Organics Recycling = Composting

June 4, 2013

This article continues our ongoing blog series about organics management, with an introduction to home and neighborhood composting options.

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

The controlled composting process is created 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.

Backyard and Neighborhood Composting

Keeping materials onsite—at home or in neighborhoods—presents rural, semi-rural, and small towns with a relatively low-cost, but effective, organics management program option for virtually all organic wastes. Such “decentralized” composting programs have many benefits, including relatively low start-up costs. These programs require residents to play an active part in the organics management effort and help to create a sense of personal responsibility for organics management.

A well organized and promoted backyard or neighborhood composting program can divert substantial amounts of organic materials without the need for municipal or private collection, transportation, or processing.  These benefits are especially magnified when combined with organics reduction efforts such as grasscycling and leaf mulching.

Communities benefit from lower disposal costs and reduced organics management requirements. In the long-term, backyard and neighborhood composting efforts can reduce or eliminate the need for municipal composting sites and helps to reduce the need for more landfill space or incinerator capacity. Residents save on trash or yard waste collection fees in areas where collection fees are applied on volume or weight of materials disposed. Backyard and neighborhood composting creates a compost product that can be used in gardens and on landscaping as a soil amendment, helping to reduce fertilizer input needs.

Decentralized composting applications are not limited to households. Commercial developments, including parks, small-scale horticultural operations golf courses, corporate campuses, and large multifamily residential units, as well as schools, colleges, universities and other institutions with landscaped areas and/or food waste generation can manage their own onsite composting programs.

Trench Composting

The easiest way to compost at home, especially food scraps, is through direct soil incorporation. In trench composting, chopped food scraps are placed in a hole or trench and covered with at least eight inches of soil. For use of this method in the winter, a large trench can be dug in the fall, such as in a garden area. The trench can then be gradually filled in and covered during winter. Leaves can be placed over the trenches to add additional organic material. By spring the materials have decomposed and the area is suitable for planting. 

Backyard Composting

Residents have a wide variety of options available for effective backyard composting. Home compost systems can be simple and “slow,” where materials are layered in a pile or heap and turned occasionally or left to “rot.” Decomposition will occur in about a year using this method.  A more active home composting approach requires use of enclosed containers, attention to the proper “mix” of green and brown ingredients, and more frequent turning of materials in order to speed decomposition. Finished compost from this approach would result in around 4 – 6 months. There are a wide range of backyard composting bins suitable for home composting; bins can also be constructed using readily available materials or purchased.

Backyard Food “Digesters”

Although not technically composting, backyard "digesters" are an excellent option for home management of food scraps and vegetable grease. Digesters do not produce compost, but the systems allow these foods to decompose and generate some nutrients for the soil underneath the units. 

The systems produce few odors if done correctly and offer a practical deterrent against unwanted vermin. Commercial versions of home digesters, including the “Green Cone,” are promoted as an option for handling virtually all types of household food organics, including meat, dairy and egg products. Do-it-yourself digesters can be easily constructed from a metal garbage can. 

The trick to digesters is the placement of the unit into the ground to allow for proper decomposition. Communities will gain the highest diversion benefit from promoting the use of digesters along with home composting in order to capture all household organics. Digesters are designed as an effective means of handling food wastes and pet wastes, but not yard scraps.

Next up – neighborhood composting, worm composting, school composting, and composting at special events.

By Athena Lee Bradley

[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.