Compost Facility

Compost Facility

The compost facility on the Evergreen Organic Farm is the product of a student's vision and the cooperative effort of Facilities, Housing and Student Activities to recycle some of the organic waste stream from the College. The compost facility has been designed and built almost exclusively by Evergreen staff and students.

Composting recycles organic material to produce a beneficial, nutrient and microbe-rich soil amendment. It is a very old technique that combines different organic feedstocks to provide an appropriate substrate for thriving microbial populations. This reduces and stabilizes organic refuse. In the presence of water, unstable and complex organic compounds are transformed into more stable forms, which slowly mineralize in a soil environment releasing nutrients and plant growth stimulants.

Campus Collection

Presently, composting at Evergreen recycles both pre-consumer and post-consumer food residuals from our food service provider, Aramark. We also collect foodscraps from all student-housing residents that participate in the program. The food residuals are transported to the Organic Farm and the compost facility.

Compost Reactor

This on farm facility features a two-step process. The first step breaks down the organic materials in an in-vessel aerated reactor. Then the compost is put into the vermiculture finishing bins. The worm castings are collected in large, removable trays that are placed under the vermiculture bins. The Organic Farm and the Community Gardens then use the finished compost as a soil amendment, greatly increasing productivity on the sites.

Composting organic refuse keeps the most readily biodegradable portion of the waste stream from entering the landfill, where anaerobic decomposition of organic materials can create methane, an odor-causing greenhouse gas. Composting also prevents the point-source contamination of groundwater from mineral nitrates and phosphates contained in food scraps and yard waste.

Vermiculture!

Vermicomposting is a method of decomposing organic material using surface feeding worms. Redworms (Eisenia foetida) are usually used for this purpose. They are surface feeding earthworms that consume 90% surface organic matter and 10% soil.

To achieve successful decomposition worms must be given the proper habitat and adequate food and moisture. The habitat requirement is achieved by placing a layer of bedding material at least 3 inches thick in the bottom of the vermicomposting bin. The bedding material could be straw, shredded newspaper sawdust or horse manure with bedding material in it. This bedding material is then inoculated with a population of worms. Assuming the bedding material is kept slightly moist, above 50-60 degrees and adequate food is available the populations will expand.

For optimum food waste decomposition consistent monitoring is required. If too much waste is added the worms may suffocate. If not enough is added population growth will stall and perhaps the worms will die-off. As populations grow food demand increases. As temperatures decrease in winter the demand for food decreases. This bin has gone through up to five 25 gallon drums of kitchen waste per week. 

Worms do not "eat" the food waste put into the bin. They primarily feed on the microbes (bacteria, fungi and actinomycetes) that are actively breaking down the food waste. Hence all waste that is put into this bin must be allowed to partially decompose prior to introduction into the bin. The food waste is often shredded to create more surface area for microbes to feed on thus facilitating the decomposition of the material and the growth of worm populations in the bin.

Worm castings are a humus-like material rich in enzymes, plant nutrients and microbial populations. Castings contain approximately 2% nitrogen, 2% phosphorous and 1.5% potassium. They are always at a neutral pH due to earthworms capacity to neutralize even the most acidic of materials. The nutrients are also made available slowly over a period of years. These properties make castings an excellent garden soil amendment.