Organics Recycling Overview

Organics recycling—commonly known as composting—is a controlled, aerobic (requiring oxygen) biological process which results in the decomposition of organic materials into a stable, humus-like product. This decomposition process occurs naturally in nature, and is performed by microorganisms (bacteria, fungi, and other living organisms) which digest the organic residues for food and energy and contribute to the decomposition process. The primary end-products are carbon dioxide, water, and compost.

Humans can replicate the composting process by combining organic materials in proper ratios into containers, piles, or rows; turning or aerating the materials to provide adequate air flow, and, ensuring sufficient moisture to achieve accelerated decomposition. The “finished” material is then allowed to mature through a curing period, resulting in compost.

Compost users include homeowners and municipalities, nursery and greenhouse operators, landscapers, gardeners, farmers, grounds maintenance personnel, golf course managers, transportation departments, land development contractors, and others.  The act of composting can be done on a small “decentralized” scale, as in home or backyard composting, or larger scale on farms, or at commercial or municipal operations.

Compost is much different than the raw materials that went into the process. Compost is a stable, humus-like material, free of unpleasant odors, easy to handle, and can be stored for long periods. It is a valuable soil and potting media amendment that, when applied, improves the chemical and physical properties of soil, introducing organic matter, beneficial micro-organisms, and macro-and micro-nutrients, benefiting both the soil and plants.

The benefits of composting and compost use are numerous, including:

  • Organics management. An effective way to manage yard waste, brush, food scraps, soiled paper, and other organics to avoid landfill disposal or incineration.
  • Value-added product. Composting offers home owners, communities, farms, and private compost businesses with an opportunity to make compost for use or sale.
  • Soil quality. Compost is less dense than soil and thus holds more nutrients than soil. It helps to improve soil quality by adding organic matter; moderating soil pH; building cation-exchange capacity (CEC)[1]; enhancing soil porosity; increasing the microbiological ecology of soil; improving water infiltration; and more.
  • Water retention. Compost adds organic matter and other qualities which improve the moisture holding capacity of soil.
  • Improved soil quality. The application of compost helps to filter pollutants through soil.
  • Nutrient recovery. Composting organic materials helps to retain the nutrients present in the organic materials and provides these nutrients in a form for easy plant uptake, reducing the need for synthetic fertilizers.

All composting, whether at home or at a central processing facility, follows a similar process and requires five essential components.  These are:

  1. Feedstock and nutrient balance (Carbon: Nitrogen Ratio). A proper balance of “green” organic “feedstock” materials (e.g., grass clippings, food scraps, manure), which contain large amounts of nitrogen, and “brown” organic “feedstock” materials (e.g., dry leaves, wood chips, branches), which contain large amounts of carbon (but limited nitrogen), is necessary for decomposition.
  2. Particle size. Smaller feedstock particles allow for more surface area upon which the microorganisms can feed, helping to speed up the decomposition process. Smaller particles help to improve porosity (air flow), produce a more homogeneous compost mixture, and improve pile insulation to help maintain ideal temperatures. Particles that are too small, however, can pack down too much and inhibit air flow. Mowing, grinding, chipping, or shredding materials are effective ways to achieve appropriate particle sizing.
  3. Moisture content. Moisture is required to keep the microorganisms in compost alive and active. Water helps to transport substances within the compost pile and makes the nutrients in organic material accessible to the microbes. Depending on the type of organic materials being composted, additional moisture may need to be added, either through rainfall or intentional watering.
  4. Oxygen flow. The microorganisms in compost are “aerobic”—requiring air in order to be active. Aeration helps to speed up the decomposition process. Aeration can be achieved by turning or “mixing” the compost or placing the composting materials on a series of perforated pipes. Adding “bulking agents” such as wood chips and shredded newspaper will also help to aerate the pile. Aeration is essential to keep the decomposition process from becoming anaerobic, which can cause odor problems.
  5. Temperature. Decomposer microorganisms are active during a certain temperature range. Some microorganisms (“Mesophilic” bacteria) become active at lower temperatures, as these microorganisms work, their activity will cause temperatures to rise. As temperatures go above 120  F other microorganisms (“Thermophilic”) will cause the temperatures to rise even higher. These high temperatures are necessary for more rapid composting and to ensure that pathogens and weed seeds are destroyed. Microbial activity can raise the temperature of the pile’s core to at least 140  F.

Having the proper nutrient balance, particle size, moisture level, and aeration will ensure that the temperature rises and the compost process is working effectively.

[1] Cation-exchange capacity (CEC) is the maximum quantity of total cations, of any type, that a soil is capable of holding, at a given pH value, available for exchange with the soil solution. CEC is used as a measure of fertility, nutrient retention capacity, and the capacity to protect groundwater from cation contamination.