Could urine diversion disrupt proper functioning of small scale aerobic waste water system (activated sludge or biofilter)?

  • BPopov
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Will urine divertion might disrupt proper functioning of small scale aerobic waste water system (activated sludge or biofilter)?

Hello!
Could someone please give a comment if urine exclusion from WW flow prevent a small scale activated sludge or biofilter system to operate properly due to disrupted balance of BOD and NPK? Or the opposite if we exclude urine the capacity of activated sludge system can be potentially reduced?
I had a discussion recently with waste water engineers as for the UD viability and their point against was that if we exclude urine the bacteria in activated sludge will not have enough nutrients.

Thank you!

Bogdan

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Re: Will urine divertion might disrupt proper functioning of small scale aerobic waste water system (activated sludge or biofilter)?

Hi Bogdan,

Good question and there is an easy answer: no, not a problem. Why not? Because there is still enough N, P and K in feces and also other organic matter in the wastewater e.g. from food waste (washing of dishes).

If your small scale aerobic wastewater treatment plant has to achieve nutrient removal, then of course it will be easier to achieve your N and P targets without the urine - so that would be a bonus.

If you want to read more, I advise to look for the publications by Max Maurer and others from EAWAG. Max has published widely on this topic for many years. I had a publication in mind from him from 2006, so I did a quick Google search to see what is available without a paywall. If you e.g. look at this paper from 2009 and the references listed at the end of the paper you'll find lots of information:
Source Separation: Will We See a Paradigm Shift in Wastewater Handling?
pubs.acs.org/doi/pdf/10.1021/es803001r

Of course we also have a nice Wikipedia article on urine diversion:
en.wikipedia.org/wiki/Urine_diversion
(followed by my usual appeal: if you spot anything wrong or missing from this Wikipedia article, tell me or correct it yourself)

Regards,
Elisabeth

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Re: Will urine divertion might disrupt proper functioning of small scale aerobic waste water system (activated sludge or biofilter)?

Hi Elisabeth!

Thank you!

I also tried to prove that иге was shown the requirements for activated sludge process (put in official code in Russia inherited form Soviet Union) saying that every 20 mg of BOD need 5 mg of nitrogen and 1 mg of phosphorus to operate and active sludge to form. This is actually something what we have in a normal mixed flow of domestic WW. I wonder maybe the requirements for AS process are simply taken from the analyze data of WW without further bothering (as it often happened in former Soviet Union))))
True, if we exclude urine from the flow (80 % of N and 50 % of P) the balance would be changed. Are there actually any investigations showing how activated sludge or biofilter technology would perform when the balance is shifted towards 20 BOD:1N:0P?
The man I am in discussion with is the leading Russian waste water expert. It is done on the Russian internet forum devoted to small scale rural sanitaion. dacha.wcb.ru/index.php?showtopic=56783&st=1000

Neither he or other russian experts on this forum are supporting the idea of urine separating saying that this is just another “eco-friendly game” played by rich western societies and the extra-costs needed for separate piping and urine collection and disposing will not compete with conventional systems unless heavily subsidized by consumers.
Best wishes,
Bogdan

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Re: Will urine divertion might disrupt proper functioning of small scale aerobic waste water system (activated sludge or biofilter)?

Obviously you can't go to "0" phosphorous ;)

The mentioned BOD:N:P ratio of 20:5:1 is actually quite N heavy, even for an aerobic system for which an optimal C:N:P ratio of 100:5:1 is commonly assumed (anaerobic systems tend to go better with higher C thus that 250:5:1 ratios are possible for Biogas production). Of course the C (TOC) to BOD ratio calculation depends a bit on you wastewater, but in fresh sewerage it is usually not 0.2.

This paper gives a lot of good background info:
onlinelibrary.wiley.com/doi/10.1111/j.13...k9dfgjLoVvHTCkRzpnhV

Also note that the C:N:P ratio has an effect on biofilm attachment, thus an aerobic filter will work optimally with somewhat different parameters that an activated sludge system.

Edit: I guess ultimatly it is a question of the effluent quality regulation in your country. When the permissible Nitrogen content is high, then these Russian experts are probably correct in saying that urine diversion is not cost efficient. But if you need to do costly additional nitrogen removal steps to adhere to regulations (or environmental concerns) then the economic balance probably shifts to relatively simple urine diversion, especially if used to offset fertilizer use elsewhere.

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Re: Will urine divertion might disrupt proper functioning of small scale aerobic waste water system (activated sludge or biofilter)?

Hi Kris!

Thanks for the reply!
Sorry, I totally messed up the figures (this what happens when you post to susana forum first thing in the morning))). The code required BOD:N:P ratio in Russia and Ukraine is 100:5:1 (not 20:5:1 like I wrote) and I meant not total zero P but 0,5 if urine is excluded.
So it is better to operate with TOC values rather than BOD regarding the ratios to NP?
What I am really interested totally for practical reasons is whether excluding the urine from the flow can give the opportunity to significantly reduce the planned capacity of small scale waste water treatment unit (up to 50 PE) whether activated sludge or biofilter based or even constructed wetland and thus reduce the costs of purchasing or building it . Or the opposite – the WWT unit would not operate properly. Only this purely economical reason without possible benefits of using urine for fertilizer so far. The effluent quality should be let’s say 20 mg\l BOD and 5 mg \l of ammonia nitrogen
Regards,
Bogdan

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Re: Will urine divertion might disrupt proper functioning of small scale aerobic waste water system (activated sludge or biofilter)?

BPopov wrote: Sorry, I totally messed up the figures (this what happens when you post to susana forum first thing in the morning))). The code required BOD:N:P ratio in Russia and Ukraine is 100:5:1 (not 20:5:1 like I wrote) and I meant not total zero P but 0,5 if urine is excluded.
So it is better to operate with TOC values rather than BOD regarding the ratios to NP?

Yeah, I can relate... luckily on SuSanA you can't see the edit history of posts... the first version of what I wrote needed a lot more coffee as well :)

Practically speaking BOD is better as it more closely resembles the carbon based energy bio-availability during aerobic treatment, but in the scientific literature TOC or COD is more commonly used and while for fresh domestic wastewater BOD usually isn't that far off the total organic carbon content, it still adds a bit of uncertainty to the estimation.

BPopov wrote: What I am really interested totally for practical reasons is whether excluding the urine from the flow can give the opportunity to significantly reduce the planned capacity of small scale waste water treatment unit (up to 50 PE) whether activated sludge or biofilter based or even constructed wetland and thus reduce the costs of purchasing or building it . Or the opposite – the WWT unit would not operate properly. Only this purely economical reason without possible benefits of using urine for fertilizer so far. The effluent quality should be let’s say 20 mg\l BOD and 5 mg \l of ammonia nitrogen


This is a bit hard to say theoretically, but generally the aerobic digestion should not be N or P limited even if the urine is separated (and you could always dose a bit of the collected urine into the system if needed). However this doesn't have any impact on the size or cost of the primary and secondary (the biofilter / AS) treatment steps; they stay the same.
But if a tertiary treatment is necessary to remove additional N & P (e.g. the constructed wetland or Nitrification/Denitrification step) then the urine separation could probably allow a reduction in size/costs or maybe (if at all permissible) even direct discharge after the secondary treatment.

I would look for data on N / P secondary treatment effluent content of similar existing treatment plants and see how far those are from final effluent regulatory values. Typically there will be still a significant N / P excess, but if the reduction via urine diversion could potentially make plant nutrient removal unnecessary then the cost savings should be significant.

Edit: But often constructed wetlands also perform secondary polishing functions unrelated to N / P removal and thus might be necessary to reach for example the microbial effluent quality requirements.

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Re: Will urine divertion might disrupt proper functioning of small scale aerobic waste water system (activated sludge or biofilter)?

Kris has given an excellent answer. I'd just like to add: You know that biological treatment also works on greywater, don't you? Greywater has no urine and faeces in it and yet biological treatment still works, e.g. in constructed wetlands. So there you go. After all, wouldn't it be mysterious that the activated sludge process should only work on exactly the "typical" composition of municipal wastewater? Luckily all the biological systems are rather versatile. :-) (and even the "typical" composition can vary widely from one country to another, e.g. with regards to concentrations due to different amounts of water used by households)

Regarding your Russian experts being critical of urine diversion systems at the large scale: I think they have a point. The research about the theoretical benefits of urine diverison has already been done a while ago - see all those publications by EAWAG (e.g. Max Maurer) that I had mentioned. But to get a cost-effective large-scale system going with dual pipework to collect the urine separately can currently not be made cost effective, as far as I know. This would change if fertiliser prices went up (e.g. due to a phosphorus shortage). Then urine fertiliser would suddenly have more value.

Or it might change if the effluent quality parameters from the wastewater treatment plant became very stringent. Not just looking at ammonia but at total nitrogen. A total nitrogen limit of 5 mg/L is very hard to achieve, some have even tried for 3 mg/L which is super hard. In such situations, keeping the urine out of the wastewater could give a real financial benefit. But if there are no nitrogen limits on the treatment plant effluent, then urine diversion is not so attractive.

How would you keep the urine separate anyhow? Waterless uinals are great but hardly anyone has them at their homes (they are common in public places). If people are used to flush toilets then theoretically you could go to "urine diversion flush toilets". These come with their own sets of problems. See e.g. here on the forum the research in Australia and Germany:
www.forum.susana.org/urine-diversion-flush-toilets

So even if it hurts us eco enthousiasts, I think your colleagues are not so far off when they say:

Neither he or other russian experts on this forum are supporting the idea of urine separating saying that this is just another “eco-friendly game” played by rich western societies and the extra-costs needed for separate piping and urine collection and disposing will not compete with conventional systems unless heavily subsidized by consumers.


I reckon you have better chances with urine diversion at the very small scale and when there is no sewers anyhow (using UDDTs).

By the way: It's great if you can be a bridge between the SuSanA forum and the Russian wastewater community (I think none of them have come across to this forum yet?). Is there anything we could do to be more inviting to them? Or is is mainly down to the language barrier. Does the Google translate button at the top help? Perhaps you could try to post a paragraph in Russian and we can check how well Google Translate works nowadays.

Regards,
Elisabeth

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Re: Will urine divertion might disrupt proper functioning of small scale aerobic waste water system (activated sludge or biofilter)?

JKMakowka wrote:
This is a bit hard to say theoretically, but generally the aerobic digestion should not be N or P limited even if the urine is separated (and you could always dose a bit of the collected urine into the system if needed). However this doesn't have any impact on the size or cost of the primary and secondary (the biofilter / AS) treatment steps; they stay the same.
But if a tertiary treatment is necessary to remove additional N & P (e.g. the constructed wetland or Nitrification/Denitrification step) then the urine separation could probably allow a reduction in size/costs or maybe (if at all permissible) even direct discharge after the secondary treatment.

Thanks Kris!
It looks like urine separation is rather unnecessary in the situation I mentioned.
Actually after reading “Treatment of source separated urine
and its effects on wastewater systems” by J.A. Wilsenach the idea of urine separation doesn’t look that attractive as before.
Best,
Bogdan

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Re: Will urine divertion might disrupt proper functioning of small scale aerobic waste water system (activated sludge or biofilter)?

Dear Elisabeth!
I think you are absolutely right – urine diversion has potential mainly for small-scale, on-site system where it can be utilized directly a s fertilizer (farm or homestead). However, the main issue is probably not technical appropriateness but I would say ideological willingness to do so based on environmental consciousness. Where society had reached that state (as result of social and economical development) -- UD and other nice eco stuff is possible. This is definitely not the case yet for Ukraine and Russia.

I do not know how you can be more inviting than you already are))) I think language is not really a barrier -- those who are interested in ecosaniation are here, those who are not -- are not here. I can try to bring some issues from that Russian forum but honestly speaking the style of communicating there is rather aggressive and competing -- not friendly and supporting like here.
Regards,
Bogdan

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