Christian Gerald

Oh, I was thinking scale as in 'engineer for greater capacity' and allow it to drain to a leach field of some sort - although after re-reading your post, I agree scale as in 'mineral deposit' in the p-trap would be a concern.

If flushed once in a while (maybe using water from small cistern plugged to outhouse roof drainway?) maybe the residual would sufficiently dilute to prevent build-up of struvite/apatite mineralization, but I still see buildup in conventional flush toilets where folks 'let it mellow.'

If collecting and replacing the container frequently, I guess oil would be fine, but I have no idea how much you'd end up going through. I'd be interesting to experiment. If this stuff is all getting composted anyway, my experience was that continual sawdust addition keeps the smell down until the bucket is replaced (i started to notice the 5 gal bucket needed attention about halfway full, ~every week for a family of 4). Also, the oil would take longer to break down in the compost than if it were just browns and pee. I just wonder if the cost/effort to source the oil would justify the decrease in smell.

Maybe have it drain into a wood chip bioreactor? Wouldn't have to be fancy - maybe keep it punx by having a french drain (perforated pipe) into a buried but accessible sawdust trench outflow, where the sawdust/leaves/browns are periodically removed/refreshed? If allowed to drain greywater style into a leach field, that inorganic N gets immobilized more quickly by plants and soil microbes than it would sitting in a bunch of sawdust - but I'd want to prevent nitrate leaching through the soil profile (nitrate is the speediest form of plant-available N that can move through the soil) by lining a trench with clay or something impervious. I remember talking to Abel Kloster about something they had like that at Aprovecho in Cottage Grove, OR.

As for the efficacy of woodchip bioreactors, it would be effective until it needed to be recharged - midwest conventional ag leaches lots of nitrate from ammonia applications, and now some folks are piloting research where they pump their drain-tile flowage through woodchip bioreactors to immobilize N. but that's just a whole mess of problems that could be solved by applying just about every other post in this forum.

Professional environmental microbiologist here...

Urea in urine will break down to ammonium ions (and ammonia gas, thus the volatilization and smell) - and some of this will be nitrified to nitrate by aerobic bacteria and archaea (ammonia oxidizers or nitrifiers, coupled with nitrite oxidizers or nitrosifiers). These 'guilds' of microbes (in the traditional ecological science sense of the word 'guild') work together to turn that ammonia/um (NH3/NH4+) to nitrate (NO3-). Nitrite or nitrate itself doesn't stink, but these organisms need oxygen to do this! Once the oxygen is gone, the ammonia will mostly just be taken up directly by cells (immobilization) into biomass. If anaerobic, this will be slow.


Also, any nitrate produced by the nitrification when there -WAS- oxygen around (and there is always at least some, unless you are in a hermetically sealed chamber with the O2 scrubbed out intentionally) is going to be food for denitrifiers, another guild of bacteria that complete the nitrogen cycle, thus turning that nitrate back into ammonia (stink) or gases (unusable by plants) - namely N2 which is 79% of our atmosphere, NO (reactive, creates acid rain) and N2O (laughing gas, but 300x times as potent a greenhouse gas as carbon dioxide).


So, in general, I would discourage trying to cultivate an anaerobic chamber for the urine - you'll lose N, it will still be stinky, and it would be more 'pollution' than if you were to keep it aerobic. Plus, unless your holding tank was tall and skinny, it might need a fair amount of oil (the gasses would still bubble up out of it). The slurry would also get acidic over time (start off going alkaline up to pH9, but over time, then drops to pH < 3). I guess aside from scaling up a p-trap for leaching (probably my favorite option), one could do some active sawdust composting (i've done this with some success), but this is labor intensive, requires constant input of raw materials, and is still kind of stinky. But you'd avoid making an acidic substrate, the compost would retain the highest amounts of N per volume of urine treated (although subsequently diluted by the sawdust component), and you'd keep down the greenhouse gas production.


My gears have turned on this for a bit from time-to-time over the years, and I would love to hear what you come up with!

(edited for spelling)