Techniques & Technologies

Below are composting systems that you may want to consider for your site or in your home.
Contained Compost Solutions
Tumbler
A tumbler is a completely enclosed container, usually made out of plastic, with a mechanism for turning or spinning the container. Tumblers are great for containing odors and moisture, keeping out pests, and easy turning and maintenance. They have limited space, though, and can be expensive. A tumbler won’t necessarily speed up composting time, it will only make it cleaner and easier.
Modified Trashcan
A modified trashcan is just what it sounds like – it’s a trashcan that has ventilation holes, so it can be used for composting instead of trash. It’s an easy, inexpensive DIY project. The trashcan will deter pests and can easily be rolled on its side for turning. The downside of a trashcan is that in can confuse users, causing contamination from non-compostable items.
Bottom-Access Plastic Bin
A bottom-access plastic bin has a plastic tray on the bottom that collects finished compost, so it’s easy to remove and use in the garden. While less attractive than slatted wooden bins, they are usually better in price, and helpful for keeping pests out and moisture in.
Slatted Wooden Bins
This three-bin system can be made of rot-resistant cedar, with removable front planks for easier turning.
There are many different building plans available for bin systems, however, in urban composting, it is important to include rat-proofing measures as part of your plan.
In-Vessel Systems
In-vessel composting is exactly what it sounds like - organic material is broken down inside a vessel or container. The temperature and air levels are controlled, and it usually has a mechanical apparatus for turning or agitating the material for proper aeration. They often have biofilters that provide negative pressure, meaning that air is sucked into a pipe and through a filter - this greatly reduces odors. In-vessel systems have the highest startup cost, but advantages in size, leachate control, vermin, and odor.
Compost Pile Systems
Turned Windrows
Windrows are long piles of organic material, typically 4-8 feet tall and 14-16 feet wide. They are organized in rows, which allows them to be manually turned into the next row or turned in place by a machine. Windrows are big enough to retain heat and moisture, but small enough to allow air to pass through. They are typically covered with a biofilter, such as finished compost or wood chips, to help trap odors. Turned windrows require a good amount of labor, since they must be turned frequently, especially in the early stages. They can be turned by manual labor, though many facilities will use equipment for this. This approach also requires a larger amount of space.
Aerated Static Piles (ASP)
ASP forces air into organic material via a ventilation system, which rapidly speeds up the composting process and greatly reduces labor. Usually, the ASP system is a series of tubes or pipes with holes, and air is pushed through the holes with a fan. The organic material can sit on top of the pipes, in a windrow or pile, or it can be kept in a closed container. The fan can be powered by a solar panel, or attached to an electrical source. Due to cost, ASP systems are usually utilized by larger-scale operations.
Underground Composting Systems
Soil Incorporation
A century old style of composting, just bury your food scraps in the soil! Make sure to cover them with at least 8 inches of soil to prevent pests from detecting the food.
In-Soil Digester
An in-soil digester is like a modified trash can, but it’s buried in the soil. The digester is buried about 2-3 feet in the ground with the top 1/3 to 1/2 of the can raised above the ground. To add food scraps, you can simply open the lid and add them, along with a layer of sawdust or dirt (to prevent odor). The water and leachate will leak into the soil via the holes in the can. The food scraps will compost over a year, and for an average sized family, the digester takes a few months to fill.
Trenching
This is a more organized method of soil incorporation. Essentially, a gardener will bury food scraps in rows. Rotating each year, one row is for burying new organic material, one is for planting, and one is left as is.
Sheet Composting
A little more advanced than simply burying food waste, sheet composting is designed to save space in a garden. To start, build a lasagna of 1 inch newspaper, 4-6 inches of browns, 3-5 inches of greens, and 1 inch of peat moss or finished compost. Then, water the bed. You can stop there, or add another round of layers until you reach the top of the soil. The last layer should be finished compost. You can plant it immediately, or wait.
Worms & Fermentation
Vermicomposting
This is the process of using red worms to break down organic material into high value compost. A pound of worms, or about 1,000 worms, can eat a half a pound of compost a day. Vermicomposting operations can range from a small bin to large system that process thousands of tons per year. Worms are sensitive to temperature, and prefer an environment that is 55 to 77 degrees F. Therefore, it's ideal to keep worm bins indoors. The worms will eat almost any type of organic material other than compostable plastics.
Bokashi
Japanese for "fermented organic matter", Bokashi is the process of breaking down food scraps via anaerobic fermentation. Typically considered a type of composting, bokashi does not use oxygen, fermenting the organics instead.
Food scraps (including meat and dairy) are placed in an airtight container and sprinkled with a mixture of something carbon-based (such as bran or saw dust) and Effective Microorganisms (EM1). This mixture can be purchased or made at home. Once the food and mixture are added, the container is sealed to keep oxygen out.
Allow the mixture to ferment for a couple of weeks. When this process is complete, the fermented food scraps should be buried or added to a compost pile so that it can mature into compost.

Bokashi is easier than some other forms of composting because it is low maintenance, can be done indoors or outdoors, and does not produce foul odors. However, keep in mind that "finished" bokashi is not really compost. It needs to be buried or composted before it can act as a soil amendment.

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