compost decision guide

Section 1.0 Introduction

What is and is not covered?

Getting the most from this Guide

Structure of this Guide

How to Use the Composting Scorecard

How to Move Ahead After Completing this Guide

Section 2.0 Composting Basics

Why Compost?

Steps in Composting

Composting Technologies

Section 3.0 Information Gathering

Section 4.0 Avoided Cost Threshold

Avoided Cost Threshold Worksheet

Section 5.0 Materials Analysis

Material Types Available

Material Qualities

Porosity

Moisture Content

Available Carbon

Nutrient Content

Visual/Qualitative Factors

Collection Issues

Trade-offs

Scorecard

Section 6.0 Siting Analysis

Evaluation Factors—What are We Looking For?

What are the Possible Locations at Your Facility?

Trade-offs

Scorecard

Section 7.0 Resources Analysis

Types of Resources

How are Resources Used?

Labor Versus Equipment

Trade-offs

Scorecard

Section 8.0 Environmental Analysis

Regulation of Composting in Washington State

Solid Waste Regulations

Product Quality

Other Environmental/Regulatory Considerations

Process Management to Protect the Environment

Trade-offs

Scorecard

Section 9.0 End Uses/Marketing

Qualities of Compost

Basic End Users

Calculating Value—From Bulk to Bagged Uses or Markets

Trade-offs

Scorecard

Section 10.0 Economic Analysis

Composting Economics—Past Experience at Institutions

Composting Economics—Preliminary Cost Estimates

Now It’s Your Turn

Section 11.0 Next Steps

Choosing a Composting Method

Tips for Follow Through

List of Valuable Resources

Acknowledgments

List of Tables

Table 2-1 Summary of Composting Technologies

Table 5-1 Compost Monitoring and Control Parameters

Table 7-1 Equipment Options

Table 8-1 Recommended Testing Schedule and Estimated Costs

Table 8-2 Allowable Contaminant Levels for Compost

Table 8-3 Control Parameters

Table 9-1 Compost Use Guidelines Summary Chart

Table 10-1 Ranges of Costs for Various Levels of Technology

Table 11-1 Ranges of Composting Methods to Levels of Technology

Table 11-2 Institutional Composting Methods in Use in the U.S. and Canada

List of Figures

Figure 2-1 Front End Loader Can Be Used to Form and Turn Compost Piles

Figure 2-2 The Aerated Static Pile Method Uses Blowers to Push or Pull Air
Through Compost Pile

Figure 2-3 The Extended Aerated Static Pile Method Places Piles with Blowers
Next to Each Other to Conserve Space and Retain Heat

Figure 2-4 Bedminster Bioconversion Corp. Manufactures a Composting System
that Moves Materials from One End of a Drum to the Other

The Clean Washington Center developed this guide to help managers and decision-makers evaluate the feasibility of composting food scraps and other organic residuals. In its approach, the guide targets the following types of businesses or organizations:

• Food processors or wholesalers;

• Hospitals, group homes, and other institutions;

• Schools and universities;

• Corrections facilities;

• Military bases;

• Hotels, camps, and resorts; and

• Farms (especially as part of other facilities).

The users of this guide would likely have titles such as facility manager, operations manager, materials manager, solid waste or recycling coordinator, environmental or safety manager. In a small organization, an individual may simply have one or more of those job duties without a specific title. Others who might benefit from using this guide include solid waste and recycling managers, consultants, and equipment vendors.

Experience with composting is not necessary to use this guide. Some readers will have little or no experience with composting. Others will have some experience composting leaves and garden debris at home, or they may even have tried composting at their facilities. Finally, some will have experience separating materials for collection and transport to a commercial compost facility.

The guide was developed as an easy-to-follow, hands-on approach to help managers decide whether composting at their facility would be compatible with the budget, space, and other resources they have available. In other words, it will help you answer the question: Will composting work for us? The guide organizes technical information in a step-by-step format and uses information you provide to match your goals for waste diversion, cost savings, or end uses for compost to the many kinds of composting technologies available.

What is and is not covered?

The guide provides information needed to analyze and evaluate potential costs and benefits of composting at a wide variety of institutions and sites. It starts by asking you to gather composting at your facility could save information that will show how much money. This “avoided cost threshold” will establish a baseline budget to which you can add other potential benefits when comparing composting options.

Further, the guide will show you how to evaluate advantages and disadvantages of different levels of composting technology and develop recommendations about specific systems or methods. The guide also provides lists of general resources for further study.

What the guide does not do is teach composting. Learning more about composting basics may help some readers get more out of this guide, so we have included an introductory section about composting. Many excellent how to composting guides have already been written, so the last section provides references to additional sources of detailed information about the science and art of composting.

The guide does not promote or endorse any particular technology, system, or type of composting equipment. Instead, it was designed so you could understand the differences among systems and prepare your own recommendations.

Finally, and significantly, the guide does not provide the information needed to design or build a composting facility. Building a composting operation can be a complicated task. Once you have used this guide to narrow your decision to a level of technology and a specific method, you should consult other resources for help in building the composting facility. For some larger-scale facilities or those that involve regulatory issues, it would be appropriate to work with consultants or engineers experienced in composting. These can be identified by talking with managers at facilities who have done composting, or by contacting the local cooperative extension office, the Washington Department of Ecology, the Washington Organic Recycling Council, or other similar agencies or organizations. (See the resources listed in Section 11-Next Steps.)

Getting The Most From this Guide

We want this guide to meet your needs for a quick, easy-to-use tool for decision-making about composting. Following is a suggestion for getting the most from this guide:

• Quickly scan the sections—Get a quick understanding of the information gathering and analysis phases and how they work together.

• Become familiar with the technology descriptions—The technology descriptions, contained in the following section, relate directly to the scorecard and to the detailed information about composting that you will find in other books. If you are unfamiliar with composting methods and want to learn more, review some of the books listed in the resources section.

• Get to know the scorecard—The scorecard will be used throughout the analysis phase, so become familiar with how it relates information from the different analyses to the different composting technologies. (If you are using an electronic version of this guide, you may want to print a copy of the scorecard to use throughout the process.)

• Gather necessary information using the forms provided—Once you have become familiar with the different parts of the guide, gather as much of the information called for in that section as possible. As you do the analyses, it will become clear how important the information is, so don’t skimp on this part of the process.

• Work through the analyses and the scorecard—Complete these sections, step-by-step. When you get through all the sections, the possibilities will begin to emerge.

• Review the trade-offs and develop a recommendation—Evaluating the different trade-offs can change the options you have available and possibly improve the cost-benefit analysis of a decision to start composting. Consider the opportunities you have and develop a recommendation that you can propose to the decision-makers in your organization. With the information you have gathered and the analysis you have completed, you will be ready to support your recommendation and move ahead.

Structure of the Guide

After a brief discussion of the potential benefits of composting, the guide follows a simple approach, used commonly by managers who must develop recommendations about major decisions. This process starts with gathering information about your specific situation, followed by using this information to complete a series of analyses designed to help you develop specific recommendations for your facility.

	Why compost Successful case studies and important issues
	ß
	Information gathering Audit/questionnaire (Section 3)
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	Avoided cost threshold What can you afford? (Section 4)
	ß
	Composting potential analyses Materials (Section 5) Siting (Section 6) Resources (Section 7) Environmental issues (Section 8) End uses (Section 9)
	ß
	Economic costs-benefits analysis Make a recommendation (Section 10)
	ß
	Next steps and resources Where to get additional help? (Section 11)

How to Use the Composting Scorecard

Professionals who work in the organic recycling industry understand how many possible solutions can be developed for a specific situation. They also understand how different tradeoffs can be made to arrive at different solutions.

To help you make sense of the different possibilities that result from your analyses, we have provided a simple scorecard to use as you complete the analyses in this guide. At the end of each analysis section, the guide describes which levels of technology may be preferred or eliminated according to the results of your analyses. Using the scorecard as you complete each section of the guide will provide a quick view of the emerging possibilities and the impact of various trade-offs.

How to Move Ahead After Completing this Guide

As you will discover from using this guide, composting is not a passive activity. It will require significant amounts of thought and management. Completing the steps in this guide will get you through the initial feasibility study/decision-making process. It will answer many of your questions and help you determine if you are ready for the challenge. If your organization decides to move ahead with composting, you’ll need to develop more specific plans for developing the site, purchasing equipment, training personnel, and using or marketing the compost product. Section 11–Next Steps will help you find resources you will need to follow-up on a positive decision about composting.

Composting Scorecard

When you complete each of the analyses in the guide, it will describe what levels of composting technology may be preferred or eliminated according to your results. Use this scorecard to keep track of the results. At the end of each section: 1) Cross out options that are eliminated. 2) Leave open all the options that are OK. 3) Circle any options that are preferred.

Analyses

Technologies

Minimal

Low

Medium

High

Section 4: Avoided Cost Threshold

Section 5: Materials

Section 6: Siting

Section 7: Resources

Section 8: Environmental Issues

Section 9: End Use/Marketing

Summary of Analyses

Which levels of technology are viable?

Is any level of technology preferred?

Section 10: Economic Analysis

Compare the potential start-up and operating costs of different levels of technology with the avoided cost threshold you established earlier.

What level of technology do you recommend?

Recommendation and Next Steps

Based on the recommendation you have developed and your knowledge of composting methods, is there one method you will pursue? What are your next steps?

This section provides information about successful composting projects at institutions around North America. It also provides background on a few basics of composting needed to understand subsequent sections of the guide. For more information about how to do composting, refer to the publications listed in Section 11–Next Steps.

Why Compost?

Successes in mid-scale and on-site composting can be found all around the United States and Canada. As interest in waste diversion and recycling increased in the late 1980s and early 90s, interest in composting expanded as well. Much emphasis was placed on home composting and on large-scale, centralized composting. Mid-scale composting has been slower to develop. However, composting studies and industry trade journals provide considerable information about many success stories.

Zoos were among the first institutional success stories. The Woodland Park (Seattle) and Bronx (New York) zoos began “Zoo Doo” programs in the late 1980s. These programs focus on composting manures from herbivores, and they produce a good quality compost that is sold for premium prices because of its novelty. The Woodland Park Zoo composts about 600 tons of material each year, raising about $23,000 in revenue from sales, including the lucrative “holidoo” sale at Christmas. Landfill savings from the composting program top $60,000 annually.

Camps, schools, and universities have been another source of information and practical experience in mid-scale composting. In the early 90s, composting began at the Frost Valley YMCA in Claryville, NY. Each year, the facility composts 60 to 70 tons of pre- and post-consumer food waste, plus hundreds more of wood and yard debris, soiled paper, and other organic materials. The camp invested $200,000 in its aerated static pile compost facility, which produces compost for the camp greenhouse. The compost facility and greenhouse serve additionally as education opportunities. (See BioCycle, April 1991, pp. 42-44, plus other sources).

Several university composting operations have been profiled in industry journals (see BioCycle, July 1993, pp. 55-57). The following examples show the range of methods and scale of campus composting:

Campus	Method of Composting	Scale (tons per day)
Brigham-Young University, Provo, UT	static piles	14
Dartmouth College, Hanover, NH	in-vessel	1.5
Ithaca College, Ithaca, NY	aerated static piles	1
Univ. of Illinois, Champaign-Urbana, IL	windrow	3
Univ. of Maine, Orono, ME	windrow	4-5
Univ. of Vermont, Burlington, VT	windrow/static piles	12-14
Washington State University, Pullman, WA	windrow	40

Washington State University in Pullman, WA, leads all others by composting the largest volume and the widest variety of organic materials, including food wastes and coal ash. Counting the $300,000 initial investment and $150,000 in annual operating costs, the facility nets the university $200,000 in disposal fee and other savings annually. (See Lewiston Morning Tribune, Nov. 13, 1993, pp. 4A & 8A; Compost Science & Utilization, Summer 1994, pp. 18-21; and BioCycle, Mar. 1995, pp. 87-89.)

Corrections is another type of facility that has benefited from composting. In Florida, Georgia, Maine, New York, Texas, and Washington, corrections facilities have started composting. In New York state, the Department of Corrections, led by Jim Marion, has developed composting operations at 48 prisons. Using aerated static pile, windrow, and agitated bay methods, these facilities average processing of 4 tons daily. Begun in 1989 to reduce waste management costs, the New York program in just three years topped more than 1.2 million dollars in savings annually.

The province of Ontario, Canada, has invested heavily not only in home composting, but also on-site/institutional composting. Methods used include aerated static piles, in-vessel, and vermicomposting. A summary of these projects showed investments ranging from $20,000 to $75,000 (Can$) were generating savings from $6,000 to $13,000 each year (See BioCycle, Jan. 1994, pp. 42-43; Resource Recycling, Nov. 1993, pp. 33-36.) Canada’s interest in mid-scale composting extends to multi-family complexes as evidenced by projects in Ontario and British Columbia. (See “Multi-Residential Composting in Ontario,” Recycling Council of Ontario, May 1993.)

Other Washington state projects of interest include the development of a mid-scale vermicomposting project at Food Lifeline, a distribution center for food banks and meal programs located just outside Seattle, WA. This project combined food and produce scraps with leaf bedding in a series of worm bins fashioned from reused pallet crates. Used at roughly 50% efficiency, the system still saved the center more than $6,000 a year in disposal costs.

In 1994-95, a pilot composting operation at the Echo Glen Children’s Center (WA Dept. of Social & Health Services) in King County, WA. Using medium-tech, aerated static pile methods, the project combined food waste and wood shavings to produce compost used on the facility grounds. Information about the project feasibility study and the Echo Glen operation is available in reports published by the King County Solid Waste Division.

What is Composting?

Composting refers to the accelerated decomposition of organic materials to a dark-colored, fine-textured product that has an nice, earthy odor. During the composting process, bacteria and fungi decompose or "eat" the organic fraction of the waste material. The goal of composting is to produce a well-decomposed or stable product that has little "food" content left for microbes. The resulting product has chemical and physical characteristics that promote plant growth. In contrast, an unstable or incompletely decomposed product can slow or harm plant growth.

The length of the composting process depends on the feedstocks and composting process used, and the intended use of the final product. Feedstocks such as food wastes become biologically stable more rapidly than woody materials that have a high cellulose content. Composting processes that provide mixing or aeration and that maintain optimum temperatures (130°F to 150°F) will accelerate the process. In general, a stable, well-decomposed compost product can be produced in as little as three months.

Carbon and nitrogen balance—These essential nutrients are food for the decomposer microbes. They must be provided in the organic materials being composted.
Moisture—The moisture used is contained in the materials or added if necessary. Active composting is often a net user of water.
Oxygen—Distribution is governed by the porosity of the materials and can be increased during processing by mixing, turning, or other methods of aeration.
Surface area—Reducing the particle size by grinding, chopping, or shredding materials increases surface areas, making the nutrition value of the raw materials more available to the composting microbes.
Volume/pile size—A function of available materials and space, the volume or size and shape of the compost pile should be sufficient to create and hold heat generated by biological activity, but not so large as to inhibit air flow.
Temperature and time—Effective composting can produce temperatures sufficient to reduce weed seeds and pathogens. More efficient hot composting reduces overall composting times and improves product quality.

In summary, these projects and the literature resulting from them provide substantial proof that mid-scale, institutional composting can be a viable, cost-effective method of diverting organic residuals for beneficial end use. The keys to success lies in effectively evaluating the feasibility of composting at each facility and in choosing the appropriate level and scale of technology.

Steps in Composting

It should be clear by now that composting involves work, time, and energy. Human and mechanical labor are combined to prepare and process the materials being composted. The following basic process steps occur in any composting operation. For continuity within the industry, these steps match the process flow descriptions developed as “best management practices” by The Composting Council, a national organization of compost producers.

Step 1. What to compost (feedstock recovery)

Choose the materials you want to compost carefully. Feedstock recovery influences the difficulty and cost of composting; the potential for dust, odors, leachate, flies, rodents or other environmental problems; and the quality of the end product. Some materials compost well on their own, while others need to be mixed with “bulking material” that will help it compost better. (See Section 5-Materials Analysis for more discussion.)

In addition to simply gathering materials together for delivery to the composting site, this step may include some initial separation or, in the case of chipping brush or putting food scraps through a pulping machine, some initial processing of the feedstock materials.

Step 2. How to prepare (feedstock preparation)

Some of the activities that may occur at this stage include

• sorting different types of materials (includes removing contaminants);

• chipping, grinding, or shredding;

• blending of materials for an optimum mix; and

• moisture adjustment.

The initial mix of materials should take into account the blend of carbon and nitrogen, moisture, and density, which relates to air penetration. Achieving the optimum balance of these factors is both a science and an art. The science can be found in a variety of composting reference books and would be included in the facility’s operating plan (see Section 11–Next Steps). The art derives from experience in working with the materials and equipment at each facility.

Material handling and preprocessing activities can add significantly to the time and cost of a compost operation. Consider these activities carefully before deciding that they are necessary in your case.

Step 3. Composting and monitoring

We often think of compost workers as the employees on the site driving loaders or operating screens. But the real work in composting is done by billions of microscopic organisms whose natural purpose (aside from surviving and reproducing) is to recycle dead or decaying organic materials back into the soil. Successful operators strive to maintain compost conditions to meet the needs of these microbes.

Monitoring various biochemical factors is crucial to maintaining optimal microbial conditions. Managing the composting operation as a optimal biological process influences three important factors: speed of processing (and thus facility space requirements), control of environmental and neighbor impacts, and product quality. The biological process demands adequate moisture and aeration. After getting a good initial mix, operators assure optimum processing by adding moisture and air into the composting materials at key stages in the process.

Step 4. Compost curing

After the initial stages of high-rate or “hot” composting, the decomposing materials will become “stable,” meaning they cannot be reheated by bacterial activity. At this point, the compost can be used with care to build or condition soil. However, compost used at this stage may still have “phytotoxic” compounds that could harm plants. For this reason, many compost producers provide additional time for “curing” the compost. After the one to two month curing phase, tests will show if the compost has broken down the phytotoxic compounds. At this point, the compost is said to be “mature.”

As materials decompose, they lose volume, making it possible to combine piles for this final curing phase. But curing still increases the cost to make compost because of the additional time and space required and because of the additional handling. Curing is essential though if you want to grow plants in the compost amended soil within a week or two of the application.

Step 5. Compost screening and blending

After composting is complete, processors will often screen their product to remove oversized materials. Physical contaminants, such as plastic or rocks, that would negatively impact the likely end use are also removed. Oversized organic materials, such as large wood chips, may be returned to newly prepared piles for additional processing. If you purchase bulking material, screening it out for reuse can save money.

The equipment and labor involved make screening compost costly. Depending on the initial compost mix or the ultimate end-use, screening may not be necessary. This is especially true when the processor is also the user, when the product is not intended as a top dressing in areas within public view, or when a fine-textured bulking agent is used.

Another activity occurring at this stage is blending the compost with other materials. Compost itself may not offer the right characteristics needed for each specific use. For example, compost itself is not used for potted plants. Instead compost is blended with shredded bark, peat moss, vermiculite, sand or other materials to make a satisfactory potting mix.

Step 6. End use or marketing

Finding the right balance

Talk with facility managers who have developed successful composting programs and one word keeps being used: balance. Success in composting comes from finding the “right” balance in technical, process, and management factors. Technically, compost operators must balance carbon and nitrogen, air and water, and time and temperature. When choosing processing equipment, operators strike a balance between using generalized and specialized equipment and between capital intensive and labor intensive methods.

Feedstock recovery decisions, as well as processing decisions that affect the quality of the product, must be balanced with the most valuable end uses for the product and with the potential for environmental problems. Similarly, management of your compost facility would be impacted by goals for waste management versus goals for product end use. Choices about doing slow composting on lots of space will have to be balanced with doing fast composting on less space. As you work through the guide, keep this concept of balance in your thinking about composting.

Compost has many valuable uses as soil amendments and mulches. Depending on the materials and techniques used to make the product, the composts will have different characteristics. Your own organization or other entities near your campus or facility will likely have valuable uses for the finished products from composting. If these needs are insufficient to use all of the material, it may be possible to market the material to private users, topsoil dealers or directly to landscapers or the general public.

Composting Technologies

To assist in the evaluation of composting options without getting caught up in technicalities of different methods, this guide distinguishes levels of composting technology from composting methods. Following are descriptions of minimal, low, medium, and high levels of composting technology. You will also find descriptions of a variety of composting methods, which may include low-, medium-, or high-technology variations.

Later sections of this guide will help you select an appropriate level of technology for your facility. Table 2.1 summarizes general differences and similarities among the various levels of technology described in this section.

Minimal-technology

This is a common method for managing leaves and some types of manure and bedding. Such materials offer a good nutrient balance to start with, so with little equipment or effort, large, unmanaged piles will compost slowly over a period of 18 to 24 months.

Because simple, separated materials are used, pre-processing is not required. The presence of coarse materials helps keep the pile from compacting, improving air flow, and facilitating composting of the finer materials. However, depending on the end use, the coarser fraction may need to be removed by screening, recycled into the next pile, or processed separately.

Because minimal-technology piles are large, anaerobic (no oxygen) conditions can develop resulting in odors. As a result, this type of operation may meet with considerable resistance from nearby residents or regulators. A large buffer area and a remote site may offset these potential impacts.

The primary advantage of this approach is that it is comparatively inexpensive. Assuming that the piles are turned every few months, relatively few days per year of equipment (typically front-end loader) operation is required.

PILES VS. WINDOWS

A compost pile is fairly simple to imagine. Starting at a minimum size of about one cubic yard to generate and retain heat, compost piles have been known to become quite large. But height can be detrimental when the weight of materials compacts the pile and keeps air from passing through. As the volume of materials being processed increases, it becomes prudent to make additional piles, often side-by-side, until you have created a long row. Hence, a “windrow” is nothing more than an elongated compost pile, designed to allow for better air flow.

A major disadvantage of minimal-technology composting methods is that more space is required than for other methods. Although the piles are large and little space is needed between piles, the long time required to develop a finished product means materials occupy space for months on end. Other disadvantages include the preference for a remote site, which can result in higher transportation or handling costs. It is also difficult to maintain high-rate or “hot” compost conditions, so the compost products from minimal-tech methods will likely be lower in quality. They will also be coarser, and when screened will have a larger oversize fraction.

Technology	Minimal	Low	Medium	High
Process Speed	very Slow	slow	fast	fast
Space	very space intensive	requires good sized area	reduces space requirements	very space efficient
Spce Buffers	1,500 feet+	200-500 feet	200-500 feet	200-500 feet
Aeration	passive	passive	active	active
Warter Makeup	no	yes	yes	yes
Temp. Control	no	no	yes	yes
Cover	outside	mostly outside	sometimes with floating cover,under roof, or inside building	enclosed system or inside building
Odor/Control	none	little	good, emphasis on prevention, sometimes uses control systems	excellent, emphasis on prevention and control using biological controls
Electronic or Computer Controllers	none	manual monitoring	sometimes, mostly for monitoring purposes	yes, for monitoring and process control
Time Period	18-24 mo.	9-12 mo.	4-6 mo.	3-6mo.
Product Quality	poor	fair	good	good
Capital Costs	minimal	low	medium	high
O&M Costs	minimal	low	medium	high
Equipment Types	general	general	general + specialized	general + specialized
Equipment Examples	loader	grinder, loader, Screen	grinder, loader, screen blowers, compost turner, or other specialized compost system equipment	grinder, mixer, loader , screen, conveyor, blowers, compost bays, invessel unit + handling equipment, or other specialized compost system equipement
Example of Composing Methods Used at Different Levels of Technology	static piles (no air)	compost bins or barrels, static piles (passive air), turned windrows, and vermicomposting (worm boxes or windows)	static piles (forced air), turned windrows, drum-type composters, bag-type composters, and mechanized "continuous flow" worm systems	turned or agitated bays or beds (forced air), box-type invessel units (forced air), and "Dutch tunnels" (forced air)

Low-technology

Low-technology composting using windrow methods can work well because you can manage the windrow with just a bucket loader. Operators use the loader for material handling and mixing. During composting, the loader is used to roll the windrow, also described as “turning.” This mixes and aerates the compost materials. Turning piles or windrows with some frequency (usually determined by internal temperature and moisture conditions), maintains high-rate composting.

Passively aerated static piles offer an alternative to turning for low-tech composting. Passive aeration methods use perforated pipes laid horizontally or “not quite vertically” throughout the pile or windrow to enhance the penetration of air to interior sections.

When using a heterogeneous mix of materials, low-technology composting typically involves some preprocessing—first, grinding or shredding materials to reduce particle sizes and increase surface area, and second, mixing materials for a good carbon-nitrogen balance.

Low-tech windrows vary greatly in size, but typically range by widths of 12- to 20-feet and heights of 6- to 12-feet. The height of the windrow is determined in part by the ability of your equipment to stack and turn the materials.

You will also find that the allowable height also depends on the particle size and initial density of the feedstock. Smaller particle sizes and higher densities cause a windrow to compact under its own weight. This in turn, reduces air flow and requires more frequent turning to avoid anaerobic conditions and problem odors. Windrows can be any length, limited only by the size of the facility and the spacing, or aisle width, needed to maneuver equipment.

In many instances, low-tech composting is done on a paved surface, such as asphalt or concrete. The surface is graded to drain and collect leachate (also called “percolate”) and thereby reduce the potential of groundwater contamination.

Leachate may be treated on site using drain fields, bioswales, sand filters, or treatment ponds. The leachate may also be disposed of in a community sewage system, if a sewer line is located near the compost facility. If the paved surface is not graded properly or suitable drainage is not provided, ponding of the leachate may occur, resulting in potential problems with odor and insects.

After completing the high-rate composting process, materials are moved to a curing pile for curing and maturation. The location and area requirements for the curing pile(s) must be considered in the facility design.

Some advantages of low-technology composting include: 1) moderate cost, 2) ability to use a loader and other generic types of equipment, and 3) generally satisfactory quality and marketability of the final product.

Disadvantages include: 1) labor intensive, 2) more difficult to achieve consistent results, 3) potential for odors.

Figure 2.1 A Front End Loader Can Be Used to
Form and Turn Compost Piles

Reprinted with permission from On-Farm Composting Handbook, NRAES-54, published by NRAES, Cooperative Extension, 152 Riley-Robb Hall, Ithaca NY 14853-5701. (607) 255-7654.

Vermicomposting

The term “vermiculture” refers to techniques used for growing earthworms. “Vermicomposting” refers to the controlled degradation, or composting, of organic wastes, primarily by earthworm consumption. Bacteria and other microorganisms also contribute to vermicomposting processes, but the deliberate use of vermiculture technology to develop and feed a large population of redworms in the composting materials distinguishes vermicomposting from other methods.

Low-tech, home- and business-scale vermicomposting is typically done in covered boxes, bins, or troughs. The enclosed containers act as barriers against both large scavengers and small pests. Combined with restrictions against the use of fat, meat scraps, or other animal products as feedstock, these steps help make vermicomposting a good method for composting food materials on a small-scale.

A few projects in Washington and California have found windrow-based vermicomposting methods adequate and cost-effective for handling manure or yard trimmings. Operators often consider these materials lower risk for windrow vermicomposting, because they lack the putrescible quality of food scraps.

Any feedstock containing food scraps or mixed wastes requires protection provided by covered bins or sheltered troughs. The choice of bins is based on cost and availability. Many small producers use bins with custom-built lids, often in a series. Food Lifeline, in Seattle, WA, adapted pallet boxes reclaimed from a nearby orchard, and Woodland Park Zoo purchased steel watering troughs. The Evergreen State College, in Olympia, WA, built one large wooden trough, which has plywood lids and is sheltered under a roof.

Two medium-technology systems for vermicomposting are available commercially. To date, no system has been developed that could be termed high-tech. Vermitech, Inc., Toronto, Canada, has developed a completely enclosed system that fits in a standard parking space. Oregon Soil Corp., Oregon City, OR, has demonstrated the effectiveness of a continuous-flow vermicomposting system, which has a mesh floor on the bottom of a raised trough. This allows a mechanical bar to automatically scrape finished vermicompost from the bottom of the pile. Its raised design also improves drainage and aeration. It is sheltered by a greenhouse-type structure.

The capital costs of intermediate and large-scale vermicomposting projects vary significantly depending on the extent of investment in equipment, while operating costs will vary depending on the amount of labor required. Capital costs relative to processing capacity can vary widely. Several projects described earlier had capacities of around 0.25 tons (500 lb.) per day. Capital costs for these projects ranged from $1,500 for a low-tech system to $6,000 for a medium-tech system.

The cost of labor represents the largest percentage of operating costs for many vermicomposting projects. As a result many of the existing vermicomposting projects depend on the use of volunteer, student, or prison labor.

Medium-technology

For windrow methods, the step up to medium-technology composting consists of turning the windrows using specialized windrow turners. The windrows may be smaller in width and height to accommodate the turners; however, the requirements for aisle space are reduced or eliminated, compensating somewhat for the increased number of piles.

In the case of aerated static piles, medium-tech composting includes the use of aeration systems to push or pull air through the piles (by applying a positive or negative pressure). This enhances the aerobic decomposition process. In a further development, aeration systems are sometimes used in combination with a windrow turner.

Medium-tech composting is generally conducted on an impervious surface with leachate collection and treatment, as discussed previously for the low-technology option. Another trend is toward conducting medium-tech composting under cover in a further effort to control the composting process and to eliminate the need for runoff and leachate collection.

Primary advantages of medium-tech composting include: 1) a large volume of organic material can be composted quickly with less labor, 2) improved odor control, and 3) the quality of the end product can be controlled better. The labor savings can be significant. A major guide to farm composting found that the rates for turning compost with a bucket or front end loader ranged from 60 to 135 cubic yards (cy) per hour. With a small windrow turner, turning rates were increased to about 1,000 cy per hour.

Major disadvantages of medium-technology composting include: 1) the comparatively high capital investment in the facility, equipment and training, and 2) the cost of operation and maintenance of specialized and often complex equipment.

Figure 2.2 The Aerated Static Pile Method Uses Blowers
to Push or Pull Air through the Compost Pile

Reprinted with permission from On-Farm Composting Handbook, NRAES-54, published by NRAES, Cooperative Extension, 152 Riley-Robb Hall, Ithaca NY 14853-5701. (607) 255-7654. Adapted from Wilson, Manual for Composting Sewage Sludge by the Aerated Pile Method.

STATIC-AERATED VS. TURNED PILES

One may be tempted to say that discussions about compost aeration are just a lot of hot air, but important considerations are at stake. On the one hand, evidence suggests that turning or agitating compost piles releases trapped odors, causing unnecessary distress among neighbors. Others point out that it is difficult to fully aerate static piles—passively or actively. As a result, composting occurs unevenly and compost product quality suffers. Static-air proponents counter that turning offers only a burst of air that is quickly lost. You will find that the decision you make depends on many factors. In the end, you always have the option taken by many—use a combination of aeration and turning.

Figure 2.3 The Extended Aerated Static Pile Method Places Piles with Blowers Next to Each Other to Conserve Space And Retain Heat

DRUM COMPOSTING SYSTEMS

Cylindrical drums are sometimes chosen as part of a composting system for their ability to mix and tumble, and thus aerate, composting materials, like clothes in a tumble dryer. Small-scale drum systems have been used for home composting for years. The simplest method involves putting aeration holes in the side of a 55-gallon drum, filling is three-quarters full with compostables, securing the lid, and occasionally rolling in on its side to get proper aeration. Mechanical versions of a similar nature use wheels or cranks.

Add a motor, small or large, to make the jump to medium technology. The investment in motors typically justifies a jump in the scale of the system also, going from a few hundred pounds per day to half a ton or more per day. Examples of such technology are provided by Blue Planet, Inc., New York, and Augsberger Engineering, Phoenix, AZ.

For systems handling more than a ton of material per day, larger drums and motors and more sophisticated high-tech controls are required. Spectraserve Compost System makes a system similar to a concrete mixer. Bedminster Bioconversion Corp., Texas, has long been a leader in developing drum composting systems. In the past year, they have unveiled plans for marketing a version of their high-tech drum system used for municipal composting on a scale suitable for institutional use.

Figure 2.4 Bedminster Bioconversion Corp. Manufactures a Composting System that Moves Material from One End of a Drum to the Other

High-technology

High-technology composting is distinguished by several criteria:

· Enclosed—High-tech methods are used in a building or in a composting bin or “vessel.”

· Aeration/agitation—High-tech methods often combine aeration and agitation to get the benefits of both. Negative-pressure aeration is often used so exhaust air can be treated.

· Odor control—As part of active aeration, high-tech methods use biofilters to treat or remove odors from exhaust air.

· Automated—High-tech methods automate many of the process steps, such as preprocessing, composting, and process monitoring.

· Electronic controls—High-tech systems are especially noted for their use of electronic monitors and process controllers to turn on blowers, run agitators, and add moisture.

BAY-TYPE COMPOSTING SYSTEMS

One popular group of high-tech composting systems, known as agitated bays, place the prepared feedstock into long bays. The bays contain aeration pipes in the floor, and a mechanical agitator rides on rails along the sides of the bays to mix and fluff the decomposing material on a daily schedule. The agitators are designed so they gradually move the compost from the start of the bay to the finish. Because bays can be constructed side-by-side, the space under cover for composting is used efficiently.

Bay-type composting systems combine elements of aerated and windrow systems. The bay is typically 8 to 10 feet wide with 4 to 5 foot sidewalls. A bay can be hundreds of feet long, just like a windrow. A mechanical agitator riding on top of the sidewalls travels through the bay mixing the composting mass and moving it over a period of weeks from one end of the bay to the other. Aeration pipes laid in the floor of the bay provide oxygen and help control temperature by pushing or pulling air through the compost.

Bays have been used by themselves or in series. Because multiple bays can be set up right next to each other, they eliminate the aisle space between windrows. Their efficient use of space makes bays appropriate for composting under cover or inside a building.

Bay-type systems tend to fall in the medium to high technology categories, and they are commonly constructed as turn-key systems by any number of vendors around the country. But that does not preclude individuals from building their own. Howard Koozer, of Koozer’s Poultry, Sedro Wooley, WA, constructed his own agitated bay composter in a shed on his poultry farm. It operates on the same principles, but at a fraction of the cost of a turn-key system.

IN-VESSEL COMPOSTING SYSTEMS

"In-vessel" composting, involves composting in enclosed structures or containers. Because these systems use refurbished shipping containers or roll-off-type containers, they are sometimes described as “compost-in-a-box” systems. Being enclosed, these systems offer a high level of odor, nuisance, pest, and leachate control. Exhaust air from these systems is typically treated in a biofilter.

Because many in-vessel systems are “batch” processes, meaning you compost a boxful at a time, facilities often find they require the use of two or preferably three units. For example, each unit would be filled over the course of a week and then allowed to compost for an additional two to three weeks. In order to fill a 20-cubic-yard container over a one-week period, a facility would need to generate approximately one ton of compostables per day. These units require a front end loader or conveyor for loading and unloading. Systems constructed from rolloff containers also require a rolloff truck for emptying the contents.

Wright Environmental Systems, a Canadian company, manufactures an invessel system that is continuous flow. This means that shredded and mixed raw materials are regularly added to the front-end, while composted material is removed from the back end. The system automatically monitors airflow and temperature in the box, and as material is pushed through the box, it is regularly remixed and remoistened. Also, the system was designed in a way to ensure that raw materials are kept separated from older material that has reached temperatures high enough to reduce potential pathogens.

An advantage of these systems is the containment they provide. Another is their turnkey nature, that is, all the calculations and engineering design have been done. All the manager has to learn is how to operate the equipment effectively. Possible disadvantages include cost. Average capital costs for high-tech composting systems can reach $40,000 to $100,000 per ton-per-day of capacity for small systems, down to $20,000 to $50,000 per ton-per-day of capacity for larger systems. Another factor worth remembering is that although these “boxes” take up little space, the compost they produce may require additional curing after coming out of the box, which means additional space next to the box or in another location.

High-tech invessel systems are potentially viable at the institutional level for composting difficult materials, such as food waste or biosolids. While yard debris or manure could be appropriate for bulking material, high-tech systems are thought to be cost prohibitive for composting such materials alone.

In this section you will gather the information needed to perform analyses of different options. Many factors affect how composting gets integrated into an organization’s waste/resource management program. You will find some factors fairly straight-forward and easy to measure. Using the audit form that follows, you will gather information about these factors from your own facility/organization. This information will be used to analyze the potential costs and benefits of composting at your facility. Examples of these factors include:

• Materials—What do you have (types) and how much (volumes) of each? How does what you have match the requirements for good composting?

• Soil product usage—How do you currently use soil products (e.g. compost, mulch, bark, peat moss, soil mixes)? How much do you purchase? In addition to your existing needs, what might be some unmet needs?

• Space—What is needed, what is available, and advantages/ disadvantages of different types of spaces?

• Weather, climate, and other environmental factors.

• Labor—How is it used now; what is available for composting in the future?

• Equipment—What is available; how could it be used for composting?

• Waste handling—What materials are disposed or recycled? What do you currently spend to manage all these wasted resources?

• Capital and operating costs—Evaluate your organization’s access to capital and on-going budget needs.

Other factors related to composting feasibility involve more subjective questions. These questions should be discussed for your organization. To develop a measured result that can be factored into your analysis, these issues will be addressed through survey-type questions. Examples of the types of subjective factors and related questions include:

• Goals—Is your organization interested more in diversion of waste, cost savings, education, training, employment, etc.?

• End uses—What are your goals for using compost—as substitutes for existing soil products or for potential new uses?

• Potential value added—Some values such as education and training are difficult to measure in monetary terms. Even some soil enhancement benefits are know to occur by the use of compost, but may still be difficult to measure monetarily.

• Risk aversion—How does your organization respond to risk?

• Operating history—Does your organization have any experience producing or using compost or similar products?

Print or make copies of the blank form. Use one form to consolidate all the information for your organization. If it would make it more convenient to gather information, separate forms can be used for various segments of your organization.

Organization: ____________________________________ Date: _________________

Composting Information Gathering Form

Refuse

How much refuse does your organization generate each month? Methods:

1. Use refuse bills to tally your average dumpster capacity in cubic yards, then quantify what percentage is actually used. Multiply cubic yards by 175 lbs. to estimate average tonnage.

2. If you have compactors or haul your own refuse, use your bills or disposal receipts to compute the average tonnage.

_______________ cubic yards (note: 202 gallons = 1 cubic yard = approx. 175 lbs.)

_______________ average tonnage per month

Materials

Indicate the number of tons per month for each the following items. You can estimate the number according to the percentage of the refuse tonnage each item represents, then compute the number of tons. (See Section 5—Materials for detailed descriptions.)

ITEM	% of Refuse (x avg. tons refuse/mo) =	TONS/MONTH
Yard & garden trimmings	__________	_____________
Food scraps	__________	_____________
Farm-related materials	__________	_____________
Biosolids	__________	_____________
Paper materials	__________	_____________
Wood: scraps, chips, sawdust	__________	_____________
Other organic materials	__________	_____________

Here are two ways to make your estimates more precise. First, ask employees to separate the organic materials for a certain time period (day or week) and use these numbers to determine the percentage. Or, sort the organic materials from a full dumpster (this is messier). If you can do such sampling more than a couple times, the reliability of your numbers will increase.

Weather

Indicate the average rainfall per year. ____________

Indicate the highest rainfall rate (as a 25 year storm event) ____________

The local planning or flood agency should have this data.

Indicate the average high and the average low temperatures. ____________

Sites/Space

In the spaces below, identify possible sites for composting at your facility. Section 6–Siting Analysis will help you evaluate each site in more detail.

SITE	AREA (sq. ft)
_____________________________________________________	_________________
_____________________________________________________	_________________
_____________________________________________________	_________________

Equipment

Indicate which items your organization has available for composting. Mark the percentage of time each item would be available (1-100%). Finally, indicate the general condition of each item (from poor to excellent).

ITEM CONDITION

		Poor	Fair	Average	Good	Excellent	% Used
q	Skid steer or front end loader	q	q	q	q	q	______
q	Conveyor(s)	q	q	q	q	q	______
q	Chipper	q	q	q	q	q	______
q	Grinder	q	q	q	q	q	______
q	Shredder	q	q	q	q	q	______
q	Pulper	q	q	q	q	q	______
q	Mixer	q	q	q	q	q	______
q	Manure spreader	q	q	q	q	q	______
q	Moisture equipment: (sprinklers, drip hoses, sprayers, or water trucks)	q	q	q	q	q	______
q	Aeration equipment: (blowers, fans, piping)	q	q	q	q	q	______
q	Compost turner	q	q	q	q	q	______

Labor

In what department or individual would be

responsible for composting? ____________

Is supervisory or management personnel available ____________

for the composting project? ____________

What level of pay do these personnel receive? ____________

Is supervisory or management personnel available ____________

for the composting project? ____________

What level of pay do these personnel receive? ____________

Goals

On a scale of 1-5, indicate your organization’s interest in the following potential goals or benefits of composting.

POTENTIAL GOAL/BENEFIT	None	Little	Some	Big	Great
Waste diversion	q	q	q	q	q
Production of high-quality compost	q	q	q	q	q
Cost savings	q	q	q	q	q
Education opportunities	q	q	q	q	q
Training or employment opportunities	q	q	q	q	q
Public goodwill, marketing, or publicity	q	q	q	q	q

Soil product usage

Indicate how much of the following soil products you purchase each year?

ITEM	Cubic Yards/YR	$/CY	$/YR

Compost	_____________	________	________
Mulch	_____________	________	________
Bark	_____________	________	________
Topsoil	_____________	________	________

Considering the various types of landscaping you have (e.g., turf, annuals, perennials, greenbelt, forest, golf courses, ballfields), What other existing or unmet soil needs might be met by making and using compost?

_________________________________________________________________

End uses

On a scale of 1-5, indicate your organization’s interest in the following potential end uses for compost (e.g., as substitutes for existing soil products or for potential new uses)?

POTENTIAL END USE/MARKET	None	Little	Some	Big	Great
Give it away	q	q	q	q	q
Use it as substitute for current products	q	q	q	q	q
Use it for new soil enhancement	q	q	q	q	q
Sell it to landscapers or the general public	q	q	q	q	q
Education value	q	q	q	q	q

Capital and operating costs

Evaluate your organization’s access to capital and on-going budget needs. Discuss these questions with others in your organization to come up with the best estimates. _________________

What would be the maximum amount of money that your organization could raise or borrow for start-up costs (regardless of economic benefit)? _________________

What number of years does your organization view as reasonable to payback capital investments such as a composting operation? _________________

Does your organization’s budget allow for shifting money that is currently spent to dispose or recycle organic materials to the department that would be responsible for composting? _________________

Risk aversion

How does your organization respond to risk? Some organizations accept easily the challenges posed by risk. Other organizations are averse to risk and shun the potential for making mistakes that cost money. On a scale of 1-5 (not accepting to accepting of risk), assess your organization’s willingness to accept risk

RISK ACCEPTANCE	None	Little	Some	Big	Great
	q	q	q	q	q

Operating history

On a scale of 1-5, evaluate your organization’s experience producing or using compost or similar products

COMPOSTING EXPERIENCE	None	Little	Some	Big	Great
Responsible department	q	q	q	q	q
Responsible management individual	q	q	q	q	q
Facility crews (e.g., kitchen, grounds)	q	q	q	q	q
Other ________________________	q	q	q	q	q

As a facility manager, you are faced with a need to assess the costs and benefits of new projects. This assessment involves looking at tangible and intangible costs and benefits. The institutional success stories described earlier illustrate some of the intangible benefits to composting, such as public education, employee awareness, corporate or institutional image, and environmental benefits. In addition to intangibles, which by their nature are difficult to quantify, you will find some straightforward cost avoidances. This section discusses your potential to save money through composting.

What are Avoided Costs?

One of the first questions a compost professional would ask someone considering composting is “what are you spending currently to manage organic wastes and to purchase soil products?” “Avoided costs” can include disposal or recycling fees, hauling charges, or solid waste fees or taxes that you will no longer pay when you start composting. Avoided costs also include the costs of any soil amendments or mulch materials you may be purchasing now but that you can substitute with your own compost.

These avoided costs when combined provide a threshold against which to compare the potential benefits of investing in a composting solution. The avoided cost threshold will likely affect your choice of technology. For example, if a business spends a couple hundred dollars a month on disposing of organic materials and little or nothing on soil products, then a composting solution would have to be small or inexpensive to compete. On the other hand, a large college campus or corrections facility may spend thousands of dollars a month on managing a wide variety of organic wastes and have a need for hundreds of dollars a month of soil products. Composting may easily compete in terms of costs and also provide added benefits. In another example, even when high-tech composting would be preferred due to space constraints, a low cost threshold would make it difficult to justify the capital and operating expense of such a solution.

The preliminary avoided cost analysis will not calculate all the possible fees or charges, but you should be aware of the many direct and indirect costs that can be avoided. On the disposal recycling side, consider these:

• Disposal/recycling costs—These can be decreased directly and substantially by composting. (Don’t forget to include the fees and taxes portion.)

• Cost of employee or other labor—It is important to remember that current handling practices cost money for employee time. Time spent in collecting materials and making compost is not all new labor. These activities can result in elimination, substitution, or addition of labor in a variety of ways.

• Equipment operation and maintenance—Current practices may involve operation of different types of equipment, which requires periodic maintenance.

• Equipment cost (replacement)—To make a fair comparison with the purchase of new equipment for composting, the equipment currently used for waste handling would require periodic replacement that should be accounted for in the analysis.

• Utility expenses for material handling—These costs can include water, sewer, power, and fuel charges directly associated with current practices.

• Other costs—Because of unique factors related to your facility, you may experience costs not typically associated with waste management or composting. They should, however, be considered when making a decision about composting.

On the landscaping side, think about how the potential benefits of using compost can also reduce your costs. Consider the following:

• Mulch and soil products currently used in landscape, garden, or farm activities.

• Fertilizer costs—Compost is not the same as fertilizer, but using compost can reduce the amount of nutrients required from other sources, either by direct substitution or by binding with and holding nutrients in the soil longer.

• Landscape watering costs—Compost offers “moisture holding capacity,” keeping plants healthy with less purchased water.

• Pesticide and herbicide costs—Compost supports organic and integrated pest management systems. Compost also contains beneficial microorganisms that over the long term reduce the need for pesticides and herbicides

Avoided Cost Threshold Worksheet

The worksheet that follows was developed to give you a way to calculate the potential avoided cost of starting your own composting program. The worksheet takes into account a variety of costs, including:

• Disposal or hauling cost savings;

• Savings from self haul of waste materials;

• Recycling cost savings;

• Savings from substitution of compost for purchased products; and

• Potential value of other benefits of using compost in landscaping.

These various avoided costs, when taken together, can form the basis or threshold for developing a budget to fund composting activities. From a strictly bottom line perspective, your new composting project should not exceed the potential avoided costs, or savings, that can be achieved. Of course, it is wise to also consider the possible intangible benefits of such a project, such as education, public goodwill, job creation, and environmental sustainability.

Avoided Cost Threshold Worksheet

The following worksheet will help you calculate the potential savings benefits that composting can offer your organization. Complete each part of the worksheet, calculate the total potential savings, and transfer this “threshold” to the composting scorecard.

Disposal/Recycling Costs

The organic waste stream (e.g., food scraps and soiled, nonrecyclable paper) that is generated at your facility is likely disposed of with the bulk of the other garbage. There are some instances, though, that require a separate disposal and a distinct fee structure due to the nature of the material. For instance, if you’re facility generates refuse (of which a portion is organic waste), brush and yard trimmings in any quantity, and/or biosolids (derived from an on-site wastewater treatment facility), you are likely looking at three distinct disposal/reuse waste streams with three fee structures. In some cases, the costs may include transportation of the materials (such as self haul of brush to a landfill or reuse site) coupled with tip fees. In this case, you must estimate the labor, transportation, and tip fees associated with the disposal or reuse of these materials.

Considering this, you will need to calculate avoided costs based on the example in the following table. This table is designed to show the potential avoided costs for a facility which reuses or disposes of the organic portion of their normal refuse waste stream, brush and yard debris generated on site, and biosolids from an on-site wastewater treatment plant.

Soil Amendment Purchases

Any soil amendments you currently purchase should be considered. The production of compost will likely provide all of the mulch or amendment products you will need, depending on the size of your facility. This material cost is easily calculated and the total should be added to the total disposal avoided cost outlined above. This total will then be used in evaluating other options for your organic waste stream. The example below illustrates the method by which this total is derived. Again, the spreadsheets provided in Section 11 can calculate this avoided cost for you.

Soil Amendment Avoided Costs

Material	Cubic yards	Cost per	Cost/year ($)
	bought/yr	cubic yard ($)
Compost	20	$ 15.00	$ 300.00
Mulch	10	$ 10.00	$ 100.00
Bark	5	$ 10.00	$ 50.00
Topsoil	2	$ 20.00	$ 40.00
			$ 490.00

Avoided Cost Summary

Avoided Cost/Potential Savings	$Value
Disposal/hauling cost savings (based on worksheet estimate or other calculations)
Savings from self haul of waste materials (based on worksheet estimate or other calculations)
Recycling cost savings (based on worksheet estimate or other calculations)
Savings from substitution of compost for purchased products, e.g., bark, topsoil, manure (based on worksheet estimate or other calculations)
Potential value of other benefits (use your best judgment): * improved soil structure * water conservation * value of nutrients and nutrient conservation * improved plant health, fewer disease or pest problems
TOTAL AVOIDED COST THRESHOLD

Scorecard

Refer to the scorecard introduced in Section 1. Review the following descriptions of those items that would tend to favor or eliminate one or more levels of technology during your evaluation. Now mark the scorecard for the avoided cost section.

AVOIDED COST

Technology	Commentary
Minimal	Minimal technology may be your one option if there is little or no avoided cost potential and if other factors, such as education value or community good will do not help justify additional expenditures for composting.
Low	A low avoided cost threshold (<$500/month) would tend to favor consideration of low-tech options.
Medium	A low avoided cost threshold would discourage consideration of medium- or high-tech options, unless substantial revenue can be generated through uses or markets for the compost or unless development and operation costs can be shared with another organization. A high avoided cost threshold (>$1,000) does not by itself favor any particular technology, it only makes it more likely that you can justify development of a compost operation.
High	Because of the substantial capital and operating costs and economies of scale, high-tech options are more favorable if the avoided costs are also substantial (thousands of dollars per month).

Section 3.0 Information Gathering asked you to determine the volumes of different types of organic materials you had available. For purposes of discussion, the materials are described according to the following categories.

Material Types Available

• Yard and garden trimmings—Leaves, grass clippings, fir and pine needles, garden trimmings, dead plants, prunings, and wood chips made from brush and stumps represent a large portion of the waste streams from many facilities. Leaves alone can be composted with minimal technology, and along with wood chips can be an excellent mulch. Characteristics of yard trimmings vary widely and when collected and composted all mixed together need greater processing and monitoring.

• Food scraps—Food scraps represent another large percentage of the waste materials generated by facilities and institutions. Food scraps tend to be wet and heavy measured as a high bulk density. When choosing composting technology, distinctions are made between vegetative food scraps and scraps that contain meat, dairy, seafood, or oily products. Distinctions are also made between preconsumer and post-consumer food scraps. Preconsumer scraps are generated and collected in kitchens without have being served as food to people. Post-consumer food scraps include plate scrapings and leftovers from people’s meals.

Food scraps that contain meat, dairy, etc. or post-consumer materials are more likely to contain pathogens or to be contaminated with plastics or other foreign material. They require more intensive medium- to high-tech composting and must be carefully managed to prevent problems with odors or vermin.

• Farm-related materials—Many farm-related materials make great feedstock for composting. Examples include manure and bedding, spoiled straw, crop debris, and orchard prunings, which are quite woody.

• Biosolids—Once lumped together with “sewage sludge,” biosolids refers now to the materials that are left after completing the entire wastewater treatment process. They tend to be good sources of nitrogen and moisture. They need to be mixed with bulking materials to compost effectively.

• Paper materials—Paper should be recycled into new paper whenever practical. However, many types of paper are not or cannot be recycled effectively, and could be an economical source of bulking material to be mixed with food scraps, manure, or biosolids for composting. Examples include mixed used paper (i.e., newspaper, office paper and magazines), soiled paper, and waxed cardboard.

• Other organic materials—Many other types of organic materials considered by some to be waste have been proven to be good components for composting. Examples include sawdust, gypsum wallboard, coal or wood ash, ground crates and pallets, cotton mattresses, farm mortalities, and diatomaceous earth (used as a filter in making beer and wine. Somewhat marginal as compost feedstock, these materials are used as minor parts of an overall mix. They may require greater processing than possible with minimal- or low-tech composting.

Other organic materials you have available may also be acceptable for composting. The next parts of this section provide information on the qualities being looked for by successful composters.

Material Qualities

Whatever materials you have available, it is the characteristics they offer to mix ratio development that are critical to successful composting. Mix ratio refers to the ratio or portion of each feedstock in the initial mix. The initial mix impacts a number of processing parameters including: processing time, aeration, odor generation, leachate production and final product quality. The following parameters are significant in the initial mix:

• Porosity;

• Moisture content;

• Available carbon content;

• Nutrient content;

• pH; and

• Visual/qualitative factors.

This section summarizes the qualities, or “parameters,” that are important and how they relate to successful composting. Table 5.1 provides an overview of these parameters and their role in the composting process. The parameter groups relate to the period of initial mix development when critical observations are made.

Table 5.1 - Compost Monitoring and Control Parameters

Parameter

Relevance

Desired Condition / Adjustment

Initial Mix Development

Porosity	Provides access for oxygen	< 900 lb/cf initial mix bulk density
Moisture Content	Provides moisture for microbes	< 60% moisture (&>50%)
Available Carbon	Provides energy for pile heating	Generate pathogen reduction temps
Nutrient Content	Provides nutrients for microbes	C:N ratio near 30:1 preferred
pH	Provides environment for microbes	6 to 7.5 preferred

Porosity

Porosity is of primary importance for initial mixing. A mix with insufficient porosity will limit aeration. Porosity is provided in a mix by large particle size materials such as chipped brush and wood chips. Porosity is also influenced by the moisture content. If the moisture content is excessive, pore spaces are filled with water instead of air. In general, the porosity is considered optimal if the moisture content is <60 percent and the bulk density is less than approximately 900 pounds per cubic yard. The optimum porosity/moisture is dependent on the moisture holding capacity of the initial mix. Experience working with the various feedstocks at a specific site will dictate what the optimum bulk density and moisture content of an initial mix are. The wet, dense and putrescent nature of some organic materials require that the initial mix has sufficient porosity. It is extremely important that the particle size of the bulking material after grinding is substantial enough to create adequate pore spaces in the initial mix.

Moisture content

The maintenance of moisture content in an optimum range is essential. Sufficient water must be available for microbial activity. At the opposite extreme, excessive moisture content reduces porosity which promotes odor producing anaerobic conditions and slows the decomposition process. Excessive moisture also acts as a heat sink, reducing pile temperatures. The optimum moisture content for composting is considered to range from 40 to 60 percent.

Available Carbon

Heat is generated during the composting process as a result of the rapid decomposition of organic compounds that are readily available as a substrate for microbial growth. Substrates such as sugars, starches, fats and proteins are considered readily available, whereas hemicellulose, cellulose and lignin decompose much more slowly and are therefore not considered readily available. The composting process requires a certain fraction of readily available compounds to be present. For example a pile of sawdust will not generate much heat compared to a similar sized pile of sawdust and biosolids. If the amount of readily available carbon is too high, rapid oxygen depletion and odor generation can result.

In general, the older the plant tissue, the less energy or readily available substrate is present. Smaller particle sized materials will also be more readily available for microbial consumption. Digested municipal biosolids have a high content of readily available substrates, whereas wood chips are not very available. A continuum of relative carbon availability is presented below:

Raw wastewater solids = grass clippings = food scraps > green leafy vegetation > digested biosolids = brown leafy materials

Food scraps > mixed vegetation > harvested lagoon biosolids > chipped brush/twigs = fresh sawdust > old sawdust > wood chips

In general, there will be a sufficient supply of readily available carbon when biosolids or other wet organic materials such as food waste are composted with yard debris. However, care is necessary to assure adequate degradable fraction. Pilot evaluation are important for determining available carbon content from test mixes.

Nutrient content

Inorganic nutrients such as nitrogen, potassium and phosphorous are required for microbial growth. In some mixes, nitrogen can be limiting. Yard debris collected in the winter months for example can have a low nitrogen content. All other nutrients are typically present in sufficient quantity. As a general rule of thumb, the ratio of carbon to nitrogen (C:N ratio) should be approximately 30:1. A lower C:N ratio can result in the production of odorous nitrogen containing compounds such as amines and ammonia, during composting. At higher C:N ratios nitrogen may not be sufficient for active, thermophilic composting. However, initial mixes with C:N ratios as high as 60:1 have been noted to compost quite well. More significant than C:N ratio is the microbial availability of the carbon and nitrogen.

pH

Either excessively acidic or basic conditions can inhibit biological activity. Initial pH outside of the desired range of 6 to 7.5 should be adjusted unless demonstrated to perform adequately in pilot testing or operations.

Visual / Qualitative Factors

Trained and experienced compost facility operators can utilize simple qualitative tests as aids to operations. The visual appearance of the material at all phases of the mixing and composting process provides valuable insights into the status of the process. Color, moisture, particle size and void spaces, absence of sludge / mix “balls” and odor are useful visual or sensory indicators. Of primary use during the initial mix operation are the squeeze test for free moisture, the observed thoroughness of mixing, and the adequacy of void spaces in the mix.

Collection Issues

Several issues related to separation and collection of raw feedstocks should also be considered in decisions about what materials to handle.

• Average volumes vs. peak volumes—Generation of organic materials can vary greatly throughout the year. Any facility you design must be capable of handling the peak volume, while operating optimally for the average volume. You should consider ways to level out the peaks and valleys, so it matches more closely an average flow.

• Seasonality—This refers to both changes in the volumes generated, but also in the types of feedstocks generated (e.g., grass clippings in the summer, and leaves in the fall). With careful planning you can effectively match seasonal changes to optimal composting conditions. For example, generation may make it possible to do composting seasonally rather than all year round. Or if leaves upset the balance of a high-tech operation, you may compost them separately at another location using low-tech methods.

• Separation—To the extent practical, keep materials separated, so you avoid or limit preprocessing. Mixed feedstocks, such as mixed yard trimmings, are more difficult and costly to process. You want to grind or shred only those materials that require it. The exception would be when the combined collection of materials provides a good materials balance and the grinding serves a mixing function also.

• Own materials vs. purchased bulking materials—The economics of composting can be affected significantly if large volumes of bulking material must be purchased for your operation. It may be better to find a balanced mix ratio using just your own materials or those that you can get for little or no cost

• Quality—This refers to the quality of the feedstock, particularly the presence or lack of contaminants. Contaminants can hinder the compost process or degrade the final product. For example, separating post-consumer food scraps, such as plate scrapings, will likely be more difficult and have more contamination from plastics and packaging than setting aside preconsumer scraps like produce trimmings. Also be mindful of potentially hidden contaminants such as high salt levels present in some food materials or manures.

• Cost and labor—As you decide what to include in your compost feedstock, consider which materials cost more to handle or to dispose or recycle. Including these materials increases your avoided cost threshold.

• Collection containers—What containers do you use now? Will they be satisfactory for your new program or will you have to find or buy new containers?

• Collection vehicles—Similar questions. What vehicles do you have or use now? Will they work or will you need a different vehicle for collection purposes?

Trade-offs

How your organization views the goals for composting will influence the choice of materials. If your primary goal is diverting waste from disposal, then you will try to combine as many organic materials as possible into the feedstock mix. This decision will likely increase the size and complexity of your compost operation. On the other hand, if your organization is more interested in the value of making and using high-quality compost products, then you should try to be more selective about the types of materials you include.

As described in this section, your selection of feedstock affects the choice or cost of composting technology. Simple materials need only simple solutions, while more mixed feedstocks tend to require more complex solutions.

Because of the potential hauling, labor, and permitting costs, not to mention hassle, of handling materials from off site, preference is given to just managing the composting with your own organic materials. The exception could be when comparing bulking materials acquired from off site versus the potential cost of grinding or screening your own bulking materials.

Scorecard

MATERIALS

Technology	Commentary
Minimal	Good for composting on a seasonal basis or for composting simple feedstocks, such as piles of autumn leaves or horse manure and wood shavings. Because of the odor-generating potential, not appropriate for highly putrescible, nitrogen-rich wastes, such as mixed yard debris, grass clippings, manure, food scraps, or biosolids. Because of the lack of management or monitoring, not appropriate for materials containing plant or animal pathogens.
Low	Good for mixtures of yard and garden trimmings and/or manures, especially where volumes do not exceed a thousand cubic yards per year. Highly putrescible, nitrogen-rich wastes could make low-tech systems difficult to manage. Later upgrades to medium-tech composting may become necessary, so consider if it wouldn’t be better to start at the higher level in the first place. Because of the need for more intensive composting and greater monitoring, use of post-consumer food scraps or biosolids in the feedstock would eliminate low-tech methods. Low-tech worm bins can be used to process preconsumer, vegetative food scraps.
Medium	Appropriate for all kinds of materials, especially mixtures containing pre- and post-consumer food scraps, wood chips or other coarse materials, or paper by-products. Larger volumes of material (greater than 10 cubic yards or 5 tons per day) tend to favor more efficient, medium- to high-tech systems.
High	Appropriate for all kinds of materials, especially mixed materials needing lots of odor control. Economies of scale improve as volumes increase beyond 10 tons per day.

Activities involved in composting organic materials—grinding, making and turning piles, and screening products—can have significant impacts on the areas surrounding the composting site. Negative impacts can include noise, odor, dust, etc. Vermin are rarely a problem around sites composting yard debris, as long as the composting remains active. But they can be a significant issue if you hope to include food materials.

Evaluation Factors—What are We Looking For?

Considering the potential impacts, the site or sites for composting activities should be chosen carefully, even when the volumes being composted are relatively small. Before evaluating specific sites for composting, it is useful to consider what would be considered the ideal site for composting. Based on regulatory requirements and composting experience, the following minimum site criteria should be used when looking for the “ideal” composting site:

• Flat to gently sloping topography (between 2 and 5%) is preferred, though some composters have made clever use of hillside space for composting (in the top & out the bottom) or for storage.

• Outside of the 100-year flood zone.

• Stable soils that support equipment whether wet or dry.

• Access to infrastructure, providing needed utilities and a water source to keep piles moist and control dust. This water need not be potable. Of course, rainfall is good within reason. Finally, a well water or city water can be used.

• Good vehicle access, including space to maneuver equipment.

• Space for storing a week’s worth of brush and green yard debris (in two separate piles); grinding material; building, turning, and curing compost piles; and storing mulch and finished compost.

• Neighbors in homes, offices or other buildings that are far enough away to avoid negative impacts (at least 200 to 500 feet), more if using minimal technology.

• Buffer space (200 feet or more preferred) from natural water—streams, ponds, lakes, etc., more if using minimal technology.

• No history of site contamination.

In addition to those minimum criteria, you should give consideration to site characteristics that offer particular advantages.

• Split site—If you can’t find all the space you need at one site, consider how you might split activities among different sites. Good examples include grinding bulking materials at a separate site or placing curing piles or post-processing and marketing activities at a different site.

• Surface type—Packed clay, asphalt, and concrete areas have particular value for environmental protection and may be required by regulators before you start composting. Rather than pouring a new slab, consider revamping an old parking lot that is not used much.

• Covered or uncovered—Covered space also has advantages from the environmental control perspective, so if you have an old warehouse, greenhouse, or even an open-air shed with a roof that isn’t being used, consider it as a possible compost location.

Of course, no single advantage rules in isolation. All the different site characteristics must be considered together. So to get the best site might still mean pouring a new slab of concrete or putting up a prefab building or doing any of a number of improvements. Still it will be the best choice, because you have considered all the criteria together.

What are the Possible Locations at Your Facility?

Following is an evaluation form to use to gather information and evaluate one or more possible sites at your facility. (For multiple sites, make additional copies of the form.) Compare the advantages and disadvantages of your site options to choose one or to make a short list. (Final selection is not necessary until all the analyses are done.)

Trade-offs

The type and size of space available is a major consideration in choosing among different technologies. More space and larger buffers are needed for minimal- and low-tech methods. Higher-tech methods use space more efficiently. An excellent example of this relationship was demonstrated by a 1994 North Carolina State University study that compared space requirements for large-scale facilities using different levels of technology. The results were as follows:

Size/Level of Technology	Acres

10,000 ton per day facility
Minimal technology	6
Low technology	2
Medium to high technology	1

25,000 ton per day facility
Minimal technology	15
Low technology	5
Medium to high technology	2.5

Deciding whether to use or build a covered facility is another major factor. The main difference is that composting under cover results in “zero discharge” of leachate. This eliminates requirements for leachate treatment systems—a major cost and headache of uncovered facilities, especially in wet climates. On the other hand, the cost of an enclosed facility favors medium- to high-tech methods that use the covered space most efficiently. If you already have an enclosed space or an existing leachate treatment option (e.g., farm manure lagoon), these facts should influence your choice.

Finally, consider the advantages and disadvantages of putting your compost operation close to the materials source, which may also be closer to neighboring uses, or farther away from both materials source and neighboring uses.

Composting Site Evaluation Form

Print or make copies of the blank form to use to evaluate each of your potential sites.

Score each site feature with a number between 1 and 10 using the scoring key that follows. Then multiply each score by the weighting factor listed on the form and add up the total.

Site: ____________________________________ Date: ___________________

Site Feature	Score 0 (low) 10 (high)	x Weight	Total
Location (low=fatal flaw)		1
Environmental (low=fatal flaw)		2
Groundwater (low=fatal flaw)		3
Neighboring uses		3
Topography		2
Soils/surface		3
Leachate control		3
Infrastructure		3
Size/space		1
Access		1
Ownership		2
Site security		2
TOTAL

A total of 260 points is possible. Priority should be given only to those sites that can score more than 156 points. If a site is borderline, consider what can be done to raise its score.

Source: Evaluation form and key were adapted from Michael Simpson, Tellus Institute, as reprinted in Yard Waste Compost Guide for Rhode Island Communities, June 1991.

Scoring Key for Site Evaluation Form

Location

Criteria: General assessment of site. Location does not conflict with local zoning or land use policies. The location is well-suited to collection and delivery of raw materials and to probable end-uses for products.

Low—The site conflicts with allowable land uses, deliveries must occur through densely populated areas, or the site is too far from probable end uses. Any low score eliminates the site from further consideration.

Medium—The site meets the criteria.

High—The site meets the criteria and is particularly well-suited to collection and delivery of raw materials or to probable end uses.

Environmental

Criteria: The evaluation of these factors can uncover “fatal flaws” that would completely eliminate the site from further consideration. The site should be outside of the 100-year flood zone as determined by local maps. The buffer space from natural water courses—wetlands, streams, ponds, lakes—is a minimum of 200 feet. More is preferred. There should be no history of site contamination.

Low— Site cannot meet the flood zone, water course, or site history requirements. Any low score eliminates the site from further consideration.

Medium—The site meets the criteria, but is close to a flood plain, water courses or a contaminated site.

High—The site meets the criteria by significant distances.

Groundwater

Criteria: Sufficient depth to groundwater to prevent contamination, even during seasonal highs. There should not be standing water during periods of heavy rain.

Low—Bedrock or seasonal high water table is at or near the surface. Any low score eliminates the site from further consideration.

Medium—Bedrock or seasonal high water table is less than 5 feet from the surface.

High—Bedrock or seasonal high water table is 5 feet or greater from the surface.

Neighboring Uses

Criteria: Neighbors in homes, offices or other buildings are far enough away to avoid negative impacts, such as traffic, odor, or noise. Preferred buffer zones around the site measure at least 200 to 500 feet for most compost processes, to as much as 1,000 feet for minimal technology composting.

Low— Setbacks from neighboring uses are significantly lower than preferred.

Medium—Setbacks meet the criteria.

High—Setbacks are significantly greater than preferred.

Topography

Criteria: Flat to gently sloping topography (between 2 to 5%) is best, though some composters have made clever use of hillside space for composting (e.g., in the top-out the bottom) or for storage. The slope should help move rainfall away from piles.

Low—The site slopes more than 6%; major clearing, grading, or filling would be required.

Medium—Site is close to the preferred slope; minor clearing, grading, or filling would be required.

High—The site meets the criteria with little or no clearing, grading, or filling.

Soils/Surface

Criteria: Stable soils that support equipment whether wet or dry. Possible surface types include: soil, packed clay, or impermeable (i.e., Soilcrete, asphalt, concrete).

Low—Unstable, excessively well-drained, or very poorly to poorly drained soils.

Medium—Stable, well-drained soils.

High—Stable, moderately well-drained soils; or stable soils covered by an impermeable surface that would allow for run-off diversion and treatment.

Leachate Control

Criteria: A large covered space in which to do composting is best. Access to wastewater treatment: sewer, septic, leachate pond, or manure lagoon is also good.

Low—Potential exists for leachate contamination of ground or surface waters.

Medium—Covered space or adequate treatment systems would have to be built.

High—Adequate covered space is available or there is existing access to treatment facilities.

Infrastructure

Criteria: Composting activities require access to a range of utility services, such as electricity (3-phase power may be needed), communications, and a water source to keep piles moist and control dust.

Low—Access does not exist and would be costly to provide.

Medium—Access is limited, but could be provided for reasonable cost.

High—Access to all needed utilities, especially power and water, already exists.

Size/Space

Criteria: Space requirements are determined by the peak volumes of materials received and stored combined with the space required for composting (as determined by the level of technology and method) and buffers. The shape of the space should allow for rational, efficient layout of various compost activities.

Low—The site is inadequate to handle even the average flows using any level of composting technology.

Medium—The site is adequate. Score it lower if it can only handle the average flows, somewhat higher if it can handle the peak flows of material.

High—The site is more than adequate to receive all the projected volumes for the foreseeable future.

Access

Criteria: Good vehicle access, including space to maneuver equipment. The driveable areas at the site must be able to handle equipment and emergency vehicles at all times of the year.

Low—Inadequate access, which would cause crowding, traffic problems, or potential for accidents.

Medium—Meets the criteria: adequate access on site and through the entrance/exit point.

High—Exceeds the criteria, offering ample maneuverability on site and multiple entrance/exit points.

Ownership

Criteria: Ownership of the site can cause difficulties if the owner is different from the composting organization. Involving the owner and getting permission can add to the work or cost of the compost operation.

Low—The owner’s permission may be difficult or costly to secure

Medium—The owner’s permission could be secured with little work or cost.

High—The composting organization also owns the site.

Site Security

Criteria: The site should discourage illegal dumpling, and all equipment must be protected from theft and vandalism, including arson. Natural barriers or fencing are most often used. Some sites, such as those at corrections facilities, will have special security needs that will require their own scoring criteria.

Low—Control of access is minimal and the site is in an area where illegal activity or vandalism is probable.

Medium—The site may be in an area where illegal activity or vandalism is possible, but adequate security can be provided. Or the site cannot be secured, but it is in an area where illegal activity or vandalism is not likely.

High—Control of access is more than adequate and the site is in an area where illegal activity or vandalism is not likely.

Scorecard

SITING

Technology	Commentary
Minimal	OK when sites are large, have lots of buffer space between the composting and other activities, and there is a low potential for environmental harm. If your site lacks the larger 1,000-ft buffer considered necessary for minimal-tech methods, then eliminate this option.
Low	Low-tech compost or worm bin systems can work well on many sites, though the potential for odor limits their use near residences or offices. Low-tech windrows require impervious surfaces and water, but can work where there is no power.
Medium	Appropriate for a wide variety of sites, including urban sites. If your site scores low on “Neighboring Uses” (i.e., close to where people work or live), and your material flow is more than a few hundred pounds or 1 cy per day, then you should give preference to higher level technologies that offer greater control of odor. If your site scores low to medium on “Site/space,” because you are not sure if there is enough space to handle the volume of material you have or if the cost of value of land/space in your area is high, give preference to medium- and high-tech methods that compost more efficiently. Because of their greater efficiency, medium-tech, aerated static pile systems are especially valuable for covered sites or inside buildings or at sites where turning piles with loaders or turners is not practical.
High	Appropriate for a wide variety of sites, especially sites, where the proximity of other activities warrants greater emphasis on odor control. Potentially a good choice for raining locations, where composting should be enclosed but no building is available or the cost or effort of building would be prohibitive.

This section takes a look at the variety of “resources” used to make compost, with particular emphasis on items like equipment, labor, and skills. One caveat: many clever people have used some pretty amazing things to make compost, such as silos, utility vaults, shipping containers, and cement mixers. It would require more space than we have here to describe all the creative options. Instead, we have focused on more conventional uses for equipment and labor in composting. But don’t let that stop you from being inventive. The solution must meet the technical and economic criteria for effective composting, but after that it is imagination and innovation that can make the difference between failure and success.

Types of Resources

It has been said before, but it bears repeating: the major work of composting is done at the microscopic level. We can’t see the billions of microbes consuming, reproducing, and expiring as they produce earthy, rich compost, but they are nonetheless a resource that we can fritter away or work to optimize. The resources we discuss here—equipment, labor, and skills—are used simply to optimize the growth of composting microbes.

Many types of equipment are used at compost facilities. Machines are used to grind, chip, shred, size, mix, moisten, aerate, turn, fluff, screen, blend, and bag the compost materials. Human labor can be used just as well for these same purposes, just ask gardeners who make great compost in their backyard with a few hand tools.

However, on the institutional scale we are talking about, there is just too much material to handle. Machines and other equipment is needed to help make the human workers more efficient. The challenge for managers is to make wise choices about human and mechanical labor, to balance the capital, operating, and maintenance costs of equipment with the wages, benefits, and other costs of human labor to get the most work done for the least cost.

Finally, let’s talk briefly about skills. Knowledge and experience about composting is another valuable resource for making compost. Obviously, higher skill levels result in better compost, made more efficiently. But skills and training, especially as it relates to monitoring and managing compost processes, cost money too. Automated composting systems or contracted professional services can fill in where skills are lacking. They can also help in situations where turnover is high.

How are Resources Used?

1. Preprocessing activities

As described in earlier sections, much work can be done before composting begins to make certain the process will occur fast and efficiently. Examples include:

• Collection and separation

• Sizing (screening and/or grinding, shredding, chipping)

• Feedstock mixing and water make-up

• Pile or windrow building

2. Composting

During the compost phase, resources are used to maintain optimal conditions for the microbial populations. Equipment choices for some of these include:

• Passive or active aeration—blowers or fans and piping. Sometimes durable piping can be used multiple times; otherwise, new piping is used for each new pile, and the old is recycled or disposed.

• Turning and mixing—front end loaders, windrow turners, or a variety of engineered turning systems can be used for this purpose. Also drum-style composters use the turning action of the drum to physically turn and aerate the composting materials.

• Water make-up—water trucks, tanks, or spray systems can help to maintain proper moisture.

3. Postprocessing activities

Post-processing is sometimes overlooked in compost planning, but it can be critical to effectively using the finished compost product. Examples of how resources are used in these phases include:

• Refining (screening)—Screens are used to remove the large particle size material that remains after the active composting phase.

• Curing—Loaders combine and turn curing piles and sometimes blowers are used to maintain aerobic conditions in curing piles.

• Product mixing—A front end loader or any of wide variety of mixers can be used to blend the compost with other materials if the end use requires.

• Packaging, bagging, or other storage and handling

Table 7.1 shows how different kinds of equipment you may already have can be used for composting. Don’t forget to use your own knowledge of composting to find solutions of your own.

Table 7.1 Equipment Options

Front End loaders	Front end loaders are likely the most versatile pieces of equipment at a compost site. It is often the first, and occasionally the only, piece of equipment purchased. Front end loaders are used to move materials, build piles, turn piles, and move compost to places where it will be used. Though they have smaller buckets, tractor loaders or skid-steer loaders are popular at some operations because of their maneuverability. Skid-steer loaders can be fitted with grapples, bucket screens, and other attachments, offering a range of flexibility preferred by small-scale operators.
Conveyors	Conveyors can also be used effectively to move materials at a compost facility. They are used to lift material up to a raised screen and can even be used to make piles for composting or storage. They are most often used in combination with loaders, but for a small operation, a conveyor moved and loaded by hand could be used instead of a loader.
Chippers	Used by tree service companies, chippers make turn brush and tree limbs into mulch or bulking material for composting. Their use is fairly limited to brush or tree by-products.
Grinders	Tub grinders and horizontal hammermill grinders use swinging hammers to grind or bash a wide range of materials. Yard and garden trimmings, brush, food by-products, cardboard, and wood scraps represent just some of the possible feedstocks that can be processed with this equipment. Such grinders are very popular among compost producers, and in recent years, models for the small- to medium-scale compost facility have come to market. Replacing dull hammers is one of the major maintenance expenses of grinders.
Shredders	Shredders contain sets of counter-rotating blades or knives that cut materials into predetermined sizes. They can also handle a wide range of materials, both wet and dry.
Pulpers	Pulpers have a limited but very effective use in preparing food scraps and paper diningware into compost feedstock. Like those manufactured by the Hobart or Somat companies, pulper grind food scraps and remove a significant portion of the water content of the scraps.
Mixers	Agricultural feed mixers or mixers designed for biosolids composting are also being used for composting operations at institutions and campuses. Mixers are used to create a homogeneous mixture, which is particularly important for static pile methods that won’t be mixed after building the compost pile. Mixers offer a limited ability to grind or mash feedstock materials, so they are most often used in combination with a grinder or pulper.
Manure spreaders	Conventional agricultural manure spreaders are also used to mix materials, while at the same time building a pile or windrow.
Moisture	Moisture is typically provided by sprinklers, drip hoses, sprayers, or water trucks.
Aeration	Active aeration is typically provided by standard types of blowers and fans and off-the-shelf plastic piping.
Compost turners	Not likely something you have just laying around, compost turners are one of the specialized types of equipment used for windrow-style composting. Turners come in many styles and sizes to meet any particular need. To save costs, some operators have modified old highway snow blowers for use as compost turners.

Labor Versus Equipment

The choice between using human labor and skills versus greater mechanization can be difficult. Equipment is expensive to purchase or lease and maintain. But after adding together wages, benefits, taxes, and insurance, labor is costly too. The exception would be those organizations that have access to less costly labor, such as student labor or prison labor. This is why such organizations have often chosen more labor-intensive low-tech composting methods in the past.

For organizations that pay “market rates” for their labor, even basic-skill labor, it makes sense to use available equipment to improve the efficiency and effectiveness of your workers. For example, material handling has big impact on efficiency/cost. Especially before and after composting, handling materials can be time consuming, which raises overall costs. Moving materials as quickly and as efficiently as possible (e.g., with loaders and conveyors) is critical to long-term success.

For another example, consider windrow turning. If your operation handles large volumes of material, say more than a few thousand cubic yards per year of raw materials, the potential benefits of choosing specialized turning equipment increase. One operator in a specialized windrow turner can turn and aerate compost 10 to 20 times faster than in a front-end loader, and the turner will do a better job.

Once you make the decision to acquire needed equipment, you should consider how to balance the capacity limits of different pieces of equipment with your processing needs. Equipment capacity is often measured in terms of the number of cubic yards or tons that can be handled or processed per hour. To make the most efficient use of equipment resources, it makes sense to match as closely as is reasonably possible the capacities of all the different pieces of equipment.

Also consider the need for back-up systems. As you plan your need for resources and equipment, consider what processes would be most affected by equipment breakdown and consider the issues and costs involved in planning for back-up systems or for diverting feedstocks when equipment breakdown prevents storage or processing.

Trade-offs

Many trade-offs are made as operators consider the use of various resources. Along the way, operators must consider what resources are needed and what’s available and then change those two things to reach a balance of start-up and annual costs. Examples of these trade-offs include the following.

• Human labor vs. mechanization—The cost of labor has tremendous impact on annual operating costs. Where low-cost labor is available, it makes sense to make the most use of it.

• New vs. existing vs. rented equipment—This is a particularly challenging question. New equipment costs more up front, but will likely have lower maintenance costs and may fit the application more exactly. On the other hand, existing or rented equipment is less costly up front, but may be more costly to maintain or may not meet the process specification as closely.

• General or multipurpose vs. specialized equipment—Another tricky question. General, off-the-shelf equipment may serve many purposes at the compost site and may be less expensive to buy and maintain. Specialized equipment, though, may offer greater production or efficiency. Because of its cost, specialized equipment will more likely be used where greater volumes of material are processed.

• Management/monitoring of low vs. high technology—Lower levels of technology can require more monitoring and skill in composting than more automated high tech systems. The skills required to effectively manage lower tech systems can be gained through training/experience, which costs money. Just one more consideration in the balance of human and mechanical resources involved in composting.

Scorecard

RESOURCES

Technology

Commentary

Minimal

Availability of low-cost or “free” labor favors minimal- or low-tech methods.

Low

Availability of existing, general purpose equipment, such as a loader, mixer, or manure spreader, favors low- to medium-tech options.