Dear Elizabeth,

Thank you for your reply. It is helpful to know that some urine entering the digestor is ok. It was especially important to know that the effluent of the anaerobic digestor is not strictly safe for environmental disposal.

We have had a look at Flycatcher's digestor. They claim to get good rates for kitchen wastes: something like 2 kg/day of waste treated in a 250 litre vessel. Their effluent is a low viscosity liquid that does not have a repulsive odour: which can be used as fertilizer for flower beds. This unit seems good for treating the fecal matter of a family of 5 (assuming 250 gms/day of fecal matter produced per person).

We are developing a unit that uses air to flush. The fecal matter is sequestered from the environment by allowing it to sink through a bed of particles and is removed from the bottom. The problem was what to do with this fecal matter and how to recover the particles that are lost with the fecal matter.

The anaerobic digestor seems to address both problems. By dumping the fecal+particle mix into the digestor, the particles (which are hydrophobic and lighter than water) will separate from the fecal matter: which will degrade. The particles can be collected from the overflow of the digestor and dried (basically to destroy the liquid bridges that make them clump) and recycled to the "flush" system.

A readily apparent problem with Flycatcher's systems are that the digestor gets upset without warning. Once it is down, it needs something like 30 litres of inoculum to get going again.

Another problem is what happens if there is a sudden spike in toilet use (guests coming to stay) or a drop (family goes on vacation). Anaerobic systems go belly up in such cases. Is there a solution?

Could an aerobic system be preferred in this case: we will forego the methane in exchange for reliability?

Really appreciate your inputs.

Vishwanath

Dear Vishwanath,

Your question was rather broad. What would be your treatment objectives with the anaerobic digester technology?
I had a quick look at the "Flycatcher" website link. The website looks quite snazzy but without much details. It seems to me that they have only used organic solid waste as in input but not fecal matter.

Anaerobic digestion will not destroy the pathogens in the faeces, so therefore the question is what do you plan to do with the digestate? Using it as fertilizer could be an option but safety precautions would apply.
Adding the urine is not a problem as such but it won't give you any additional biogas and will instead shorten the hydraulic retention time which is a disadvantage.

These are just some pointers. Maybe you could tell us more about your project and plans?

(more details on your research project are available here but it is not saying anything about anerobic digestion there:
forum.susana.org/forum/categories/141-ot...the-toilet-challenge)

You might also find some pointers in the other threads here:
forum.susana.org/forum/categories/35-bio...n-systems-and-dewats

Regards,
Elisabeth

Dear SuSanA community,

We are designing a waterless toilet at the Institute of Chemical Technology, Mumbai. An important consideration is disposal of the concentrated feces+urine.

We are seriously considering using an anaerobic digester using the Dedko digester technology developed by Flycatcher Technologies (flycatchertech.weebly.com/).

We would really appreciate any heads up about potential pitfalls of anaerobic digesters especially when urine is added straight to the digester.