**5. Summary review of techniques for producing compost**

Whereas the intention of this chapter is not to explain new technologies for the production of compost, it is useful to review of how one makes compost, such as the careful mixing of brown and green raw material. It is important to point out that no animal manure or carcasses are used because animal waste can spread diseases. The composting process presented in this chapter describes the use of organic plant material often referred to as brown and green material (**Table 1**) [38]. Brown material is comprised of shredded wood chips, dry grass stalks, or cardboard and


#### **Table 1.**

*The differences between brown and green organic material.*

thus does not decompose as rapidly as green material. So why use brown material? It provides the finished compost product with a light texture. In comparison, green material refers to more recently cut or harvested wet waste such as vegetables or plant biomass and will decompose quickly. In the mixing of brown and green, the brown material is more stable, meaning that the amount of time required for it to break down or decompose is more predictable [39], likely due to the fact that it contains much less moisture.

Organic waste is comprised of the leaves, stems, and bark of plants and insects. Interestingly enough, manure or animal feces is also a fertilizer that is referred to as organic. Brown materials such as wood chips, sawdust and cardboard, although processed by man, comes from trees and is organic unless it contains dyes or is coated with plastic. Man-made pesticides are natural and are not considered as organic material. However, it is important to understand that sometimes pesticides are organic because some plants will create chemicals naturally in their leaves to protect against insects [7].

The natural process of decomposition of organic material can be described as the breaking down of organic material. We can observe this process in the forest understory, within the leaf litter or dead wood from trees and shrubs. Nutrientenriched humus returns organic material to the soil providing essential minerals supporting and accelerating plant growth; it should be thought of as enriched food stock for root system of plants [40]. Much of the decomposed humus is often in the top layers of soil—typically the O-layer—and is the darker color that can be seen when inserting a soil probe and extracting a sample. Non-organic waste is very slow to decompose and can take hundreds of years to break down into useful material [41].

A commercial or production compost operation manages the decomposition of organic material in a more controlled environment, allowing the process to occur more rapidly to produce a consistent and useable quality product. It does this by regulating the amount of oxygen, water, and brown to green material intentionally. When we refer to a 'compost pile' it suggests a mound or pile of organic measurable waste that is undergoing decomposing [42]. This finished end-product we call 'compost' (**Figure 6**), and can be used to amend existing soil, making that soil healthier or more alive and better suited for retaining soil moisture content and thus the growing of plants. When one tills the soil and harvests fruit and vegetables, the soil can become less vital or degraded. By adding compost or barnyard waste into soil, it becomes replenished with fresh nutrients, contributing to increased soil fertility [43].

In a healthy forest, decomposition of organic matter occurs as part of the digestive processes enabled by a variety of microorganisms [41] that feed on dead or dying plant material and animals. The organisms reproduce, die, and recycle themselves as new organic material through the process of decomposition. These

#### **Figure 6.**

*This large pile of newly produced compost is mixed with existing soil to increase fertility and plant growth.*

tiny creatures are contained in decomposing organic material and do not need to be added to a commercial composting pile. As with any alive material, these microorganisms require food, water, and air to live, consuming some of the organic material found in a compost pile. Whereas insects, worms, and even snails are valuable for making compost, they actually perform less work to in the decomposition process than do the microorganisms. Thus, microorganisms are an essential and necessary component for the production of compost.

As mentioned above, air, water, and the appropriate mix of organic material will allow the decomposition of organic material to reach its finished state in a predictable amount of time yielding healthy and useable compost. Typically, the composting process for organic material (in a compost bin, windrow, or pile) requires 90 to 120 days to occur [44], provided that the organic waste is receiving the needed combination of oxygen and moisture, and most importantly and that it is turned or churned regularly to allow air and moisture to effectively enter the pile [45]. Of course, this entire process can be accelerated significantly by increasing the amount of oxygen that enters the composting material; some operations can produce useable compost in very short time of 30 to 45 days, although the energy and financial costs of doing this may not be realistic.

How should one then choose to produce useable compost from organic brown and green waste? There are two commonly used technologies employed today; commercial operations often use a approach commonly referred to as windrows [46], which are basically very long and narrow piles of compost (**Figure 7**). A windrow is at a minimum 1.5 m (5 feet) tall with equal width and are difficult to manage with only manual labor [7]. As mentioned, a commercial operation often will use the windrow method due to their efficiency in accommodating a larger mass or volume of organic waste material. Due to their size and particularly their length, the windrow technology typically require many hectares of useable surface area and expensive commercial machinery such as a tractor that can effectively pull the mechanized windrow turner (**Figure 8**) which creates a uniform shape of the windrow pile while also churning or mixing the compost allowing necessary oxygen to enter and accelerate the decomposing process. Trial and error have determined that the tractor must use a 'creeper' gear whereby it moves very slowly yet allows the PTO (power take off drive) to spin the turner at a fast speed.

#### **Figure 7.**

*This is an example of a municipal compost facility using wind-rows for large-scale production.*
