Worm Away Your Cafeteria Food Scraps
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Worm Away Your Cafeteria Food Scraps
Prepared by
Rhonda Sherman
Extension Agricultural Engineering Specialist
Published by
NORTH CAROLINA COOPERATIVE EXTENSION SERVICE
4/97—1M—SAF—270078 E97 30393 AG-551
Every day, schools and businesses
throw leftover food and table scraps
into the garbage. The garbage must be
picked up and transported to a
disposal facility-at significant
financial and environmental cost.
Through a process called
vermicomposting, food scraps are fed
to worms and transformed into a
nutrient-rich compost for plants and
gardens. Vermicomposting can help
businesses and schools save money. By
diverting food scraps from a dumpster to worm bins, it might be possible to switch to a smaller dumpster
and thus reduce solid waste disposal fees. Through a school cafeteria vermicomposting program, students
can learn a valuable, hands-on recyc1ing lesson: food doesn't have to be thrown away. Worm castings
can be used to help plants grow in their school or home gardens and grounds. Although this publication
focuses on setting up vermicomposting programs in schools, the same guidelines can be used by
companies and other institutions that generate food scraps. The Seattle Kingdome and the National
Institute of Environmental Health Sciences are two vermicomposting success stories discussed here.Classroom Vermicomposting One of the hottest trends in environmental education is vermicomposting in classrooms. Kids love worms and find vermicomposting a fascinating way to learn about living things, soil fertility, and recycling. A natural next step is for students to move beyond the classroom and get involved with vermicomposting their school's cafeteria food scraps. Getting Started Vermicomposting cafeteria food scraps is similar to home and classroom vermicomposting-it's just on a larger scale. Before getting started, get approval from your local health department-they may have restrictions such as not using post-consumer food scraps. (See the sidebar on page two for information about pre- and post-consumer scraps.) Next you can gather your materials; you will need worm bins, bedding, water, worms, and food scraps. Worm Bin You can buy large-scale bins, or wooden bins can be constructed by students, staff, or parents. The size and number of bins needed will depend upon the amount of food scraps produced by your school. Roughly one square foot of worm bin is needed for each pound of food waste produced per week. For example, if your school generates 30 pounds of food scraps each day, five days per week, you will need 150 square feet of bin space to handle the 150 pounds of food each week. Five bins that are each 4 feet by 8 feet (32 square feet) will give you a 160-square-foot area for food scrap recycling. Bedding Worms need bedding material in which to burrow and to bury the garbage. Bedding should be pH-neutral, non-toxic, fluffy material that holds moisture and allows air to circulate. Suitable bedding materials include shredded paper (newsprint, paper bags, cardboard, or office paper-no glossy paper or magazines); composted animal manure (cow, horse, or rabbit); shredded, decaying leaves; peat moss (which increases moisture retention); or any combination of these. There should be at least 6 to 8 inches of moist bedding in the system when you start vermicomposting. A combination of microbial activity and worms ingesting bedding causes it to reduce in volume. As long as food scraps are being added on a regular basis, new bedding will not be required. Water Although worms need a damp environment to help them breathe through their skin, they will drown in standing water. Therefore, bedding material should be moist, but not soggy. If you are using paper as bedding material, simply dampen the paper by placing it in a bucket of water, then squeeze out excess moisture and fluff it up (to allow air to circulate) before placing it in the bin. If the bedding becomes dry, spritz it with a plant mister. Worms Two species of red worms, eisenia foetida and lumbriscus rubellus, work best for vermicomposting. They're also called bandling, red wigglers, or manure worms. These worms are surface feeders and
tolerate temperature ranges from the low 40s (F) to the high 70s (F), but 55 to 77 degrees is ideal. Worms
eat half their weight in food each day, so one pound of worms will eat half a pound of food scraps daily.
In the example of the school with five worm bins, the 30 pounds of food scraps generated each week day
can go into a different bin each day. This means that each bin will go seven days (including weekends)
between feedings. Therefore, a little more than 4 pounds of food will be consumed by the worms daily, so
9 pounds of worms in each bin should be enough.
Food Scraps
You can feed worms any nonmeat organic waste such as vegetables, fruits, eggshells, coffee grounds and
paper coffee filters, and shredded garden waste. Worms especially like melons and pumpkin. Drain
excess liquid off food before adding it to the bin. Smaller pieces of food will break down easier because
there is more surface area for microbes to attack, so try to crush, grind, or break food into smaller pieces
before adding it to the bin. Do not add meat scraps or bones, fish, greasy or oily foods, fat, tobacco, or pet
or human manure. Be sure to cover the food scraps completely with the bedding to discourage fruit flies
and molds.
Aren't all food scraps the same?
Actually, no-- Food scraps are classified into two general categories: pre-consumer
and post-consumer. Let's take the example of a corporate cafeteria where a cook is
making a salad. When the cook tosses aside the core of a head of lettuce, that’s
considered pre-consumer food scrap. When the employee, done with the salad and
ready for dessert, scrapes the remainder of his salad into the trash bin, that is post-
consumer food scrap
Remember, 1 pound of worms will eat about 4 pounds of food scraps per week. If
you add more food than your worms can handle, anaerobic conditions may set in
and cause odor. This should dissipate shortly if you stop adding food for a while.
Snapshots of School Vermicomposting Programs
Waterville Elementary School (Oregon)
Fourth grade students helped a parent volunteer build five worm bins, which they set on concrete blocks.
To test the effectiveness of different beddings, they placed shredded newspaper in two bins, pulverized
cardboard in another, old corn silage in the fourth bin, and composted horse and cow manure in the last
bin. Of these beddings, the manure worked best, because red wigglers love manure. Newspaper also made
a fine bedding, but dry cardboard was a hassle to handle; when it was moistened, it got too soggy. The
class received about 30 pounds of worms from a local farmer, so roughly 6 pounds of worms were placed
in each bin. Although it is not recommended to put meat and dairy products into worm bins because they
can create odors and attract rodents, the students decided to put hamburgers, tacos, and sub sandwiches
into the bins, because they are located at the edge of the school grounds. They also added paper portion
cups, paper napkins, and straw wrappers. All of these items were eaten by the worms and turned into
castings.Each day, students from second through fifth grade (assigned on a rotational basis) scrape off the plates,
weigh the food (15 to 30 pounds per day) and take it out to the worm bins. Students spread the food out
on top of the food scraps already in the bin, and cover the new scraps with a layer of bedding. Doing this
adds more air to the bin environment and allows the worms to eat as they move upward, which is their
natural instinct. Students discovered that the best way to harvest worm castings was to leave the lid off
the bin, which allows light to penetrate and dry out the bedding, causing the worms migrate downward.
Castings can be removed from the top of the bin as the worms move toward the bottom.
Cinnabar School (Petaluma, California)
Students constructed eight wooden 3-foot by 3.5-foot worm bins and set them on top of pallets. The
school generates about 30 to 40 pounds of food scraps each day for four days a week. Two bins of worms
are fed each day (15 to 20 pounds of food per bin), so they go one week between feedings. The students
started with 5 pounds of worms in each bin with a variety of beddings, including horse manure, leaves,
and wood shavings. They bury the food in a thin layer, because they found that food buried in one trough
or lump could become anaerobic, giving off foul odors and heating up too much. Another discovery was
that pizza crust should be soaked before it's added to the bin, because it gets moldy quickly.
University of Oregon ( Eugene, Oregon)
The university has an organic gardening program called the Urban Farm. In 1994, the Urban Farm staff
teamed up with the Physical Plant grounds crew to begin an unusual vermicomposting experiment. They
developed a system that could turn 2,000 pounds of food waste per day and several tons of yard waste per
year into a nutrient-rich material that could replace the soil enhancers and fertilizers purchased by the
university. What is unusual about their method is that they did not build bins or add worms to the system.
Instead, they spread organic wastes on the ground and relied on worms that naturally occur in the soil on
the site; within six months, the area was teaming with red worms and burrowing earthworms. On a half-
acre site, two areas measuring 180 feet by 8 feet were cleared of rocks and plants. At 10-foot intervals,
fruit trees and blueberry bushes were planted in rows. Every few days, about 250 pounds of pre-consumer
food waste (mostly lettuce, bread, onions, and tomatoes) is collected from a local restaurant. The food is
spread in a thin layer on the ground between the fruit trees; it's rotated between the trees, so each area is
fed once every 14 days. A thin layer of rock dust from a local quarry is sprinkled on top of the food waste,
which is then covered with a layer of yard debris (grass, leaves, and shredded branches) delivered by
campus grounds crews, the City of Eugene, and private landscapers. The project has been very successful
so far; there are no visible signs of pests or offensive odors, and the fruit trees and vegetables (tomatoes
and squash) planted in the test area are thriving.
Sample Vermicomposting System
As the snapshots here demonstrate, there are numerous ways that worm bin systems can be designed.
After reading through this guide, decide which design meets the needs of your school or business, or
create your own design. To assist you in setting up a worm bin system, the following strategy is described
in detail, and dimensions are provided.The Beaver River System, designed by Josh Nelson, an Worms in the working world
internationally- renowned worm expert, is inexpensive, easily
maintained, and developed for use in temperate to extreme weather Worms aren't just for kids. Several high-
conditions. The multi-level system will stand about 4 feet high, profle businesses successfully recycle
their cafeteria's food scraps with
and it can be assembled in 10 easy steps. Before beginning this
vermicomposting. For example, the
project, decide if you want the system to be either 4 feet by 4 feet
National Institute of Environmental
by 4 feet or 4 feet by 8 feet by 4 feet. Health Sciences (NIEHS) in Research
Triangle Park, North Carolina, had
Step 1 - Dig a Pit.
already made significant progress
A pit filled with gravel or sand will enhance drainage and keep out toward becoming an environmental
model for commercial and institutional
frost in cold weather. (A pit is not necessary in warmer climates;
agencies. However, like most businesses
instead, the worm bin may be placed on well-drained, sandy soil.)
with cafeterias, NIEHS generated a lot
Prepare the pit so that the first frame can be placed inside it and sit of food scraps that were being thrown
flush with the ground. If you intend to use a 4-foot by 4-foot by away. An employee there, after
12-inch frame, dig a hole that is 6 feet wide by 6 feet long and 18 attending a seminar about backyard
inches deep. The 4-foot by 8-foot by 12-inch system will require a composting, received permission to set
hole that is 10 feet long. Line the hole with hardware cloth (1/4- up a verrnicomposting system.
inch to 3/8-inch mesh) to keep out voles and moles. Then place 6
NIEHS bought two heated womm
inches of crushed stone, gravel, or sand into the pit to facilitate
composting units, called Worm
drainage, and level it off with a steel rake.
Wigwams, for $375 each. Each unit
contains 10 pounds of wonms. The
Step 2 - Build the Frames.
bedding is composed of shredded
Construct four or five frames, using stock lumber or rough-sawn confidential office paper and finely
shredded wood that was rejected as
wood, with outside dimensions of either 4 feet by 4 feet by 12
animal bedding for NlEHS's labs. Staff
inches or 4 feet by 8 feet by 12 inches. Either use pressure-treated
volunteers take turns bringing 10 to 20
wood or seal the frames with a preservative. Try to obtain non-
pounds of food scraps each day from the
arsenic-treated wood; however, if none is available, the arsenic- cafeteria to the worm bins, located
treated wood will not harm the worms-they will just avoid contact outdoors, near the facility. Employees
with it. Assemble the frames using long shank, ringed nails or long are looking forward to using worm
screws. Make handles for the frames by attaching a strip of wood castings on their plants.
measuring 2 inches by 4 inches by 4 feet to the outside of each
The Seattle Kingdome stadium, home of
frame toward the upper edge.
the Mariners and the SeaHawks, also
decided to expand their already
successful recycling program by putting
worms to work. About 18,000 worms in
12 containers eat 50 pounds of food
scraps (or 30 percent of the stadium's
total food waste) per week The red
wigglers live in bedding of leaves and
newspaper and eat mostly salad scraps,
although workers discovered that the
worms don't like red cabbage.
Maintenance workers report no
problems with odor or pests, and worm
castings are used on the Kingdome's
flower beds.Step 3 - Keep Rodents Out. Metal hardware cloth on the outside of the bottom frame will keep rodents out. Cut two pieces of the cloth, one that is 3 feet by 6 feet for the 4-foot by 4-foot frame, and one that is 3 feet by 10 feet for the 4-foot by 8-foot frame. Lay the two pieces of metal hardware cloth on the outside of the frame so that there is a 6-inch overlap running down the length of the unit. Using twist ties or workable wire, attach the two pieces along the length of the middle seam. About 1 foot of cloth will hang over each end, and 9 inches will hang over each side. Use tin snips to cut the corners of the cloth so that the excess wire can be bent and folded to sit flush with the sides of the bottom of the frame. Do not attach the wire to the frame; it should just fit snugly. Step 4 - Set Up the System. Set the frame with the hardware cloth on top of the gravel in the pit (doth side down), and center it. The top of the frame should be flush with ground level. Fill in the 1-foot gap around the perimeter of the frame with cinder blocks. Place the cinder blocks so that the solid side is parallel to the ground, and so they hold the wire against the wood frame. Try to leave about 1 inch between the cinder blocks and the frame so it will be easy to remove the frame later. Fill in the gap between the blocks and the pit wall with the excavated material or sand. Step 5 - Stack the Frames. Stack the next two frames on the base frame. To keep the frames from slipping, nail 1-foot-long pieces of 2-inch by 4-inch wood onto the inside corners of the frames so that 6 inches of wood projects into the frame below. Step 6 - Construct a Lid. Use either a half or full-size sheet of plywood l/2- inch thick or greater, depending on the size of your system. Screw 2-inch by 2-inch wood strips into the underside of the plywood lid so that it fits snugly in the frame. The wood strips will add weight to the lid and should fit inside the frame to keep the lid from sliding sideways. Use an adhesive to attach insulating
blue board (at least 1 inch thick) to the lid on the inside of the 2-inch by 2-inch wood strips. Paint or Seal
the lid so that it is weatherproof. Another option is to construct a reversible lid. Begin by attaching the
insulating board and wood strips to each side of the lid. Paint a reflective material on one side for summer
use, and paint the other side with a dark color to absorb passive solar rays during winter months.
Step 7 - Add Bedding and Worm
Fill the bottom of the system with moist bedding up to ground level or slightly above. Place worms on the
bedding and leave them alone for a few hours while they get acclimated to the bin. As worm castings
begin to build up over a period of weeks, add more bedding to raise the level to the next frames.
Step 8 - Attach Insulation During Winter Months.
During cold weather, you can use duct tape to attach 1-inch to 2-inch-thick blue board insulation to the
outside of the frames. Piling leaves around the base of the system will also provide insulation.
Step 9 - Add Food to the System
Drain off excess liquid from food scraps and, if you have the time and energy, chop them up before
adding them to the worm bin (the food will be consumed faster). Dig a hole in the bedding, place food in
the hole, and cover it back up. Be sure that the food scraps are covered with at least 1 inch of bedding
material.
Step 10 - Harvest the Castings.
After about six weeks, you will notice quite a bit of dark brown, earthy-
looking worm castings. You should harvest the castings (remove them
from the bin and separate them from the worms) every three to six
months. When you are ready to harvest the castings, Josh Nelson
recommends that you buy a few inexpensive children's wading pools
and pitchfork the material from the top frame into the pools. The
highest concentration of worms and bedding will be in this top frame.
The lower frames will contain mostly castings and very few worms.
After you empty and remove these frames, transfer the worms and
bedding from the wading pools into the bottom frame and start the
process over again.
For schools that do not operate year-round you will need a strategy
for feeding the worms during the summer One solution is to apply a
layer of horse manure every two weeks. Make sure the moisture
level is adequate.Using Worm Compost
The worm compost, or castings, may be used as a natural plant food. Castings improve soil
fertility and structure, stimulate essential soil microorganisms, and slowly release plant
nutrients. The castings collected from your bin system can be used immediately or stored for
later use. The material can be used as a top dressing on outdoor or indoor plants and flowers,
or sprinkled on lawns as a conditioner. If your school has a garden (if it doesn't, now would
be a good time to start one!), the castings can be mulched or mixed into the soil. Students
will learn a valuable lesson as they see their food scraps turned into fertilizer that helps create
new food.
Worm Bin Troubleshooting
Problems Causes Solutions
Bin smells bad -Overfeeding -Stop feeding for two weeks
-Food scraps exposed -Bury food completely
-Bin too wet -Mix in dry bedding; leave lid off
-Not enough air -Fluff bedding; drill holes in bin
-Food scraps exposed -Bury food completely
Bin attracts flies
-Rotten food -Cover with bedding
-Too much food; especially citrus -Don't overfeed worms
-Bin too wet -Mix in dry bedding; leave lid off
Worms are dying
-Bin too dry -Thoroughly dampen bedding
-Extreme temperatures -Move bin where temperature is between 55
and 77 degrees F
-Not enough air -Fluff bedding; drill holes in bin
-Not enough food -Add more bedding and food
-Bin conditions not right -See solutions above
Worms crawling away -Leave lid off and worms will burrow back
(very rare) into bedding
-Excess vibration -Eliminate vibrations
Mold forming -Conditions too acidic -Cut back on citrus fruits
Bedding drying out -Too much ventilation -Dampen bedding; keep lid on
-Poor ventilation -Leave lid off for a couple of days; add dry
Water collecting in bottom bedding
-Too many watery scraps
-Cut back on coffee grounds and scraps
with high water contentSources of Additional Information and Supplies North Carolina Cooperative Extension Service Contact your county Cooperative Extension center or: Department of Biological and Agricultural Engineering North Carolina State University Box 7625 Raleigh, NC 27695-7625 Attention: Rhonda Sherman Telephone (919) 515-6770 e-mail: sherman@eos.ncsu.edu Directory of Vermiculture Resources: Worms, Supplies, and Information This guide lists known resources nationwide Beaver River Associates P.O. Box 94, West Kingston, Rl 02892 Attention: Joshua Nelson Telephone (401) 782-8747 e-mail: riwiggler@aol.com Worm Digest - Edible City Resource Center P.O. Box 5 44 Eugene, OR 97440-9998 AG 551 Return to: BAE Extension Publications
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