We have one Biokube installed at a workshop. The scenario is: people would be using it for urination mostly - so no surprise the treated water is just acidic (pH ~4.5 to 6.5). Otherwise the water is found to be normal. Is my hypothesis correct - that is the treated water is mostly acidic as people would use the toilets mostly for urination only? Next, how can I mitigate this issue - would I have to pump sewage (camp facilities which would have much more solid materials and grey water)? This would cost me time/money in labor.
The explanation is that you are almost only treating urine which has a lot of nitrogen containing molecules that will all be oxidized to nitrate. The nitrification process creates acid.
As an example the most abundant constituent in urine is urea that is first hydrolyzed to ammonia and then oxidized to nitrate and a proton.
CON2H4 + H2O -> 2NH3 + CO2
NH3 + 2O2 -> NO3- + H2O + H+
If you are able to denitrify the water in a further treatment step it will remove the acid:
4NO3- + H+ + 5{CH2O} -> 2N2 + 5CO2 + 2H2O
You need to have some source of organic material ({CH2O}) to make the process run.
There is an ongoing discussion about denitrification options on Researchgate. The most practical for a small scale system is properly the constructed wetland suggested by Boris Kompare.
https://www.researchgate.net/post/Does_anyone_have_any_ideas_for_a_mobile_Nitrate_removal_system_for_rural_waste_water?ev=home_person_like_comment_question_target
I once participated in building a constructed wetland for high nitrogen wastewater at the campus of University of Dar-Es-Salaam, Tanzania which used limestone as the filling material. This would give you the added functionality of the limestone neutralising the acid if the denitrification is not sufficient.
I think the Biokube is a small scale system based on aerated fixed biofilm. The treatment goal is BOD and ammonia, so it is not supposed to denitrify.
A risk with just turning power to the unit on-off would be that it can get very unstable pH if the intervals get to long. Water diluted urine can develop very high pH as urea hydrolyse to ammonia.
If the water is just diluted urine there is a fair chance it doesn't contain enough BOD to reduce all the nitrate.
http://www.biokube.com/
Thank you H. Anderson, very valuable information, denitrification is the right choice but the end product is nitrogen, which is pollutant, what I think (may be wrong) treating with organic matter, in your suggestion, can be replaced with washing soda or NaOH to get NaNO3 precipitates
Need your comments please!
Bruce is correct.
After denitrification there is no pollution problem as N2 is harmless:
4NO3- + 3H+ + 5{CH2O} -> 2N2 + 5CO2 + 2H2O
It isn't possible to precipate nitrate no matter the amount of soda or NaOH added so the treatment has to be denitrification.
Regarding the pH fluctuation in the anaerobic phase this is a relevant problem for small systems treating diluted urine that I have seen on real systems. It can be solved by design of the system. If the water is more like municipal WW this would not be a problem.
Not so complicated chemisteries for me...anyway I was OK with Henry's point as we naturally have the two scenarios - the reed bed & the limestone..the treated water passes through the naturally existing reeds before which it rolls over the drainage in the limestone platform...so should be ok I guess...Thank u friends,
Yeah, agree with you guys, I was confusing NOx with N2, thanks for correction...:)
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Dr. Sinha, How does the earthworms solve the acidification problem with the wastewater under discussion? Does it have any special properties related to the problem or is it just a new treatment method?
Dr. Sinha , I am very interested into know where in Venezuela is your vermifiltration process installed...
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