Composter Design

As I said in my last post, the composter is one of the four technologies for bootstrap food self-sufficiency for a functional activist community.

This is the initial design for the electric in-vessel hot composter, the first DIY version of its kind that I know of. It's intended to be one of the many and expanding uses for the keg.

It uses a solid state relay to allow a motor to spin the axle a few revolutions several times a day (i.e. usually off), the keg, the electronics techniques, plus two cpu fans (always on) and a heating pad from Walgreens which takes another relay node and, together with a temperature sensor, forms the thermostat that keeps the temperature between 40-60 degrees Celcius. Naturally, it collects data, and is generally operated, wirelessly from a laptop (windows, mac or linux) but it could also work strictly off the wireless nodes themselves without a laptop or jeelink. It still needs an electrical outlet for the heating pad, however, although even this could be converted to passive solar or use a larger static compost pile for heat.

The hot composting process is like a fire. It requires heat and oxygen.

The cpu fans circulate air. The agitator arm when rotated (by "something") also aerates the compost.

People sometimes ask why use electricity for something that already occurs in nature? Is electricity needed at all for an exothermic process?

The electricity is needed because the compost "pile" is so small compared to, say, a cube of 4'x4' wooden pallettes or a windrow. The diminutive nature of our compost heap would lead to a heat loss that doesn't allow the thermophilic bacteria to thrive. As for the power consumption, it is less than 1/100th of what your computer uses, or 60 watts. And it doesn't stay on all the time--there is the solid state relay cord and temperature sensor for that.

My back of the envelope calculation for the reaction time is somewhere between two weeks all the way down to three days! (This more optimistic figure may require innoculation with special thermophilic microbial life.) This is because conditions can be made much more precise than in aerated static piles or windrows that take months to complete. The science of this could be made one of the objects of our study.

It currently has no means by which to turn so if you have any experience with mechanical projects or want to get it, the site has groups and members for a reason.

As testing proceeds or in the course of other keg-wise developments, a ball valve for drainage will be added.

More details on this process will ultimately be available in the composter group.