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karen_pease

Considering a system / scientific method

Karen Pease
15 years ago

The challenge:

I am attracted to the concept of hydrponic gardening from its simplicity of purpose (isolating plant growth down to its barest elements) and its potential for significantly reducing plant nutrient requirements. Unfortunately, hydroponic systems often have a problem with the balance of individual nutrients and/or the pH getting off target over time. Some gardeners approach this by simply disposing of the nutrient solution without recovering it at all. Others approach the problem with limited reuse for a couple weeks, followed by disposal and complete replacement of the solution. Some commercial growers use ion-selective electrodes to measure the quantities of individual nutrients, but these cost hundreds of dollars each, and integrating them with an automatic replacement mechanism adds more complexity still -- pricing this approach out of the range of most home-growers. Disposed-of nutrient solution imposes environmental consequences, in the form of encouraging algal blooms if it makes it into waterways.

Concept:

To counter this, I came up with a process, and a method of testing the process, to provide automatic nutrient balancing for a continuous flow hydroponic system (such as NFT). Powders of the nutrients, such as potassium nitrate, calcium nitrate, monocalcium phosphate, magnesium sulfate, copper sulfate, manganese sulfate, ferrous sulfate, sodium molibdate, boric acid, and zinc sulfate, and optionally other trace elements, buffers, and disinfectants are stored in individual waterproof containers with a layer of water over them. This water will stabilize at the solution's saturation point; any new water that gets added will become saturated with this nutrient. The containers are kept at a level just below where they would overflow into a common "refill" container.

Solution for the NFT system is pumped from a low base reservoir through a filter up to the top, where it flows down past the roots back into the base container. A float in the base container opens two valves when the level falls too low: one for freshwater into the refill container, and the other offering a diversion route for the nutrient solution feeding back from the NFT system. The diversion lets it empty into the far end of each of the nutrient concentrates. The rate at which it flows into each is controlled by user-adjustable taps, as is the rate at which freshwater flows into the refill container. The addition of nutrient solution into the concentrates causes overflow of concentrate into the refill container at a level proportional to how fast liquid is flowing into it. When the refill container gets high enough, a siphon fills, emptying its contents into the base reservoir. The float raises, shutting off the valves and thus shutting off the filling of the refill container.

One potential issue that comes to mind is whether the concentrates of the various nutrients will truly remain concentrates of *that* nutrient over time. After all, the concentrate that leaves into the refill container is being replaced with not pure water, but water with a mix of various nutrients in it. Will the nutrients that are already in solution in that replacement remain in solution and thus leave the tank harmlessly on every cycle, or will less soluble ones be deposited and replaced by a more soluble powder in a given container, hence gradually converting the concentrate to a different type of concentrate and leading for the potential for nutrient swings down the road? I set out to find out. If the results prove to be favorable, and no big flaws are seen by those with experience, I intend to eventually try setting up such a system.

Testing Process:

I took two clear 2-cup measuring cups. To one I added 1/2 cup of white sugar, then filled up to the 2/3 mark with water. To the other I added 1/4 cup of salt and then filled up to the 1/3 mark with water. Sugar and salt were selected because of their ready availability and ease of distinction by taste. I then stirred the two containers until their respective liquids reached saturation. It took notably more sugar to reach saturation than salt (** After the fact, I looked up their saturation points, and this makes sense; salt's is 35.9g/100ml, while sucrose's is 211.5g/100ml). The undissolved sugar and salt remained at the bottom of their respective containers to keep them saturated.

I then repeatedly filled a third "mixture" container with 1/2 cup of water and a teaspoon of water from each of the sugar and salt concentrate solutions, taking care not to skim any undissolved solute from the bottom. After a quick swish of the mixture container to mix it up, I then added one teaspoon of it into each of the sugar and salt concentrate solutions (note: the taste of the mixture cup was of both sugar and salt, although the salt was somewhat stronger). The mixture cup was dumped and then refilled with a new 1/2 cup of water, a new teaspoon of salt and sugar concentrates, and so forth, starting the process over. Approximately every third cycle, I gave the sugar and salt concentrates a good stir to ensure that the liquid in them remained saturated, and let the undissolved solute settle.

Results:

I went through approximately 16 cups of fresh water before the sugar container contained only the tiniest amount of visible sugar remaining (the salt container still had a measurable amount left). I then did taste tests

Sugar concentrate container "At least" 20:1 sugar:salt by taste, in comparison to manually titrated sugar/salt solutions. Could be much higher. I'm not really sure I could taste the salt at all.

Salt concentrate container: could not detect sugar taste at all

Conclusion:

The approximate 32 water replacements amount to 2/3rds of a cup for each concentrate container, meaning that as a net result, the initial water in each container (appriximately 1/6th and 1/12th cup, respectively) was replaced several times over. This is a very encouraging result; despite the extensive replacement and near-exhaustion of the sugar, both cups remained, essentially, a concentration of their respective "nutrient", boding well for the proposed hydrponic nutrient balancing system.

One untested issue that remains is the effect of time on the solutions in the concentrate containers. Some nutrient solutions come in A-B mixtures to prevent the slow side reactions that could render certain nutrients either unavailable or of limited availability to plants. How significant of an impact this will have on an implementation of this system is unknown. An additional issue in regards to time is to whether some nutrients will prefer to precipitate out and be replaced in solution by their more-soluble concentrate over prolonged periods not experienced in this test. An actual implementation of such an irrigation system will need to be built to determine whether this is a problem.

Thoughts?

Comments (18)

  • freemangreens
    15 years ago
    last modified: 9 years ago

    "I am attracted to the concept of hydrponic gardening from its simplicity . . ." This would be a good place to stop.

    My first thought is this is WAY too complicated an approach you're describing. Hydroponics is really pretty easy and to top it off; it works and it's relaxing and fun!

    One factor you didn't consider was that the plants actually "use" the nutrients dissolved in their water. Although there is a system called "Drain-to-waste", it is not used much. Wouldn't you know -- I happen to use it, but I capture any "run-through" waste so I guess that means I actually don't, right?

    I use static culture and actually measure the amount of nutrient given each plant so as to not run to waste. When it rains, the 'drain catches' come into play and I recover any "wash-through" nutrient before it gets into a waterway.

    As far as "nutrient balancing" all you have to do is watch your plants. Nothing is written in stone. It's all on a crop-by-crop basis.

    As for pH balancing, I developed a self-buffering nutrient, so I don't even have to think about that any more.

  • grizzman
    15 years ago
    last modified: 9 years ago

    That was a vague useless reply. only thing you forgot was the plug for your website.

  • Karen Pease
    Original Author
    15 years ago
    last modified: 9 years ago

    "One factor you didn't consider was that the plants actually "use" the nutrients dissolved in their water. "

    That's why, as you'll note, "The mixture cup was dumped and then refilled with a new 1/2 cup of water". If you think I should repeat the experiment simulating a nutrient imbalance by tossing half of one of the solutions but not the other, I can, but the results were so overwhelming, I don't think it'd make a difference.

    What comes across as so complex, out of curiosity? There's only two valves and a ball float, like you'd find in a toilet. And a couple taps to adjust nutrient ratios. Apart from that, it's just containers, tubing, gutter, a pump, a filter... usual stuff.

    Thanks for your input!

  • greystoke
    15 years ago
    last modified: 9 years ago

    Not so fast guys! I'm still reading karenrei's 1st post [LOL]

  • Karen Pease
    Original Author
    15 years ago
    last modified: 9 years ago

    Here's a quick diagram. It loses something because you can't see the height differences, but it should give a general idea:

    http://www.daughtersoftiresias.org/images/hydro-system.png

    In normal operation, solution circulates from a somewhat small reservoir up into the gutters and back down into the reservoir. However, when it gets low enough, a float valve opens up two paths: one, a diversion for returning NFT solution into the nutrient concentrate containers, and one for freshwater directly into the refill tank. The (small amount of) overflow from the concentrates fills the refill tank as well. The rate of flow of each source -- freshwater and each concentrate -- is determined by a tap. Since there's constant pressure behind each (the mains pressure for the water and the pressure determined by the height change for the concentrates), there will be a predictable, constant flow for each. When the level in the refill tank gets high enough, it fills a siphon (just a curved piece of tubing), emptying its contents into the reservoir, thus raising the float, thus shutting off the valves.

    As for the experiment, it's designed to be a direct parallel of normal operation. Filling the "mixture" container with a half cup of water and a teaspoon of each of two "nutrients" is akin to filling a low reservoir. Adding a teaspoon of each back to each "nutrient" concentrate is akin to what happens when the float valves open. Dumping the "mixture" before refill is akin to having the plants make use of it. Again, I could always simulate a higher uptake of one nutrient or the other through selective addition of it to the mixture container, but the results were so overwhelming, I don't think it'd make a difference. In the end, the sugar container continued to taste exactly like sugar, and the salt container like salt, despite replacing the water in those containers several times over. Meaning that if these were nutrient concentrates in the above described hydroponic system, they'd continue to reliably supply the proper amount of the proper nutrient to the refill tank, and thus the reservoir. Assuming that adding in the unknown factor of "time" doesn't throw things off.

  • Karen Pease
    Original Author
    15 years ago
    last modified: 9 years ago

    URL-ifying the link: {{gwi:1002156}}.

  • gringojay
    15 years ago
    last modified: 9 years ago

    Hi karenrei,
    Your return flow nutrient solution from NFT growing site is routed back through all the individualized elemental nutrient stock containers & then their out flows all get mixed together for use in the next flood of nutrient solution.
    You tested the concept with 2 "tastes", salt & sugar, for automatic balancing of nutrients.
    The "used" nutes' % ratios may be altered by variable plant uptake. Refreshing this "used" blend, by transit through the individual stock containers, could compound total dissolved solids.
    Adjusting the individual nutrient stock container valves controls the volume of each solutes' refreshment of the whole. Each setting must keep the recycled nutes flowing through fast enough, so they can not sediment out; operation would need to be continuous to avoid any back wash.
    Do you have a calibration plan?

  • Karen Pease
    Original Author
    15 years ago
    last modified: 9 years ago

    True. My test case only really tested whether the nutrient solutions would get contaminated, and suggests that they wouldn't (at least in the short term, and at least in the case of my two test "nutrients"). In theory, there should be a slow rebalancing of the nutrient ratios in the reservoir because if the solution becomes deficient in a particular nutrient, there should be slightly more of that nutrient dissolving when water passes through that particular concentrate container. However, since only a small amount of water passes through a given concentrate on a given pass, it may be too slow; I may need to code a quick python simulator to determine whether this rebalancing effect should occur fast enough to compensate. Also, it occurred to me that there's nothing in the design that would rebalance water levels. An osmotic membrane should do it; I may have to try another test here.

    So, not as simple as I initially had hoped. :P

  • gw:karenrei~gw:karenrei
    15 years ago
    last modified: 9 years ago

    Another thought that occurred to me... I should experiment around with antisolvents like glycerin and polyethylene glycol to see if the maximum concentrations of various nutrients could be capped without posing a threat to the plants. And higher molecular weight antisolvents could potentially be kept from the plants altogether without requiring huge pressures. May need to look into that...

  • Karen Pease
    Original Author
    15 years ago
    last modified: 9 years ago

    Scratch that, at least in the case of letting it freely circulate. Apparently that induces drought stress in plants.

  • gringojay
    15 years ago
    last modified: 9 years ago

    Hi karenrei,
    You are having too much fun, so I have a detail for you to help me with. It isn't related to your project, it's for a concept of mine .
    I am trying to determine what kind of readily available material could be made into an osmotic membrane. You speculated about experimenting with one for your system.
    ? Do you have any osmotic membranes to suggest for me ?

  • freemangreens
    15 years ago
    last modified: 9 years ago

    Maybe Grizzman is right. I don't think I understood the whole thing and should have passed it up. I tried to help by suggesting the methodology was a bit too complicated.

    From now on I'll just mind my own business. I will confine my comments (if any) to strawberry and tomato growing.

    As for the "plug for your web site" comment; the Web site is up there for folks to get help. I wish I had been able to avail myself of all the information on there 30 years ago. It would have saved a lot of effort and wasted time.

    As yet, there's nothing for sale on the site and it may very well stay that way, I dunno. I wrote it to help folks, that's all.

    Well, enjoy the forum folks; I'm outta here!

  • greystoke
    15 years ago
    last modified: 9 years ago

    Freemangreens,
    Cool it my friend. A bite from a single member and you're outa here. Not how I understood you! Stay man - please - we need you.
    Grizzman is a bit outspoken. That's not so bad . . . it makes me think.

  • Karen Pease
    Original Author
    15 years ago
    last modified: 9 years ago

    I am trying to determine what kind of readily available material could be made into an osmotic membrane. You speculated about experimenting with one for your system.
    ? Do you have any osmotic membranes to suggest for me ?

    "Readily available" -- i.e. not ordering online? There are lots of options online -- everything from the obvious (like reverse-osmosis filters) to the less obvious (such as dialysis tubing -- but check the MWCO! What are you trying to prevent the diffusion of?). But around the home? Hmm. No real good ideas for that. I mean, obviously, you could dissolve eggshells in vinegar and empty their contents, but that's not exactly durable. ;) I suppose you could try any high-tech water resistant/breathable fabrics you might have as part of backpacking or camping gear, such as pertex, goretex, epic, event, etc; they use tiny pores to let water vapor readily pass through, but liquid water only slowly through. I really don't know if they'd work, though; that's not what they're designed for. Really, your best bet is to order online something specifically designed for osmosis purposes.

  • gringojay
    15 years ago
    last modified: 9 years ago

    Hi karenrei,
    I'd like to make a do it yourself "functional" water apparatus. This is not for me to drink ionized alkaline water or sell.
    I just started to read about them & have some interesting experiments in mind. The commercial machines are too expensive for me.
    Since electro-reduction drives the process I think I need a polymer electrolyte membrane in a flat sheet.
    I am not sure if an ion selective membrane, like Dupont's Nafion, will work. Nafion incorporates an acid side group to conduct protons from anode to cathode.
    For this "functional" water system I think a bi-polar membrane, with one cationic & one anionic potential, is what is needed.
    Production goal is that one side of the membrane should get to pH 2.5 - 2.7 water & other side of the membrane to pH 11-13 water; in a container divided by the membrane.
    Any advice concerning the correct membrane & where to buy it is requested, from anyone.

  • freemangreens
    15 years ago
    last modified: 9 years ago

    Oops! Regarding my "bowing out" -- I meant to say adios to this "thread" and not the entire forum. Sorry Red, you're still stuck with me elsewhere!

  • danielfp
    15 years ago
    last modified: 9 years ago

    I am sorry to be pessimistic, but the method you describe here will not work for a large variety of reasons (in my opinion as a chemist). The strongest ones are related to the different salt solubilities and the formation of very insoluble solids in your concentrate solution containers due to different ions mixing together in high concentrations. You are also forgetting that plants also release substances into the hydroponics solution, no solution can be used forever, even if totally exact nutrient replacement is done.

    The most efficient way to use nutrient solutions is to have very reproducible crops. Then do an atomic emission analysis on the crop once each month for a crop cycle, that way you'll now exactly what nutrients need to be replenished when. If your crop is always exactly the same you can then just guide yourself with the previous analysis instead of doing them all over again. This is what large commercial growers tend to do, it is the smartest way to keep solutions for long periods of time with minimal waste of salts.

    Here is a link that might be useful: Everything Hydroponics !

  • Karen Pease
    Original Author
    15 years ago
    last modified: 9 years ago

    I actually agree; I've identified a number of the same issues myself when thinking about it after posting. I'll keep thinking about the problem, though.

    It'd be a lot simpler if, say, ion-selective membranes or ion-selective electrodes weren't so expensive.

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