Earth Tub Description of Operations

The Earth Tub is easy to load and operate. In order to produce a healthy composted soil, the following steps should be followed:

1. Food Scrap Collection - The first step is to make sure that the right material is sorted and collected for composting with as little contamination from plastics, etc. as possible.

Acceptable Kitchen Materials for Composting

Vegetable prep waste

Post-consumer plate scrapings

Napkins or absorbent paper products

Shredded paper or cardboard

Any yard waste from the grounds

It is important that the kitchen staff be trained for sorting out the prep waste acceptable for composting. In general, material should be two inches or less in diameter. Whole oranges, melons or other soft fruit is an exception to this rule. Hard foods such as pineapples, stale loaves of bread, etc., should be chopped up prior to disposing in the Earth Tub to two inches or less. Meats, cheese, and other fatty foods should be kept below 10% of total waste input. Avoid adding large pieces of meat, fats or oils to the system.

Containers for Collection
A separate container should be used for collection of organics in the kitchen and cafeteria. The size of the container should depend on how the material is loaded into the Earth Tub and the volume of organic waste generated. The Earth Tub is four feet high, therefore, containers used to collect and transport food waste to the composter should not be so heavy as to make lifting and loading difficult for the operator. A five-gallon bucket or small garbage can on wheels is suggested for food waste collection. A five-gallon bucket weighs about 20 pounds when full of organics and can be easily carried for manual loading by a single person. Small garbage cans (33 gal), partially filled, should not exceed 75 lbs and can be loaded by two people. Other options include delivering and loading materials by truck in larger tilt containers for discharge into the hatch.

2. Loading and Mixing

Because food scraps are wet, a dry bulking agent must be added to the mix. To make a good analogy, think of composting as baking. Bulking agents are like the flour to a recipe. Bulking agent is required to balance moisture and porosity of the mix. Like all recipes, the compost "recipe" must be measured and mixed in order to maintain optimal conditions for the "baking" process.

Bulking Agents

Wood Shavings

Wood Chips

Sawdust

Leaves

Shredded Paper Products

Hay

(NOTE: Avoid using pressure treated wood shavings or chipped particle board for composting.)

Once loading is complete, mixing is done by the flick of a switch. The powered auger system has been designed to perform this function quickly, effectively, and, above all, is hassle-free. The mixing process is accomplished by slowly turning the powered auger/lid assembly in a counter-clockwise direction for several complete rotations. A complete mix should take approximately 10 minutes, and should be performed at least two to three times per week.

3. The Compost "Baking" Phase

When the Earth Tub has been loaded to its capacity, no additional food waste should be added to the unit while it completes the "baking" or "final cooking" process (high temperature or thermophylic composting). This phase takes approximately 14 days. During this time, material mixing should continue one to two times weekly.

4. Unloading and Curing the Compost

Once the compost has finished cooking, it looks like rich brown soil and is ready to be unloaded. The Earth Tub is not usually emptied 100%; a small amount of compost remains and serves as a bulking agent and microbial starter for the next cycle. Discharge of the composted soil from the Earth Tub is easy:

Place a tarp or container on the ground below and outside of the two side discharge doors.
Turn on the auger and watch it discharge the compost out of the side doors.
Sweep the auger back and forth across the doorways to discharge the majority of the material.
The compost could be used directly as a thin mulch or cured for further stabilization.
To cure, the compost should remain in an undisturbed pile for approximately 30 days before use.
The compost can be screened, if desired, to produce a more refined compost product and recover any remaining bulking agent.

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