Wouldn't sawdust (to a lesser extent woodchip bacause of smaller surface area) provide the carbon and utilise the ammonium for organic decomposition (i.e. carbon cycle) provided there is oxygen present (meaning no free ammonia)?

The amount of phosphoric acid to use for suppressing ammonia release would be calculated according to the volume of N being produced (which is volume of urine x estimate of N concentration in the urine) and the desired nutrient ratio of the fertiliser (often 2:1 N:P). This method produces a very effective fertiliser.

cheers
Dean

I looked a bit around regarding the wood-chips (and biochar) ideas, and it seems that at least in livestock rearing it is mostly used as an absorbent substance (for litter) to hold the acids and other urease inhibiting substances.

I found an interesting old patent ( www.google.ch/patents/US5054434 ) regarding that, which also mentions some other interesting means of suppressing the ammonia release:

Acids may function to prevent the accumulation of gaseous ammonia formed from urine in animal areas by one or more means. First, the urease enzyme is a less effective catalyst outside of some optimum pH range. Adding acid to a medium lowers the pH outside of this optimum, and thus retards urea hydrolysis and consequently ammonia formation. Second, some acids are inhibitors of the enzyme, and therefore impede its catalytic performance. Third, urease-producing bateria grow more slowly in acid media. When fewer bacteria are present, less urease is present, and so less ammonia will be formed. Fourth, if ammonia is formed, it will react with acid to form a non-volatile ammonium salt. For example, citric acid will react with ammonia to form ammonium citrate. By trapping ammonia, less will be free to diffuse to the gas phase. While not wishing to be bound to any particular theory, we believe that one or more of the above mechanisms is responsible for the action of the acids.

The acid will be particularly effective when applied to litter or bedding with water absorbent properties. Water-absorbent materials such as wood shavings will reduce the amount of free liquid in which the urease-catalyzed hydrolysis of urea may occur. Thus, the acid will act in combination with an absorbent litter or bedding to result in greatly reduced levels of ammonia.

For urease inhibiting acids, it specifically mentions phosphoric acid:

Some acids also may act as inhibitors of urease. For example, it is known that phosphoric acid is an inhibitor of urease; see H. L. T. Mobley and B. P. Hausinger, "Microbial Ureases: Significance, Regulation, and Molecular Characterization", Microbiological Reviews, volume 53, pages 85-108, 1989.

That mentioned paper is quite interesting in general, here is the full text PDF:
www.ncbi.nlm.nih.gov/pmc/articles/PMC372...crorev00040-0097.pdf

On page 14pp (98pp in the document) it mentions several urease inhibiting substances and their method of interaction. Of those phosphoric acid is probably the easiest to obtain (ask at your local Coca-Cola plant ). For phosphoric acid it mentions the following:

Recent studies with K. acerogiees urease have indicated that fully protonated phosphoric acid is a competitive inhibitor (...). Little inhibition is noted at neutral pH because partially deprotonated phosphate binds poorly to the enzyme.

Thus under acidic conditions (fully protonated), it should be very efficient to suppress ammonia release as it acts in several ways the same time.

Thanks Marijn!

Apparently, there is a special mechanism with wood chips and other cellulose containing materials. This was discussed earlier in the forum, but I can't find it. What I remember is that it suppresses that enzyme that is triggering the decomposition of urea.

H-A

Dear Hanns-Andre,

I have never worked with adding either wood-chips or (bio)char to urine, so I can only offer you some hypotheses.

I see no other pathway for either wood chips or (bio)char to change the smell of urine than some form of adsorption, where NH4+ ions are bonded to negative charges on (bio)char or wood particles. A process very similar to what happens in soils. But I don't think there is a practically workable amount of wood chips to make urine smell free.

Therefore, I must say that I am quite skeptical of claims that adding biochar or wood chips will eliminate all smell. I guess this would not be too complicated to study. The ammonia losses in jars filled with various mixtures of urine and wood/biochar could be measured. However, I don't think anyone has done this.

In theory, woodchips, or biochar, that have been soaked in urine should be good to add to (nutrient deficient) soils, as they would act like a "slow release" sort of sponge for nutrients. As I understand it, this is part of the Terrapreta thinking.

Regards

Marijn

Dear all,

From previous posts, I remember that wood chips suppress odor - do you know how that is linked to what you have been discussing?

Thanks in anticipation,

H-A

Dear all,

What I remember from my time working with urine.

1.) Urease is a very common bacteria, and works very effectively. Urine itself contains more than enough carbon to turn all urea into ammonium within 24 hours. I remember taking samples every day out of a urine collection system, and the pH was always above 8.5, indicating full conversion of urea to ammonium. Even if the system had been almost completely emptied out the day before.

2.) In practice, it is very hard to build a system -in the developing world- where there is so little gas exchange (air flow into the collection system) that you can prevent nitrogen losses through evaporation. at a Nitrogen content of around 2.8 g/L the NH4-N losses stop because an equilibrium is reached. In my view, for practical purposes, this is the Nitrogen level you should expect once using stored urine.

3.) One of the implications of 2 is that after some storage time (say 2 weeks), so much ammonia nitrogen will have escaped (final NH4-N level around 2.5 - 3.0 gNH4-N/L) that you are at the equilibrium state, and no more ammonia volatilizes, which means that smells are very much reduced. (In my memory it still smells, but almost more humic than ammonia.)

4.) Regarding the addition of acids, this has always been considered in literature to be too expensive/impractical for field situations. (I think some of Kai Udert's articles from 2003/2006 may partly deal with this). It would be interesting to know how much phosphoric acid Goeco is adding to get good results.

5.)I think the smell issue with toilets that are not cleaned regularly is very much due to the fact that the urine is spread out, and thus that the ammonia very effectively evaporates.

Regards

Marijn Zandee

Hmm, have you done some longer term tests with the biochar? While it is probably not supplying the urease producing bacteria with carbon energy, the large surface area would probably be a great habitat for them. Do you replace the charcoal very often?
It is possible that it works like you describe, but from what I know it is a bit surprising theoretically...

@Goeco: phosphoric acid sound like a good solution, have you tested what pH you commonly have in your containers?

In a sealed container ammonia gas quickly reaches saturation level, inhibiting further production of ammonia. A weak solution of urea in an open container soon becomes an open container of water because the ammonia volatilises. To remain useful as fertiliser, if the container is sealed the urea does not volatilise. I add phosphoric acid to stabilise urine and make a balanced fertiliser.

Thanks for this good info on urine odor. Please forgive if below is too far off-topic. We use crop waste charcoal as a bed for the urinal in our UDDT and add enough to prevent splashing. Completely odor free and a ready source of inoculated biochar. BTW, we also sprinkle charcoal over the feces. When full, the feces bucket is set over the charcoal retort or TLUD stove for pathogen kill off. It is then safe to handle for fuel briquetting or fertilizer.

canaday wrote: Thanks for this info, which helps us understand why stored undiluted urine does not stink so much, as the bacteria need a carbon source and they would be somewhat self-limiting.

Hmm, not sure, but I guess that for long term stored urine (that is not totally shut of from the atmospheric oxygen), the conversion from NH4+ to NO2/NO3 is probably what removes most of the smelling ammonia?

Hi Krischan,

Thanks for this info, which helps us understand why stored undiluted urine does not stink so much, as the bacteria need a carbon source and they would be somewhat self-limiting.

The agrienvarchive.ca document archive you cite is very interesting and extensive, but most of the texts are about animal husbandry, in which urine is never stored undiluted.

Adding wood ash from the start would apparently make the urine better fertilizer for plants (according to several recent studies), but it would also raise the pH and potentially provide nutrients to the bacteria, so it seems the stench may be greater. I will experiment with this, anyway.

Any other thoughts on this would be welcome.

Best wishes,
Chris Canaday

This is indeed an interesting question.

The relevant factor is probably the activity of an enzyme called urease that splits urea into CO2 and NH3/NH4+. This enzyme is produced by many common soil bacteria, but they need a carbon source (e.g. sugar) to produce it.

As a secondary step there needs to be a shift towards NH3 in the water solved NH3/NH4+ so that the ammonia gas is released to the air. This is usually a question of temperature and pH. The higher both get the more is released (basically).
This page might give you some good ideas on that:
agrienvarchive.ca/bioenergy/ammonia_emissions.html

Adding an acid to the urine might help keeping the smell down, but if it is an organic acid (like vinegar or citric acid) it might only work in the short term, while in the medium term it could serve as an carbon source to the bacteria. Hydrochloric ("muriatic") acid should not have this problem though.

The urease activity is also somewhat self-limiting in the sense that the produced NH4+ rises the pH in the solution, which after a while becomes toxic to the bacteria (but it also increases degassing, so the pH will fall after a while again). So keeping the pH lower might also result in a more lively bacterial community that produces more urease. So my guess is that it would probably have to be quite acidic (<4 pH) or it might turn out to be counter productive.

Anyways, just some untested theoretic thoughts... maybe it helps.

P.S.: for larger urine treatment applications, I still think that simple filtration followed by acidification and UV radiation (using off the shelf water treatment UV lights) would probably work very well for sterilizing the urine (due to the UV light induced production of bacteriostatic NO under acidic conditions).