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josko021

Ammonia ooutgassing

josko021
13 years ago

I have a compost pile that's outgassing ammonia. It's not objectionable, but one can smell a distinct 'barnyard' ammonia smell a few steps downwind of it. It's a 4'x4'x4'6" pile built up of fresh weed, dry leaves, fish scraps and hardwood shavings. I tried to balance it out to a C:N of 30:1, but may have come up slightly green. It's been running at 160F+ for the past week, and the top is already down some 6" from the original 5' height. I tried a 2" layer of oak sawdust on top, but it didn't have a noticable effect on outgassing.

I understand ammonia should convert to nitrates and then nitrites via an aerobic process and am wondering if there's a way I can enhance ammonia conversion at this stage. I don't want to turn the pile until it cools. Thanks in advance.

Comments (21)

  • toxcrusadr
    13 years ago

    Based on your description of the chemistry, I think the only way you can convert that ammonia is to trap it in a very aerobic AND biologically active environment, and the sawdust has no bugs. Maybe a layer of screened compost surrounding the pile would work better, but you could have problems getting air into the pile, further pushing it toward anaerobic conditions.

    I think your problem is to much greens in that pile - the fish scraps could be the problem. It's actually running at the top end of the ideal temp range, so pulling it apart and mixing in some of that sawdust or leaves would likely straighten things out without stopping the cooking.

  • shebear
    13 years ago

    Too much moisture can also be a source of ammonia odor. Turn the pile more often and add some carbon too.

    And turning a hot pile won't necessarily cool a pile for very long. In fact it can make it even hotter by the next day. If you're smelling ammonia, you could be losing nitrogen too.

  • Kimmsr
    13 years ago

    Your mixture has too much Nitrogen in an unstable form, so you need to add more carbon. If too much moisture were present the odor would be putrid, not ammonia, since excess moisture displaces the oxygen needed for aerobic digestion and the pile goes anaerobic, in the absence of air.

  • toxcrusadr
    13 years ago

    If you smell ammonia you are DEFINITELY losing nitrogen.

    The solution is to put the browns where they are available to the microbes at the source of the ammonia, and that means mixing browns into the pile.

  • josko021
    Original Author
    13 years ago

    Thanks folks,

    I didn't want to turn my pile because I didn't want to expose some unfinished pocket of fish scraps, but it's starting to calm down all by itself - it was down below 150F just now, and the smell is all but gone. I can see it steaming as I write this.
    I have an essentially unlimited amount of fish scrap available, and am learning how to compost it in my 4x4 piles (made of pallets) without stinking up the neighbourhood. A bit of ammonia outgassing is vastly preferable to what CAN happen to a pile of fish scrap (I speak from experience), but it would be nice to capture and convert as much of it to nitrites as possible. I just read that an acidic carbon-rich material might slow down ammonia production, and that hosing it down night put some ammonia into a water solution, so I might try a bale of moist peat mixed in on top next time, just to see if it works (although I can't really afford a bale of peat for each pile).
    So, the experiment continues. The compost that's been coming out is great.

  • bob64
    13 years ago

    Try leaves or leaf mold as a peat substitute and see how that works. I think there are anaerobic ways to capture nitrogen/ammonia also but not sure now about the details. I think one version is to just contain the fish, cover in several inches of soil and wait (you'd need a critter proof container). That's probably not for you but something to consider if you have an excess of fish scrap. I've seen some devices for using BSF larvae to compost such nasty stuff as well but I'm not sure if that helps with odor.

  • Kimmsr
    13 years ago

    The mild ammonia odor is much preferable to the pungent and grossely offensive odor anaerobic digestion would produce. If you have no shredded leaves, or a similar carbon source (not peat moss), I would leave that pile alone. More water probably is not needed, and enough to exclude the air necessary to maintain an aerobic digestion process is definitely not needed.

  • josko021
    Original Author
    13 years ago

    Oh, I'm definitely going to leave that pile alone, as it's calming down all by itself. I was able to process about 300 lbs of fish scrap in that one pile alone with minimal outgassing, and really no objectionable odors.
    However, I'm already setting up for the next one. I think I understand how to layer scrap and wood shavings to preclude anaerobic 'putrefaction' but any additonal hints on how to structure the (next) pile to minimize ammonia outgassing would be welcome. I've been reading that an acidic carbon material (such as peat) is preferable but don't really understand the related chemistry well enough.

  • toxcrusadr
    13 years ago

    Egad, 300lb of fish scraps! You are a brave compost-maker. And if all you got was a little ammonia smell, you're doin' it right. Hard to improve on that.

    I suspect the effectiveness of acidic materials works like this: Ammonia gas (NH3) is in equilibrium with ammonium hydroxide solution in the water:

    NH3 + H2O NH4+ + OH-

    If you add acid to the system, it will react with the OH-,

    H+ + OH- ---> H2O

    pulling the ammonia/ammonium equilibrium to the right, thereby reducing the amount of free ammonia that can offgas, and trapping it in the form of ammonium which can't offgas.

    I once had the opposite problem. I used to make a lot of compost with grass clippings, sawdust, and leaves. I also burn wood so I had a lot of ash. When mixing up cubic yard batches, I would add a couple quarts of wood ash to the mix to recover some of the nutrients and reduce my landfill-bound waste stream. I got a lot of ammonia smell off those piles, and finally figured out the ash was throwing the pH too high until it was neutralized. I quit the ash and the ammonia loss decreased. One of these days I'll make an ash leaching hopper to recover the lye for soap making, and put the neutralized ash back in the ground.

  • josko021
    Original Author
    13 years ago

    Thanks for the explanation of how acidity helps. I tried pouring a couple gals of very dilute vinegar on my pile, and the odor dropped off amazingly! I suppose as long as there's no risk of driving the pile anaerobic, watering it down with a mild acid is a way to put some ammonia back into solution.

    But now I wonder why I've heard it suggested to add lime to 'help things rot'. Is that an old wives' tale, or is there another process where a high pH will enhance decomposition. Does reducing ammonium hydroxide (converting to ammonia) actually speed up aerobic decomposition?

  • toxcrusadr
    13 years ago

    I have never heard a scientific explanation for adding lime to compost.

  • tracydr
    13 years ago

    We add lime to horse stalls to reduce ammonia. Don't know why but it works better than anything.

  • josko021
    Original Author
    13 years ago

    Lime has really piqued my curiosity now. Is there something in lime (besides the pH change) that would reduce ammonia outgassing?
    The added alkalinity would ENHANCE ammonia generation, if I understand the chem. process described above.

  • josko021
    Original Author
    13 years ago

    For completeness sake, here's an answer to this question:

    From "On-Farm Composting", pp 59:
    "Large amounts of lime are often used to raise the pH above 10, which limits odors by reducing the microbial activity. This is frequently done with sewage sludge. However, the effect is only temporary; and lime can aggravate the situation because the high pH causes greater ammonia loss and odor."

    So that would at least explain why dumping lime on smelly pile or carcass might alleviate the odor problem.

  • toxcrusadr
    13 years ago

    That would have been my first thought too - it just kills off the microbes for awhile.

  • josko021
    Original Author
    13 years ago

    For completeness sake:
    The June 1 pile is still running at 135-140F (12" from the top middle) with no discernible outgassing. It's dropped another 6", and I added a 4" cover of lawn trimmings and wood chips.

    I started a new pile on 6/18 with ~250 lbs of fish, 1 yd^3 of ramial oak wood chips (The pile went to ~150F within 36 hrs and has stayed there with no discernible odor since. I'm prepared to water it with dilute vinager should it start putting out ammonia, but so far it hasn't been necessary.

    I think I was a bit heavy with fish on the last pile.

  • josko021
    Original Author
    13 years ago

    As I turned the June 1 pile (on 8/14), there was a very strong ammonia smell as I opened it despite thhe 110F temps and not much activity in the last month. The smell died down in a few hours, but I wonder if I'm better off leaving a pile be or turning it and dealing with ammonia outgassing. There are no nuisance issues; I just wonder about looking nitrogen.
    The material in the pile looks great with no detectable fish parts evident. My hope is to put the stuff on the garden in late fall.

  • Kimmsr
    13 years ago

    There are two reaons to turn a compost pile. 1. To put the material on the outside into the center where the bacteria will work on it, and 2. to control the temperatures, ie. keep them from getting too high. If the original mix had too much N in it ammonia like odors probably will be present for several turnings, whether that is good or bad depends on you perception.
    Once upon a time people though that mixing in lots of Oak leaves would an acidic compost make so adding lime, to neitralize that, was necessary. Since today we know that will not happen, compost tends to be near neutral when finished, lime is not necesary nor desireable in the compost pile.

  • gargwarb
    13 years ago

    "NH3 + H2O NH4+ + OH-

    If you add acid to the system, it will react with the OH-,

    H+ + OH- ---> H2O "

    Not so sure about that. First, the system is nowhere near as simple as just ammonium, ammonia, water and hydroxyls reacting with each other and nothing else.
    Second,(even if that was the only reaction taking place) you could only push that reaction from right to left by adding hydrogen if the mechanism pushing left to right was deficit of hydrogen. Pretty tough to turn NH4 into NH3 by giving it more hydrogen.
    Dropping the pH can reduce off gassing of ammonia but that's because it decreases enzymatic and microbial activity as well as increasing the solubility of the ammonia, allowing it to "dissolve" into the water present in the compost.

  • toxcrusadr
    13 years ago

    Acid is not giving it more hydrogen, it's depleting OH-, which affects the base/salt equilibrium of ammonia. H+ does not even appear in the ammonia/ammonium equilibrium, so it's irrelevant in that sense. Fundamentally it seems like a simple acid/base equilibrium to me, but...

    However, I agree these processes don't occur in a vacuum, there's all kinds of stuff going on in there. I freely admit I don't know much about the effect of pH on microbial and enzymatic action, so maybe those factors are more important. It's been so long, I don't know if I read the theory I've presented somewhere, or just synthesized it out of my tangled little chemist's brain. I've been wrong before. (I was wrong once in 1978 .. :-D )

  • gargwarb
    13 years ago

    You're right. I'm a horrible listener and communicator pre-coffee.
    You said, "pulling the ammonia/ammonium equilibrium to the right"
    Which I read completely backwards and responded, you could only push that reaction from right to left...
    I was befuddled as to what you could possibly be getting at.

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