A pressure vessel or distilling with subsequent carbon-dioxide washing would probably work, but given the low profitability of urine reuse, I doubt that any such idea would be cost efficient or scale up easily.

UV irradiation on the other hand can be done with common of the shelf component in a non-pressurized & ambient-temperature environment that can be easily replicated at scale where ever there is an electricity connection.

It should also be highly efficient in deactivating viruses as its mode of operation directly targets the DNA/RNA. Spores and cysts are easy to filter out (or settle down during storage), and also should not be in source-separated urine in large quantities anyways.

However Nitrate (a mayor component of stored urine) adsorbs at 200-220nm, thus UV will not be as efficient as in clear water. Together with the above Nitrite/NO effect, it might be quite efficient at sterilizing stored urine though.

I doubt that adding chlorine will be very efficient due to the lower disinfecting strength of the chloramines as you mentioned. It is also in general not that effective for destroying viruses, which I would guess are the main concern in Urine.

Regarding the silver and other metallic disinfection: I contributed to some research on their use in drinking water treatment a while ago, and our results showed that it was only effective against certain groups of pathogenic bacteria and the die-off effect was rather slow. I think it's good for keeping low contamination surfaces sterile, but not so useful to treating water (or urine for that matter).

But it would be great if you could make some tests on all of this and post these results here!

Dear Makowka:

The heat inactivation and UV radiation you mentioned are intersting possibilities. Is it not possible ( for the purpose of inactivation of pathogens) to heat the urine say using solar concentrators in tight closed container so that the ammonia does not escape and when the container cools the ammonia remains dissolved?

Regarding the UV radiation the information i have is that UV radiation may not be much effective against spores, cysts and viruses as much as it is against bacteria. To what extent would UV radiation be effective as a disinfectant? However, the NO formation synergy you mentioned is very intersting and could make the difference.Filtration of urine is also important as you said as otherwise solid residues might absorb at 254 nm something that i have abserved when i did grey water treatment experiment with activated charcoal.The yellow colour of the urine would most probably absorb maximum at around 310 nm and it would not absorb at 254 nm.

On the other hand, is it not possible to add small amount of chlorine so that mono-chloramine forms that has longer disinfecting power though weaker compared to HOCl. This is ofcourse assuming urine does not exert a lot of chlorine demand something that i am not sure about! According to one experimental result whcih often I use for teaching students in water treatment class 1 mg/L of chlorine in the form of hypochlrous acid (HOCl) in clean water required a contact time of 15 minutes to achieve 99% removal rate of Ecoli compared to holding time of 100 minutes for monochloramine ( NH(2)Cl). Would a small amount of addition of chlorine have an effect on plant growth?

What about using silver colloids such as by storing urine in nano silver coated pots or storage containers. Or may be using copper wires as copper is also a known disinfectant. I believe that looking at the stability diagram of copper with respect to dissolving/corrosion it is at the immunity range in the prevailing pH-redox environment of urine.

Another possibility is to volatlise the ammonia by heating and capturing it by reaction with carbondioxide so that, at the right environment, ammonium bicarbonate forms. We are currently attempting such experiment in collaboration with the Chemistry Department of the University of Swaziland using carbondioxide byproduct sold from distillery plant at Simunye. About 33 kg of carbondioxide cylinder gas costs around 1500 Rand. However, cheaper carbon dioxide sources such as methane or wood burning can also be used. We borrowed this idea from old abandoned Chinese fertilizer plants where ammonia derived from catalytic heating of methane gas with air was used to create ammonium bicarbonate fertilizer by reaction with carbondioxide. They have now abandoned such plants in favour of urea. The problem is the phosphorous and potassium which may have to be mixed later with the ammonium carbonate once everything is distilled from the urine. I also think such heating will inactivate the pathogens although i am still in the dark about the fate of the pharmceuticals.

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Do they mention other forms of treatment?

Heat inactivation of pathogens might not work so well as above 70°C all the voiatile ammonia is released (but they mention distillation of that, so maybe that was part of such an experiment?)

After a rough filtration of solid residues (or decantaion of clear supernatant after storage), it might also be quite feasible to treat clear urine with UV light for destroying viruses and maybe deactivating anti-biotic resistance genes.

UV doses would probably have to be a bit higher than in drinking water applications, as nitrate is also adsorbing UV light to some extend, but I just came across an interesting side effect that might help greatly:
www.ncbi.nlm.nih.gov/pubmed/9255286
i.e. Nitrate is converted to nitrite by UV, and under acidic condition this is in turn converted to NO, which is a powerful bacteriostatic substance.
Somewhat acidifying the urine should also help with smells from the process, as it suppresses the ammonia release that occurs at higher pH. Hydrochloric or citric acid are also rather cheap and easy to source, and chinese produced UV equipment for drinking water disinfection is getting very common and relatively cheap also.

Thank you again for the detail information. It certainly helps me a lot. Such research for me is very valuable, as it tries to address the grey area about microbiological safety of urine application.

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Hi Ababu Tiruneh,

Just to be clear, this is not my research - but I think your questions are important, so maybe we should try to get the authors to come to the forum to discuss the implications.

It seems that the urine had not been stored (so it is either "fresh" or a mix of ages), and did not look at this. However they do say in the paper that the fate of viruses and the residues in stored urine is not clear.

They also talk about "precipitating the urine using a magnesium source such as MgO, MgCl2 or bittern" to produce struvite, They say that the virus inactivation increased as the moisture of the struvite decreased and that washing the struvite decreased pharma concentrations and likely other pathogens.

They say:

With proper washing and drying procedures, the production of struvite can thus promote the inactivation or removal of bacterial and viral pathogens in fertilizers produced from source-separated urine and reduce end-product pharmaceutical concentrations.

They also considered nitrification and suggest that this is it is insufficient for bacterial or viral inactivation. But they also say that volatile ammonia is converted to nitrate can be distilled and this is likely to be microbially safe.

Most of the pharma residues were unaffected by nitrification.

I hope that helps, I will try to see if there is anyone who can talk some more on the forum about the findings and answer questions.

Thanks for this information. Was this result based on fresh urine sample (the assumption is the worst case scenario... that they are cross-contaminated ) or urine samples stored over some recommende period of time such as one month for household application? What can be done regarding the geno toxic/cyto toxic substances and other pharmaceutical residues present in the urine? We are currently running a urine fertilisation community driven research program on urine fertilisation at household levels. Participants often ask the health risks associated with urine usage as fertilizers. I always do not feel comfortable with the answer i give them. When you said downstream urine treatment, the only viable treatment option available for us at household level is storing the urine.Are there other options available that can be applied?

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This is a new paper out of eThekwini, South Africa:

Pathogens and pharmaceuticals in source-separated urine in eThekwini, South Africa by Heather N. Bischel and others

www.sciencedirect.com/science/article/pii/S0043135415301731

The researchers looked at urine collected from households to assess the pathogens, pharma residues and antibiotic resistance genes.

They found that:

The most frequently detected viral pathogens were JC polyomavirus, rotavirus, and human adenovirus in 100%, 34% and 31% of samples, respectively. Aeromonas spp. and Shigella spp. were frequently detected gram negative bacteria, in 94% and 61% of samples, respectively. The gram positive bacterium, Clostridium perfringens, which is known to survive for extended times in urine, was found in 72% of samples

They conclude:

The present study is the first of its kind to assess a broad diversity of fecal pathogens in source-separated urine. The urine storage tanks represent a composite of urine from potentially hundreds of individuals. Any urine handled downstream of this set-up is likely to contain a mixture of pathogens originating from fecal contamination. This assumption is corroborated by our findings that demonstrate the ubiquitous presence of a wide spectrum of fecal pathogens in source-separated urine in Durban. The pathogen load and diversity will depend on the extent of fecal contamination of the urine, which in turn depends on the toilet user interface design, usage and maintenance patterns, and disposal processes, in addition to local cultural practices. For example, whether or not children use the UDDTs, especially during an active gastrointestinal infection, will influence the pathogen profile of the collected waste. The detection of rotavirus, a common infection in children, indicates that children likely use the UDDTs in eThekwini.

A safe assumption for the human pathogens detected is that they are infective in fresh feces and therefore also in freshly contaminated urine.

Beyond the human health concerns associated with antibiotic resistance determinants, pharmaceutical usage and environmental release pose potential ecotoxicological risks. Urine discharged from UDDTs or urine collected and applied directly as fertilizer may contribute to such risks. However, recommendations regarding environmentally safe concentrations of pharmaceuticals are limited, especially for soil applications of human-waste derived fertilizers

Due to the widespread detection of pathogenic viruses and bacteria as well as high concentrations of several pharmaceuticals in source-separated urine in eThekwini, thorough consideration of the downstream urine treatment processes is imperative for the protection of individuals handling stored urine and for its use as an agricultural fertilizer.

Of course, storage is one important method to reduce risks from urine, but the authors say that it is not clear how the viruses and pharma residues are inactivated in stored urine and point to the need for better risk assessment via QMRA.