Chapter 3 - Composting Programs

Yard waste, by weight, may constitute up to 20 percent of the solid waste stream at an Air Force installation. Many states already ban landfilling of yard and other organic wastes. Composting is a well-known technology for processing organic materials that can help installations meet solid waste reduction goals, produce a beneficial end-product, and minimize environmental pollution from organic solid waste.

3.1 Elements of an Effective Composting Program. Many factors must be considered in deciding whether an on-site composting program is feasible at an installation. Some of these factors are waste stream composition, regulatory requirements, siting issues, funding availability, manpower and equipment requirements, and the availability of existing municipal composting programs in the area.

3.1.1 Waste Stream Investigation. Identifying and quantifying the components of the solid waste stream are an integral part of preliminary planning for a composting operation. Excellent sources for this information are the initial installation Solid Waste Baseline Survey and annual solid waste stream evaluations. Other sources include federal, state, and local environmental agencies.

3.1.2 Regulatory Requirements. Regulations governing the location and operation of composting facilities vary from state to state; some areas have strict guidelines, while others have minimal requirements. Generally, stricter regulations apply for the composting of sewage sludge, food waste, and municipal solid waste. State and local regulatory requirements can include permitting requirements, groundwater monitoring requirements, runoff control, operator certification, and other operating and record keeping requirements. Before establishing an on-site composting program, coordinate with your local and state environmental regulators.

3.1.3 Siting Issues. The location and size of a composting facility must comply with any existing regulatory requirements and the installation's Base Comprehensive Plan. Federal Aviation Administration (FAA) guidelines recommend against siting any type of solid waste facility, other than yard waste composting facilities, within 10,000 feet of a runway. This requirement is to prevent birds, which could be attracted to the site by potential food sources, from interfering with aircraft. Potentially suitable locations for these facilities are areas adjacent to buffer areas of existing or closed landfills or wastewater treatment plants. Other factors to consider in facility siting include convenient location to minimize hauling distances, suitable site topography and soil characteristics, sufficient land areas for the volume and type of materials to be processed, and adequate distance from public areas to minimize odor concerns.

3.1.4 Funding. Composting operations can vary from very low-end, low-cost programs to high-technology industrial operations. Sound financial planning is a crucial step in successfully developing a composting program. To determine funding requirements, complete an economic-benefit analysis. This analysis should consider organic waste volumes, availability of existing equipment, manpower requirements, most suitable technology, facility and equipment requirements, contract costs, and recurring costs. Funding to support start-up and recurring operation costs for composting programs shall be in accordance with AFI 32-7001, Environmental Budgeting. Funding requests must be budgeted through installation and MAJCOM Financial Plans and programmed in the POM development process.

A number of potential funding sources may be used. Choice of funding sources will vary depending on the policies of the installation's MAJCOM. Several of the available sources are:

Pollution Prevention Funds can be used to cover composting program start-up and recurring operating costs. Funding needs are identified through the WIMS-ES A-106 and Pollution Prevention Modules. Pollution prevention funding requests should be coordinated through the base environmental engineering flight or office;

Military Family Housing Funds can be used for costs associated with curbside collection in military family housing areas. MFH funding requests must also be included in Financial Plans and in the POM. Funding requests are coordinated through the civil engineering resources flight;

Installation O&M Funds may be used for start-up and operation of composting programs, at the discretion of the Installation Commander; and

Federal, state, local or private grants may be available to assist in set-up or operation of installation composting programs. For information on grant availability, contact the regional EPA or the state environmental department.

3.1.5 Manpower. Another major resource needed to successfully operate a composting program is manpower. The Air Force Manpower Standard (AFMS) only identifies one man-year for solid waste management and recycling in the core manpower requirements. This shortage has challenged program managers to become innovative in sourcing manpower.

There are a number of ways to obtain manning for composting operations. Potential personnel sources are military, civilian, contract, federal and state prisoners, and volunteers. The manager must weigh various factors when deciding which labor source to employ. Military and permanent civilian personnel are applied against the Unit Manning Document (UMD), but military manpower does not have to be reimbursed by program revenues. Contract labor does not count toward the UMD, but is generally more expensive. Prison labor is inexpensive, but not always available and may require escorts. Volunteers, while usually enthusiastic, are not always consistent.

3.1.6 Facility Requirements. Most small to medium scale composting operations do not require building facilities; however, minimum facility requirements include a fenced site and a composting pad surface. To operate efficiently, a composting facility must have sufficient space for the preprocessing, processing, and post-processing stages of the composting cycle. The composting pad surface does not have to be paved, but it must be designed to prevent ponding and to control erosion and runoff. Soil permeability should also be considered. Regulatory and permitting requirements, if applicable, will provide the basis for facility design and must be thoroughly researched. In addition to facility requirements, the type and amount of traffic into and out of the facility should be considered in the design process.

Site access must be controlled at all times to avoid compromise of the composting process and ensure a safe operation.

3.1.7 Vehicles & Equipment. Vehicle and equipment needs will be determined by the level of composting operation to be implemented. Small, low-technology operations such as static pile composting can usually be operated using existing base vehicles and equipment while most intermediate-technology operations, including windrow operations, require substantial, dedicated, vehicle and equipment support. Vehicle and equipment needs, depending on the level of technology used, can include a front-end loader, windrow turner attachments, grinders or shredders, screening equipment, portable storage bins, aeration equipment, odor control equipment, in-vessel equipment, etc.

After vehicle and equipment requirements are established, authorizations must be obtained and added to the shop TA (Table of Allowance). Changes to TAs should be coordinated through the base logistics transportation office and approved by the MAJCOM. After TAs for vehicles and equipment are approved, leasing is an option to acquire short term use of vehicles and equipment.

3.1.8 Existing Municipal & Community Programs. Many cities and communities operate successful composting operations. When these programs are available, installations should consider participating in these existing composting programs in lieu of implementing in-house composting.

3.1.9 Air Force Installation Programs. Composting managers can network with installations that already have or plan to start yard waste composting operations. To obtain a copy of Air Force current and planned yard waste composting programs, contact Mr. Wayne Fordham, AFCESA/CESM, DSN 523-6465.

3.2 Composting Facilities & Operations. The composting process occurs in two major stages. In the first phase, microorganisms decompose the organic material through metabolic activity and the size of the composting pile is reduced. During the second stage, the compost is "cured" or finished and further microbial decomposition will occur very slowly. Because microorganisms are essential to composting, environmental conditions that maximize microbial activity will maximize the rate of composting. Microbial activity is influenced by oxygen levels, particle sizes of the feedstock material, nutrient levels (indicated by the carbon-to-nitrogen ratio), moisture content, temperature, and pH.

3.2.1 Composting Methods. The most commonly used processing methods are static piles, turned windrows, aerated static piles, and in-vessel composting systems. The level of technology selected will depend on the type of feedstock materials, requirements for odor and leachate control, quality requirements for the finished material, funding availability, and space availability. Brief discussions of each of these methods follow: Static Pile Composting. Static Pile Composting is low technology composting. Static or passive piles are piles of composting material that are turned infrequently, as little as once per year. This method requires only minimal labor and cost and is especially suited for backyard composting in military family housing areas and for small volumes of ground maintenance wastes. Before promoting backyard composting programs on an installation, the support of the base Environmental Protection Committee (EPC) and Installation Commander are required. Composting under these conditions is very slow and odor problems can result if food waste materials are incorporated or when large quantities of green materials are added to the piles.

With all composting methods, regular monitoring of temperature and moisture conditions is recommended. For static piles, the moisture content of internal and external layers should be occasionally checked. When moisture conditions are too low, the piles can be watered with hoses or sprinklers. Temperature and oxygen levels can be controlled by forming piles of the appropriate size for the region. Larger piles have greater insulation and can sustain higher temperatures. However, passive piles should not be constructed so large as to overheat. At temperatures greater than 140F, microorganisms may die off and anaerobic conditions can develop.

The disadvantages to static pile composting are long composting times (often longer than one year to produce finished compost) and the possibility of anaerobic conditions and accompanying odor problems. Despite these disadvantages, static pile composting can be a simple and effective method for some programs. Turned Windrow Composting. This process is a more efficient method to static pile composting. Turned windrow is the most widely used intermediate-technology composting method. Windrows are long composting piles that are mechanically turned at regular intervals to enhance environmental conditions for microbial decomposition. As windrows are turned, cooler outer layers are moved to the center of the pile where there are higher temperatures and intensive microbial activity. The turned windrow method produces compost material in two to six months.

Optimum size for windrows are 8 to 12 feet at the base and 5 to 8 feet high. Windrow cross-sections should be rounded, concave or trapezoidal to allow proper insulation. Progressive decomposition of the composting material reduces the size of the windrows and two decomposing windrows can be combined to create space for new windrows or for stockpiling.

Turning frequency is generally once or twice per week. The turning equipment used will determine the size, shape, and space between the windrows. Front-end loaders are commonly used, however specialized windrow turning equipment is recommended to compost large volumes of material. Windrow turning attachments are available that hook up to most front-end loaders. Monitoring for moisture content, oxygen content, and temperature should be done frequently, generally daily, and operating logs should be maintained. This operating data is evaluated to optimize windrow turning frequency, windrow composition, and watering frequency. Aerated Static Piles. These are a higher technology application than turned windrows. In this method, piles or windrows are placed on top of a grid of perforated pipes and air is forced through the piles or windrows using fans or blowers. This action maintains aeration in the composting process and minimizes, or eliminates the need for turning. Air can be supplied through a suction system or a positive pressure system. In a suction system, air is drawn into and through the pile and then vented through a pile of finished compost or a filter to control odor. With a positive pressure aeration system a blower pushes air into the compost pile and the air is vented over its entire surface. Because of the way air is vented, odor treatment does not occur in a positive pressure system.

To ensure proper decomposition, temperature and oxygen levels must be closely monitored. Aeration is controlled by running blowers continuously or intermittently. In general, aerated static piles are best suited for granular and relatively dry feedstock materials with a relatively uniform article size. In-vessel Composting. These systems are high technology methods in which composting is conducted within a fully enclosed system. All critical environmental conditions are generally controlled through fully automated built-in systems. In-vessel composting systems are generally expensive; however, they may be justified where space is limited and careful odor and leachate control is required.

There are two general types of in-vessel composting technologies: rotating drum systems and tank systems. Rotating drum systems use a tumbling action to continuously mix the materials. The rotating drums are long cylinders, typically nine feet in diameter, that rotate slowly. Oxygen is forced in from exterior air pumping systems, while the tumbling action allows temperature to be maintained at high, uniform levels. In general, complete stabilization of the composting material is complete within one to three months. Tank in-vessel systems use long, rectangular vessels and external pumps which force air through a perforated bottom. Materials are mixed within the tank by a moving belt, paddle wheel or other device to break down clumps. The composting process can be completed within 30 days, but often the materials must be cured in windrows for an additional 30 to 60 days.

3.2.2 Curing Stage. After materials have been composted using one of the methods described above, curing should be allowed until the materials are stabilized. During the curing stage, compost is stabilized as the remaining nutrients are metabolized by any microorganisms that are still present. Since curing piles undergo slow decomposition, care should be taken to ensure anaerobic conditions do not develop. The curing process generally takes approximately one month and requires much less space than the actual composting process. Materials can be placed in small piles during the curing stage.

Once the curing process is complete, the finished compost should have an earthy odor. In addition to relying on odor to determine when the compost is sufficiently stabilized, temperature checks and oxygen and carbon dioxide testing can also provide evidence of compost maturity.

3.2.3 Odor Control. Odor production can lead to installations, or communities, wanting to close the composting site. Odors are often properly controlled by adjusting the composting process to provide ideal environments for aerobic bacteria. Serious odor problems may require covering the active composting area, incorporating biofilters, or adjusting facility operations to decrease odor production.

3.2.4 Composting Operations Plans. A clear, detailed composting operations plan should be developed prior to beginning a composting operation. These plans should be annually revised or verified. A composting operations plan may also be required by state and local environmental regulations. The operations plan should include operating procedures, safety and emergency procedures, operational checklists, and process troubleshooting. Along with the composting operations plan, facility monitoring logs should be developed to record operational parameters (turning frequency, temperature readings, watering frequency, windrow/pile composition, etc.).

3.2.5 Watering. Maintaining a moisture content of 40 to 60 percent can significantly enhance the composting process. Before composting begins, the moisture content of the feedstock materials should be determined. The "squeeze test" is a simple way to estimate moisture content. If just a few drops of water are released when a handful of feedstock material is squeezed, the moisture content is generally acceptable. For more definitive moisture content determinations, a sample of material can be weighed wet and weighed after oven drying. Moisture content is then established using the following formula:

moisture content = (wet weight - dry weight)/wet weight

Depending on climate conditions, composting technology used, and operational factors, a water supply may be required on-site to meet compost watering requirements. Water requirements should be incorporated into the facility design. Storm runoff retention ponds can provide a source for meeting watering needs.

3.2.6 Operator Training. Operator and compost facility worker training is an essential element of a successful and safe composting program. The level of training required will vary with the type and level of composting technology used, and with state and local requirements. Currently, there are no specific composting training programs offered through Air Force or DoD schools. Best sources for training include university-offered courses, community-sponsored training programs, and private firms that offer on-site training services.

3.2.7 Feedstock Materials. Virtually any organic material can potentially be composted and composting programs can be designed to handle yard trimmings (leaves, grass, tree prunings), food wastes, sawdust, wood, scrap paper products, sewage biosolids, and animal manure. More recently, composting has been used to bioremediate petroleum-contaminated soils. In deciding which organic wastes to incorporate into a composting operation, several factors (e.g., cost, site size, amount of waste, environmental regulations) must be considered. Generally, more stringent environmental regulations will apply when composting sewage sludge and animal manure. In addition to environmental requirements, the type of composting method employed (low tech or high tech) will also determine which materials should be composted.

Once an initial decision is made on the materials to be used for feedstock, each facility should experiment to establish proper feedstock blend ratios. For composting to proceed efficiently, microorganisms require specific nutrients in an available form, adequate concentration, and proper ratio. The essential macronutrients needed by microorganisms in relatively large amounts include carbon (C), nitrogen (N), phosphorus (P), and potassium (K). Microorganisms require carbon for an energy source and they need carbon and nitrogen to synthesize proteins and reproduce. Potassium and phosphorus are essential to cell reproduction and metabolism. Composting organisms also need trace elements to foster proper assimilation of all nutrients. However, in a composting system, carbon and nitrogen are usually the limiting factors for efficient decomposition.

The carbon to nitrogen ratio, commonly known as the C:N ratio, is a common measure of the availability of nutrients for microbial use. For proper decomposition the nutrients in the compost pile or windrow should be in the right C:N proportions. The table below shows C:N ratios for common composting feedstock materials. High C:N ratios (high C to low N) inhibit the growth of microorganisms that degrade compost feedstock. Low C:N ratios (low C to high N) initially accelerate microbial growth and decomposition. However, with this acceleration, available oxygen is rapidly depleted and anaerobic conditions can develop if operating conditions are not carefully controlled. Excess nitrogen is released as ammonia gas and extreme amounts can form enough ammonia to kill microbes and inhibit the composting process. Excess nitrogen may also be released in the leachate.

Table 1

C:N Ratios of Common Composting Materials

Leaves and Weeds (dry)


Horse Manure








Food Scrap






Optimum composting occurs when the C:N ratio of the composting material is from 25:1 to 35:1. At C:N ratios greater than 35:1, the composting process slows down while at C:N ratios lower than 25:1, anaerobic conditions often develop. Generally, the C:N ratio for yard trimmings can be approximated by examining the nature of the feedstock; green vegetation is high in nitrogen and brown vegetation is high in carbon. More precise C:N ratios are determined by laboratory analysis. Feedstock materials with different C:N ratios must be mixed in proper proportions to obtain optimal C:N levels.

Acidity and alkalinity (pH) should also be monitored. At a neutral pH of 7, the composting process is more efficient. Different materials have different pH values and care must again be exercised in mixing them. Because pH levels are largely self-regulating, actions are rarely necessary to bring pH to optimum levels; however in instances where pH levels are significantly low, buffering agents such as lime can be added.

The final aspect to consider in compost pile and windrow composition is mixing or blending of feedstock materials. For example, bulking agents such as wood chips are often added to grass piles to increase particle size. Bulking agents are dry materials with high carbon content. They should be incorporated to maintain adequate porosity and aerobic conditions in compost piles. Mixing should be conducted after feedstock sorting and size reduction and before processing begins.

3.3 Material Collection. Separating yard wastes from other waste is easiest when accomplished at the source. Materials must be brought to the composting site in an economically feasible manner and with minimum contamination. To increase military family housing participation, frequent and convenient collection is needed. Programs can be designed to collect just yard trimmings, or yard trimmings and recyclables. Collection can occur at curbside or through drop-off sites. For collection of base grounds maintenance wastes and other organic materials, it is generally best to set up delivery to the composting facility.

There are several alternatives that can be established to accomplish collection of yard wastes and other organic materials. Curbside collection for family housing areas can be integrated into existing refuse or recycling collection contracts and funded using MFH funds. Base grounds maintenance contracts can be modified to include delivery of landscaping wastes to the composting facility.

3.4 Quality Control. After the initial processing and curing of the compost material is complete, quality control procedures are needed to refine the compost product to meet end-use specifications. Certain end uses of compost require the production of a high-quality product that does not pose threats to plant growth or the food chain. Other uses, such as for berming or landfill cover, have less rigorous requirements. Compost derived from yard trimmings contains fewer nutrients than compost produced from sludge composting; however, it contains fewer hazardous constituents and other contaminants. During post-processing, compost can be screened and analyzed to ensure that stabilization is complete.

3.4.1 Testing. Compost should be tested for chemical and pathogen contamination and to determine nutrient levels. Compost stability can be assessed by seed germination tests or by analyzing factors that indicate compost maturity, such as oxygen consumption, carbon dioxide production, C:N ratios, and cation exchange capacity. Several state and local requirements specify compost quality requirements; therefore, laboratory analysis may be required to ensure these requirements are met. In particular, when composting biosolids (sewage sludge and manure), concerns about the presence of heavy metals (lead, cadmium, copper, mercury, chromium, and nickel) should be incorporated into compost testing requirements. Finally, sampling for pesticides and herbicides may also be warranted.

Testing for contaminant and nutrient levels is important if end uses require specific nutrient ranges. Nutrient and contaminant information can be used to establish suggested uses for the compost, appropriate application rates, and restrictions on compost use.

To ensure product quality, the compost product should be laboratory tested frequently. A composite sample, composed of many small samples from different locations in piles and windrows, and/or individual samples can be taken. Field tests can also be conducted to demonstrate product utility. Finally, testing data should be recorded in a computerized spreadsheet to provide a basis for comparing changes in compost quality or characteristics.

3.4.2 Compost Screening & Sorting. Sorting and screening is conducted to remove unwanted material and larger particles that lower compost quality. Screening can be performed to generate compost of uniform size for end uses where uniformity is important, such as in horticultural applications.

3.4.3 Quality Characteristics. Product quality depends upon the biological, chemical, and physical characteristics of the compost material. Following is a list of desirable characteristics in finished compost:

Compost maturity after proper curing and stabilization;
High organic matter content;
Absence of weeds, seeds, pathogens, and contaminants;
Neutral pH;
Balanced nutrient levels (nitrogen, phosphorus, etc.);
Low concentrations of soluble salts;
Uniform particle size (less than 0.5 inch);
Dark color with an earthy bouquet;
Moisture content below 50 percent; and
Absence of heavy metals (lead, chromium, copper, etc.);

The final compost product should meet applicable regulatory standards and exhibit quality characteristics suitable to the expected end use(s) of the product.

3.5 End Uses. Finished compost is a valuable soil amendment that can be used in a variety of applications, from agriculture to landscaping to reforestation projects to residential gardening. Compost can benefit the biological, chemical, and physical properties of soil, including soil porosity, water retention, resistance to wind and water erosion, and crusting. Compost regulates the storage and release of nutrients, enhances the development of beneficial microorganisms, builds up plant resistance to parasites and diseases, and promotes faster root development. Plants grown using good quality compost can produce higher yields and show less weed growth.

3.5.1 Potential Uses at Air Force Installations. End uses for compost will depend on compost product quality, size, and local conditions. Proven applications include use of compost as a soil amendment, fertilizer supplement, top dressing, mulch, landscape planting material, potting mix component, peat substitute, landfill cover material, topsoil for road and construction work, soil erosion prevention, water quality applications, and bioremediation of contaminated soils. Compost can be provided to installation housing residents through housing self-help stores.

Although compost quality will largely determine potential end uses, both high- and low-quality compost can be used at installations. Generally, high-quality compost should be used in locations where people or animals come in direct contact with the compost or in the upgrade of public lands. Lower quality compost can be used for purposes such as land reclamation, landfill cover, berming, and to maintain road shoulders. Compost is valuable for land reclamation areas because of its high water retention capacity. A coarse compost with low water retention may be preferred for areas where weed control is necessary.

Compost used on Air Force installations must comply with both state and federal standards for land application. Beyond these standards, quality criteria for compost is discussed in the Quality Control section of this guide.

3.6 Other Alternatives. There are other alternatives available for yard waste instead of a centralized composting program or disposal. Grasscycling and backyard composting are two methods implemented at some Air Force installations.

3.6.1 Grasscycling. Grasscycling encourages leaving grass clippings on mowed lawns. A thin layer of grass clippings and leaves can improve soil moisture retention abilities and can act as a natural fertilizer, reducing the need for commercial fertilizers. Grasscycling ideas also include promoting the use of mulching mowers, advocating higher grass height standards, encouraging more frequent mowing, and instituting water-wise policies.

3.6.2 Backyard Composting. Backyard composting programs can be an integral part of a comprehensive solid waste management program. To encourage backyard composting programs, composting bins can be provided free of charge to military family housing residents, or provided on loan through MFH self-help stores. Brochures or information papers on backyard composting techniques can be provided to residents through the housing self-help store and during awareness fairs and events. Technical assistance courses can be provided to residents who are interested in pursuing backyard composting. Programs to promote interest in backyard composting can be initiated in base schools.

3.7 Summary. Compost is the natural recycling of organic wastes into one of nature's best mulches and soil amendments. Composting programs can offer an efficient, cost-effective method of reducing operating costs while complying with Air Force and DoD pollution prevention policies and achieving solid waste reduction goals.

Chapter 4

Global Recycling Network