Dr. Campbell in the MEDesign Lab

A Compact and Effective Composting System for Small Institutions

As Designed for The Unitarian-Universalist Fellowship of Winston-Salem

James S. Campbell, MEDesign®   Feb 2015

System Overview:
Multi-container composting systems were developed in China for recycling of human and animal waste as well as food scraps.  Using a prolonged period of bacterial and insect action at elevated temperatures was found to produce compost that was free of pathogens and suitable for application even to food crops.  This proposed composting system is modeled after the basic Chinese design.

Instead of one large “compost pile” where all composting material is mixed (and therefore contaminated by new, non-composted scraps), this system uses separate barrels to avoid mixing the finished compost with fresh material.  The system requires little physical effort besides filling, sealing, and later emptying the barrels in proper sequence.

A four-barrel composting system

Basic Composter Operation:
The basic system consists of five barrels - One smaller barrel for Topping Material and four industrial blue plastic Composting Barrels of 55-Gallon size.  The composting barrels are equipped with locking band clamps that can be used to seal the barrel shut.

Of the Composting Barrels, only one is unclamped, this is the Collection Barrel.  All organic waste to be composted in thrown into this barrel and a small amount of topping material such as grass clippings or mulched leaves is sprinkled on top if necessary to reduce flies or odor.  An un-clamped top is kept on the Collection Barrel to deter small animals.  When the Collection Barrel is full, it is sealed with the band clamp and dated and becomes a Holding Barrel, and an empty Holding Barrel becomes the next Collection Barrel.

The other three barrels are sealed and dated if full. These are the Holding Barrels.  They hold the composting materials for one year as dated on a sealing tag.  They may be tipped over and rolled around now and then to mix the compost, but this is not truly necessary.  The crawling insects in the compost stir it pretty well.  After one year the contents of a holding barrel is shoveled into a wheelbarrow for fertilizing plants and shrubs around the property. 

Note that no material has to be moved from barrel to barrel.  Likewise the barrels do not need to be moved from place to place (they are very heavy when filled).  Tipping over a Holding Barrel to empty it of compost is the only time a barrel is moved, except for optional roll-mixing.  See the article “Two Barrel Composter” on this site for a good explanation of composting basics.

Also note that the Collection Barrel will “move” from time to time as it becomes full and becomes a holding barrel.  A special “arrow” or other marker indicating the present Collection Barrel’s location is recommended. 

This basic 4-barrel system scales up easily should more composting volume be needed.  The selection of four barrels assumes that it will take the institution three or more months to fill a collection barrel.   This is a guesstimate on the designer’s part.  If the collection barrel fills up sooner than every three months, extra holding barrels may be added to the system.  For example, if it takes two months to fill the collection barrel, six composting barrels will be needed – one collector barrel and five holding barrels.  Time will tell whether more (or fewer) barrels will be needed.  

How it works:
A mix of household food waste, paper products, lawn clippings, leaves, and even animal waste is put in one barrel over time – this is called the Collection Barrel.
When full, this Collection Barrel is sealed closed for a full year (see details on the barrel sealing and dating procedure) and becomes a Holding Barrel. Another Holding Barrel becomes the new Collection Barrel, but if full, it must first be tipped over and emptied of black, rich, garden-ready compost (sorry, none in the first year). This cycle then repeats every time the collection barrel is full and a holding barrel is “ripe” (sealed for over one year) - for no dollars at all! By holding the mixture at composting conditions for a minimum of a year including the heat of summer, most seeds and contagious disease agents are killed. Countless bacterial species carried in by a myriad of mealy bugs and worms transform the rotting rinds and food scraps to black gold. All it takes is time. Mixing is OPTIONAL, (though it does give a better looking product, and helps relieve aggression). Listen to the barrels on a summer evening. The rustling you hear comes from thousands of scurrying critters mixing the compost for you!

To foster this wild composting activity, NEVER put anything toxic in the barrels. This includes caustic lime, acids, disinfectants, chlorine, pesticides, herbicides, and petroleum products (gas, oil, etc.). Soaps and detergents are acceptable in small amounts. Add tree leaf mulch in moderation, as it is very acidic and may retard the composting process. Plastic, metal, large sticks and stones will not hurt the composting, but also will not degrade and must be picked out of the finished compost when it is spread on the property.

What to put in the Collector Barrel:
All table and plate scraps, all leftover drinks including alcoholic beverages and ice, vegetable and fruit peelings and rinds, eggshells (best if crushed), meat scraps (cooked), smaller cooked bones (larger bones are OK also, but may need to be picked out of the final compost for aesthetic purposes), small amounts of cooking grease and oil, paper including paper towels (in moderation) and paper napkins (but not waxed or treated paper), coffee filters, coffee grounds, tea bags, dog and cat droppings (including small amounts of plain cat litter), sawdust and small chips, potted plant clippings and spent potting soils, and even small animal carcasses such as mice, birds and road kill. Add layers of lawn clippings or mulch from time to time, especially to cover the larger rotting things (reduces flies and odor in summer). During times of drought, sprinkle the barrels occasionally to give the composting critters a drink, but don't drown them with too much water.

Location of the Composter System:
The four main composter barrels should be located near the kitchen where they are out of sight to people walking in the front of the building yet very convenient to the kitchen staff.   Odor and insects are generally not a problem as long as topping mulch is put on top of any fresh compost in the collection barrel.  A thick layer of gravel area under the barrels allows any seepage from the barrels to drain away and fertilize the nearby plant roots.

Mosquito Prevention:
Water tends to collect in the grooves of the barrel tops.  If it remains there for over one week in the summer, mosquitoes may breed in the water and become a nuisance.  This should not be a problem for the collection barrel or the topping material container because they will be used frequently, but the Holding Barrels remain unopened for months and may breed mosquitoes.   To prevent standing water on the other barrels, use a towel, sponge, or brush to remove any the water at least once a week if rain has occurred.   This will prevent the mosquito larvae from maturing into adults.  

Supplies Needed for Compost System:

Initial Setup:
Four  55-gallon plastic open-top drums with banding clamps for sealing the top closed
One smaller plastic open-top drum, no banding clamp needed
One large scoop to transfer the Topping Material to the Collection Barrel
One Barrel Cover to keep rain out of a Holding Barrel for the month before emptying.
1-2+ Compost collection containers (to be chosen by Kitchen staff)

Consumable Supplies:
#1 Tyvek Tags, white, for dating sealed Holding Barrels (Uline S5983)
Marking Pens, Black, UV-Stable ink for writing date on sealing tags
18-Guage steel or brass wire to fasten tags to band clamps for sealing Holding Barrels
Topping Material (leaf or grass mulch) – to be collected from grounds maintenance

Kitchen Participation:
Provide Compost Collection vessels as appropriate for the kitchen. A loose cover to the vessels is recommended for appearance.

Instruct Kitchen Staff on the operation of the compost system as outlined here.

Advise and assist all members and guests on what goes into the compost if asked.  Signs should be provided – see examples.

Collect food and cooking scraps into the kitchen Compost Collector(s).  Be sure to keep out plastics or metals or glass (these should be recycled).  Paper napkins are OK to compost.

Empty the kitchen Compost Collectors into the unclamped Collection Barrel outside the kitchen door as required and at the end of the meal or event.  An arrow marker indicated the proper Collection Barrel.  Toss a covering of Topping Material (in the small barrel) on top of then fresh scraps if needed. Replace the top of Collection Barrel when done.  Do not clamp the top.

Clean the kitchen Compost Collector vessels after emptying them – Help Prevent Groad!

Advise Composting personnel when the Collection Barrel is getting full so they can clamp, seal, and date that barrel and prepare one of the empty Holding Barrels to be the next Collection Barrel.  (The actual full-barrel notification procedure needs to be worked out between the Kitchen and other participants).

Composting Personnel Participation:
Check Collection Barrel monthly to see if it is getting full. The Kitchen Crew may also remind the Composting personnel that the Collection Barrel is full.

Shake the Collection Barrel weekly to monthly to mix and settle the contents.  More extensive mixing by tipping the barrel over and rolling it around is optional.

The smaller Topping Material Barrel should be checked weekly or whenever lawn maintenance is done.  It should be kept full of grass clippings or leaf mulch (not whole leaves) for addition to the Collection Barrel when the compost collection vessels are emptied.  A bagging mower is a good way to easily collect the material for topping in any season (except when snow covers the ground).

In times of Drought, water the Holding Barrels enough to keep the compost moist but not drowned in water. A nearby hose faucet for water is advised.

In Mosquito season, be sure to remove any standing water from the top of the barrels at least weekly.

In rainy weather, place a Barrel Cover with no holes over a ripening Holding Barrel about a month before it is to be emptied.  This allows the compost to dry out somewhat so that it is easier to handle. 

Check the Date Tag on the Holding Barrels monthly.  When the date tag on a barrel is one year old, that barrel can be emptied and the compost spread wherever it is needed on the grounds.  Specific instructions for this are shown below.


Required Equipment:
Pliers with wire cutters
Long-handle Shovel,
Spading Fork
Brush Axe

Remove the wired-on Date Tag
Remove the Band Clamp Ring and the top of the barrel
Tip the barrel on its side
The Brush Axe helps pull out and chop the lumps of compost.
Shovel the compost out into the wheelbarrow
(A barrel may contain 2 or 3 wheelbarrows full.)
Spread the compost where needed using the Spading Fork.
Crush any eggshells and remove bones and other debris as required
If the emptied barrel is to become the Collection Barrel right away:
Tip the barrel back to the upright position
Place the Band Clamp back on
(A standard barrel clamp ring handle points to the LEFT)
Then put the top back on (it fits on top of the clamp)
Otherwise, for an empty Holding Barrel-
Put the top back on and clamp it in place
Seal the clamp with a plain wire loop to prevent use
No date tag is needed for the now empty barrel

Emptying a compost barrel


(Involves clamping, sealing, and dating a full Collection Barrel and opening another empty barrel to become the new Collection Barrel).

           Required Equipment:
Blank Date Tag
UV-resistant marking pen
Sealing wire

Pick an empty Holding Barrel to be the next Collector Barrel.
Clip off the sealing wire loop if present.
Unclamp the top of the empty barrel and remove the top.
Replace the clamp ring on the top lip of the barrel -this assures it will not get lost.
(Rotate the clamp handle to the back so others will not remove it)
Put 2 – 3 inches of Topping Material in the bottom of the barrel.
Put the top back on the barrel.
(It will sit on the top rim of the clamp ring)
The Barrel is now ready to collect compost (it becomes the Collection Barrel).

Take the top and the band clamp off the full barrel.
Add 2 – 3 inches of Topping Material to the barrel.
Then put the top of the barrel back in place and clamp it with the Band Clamp.
(The Clamp handle points to the LEFT)
Write the present MONTH and NEXT YEAR on a date tag with the marking pen.
Then insert a 4-6 inch length of wire thought the band clamp lock and tag.
Twist the wire with the pliers to seal the barrel.
(Bend the wire ends back to prevent any injury from the sharp-cut ends)
The Collection Barrel has now become a Holding Barrel to be opened in one year.

Building & Maintenance Participation
There is little need for other maintenance of the system except for making sure the area outside the kitchen door is kept clear so that the kitchen staff can have safe access to the collection barrel.  Leaf and snow removal may be necessary.  And other items for disposal should not block the path from the kitchen door to the composting barrels.

Any electric lights outside the kitchen door should be checked for proper function.  In may be dark when the time comes to empty the kitchen compost collectors, and a working light will be needed for safety and convenience.

And Keep on Composting!

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