How does fresh poo compost?

Yankeesouth · January 30, 2012, 03:01:54 PM

OK...there are some things I do not understand about composting toilets. Hopefully one of you composting guys can clear it up. How long does it take to compost the poo? What I mean is this.....regardless of the make/model or whatever of the toilet system....if the crapper is used every weekend or even every other weekend there is a constant stream (no pun attended) of new waste being added. ( I guess I am looking at it from the angle of owning a commercial model, Sun-mar, Biolet, etc.) If all the waste goes into the same holding tank you may have waste that is 10 weeks old then also the fresh contribution you made from the current weekend. So how does it, (the fresh stuff) compost? I can understand that if 4 weeks worth of waste were put into a bucket, consistently stirred, and left to compost for a few months......the composting process would happen. How does composting happen when fresh poo is always being introduced?

Maybe I am not saying it right.....Basically...... if you're constantly adding fresh poo say every weekend how are things supposed to breakdown and compost?

Squirl · January 30, 2012, 04:20:33 PM

Poo is mostly undigested food, intestinal bacteria, water, and some air. Very little of the volume is just carbon. In most commercial composting toilets there is a mixture of beneficial bacteria and other high carbon material. As long as the moisture content and temperature are right these bacteria go to town eating the undigested waste and release the energy as heat and C02. It actually goes very fast and the volume can be reduced 90% in days. As you keep the bacteria well fed and happy they eat it up. Nom, nom, nom. The devices have a few features which help with this. They have fans to move in fresh air and vent the C02. They have a drum with peat moss and wood chips, which holds the moisture and adds carbon, but the drums usually have tiny holes so that excess water drips out and is evaporated. The A/C models also come with a little heater to make sure the temperature stays ideal.

You usually flush by spinning the drum with a cup of fresh peat moss and wood chips. Most models have some type of finishing drawer. As the compost nears the end it is rotated into a special drawer, which it usually sits undisturbed for a few weeks, (IIRC 30 days) for the rest of all the bacteria to die down and finish all the rest. Then the drawer is emptied. Most commercial models state the volume they can handle, such as 2-3 adults full time, 4-5 weekends.

January 30, 2012, 05:38:38 PM

Thanks for clearing most of it up Squirl. Question.....how does the poo know when it's done and can drop into the finishing drawer? That's where I am getting confused. If one keeps using the toilet....then there is constant uncomposted fresh nasty poo.

MountainDon · January 30, 2012, 05:57:28 PM

It's more less arbitrary.... once a month or so, on a Sun-Mar, the drum is rotated in reverse. That dumps a certain amount into the finishing tray. You break up any clumps and spread it out. In a month or so it is 'finished" and you dump it and refill. As long as the temperature is above 55 it/they works well.

hpinson · January 30, 2012, 06:04:53 PM

It sounds like you are using a commercial composting toilet? Does the vendor have specific recommendations about operation? Some compost better than others, and a lot has to do with conditions - heat, cold, moisture, rotation, airflow, composting helper material used.

For humanure it takes about a year or two if best practices are followed. Good information is to be had in this series of videos by Jenkins:

http://www.youtube.com/playlist?list=PLFD5D0CE103FD3A56&feature=plcp

A good one to start with is: http://youtu.be/XXcU-JQFdms

And here:

http://humanurehandbook.com/contents.html

January 30, 2012, 06:24:36 PM

I meant to add, that as far as I am concerned I would keep any of that compost away from any human food crops.

Squirl · January 30, 2012, 09:40:52 PM

Some have the drum at an angle, as you rotate it, the finished rotates to one end away from the new additions.

Don_P · January 30, 2012, 11:56:45 PM

So these are a pretty careful mix of carbon and nitrogen maintained at an optimal temperature to keep a colony of bacteria happy. Is it that big a step to go anaerobic and make methane. Alternative energy that's more regular than the sun

.

Squirl · January 31, 2012, 09:36:45 AM

Yes and no. Commercial composting toilets are designed for aerobic digestion. I read many designs for anaerobic methane digesters, but it is a question of volume. Although humans don't process all we eat, we are fairly efficient and our waste is fairly small. Then you have the energy left that the anaerobic bacteria use to live, the excess of this is given off as heat and CH4. The volume is so low that it is not worth the cost of the building of the system. I read some reports that the average persons waste could only run a burner of methane for less than a minute a day. Many human methane digester plans are usually for a small community.

A lot of the downside to anaerobic digesters is the size(capital) to build them. They have to store all the inert large volume of contents of waste such as water and carbon in an airtight container. In addition anaerobic bacteria are even more temperature sensitive.

Commercial factory pig and cattle operations would greatly benefit from them, but it is cheaper up front to just vent the waste into the atmosphere.