactivate viruses, you basically need to bring them into contact with a certain concentration of chlorine (or other disinfectant) for a certain period of time, and the higher the concentration, the less time you need.  The amount of disinfecting powery goodness you get goes up with the “CT value,” which is the concentration of chlorine multiplied by the time the water stands for, usually in PPM and minutes, so PPM-minutes.  If the PH and temperature are staying the same, by exposing a population of (all the same) organisms e.g. e-coli bacteria to a CT of x, you divide the population by y.  y goes up exponentially with CT.

So suppose you have 10 ppm chlorine and you expose the bacteria to that for 20 minutes, you divide the population by y.  Then you let it sit for another 20 minutes, it is again divided by y.   So, 40 minutes after you started, you divided the population by y^2.    So CT is proportional to the log reduction in bacteria.   A CT of a mere 5 (so not much at all) should kill pretty much everything to several logs, I think , except for giardia and cryptosporidium, which are very resistant, and take a ct of about  630 and 7200, respectively, for a mere log 2 reduction.

So yeah, what the contact tank does is just store the water for a short time.

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Written by gregor

August 9, 2010 at 20:29

Posted in Uncategorized

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