Hi Xavier
I read read your post. What a load of cr^p! About 1,000-1,500 gallons by my estimation. I wanted to offer some thinking to an already suggested idea. First my credentials: as a boy growing up on a farm I became interested in biogas production after reading Mother Earth News Handbook of Homemade Power. I built a digester and operated it to the amazement of visitors until one day I blew myself up. Such is the life of a young inquisitive pioneer. I have also been involved in fecal production for many years. It seems your current approach has some issues:
1) Handling. The waste requires much handling due to the 20l containers. I would like to meet the brave folks who volunteered for this task. Perhaps not shake their hands but at least have a beer with them and get to know true heroes.
2) System Complexity. Separating the waste streams caused problems. What to do with all those buckets? If it were my town, just put each one in an Amazon box on the porch. It would be gone the next day!
3) Time. The aerobic process takes 1,2 years. Time for another festival, time for more buckets!
4) Cost. Lots of buckets and lids and a place to store them long term.
Although I am not aware of an example of this being done, perhaps this might better be accomplished with anaerobic bio digestion.
1). Handling. I suggest going straight into 55gallon drums (pardon my English units). Would reduce the handling by ~90%. Some styles have a completely open top and can be sealed with a clampy device lid prior to moving.
2) Complexity. Biogas production works best with the right ratio of nitrogen and carbon. Both streams go together. Perhaps the barrel is pre-seeded with the right amount of used coffee grounds or some other convenient carbon source or perhaps it could be introduced after each use.
3) Time. Anaerobic digestion occurs much more quickly under the proper conditions. Probably complete within two months.
4) Cost. Probably 1 55g drum costs less than 10 20l buckets
What would this look like? All the drums would need to be placed in a building where temperature could be somewhat controlled. If the temperature drops, no problem, process just slows down. All the drums are tied together with a gas line coming off the top. It goes to another set of drums, one upside down in water to prevent mixing of air and methane. Methane is a more powerful greenhouse gas than carbon dioxide so it is immediately burned off and used to heat the building to maintain optimal temperature. I would expect with the aerobic systems you have described that methane is still being produced and released. When the gas stops bubbling, anaerobic digestion is complete and all pathogens have been neutralized. Next step would be to spread the effluent on a farmland. Would be an excellent project to work in collaboration with a university so every aspect could be measured and documented.
