February 17, 2006 | General

Composting Cafeteria Residuals With Earthworms (New Zealand)

BioCycle February 2006, Vol. 47, No. 2, p. 55
At the HortResearch Institute in Palmerston North, a vermicomposting system has been set up to manage food scraps for staff.
Tessa Mills

TWENTY YEARS AGO, it was normal practice to dispose of organic waste in landfills, but management problems – from methane gas generation to lack of space – now lead to alternative methods. Within New Zealand, and in many other areas of the world, systems such as vermicomposting can be initiated. There are upwards of 3,000 species of earthworms currently named, but significant information on the activity of only 150 species is available. Of these species, those favored for vermicomposting systems are either brandling worms (Eisenia foetida) or redworms (Lumbricus rubellus). These prefer a high organic matter system.
Composting using earthworms in New Zealand has become popular for domestic disposal of food scraps, but there is no reason why such a system cannot make a significant contribution to the waste management of a commercial enterprise. At the Horticulture and Food Research Institute (HortResearch), Palmerston North, New Zealand, a worm composting system has been established to dispose of all food scraps from the on-site cafeteria. There are approximately 20 kg of food scraps per week produced from the staff cafeteria, which caters to 60-80 staff members. There is no food preparation on the premises, so all food waste originates from lunches and snacks brought from home. If food preparation occurred on the premises then the level of food scraps produced would be much greater. During each year, our worms process approximately one ton of food scraps.
The worm bin, typically constructed of wood but plastic can also be used, needs periodic cleaning and fresh shredded paper supplied as bedding. The casts collect at the base of the bin, the worms continually moving up towards the food source. Any drainage from the base of the bin can be collected and used as a liquid nutrient source for plants. Casts are removed by hand. The worms are temporarily moved to one side of the bin, while the casts are dug out from the other side. Fresh bedding is then laid and the worms and organic matter moved to the clean side of the bin and the process is repeated on the other side. Once casts are removed, these are ready to use as a soil conditioner or mulch.
The bin at the HortResearch’s Palmerston North site is approximately 1.5 m3 in volume. Approximately 4,000 worms were used to initially populate our worm bin in 2001. Since then, this population of brandling worms has been used to start other worm bins at other HortResearch sites around New Zealand and also domestic worm bins at home for some staff members.
When the initial bin was established, the surface was covered with old carpet to retain moisture and exclude light from the decomposing material. The worms slowly digested the carpet so the bin is now open and the worms are still performing very well. Birds also contribute to waste disposal by removing some scraps for food and turning over the composted material, helping to aerate the material. Birds may also consume some worms but this has had little impact on the worm population. Volunteer seedlings also emerge from the composted material, illustrating how good the worm compost is as a growing media for plants.
Most of the compost produced by the worms at the HortResearch site is provided to staff members for home garden use or used in the gardens on-site. The worm composting initiative at HortResearch has provided a very easy and effective way for our company to eliminate waste disposal of food scraps to landfill.
Tessa Mills is a scientist with the Sustainable Land Use Group, Hortresearch, Palmerston North, New Zealand. She can be contacted at tmills@hortresearch.co.nz.

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