Saskatchewan Waste Reduction Council

Municipal Yard Waste Composting


Composting: the Process and Product

Underlying Scientific Principles

Alternative Composting Methods

Two Versions of the Windrow Method

Grass Clippings and Wood Wastes

Facility Siting and Preparation

Use of Finished Compost


Leaves, grasses and other plants, which fall to the floor of a forest, prairie or woodland, slowly decompose and eventually become part of the soil. The nutrients that were in the dead plants then become available to the living plants, closing the cycle of growth and decay.

In contrast, leaves, grass clippings and other yard waste collected in populated areas are a waste management problem. Municipal yard waste can also decompose, as in the forest, returning the nutrient-rich organic residue to the soil. This cycle can be accomplished economically and quickly through a simple composting process.

Yard Waste as Municipal Solid Waste
Municipal waste collected routinely from households includes a mixture of paper, glass, plastic, metal, yard waste and miscellaneous materials. Unlike other household wastes, yard waste--grass clippings, leaves, garden wastes, prunings, tree trimmings and brush--occurs seasonally. In summer and fall, yard waste may account for 33 to 50 per cent of the residential waste collected and may comprise 10 to 20 per cent of the annual total.

Since yard waste occurs seasonally and is often raked, bagged or bundled separately from other household wastes, it can be collected separately. Because these materials readily decompose, they can be easily recycled by a relatively uncomplicated composting procedure. The end product of the process is compost, a valuable organic amendment for soil.

Alternatives for Managing Yard Waste
There are two major alternatives for management of municipal yard waste: composting and landfilling.

Composting -- The objective of yard waste composting as a solid waste treatment process is to reduce the mass and volume of the waste materials, diverting them from landfills, while converting the yard waste into a useful finished product for horticultural or agricultural use. The elimination of weed seeds and any plant disease is also desirable.

Generally, the biggest economic advantage of composting is avoiding disposal costs charged for landfilling. Additionally, there are usually savings in hauling distance, waiting time and vehicle maintenance. The compost produced may be used as a substitute for mulch or topsoil in municipal landscaping, thereby reducing purchase costs. Compost can also be distributed to residents as a reward for their co-operation in the composting program or may have some commercial value for sale as a product.

From an environmental perspective, composting saves valuable landfill space while adding beneficial humus and nutrients to soil. As a visible, community-sponsored recycling activity, municipal composting creates a positive image and may encourage participation in other recycling programs.

Composting can be both an economically and an environmentally sound alternative for handling yard waste. However, to fully realize these benefits and to avoid some of the potential problems, care must be exercised in selecting a site and designing and operating the composting facility.

Landfilling -- With the recognition of the need for environmental controls at landfills, the cost of this waste management method has increased dramatically. Siting of new landfills has become extremely difficult and landfill capacity has been sharply decreasing. Burying yard waste in landfills uses up this limited capacity unnecessarily.

As the number of remaining landfills continues to decline, the hauling distance and time will increase for many communities. Landfills also increase maintenance costs for the trucks which are used on-site: tires, transmissions, fuel tanks, hydraulic lines and other components endure a lot of wear and tear.

Ironically, once yard waste is placed in landfills, the biodegradability that makes it suitable for composting becomes problematic, adding to the gas, leachate, and settling that landfills typically experience. Thus, landfilling of yard waste is expensive and contributes to environmental problems.

Go to top of page

Composting: the Process and Product

Composting -- the Process
When biodegradable organic materials containing sufficient moisture and nutrients are placed in a long pile (a windrow), a natural process of decomposition will occur. Microorganisms, mainly bacteria and fungi, begin to grow rapidly on the organic materials, using them as a food source and decomposing them. Because the microbes are not 100 per cent efficient, some of the chemical energy stored in the organic materials is wasted and released as heat. Thus, the material heats up through the intense metabolic activity of the microorganism. A large enough windrow will act as an insulator, retaining heat and leading to an increase in temperature. As the readily biodegradable food supply is exhausted, decomposition is mostly completed, growth and heat generation slow down, and the windrow cools.

Composting is the process which controls decomposition of biodegradable organic waste by providing an optimal environment for microorganisms. It has been used for many years for treatment of agricultural wastes and, more recently, for treating sewage sludge, certain industrial wastes, yard waste and other elements in the municipal solid waste stream.

Composting -- the Product
As composting progresses, the original material becomes less recognizable, although certain components, such as twigs and small branches, persist longer than others. The material darkens, acquires a granular texture, increases in water-holding capacity, and eventually develops the pleasant odour characteristic of freshly turned soil. Compost bears little resemblance to the original starting material.

Incorporating compost into soil increases the soil's nutrient content and water-holding capacities. It makes soil easier to cultivate, reduces erosion, and acts as a buffer against extremes in pH, fertilization, and temperature.

Go to top of page

Underlying Scientific Principles

Quite simply, composting is the speeding up of a natural biological process. Much can be learned by actually managing a compost operation, but an understanding of the underlying scientific principles is useful.

Microorganisms found on leaves, grass clippings and other wastes initiate the composting process. As composting progresses, new types of microbes, insects, and earthworms, among others, migrate to the windrow and continue the decomposition process. Inoculants, which introduce the proper microorganisms, are commercially available, but experience shows that additives need not be purchased for yard waste composting. Once a composting operation is established, finished compost from a previous year can be used to inoculate new windrows. In fact, this method of inoculation is highly recommended.

Water is essential for biological functions and composting is no exception. Initial dryness will slow the composting of leaves and should be avoided. To discourage dryness, windrows might contain grass clippings mixed with leaves. Since a triangle-shaped windrow composed mostly of leaves sheds water somewhat like a shingle roof, application of water to the surface does not effectively wet the interior material. Adding water before windrow formation ensures adequate moisture throughout the windrow. An initial moisture content of at least 50 per cent (wet weight basis) is recommended. We have found that the addition of water on a regular basis is essential on the prairies because of the dry climate. Therefore, locating your compost site near a good water source is essential. A useful rule of thumb is to keep materials about as wet as a damp sponge.

Yard waste can be excessively wet, causing oxygen-poor conditions and lowering the internal temperature of the windrow. Instead of controlled decomposition, wastes ferment or rot, leading to odour problems. This condition is often self-correcting, as excess water drains or evaporates from the windrow. Depending on weather conditions prior to collection, leaves might be sufficiently moist upon receipt, but this cannot be relied upon in routine operation. In general, it is better to start with a windrow that is too wet than to risk dryness.

Composting is basically an aerobic process (requiring oxygen), although anaerobic (without oxygen) conditions also may occur. A 5 to 15 per cent oxygen content is ideal. Most of the heat produced in composting results from the consumption of oxygen by microorganisms and production of carbon dioxide and water. Because the windrow must be sufficiently porous to allow oxygen to enter and carbon dioxide to escape, materials should be placed loosely in the windrows, and compaction should be avoided.

Compost organisms cannot tolerate highly acidic or highly basic conditions. During the initial stages of normal decomposition, the compost often becomes acidic due to the formation of organic acids. These acids are soon converted by the decay organisms, and the ph returns to a more neutral range (about six to eight). If the ph is lowered too much, a neutralizing agent such as lime may be necessary. Generally such additives will not be necessary unless large quantities of acid-producing materials such as pine needles are regularly composted.

Carbon/Nitrogen Ratio
The composition of the compostable organic matter significantly affects the rate at which it will decompose. Of particular importance is the ratio of the nutrients carbon (C) and nitrogen (N) available to microorganisms. A desirable C/N ratio for plant waste composting is about 20-30:1. Substances with very high C/N ratios (i.e., having much more carbon) decay very slowly and may not compost properly or completely. Those with low C/N ratios are subject to loss of valuable nitrogen due to excessive volatilization of ammonia, giving the smell of manure. Generally, the carbon and nitrogen content of materials can be judged by appearance: fresh green vegetation, such as grass clippings, is high in nitrogen, while dried brown vegetation is usually higher in carbon. Inclusion of fresh grass clippings in a leaf compost windrow provides a valuable source of nitrogen for microbial activity, thus speeding decomposition. Table 1 shows the C/N ratios of some common organic wastes.

TABLE 1. Carbon/Nitrogen ratios of common organic wastes

Waste Type C/N Ratio
Grass clippings (fresh) 20:1
Leaves (fresh) 40-80:1
Weeds (fresh) 25:1
Leaves and weeds (dry) 90:1
Hay (dry) 40:1
Straw (dry) 100:1
Sawdust 500:1
Wood 700:1
Manure 20:1

The temperature of the compost windrow reflects the balance between heat generation and heat loss to the surrounding air. The rate of heat generation is a function of factors such as temperature, moisture level, oxygen, and nutrients. The rate of heat loss is a function of factors such as ambient temperature, wind speed, and windrow size and shape.

Temperature is a powerful determinant of the rate of decomposition. Properly decomposing wastes will experience a significant rise in temperature over time, followed by a gradual decrease until decomposition is nearly complete. The temperature increase is caused by increased biological activity as decay organisms grow and multiply. Temperatures of actively composting windrows can reach 70oC or more, but generally range between 45-55oC. Internal temperatures should reach at least 45oC for several days to ensure that pathogens, insect eggs and larvae, weed seeds and other undesirable organisms are killed or rendered ineffective. Precise control and monitoring of temperature is usually not essential for yard waste composting. However, if the windrow does not heat up, decomposition will proceed slowly, or not at all toward the outside of the pile.

Windrow Size and Turning
Control over temperature and oxygen content can be achieved to some extent through windrow size and turning operations. The need for oxygen must be balanced with the need for heat conservation. Adequate oxygenation requires small windrows to minimize the distance to the windrow interior that the air must penetrate. In contrast, the need for heat conservation, especially in winter, requires large windrows which provide greater insulation. However, windrows that are too large may result in anaerobic (airless) conditions. These requirements can be reconciled in part through management of windrow size and by turning. It is essential to turn the pile at regular intervals to maintain optimum oxygen levels in the pile. However, turning the pile releases substantial heat into the air. So, the art of managing windrows is to turn often enough to keep oxygen levels high but not so often as to cause excessive cooling of the pile.

Go to top of page

Alternative Composting Methods

Different methods for large-scale yard waste composting may be considered. The method most appropriate for a given application will depend mainly on the site selected, although the availability of equipment and labour are also factors.

"No Tech" Composting
As mentioned earlier, communities with a farmer, nursery or landscaper nearby who will accept municipal yard waste for either composting or direct land application will have the easiest and cheapest option available.

Communities with large tracts of rural land have the option of transferring yard waste to an area where it will slowly decompose over many years (usually five or more), as happens in a forest or grassland. This method is not actually composting since the rate of decomposition is not controlled, but it is an economical alternative to consider if land is available which is remote, well-drained, and meets the standards of Saskatchewan Environment and Resource Management (SERM). Yard waste can be dumped in unformed piles, but it must not be piled in bags. Further, it is important to monitor incoming loads to ensure that the area does not become a dumping ground for other wastes. Although this method does not compost yard waste, it must still be conducted in a nuisance-free manner (i.e., no problems with run-off or odour). Communities planning this approach to yard waste disposal should notify SERM.

Windrow Composting
In rural Saskatchewan, siting of a "no tech" composting area is often possible, but in more highly populated areas, where composting space is limited, a faster process is necessary. This involves closer regulation of moisture content, oxygenation, and temperature, commonly accomplished with the basic windrow method. Yard waste is formed into windrows which are periodically turned with a front-end loader to promote faster decomposition, a process typically occurring over a period of 12 months.

Since windrow composting is appropriate for most Saskatchewan communities, a detailed description of this process is outlined in the next section.

Static Piles with Forced Aeration
If limited space is available and completion of composting in less than one year is desired, a higher level of technology is required. Simply turning the windrows more frequently (for example, once per week) will produce a finished product in under six months. While costly specialized windrow turning machines may be used to increase turning efficiency, this actually requires more space because the starting windrow size is limited by the machine's working height and width.

An ideal rate of decomposition requires near-optimal levels of temperature and oxygen. This also minimizes odours because the putrescible (odour-causing) materials are quickly decomposed, and anaerobic conditions are minimized. Rather than turning the windrows, air may be blown or drawn through the piles by using perforated pipes and either a forced-draft fan or an induced-draft fan. Forced air systems primarily have been used in sewage sludge composting projects in which the compost is fairly moist and homogeneous. Forced air systems require careful initial processing to ensure that materials are properly mixed and have a suitable moisture content and porosity. Careful site preparation is also necessary. Once implemented, a successful forced air system may result in reduced costs and other benefits.

The forced air approach is advantageous because large windrows can be formed initially, using less space while avoiding extensive anaerobic conditions because of good aeration. Therefore, serious odours and slowed decomposition do not occur. Another benefit of forced aeration is that, as a result of rapid decomposition, the compost process can be completed within a year.

A disadvantage of forced air composting for yard waste is that these systems do not work well with grass clippings, which tend to clog the air holes of the piping. As well, the requirement for electric power at the composting site is a drawback.

In-vessel Composting
In-vessel systems have been successfully used for composting sewage sludge and municipal solid waste, but this technology has not been directly applied to yard waste composting. During in-vessel composting, incoming material is often shredded, then mixed with a bulking agent or nitrogen source, regularly turned in a digester designed to foster rapid growth of microorganisms, and then windrowed to "cook" for a short period, usually a few weeks. Although this method greatly reduces composting time, the high capital equipment and operating expenses make it an unlikely choice for composting yard waste.

Go to top of page

Two Versions of the Windrow Method

A successful municipal composting operation will ultimately be customized to the community's resources and needs. While the basic principles of windrow composting remain the same, the size of the windrows, their placement on site, the schedule of turning the windrows, and the length of the composting cycle can vary greatly. The two approaches described below have been successfully implemented by municipalities. Variations of the basic windrow method are already used by many communities. The second method described was developed at the community compost site in Saskatoon, run by Services for Seniors. Municipal planners are encouraged to use these descriptions as a guide to various methods that can be combined and expanded upon, according to the unique needs of the individual community.

Basic Windrow Method -- Minimal Effort
If an area that is well-isolated from sensitive neighbouring land uses is available, a very low-cost approach to yard waste composting is possible. This method differs from the "no tech" approach only in that the yard waste is formed into windrows and periodically turned. Even this minimal effort will produce finished compost faster than the "no tech" approach.

Materials brought to the site are formed immediately into large windrows using a front-end loader. (Recommended windrow sizes are discussed later). Once each year the windrow is turned and reformed. An additional windrow is constructed with the new materials each year. After three years, the material in a windrow is usually sufficiently stabilized to be used as compost. Inclusion of grass clippings in the windrow will shorten composting time by providing additional nitrogen and moisture.

With such minimal technology, ideal conditions for rapid composting are not achieved. Much of the windrow remains anaerobic for a full year between turnings. Odour can be expected prior to the first turning, and serious odours will probably be released during the first turn - by the second turning, odours have usually diminished. Because of these odours, an extensive buffer zone is required: a distance of one kilometre or more to sensitive neighbouring land uses is recommended.

The obvious advantage of the basic windrow method is that it is extremely inexpensive. It requires the use of a front-end loader only a few hours each year. Because of the large buffer zone needed, a disadvantage of this approach is the extensive total area required, although only a small portion is actually used for the composting. This method might be feasible in a wooded area, so that only a small clearing would be required, or at an isolated industrial site, public works yard, landfill or nearby farm field.

The Prairie Method
In some American states, yard waste has been banned from landfills for a number of years and it is mandatory for each county to have a yard waste composting program. Several states have published manuals on yard waste composting from which the following recommendations have been adapted. Ultimately, all yard waste can be successfully composted, but it might be advisable to begin with select sources of materials, adding new materials as experience is gained and the needs of the community are better understood. The inclusion of grass clippings and other yard waste in the composting system will increase the quality of the finished product as well as the speed of the process.

Balancing the need for oxygen flow with the need for a high enough temperature is a factor when determining the size of the windrow. The simplest way to achieve the ideal temperature range for composting is to build windrows large enough to conserve sufficient heat, but not so large as to overheat or cause compaction. On the other hand, smaller windrows ensure adequate oxygen flow. Unfortunately, no single windrow size completely reconciles these conflicting goals. The desired conditions can be approached by starting with moderately sized windrows (three to four metres high by four to five metres wide), then combining two windrows after the first burst of microbial activity, which lasts approximately one month. To avoid anaerobic conditions, windrows should be no higher than six metres. However, Saskatchewan's colder climate requires somewhat wider windrows of three to four metres high by seven to eight metres wide.

With this approach it is possible to produce a thoroughly decomposed (finished) yard waste compost in six to eight months. If windrows are initially formed before freeze up, the compost will be ready for use in spring, the time of peak demand for the product. Slight odour may be a by-product early in the composting cycle, but this is not usually detectable beyond 50 metres from the windrows. After 10-13 weeks, large curing piles can be formed around the perimeter of the site, freeing the original area to accept new materials.

1. Site Preparation
Prior to each collection season, the site must be readied to allow truck access and front-end loader operation. Delivery of the collected waste is the one aspect of the operation with little scheduling flexibility. Once leaves are collected, they must be formed into windrows promptly, (sections 2-4 below). Therefore, it is critical to avoid operational bottlenecks, where, for instance, an area becomes so muddy that trucks get stuck trying to drop off their loads.

The yearly site preparation should include regrading and road maintenance as well as removal of refuse and debris from the previous year's operation. This step will require a few days work at most. Site preparation should be scheduled any time after the active site has been cleared of the previous year's materials, through formation of curing piles, but before the new collection season begins.

2. Receiving and Sorting
It is recommended that trucks dump their loads of leaves in a staging area, rather than trying to form windrows directly. Although a staging area involves additional labour, its use is justified for several reasons:

Windrow formation must take place as soon as possible after yard waste is received. If freshly dumped waste is allowed to sit for more than a few days in the staging area, odour problems may develop. Some minimal supervision may be required to prevent dumping in undesired locations. Also, a record of the amount of waste delivered should be kept: a daily tabulation of the number of loads for each individual truck of known capacity may be an effective accounting method.

At most yard waste composting facilities, the waste is delivered in bulk. However, some sites may find it necessary to accept at least a portion of their capacity in plastic bags. These bags pose considerable extra problems but can be handled successfully. The bags should be dumped in a separate portion of the staging area where, in a very labour intensive process, they must then be slit open and emptied. (Some American operations use community labour service -- a Canadian equivalent might be the Fine Options Program). Any trash must be separated and disposed of along with the bags.

A difficulty with collecting bagged leaves is the odour released from some of the bags upon opening. One alternative is to open and dump the bags directly into the hopper of the collection vehicle during the collection process. While this practise slows the collection crews, it prevents double handling of the bags and provides for greater control over feedstock quality. Programs which use a drop-off site for residents should require participants to unbag their own wastes in order to take plastic bags back home for reuse. Drop-off sites should have some method for monitoring incoming loads to avoid contamination of windrows with other wastes.

3. Wetting
Due to the normally dry climate of the prairies, wetting of the yard waste is required during much of the collection season. Adequate wetting can only be achieved prior to or during windrow formation, or when windrows have been opened up for turning or other purposes. Because most of the water applied to the outside of a windrow will be shed by the waste, the water should be sprayed on the yard waste as it is broken apart by the loader in the staging area, and/or as it is placed in the windrows. Approximately 80-90 litres of water will be required on average per cubic metre of yard waste collected. Less formally, the rule of thumb is that it should be possible to squeeze a few drops of water from a fistful of the leaves.

The need to add water can be reduced or eliminated by forming windrows with flat or slightly concave tops. This will facilitate the capture of precipitation and induce seeping of moisture down through the windrow.

4. Forming Windrows
Once the yard waste has been dropped in the staging area, the front-end loader can be used to break apart and spread the compacted materials to aid wetting. The front-end loader can then be used to place the uncompacted waste in windrows.

Initially, the windrows can be three to four metres high by three to four metres wide. Any convenient length can be used. (Note: windrows that will be left over winter should be three to four metres high by 10-15 metres wide to help retain heat in Saskatchewan's cold climate.) To conserve space, two windrows can be formed side by side, with only one metre between. Remember to allow sufficient aisle space between pairs of windrows for the loader to maneuver when turning the piles.

Neatly formed windrows with well maintained aisles give a professional appearance to the facility, while messy windrows give the impression of a "garbage dump." Care should be taken so that equipment, especially the loader, does not drive up on the windrows, compacting them. Loosely piled windrows are required in order to maintain adequate air penetration.

5. Monitoring Decomposition

Compost windrows should be monitored closely to ensure that decomposition proceeds properly and does not create a nuisance. Monitoring should consist of daily temperature readings at several points in each windrow and bi-weekly inspections for moisture content, physical appearance and internal windrow odours.

Daily temperature readings are especially good detectors of problems before they become major. Sharp drops in temperature, for example, may indicate decreasing moisture content or the onset of anaerobic conditions. Failure of temperatures to rise to 50-75oC shortly after windrow construction may indicate a poor carbon/nitrogen ratio or improper moisture content. In both these cases a physical inspection of the windrows should reveal the source of the problem. An anaerobic pocket, for instance, might be tightly packed, emit unpleasant odours, be very wet, and possibly have a green or shiny black appearance. Prompt aeration would prevent the problem from becoming a major nuisance. (Further troubleshooting is discussed later).

While thermometers are available for monitoring temperatures, experienced compost program operators often find that physical inspection of windrows is adequate to determine if the material has sufficiently heated up.

6. Turning Windrows
In the spring, each windrow should be turned as early as is practical (March or April). Turning mixes the material, redistributes the moisture in the windrow, oxygenates the interior, and exposes the cool exterior to the hotter internal temperatures. This results in an increased rate of decomposition and improved destruction of any pathogens and weed seeds. For adequate oxygenation, maximum mixing and fluffing is desired during turning. Additional water may be added at this time if the material is too dry, although every effort should be made to provide sufficient water initially.

Additional turnings throughout the summer increase the composting rate and product quality. Turning at least once every week to 10 days is recommended to maintain high temperatures.

7. Combining Windrows
After approximately one month, much of the initial oxygen demand of the pile will have been exerted and the windrows reduced to about half their original size through decomposition and self-compaction. At this point, two windrows can be combined to form a single one of about the same size as each of the initial windrows. Combining the windrows will help conserve heat during colder weather. Portions of the centre of the new, combined windrow may go anaerobic temporarily, but significant odours and acidification are not expected because much of the readily degradable material has already been consumed by the microorganisms. Combining should be done by moving and turning both windrows, rather than placing one on top of the other, thereby achieving the maximum degree of mixing and fluffing.

8. Curing
Using the Prairie Method of composting, much of the product will not be completely stabilized by the end of the summer, yet the composting area must be cleared to allow for site preparation for the next year's collection. This is not a problem since the material is now well decomposed, has little oxygen demand, and is unlikely to produce odours.

At this time, therefore, the windrows can be moved and formed into a large curing pile on the perimeter of the site. This operation provides additional turning and mixing of the compostable material. To conserve space, the curing pile may be as large as desired, taking care not to compact when forming. Combining several windrows into a single pile exposes a relatively small surface area to drying and freezing conditions. Further weed and pathogen destruction is achieved at the temperatures reached within the large, well-insulated curing pile. This material should be well stabilized by the following spring but may be left in place longer if convenient.

9. Shredding or Screening
Once composting is complete (post-curing), shredding or screening is a final optional step to improve the physical quality and appearance of the finished compost. This process screens any uncomposted leaves, branches, rocks, plastic, and other extraneous materials and breaks up clumps. Organic "rejects" may be composted for an additional period, then shredded to minimize the amount requiring disposal. Shredding and screening is quite labour intensive. Leaf compost can be processed at only about half the rated capacity of the equipment. Because shredding or screening will proceed more rapidly if the compost is not too damp, moist material can be spread out for a day or two to dry.

The major advantage of using a shredder is that it yields a more uniform and debris-free final product. It also can be used to mix finished compost with soil. Disadvantages include the labour and equipment requirements, the need to dispose of rejects, and, of course, the capital cost of the specialized machine. One way to reduce costs is to share a single unit among several sites or communities. This is feasible since the specialized equipment is needed only for a month or two per year, making scheduling flexible.

Go to top of page

Grass Clippings and Wood Wastes

Grass Clippings
Grass clippings represent a significant seasonal waste management problem. In some Saskatchewan communities they may account for nearly one-half of the total municipal refuse load during peak grass-growing periods.

The best alternative for grass clippings is to not bag them at all. Turf specialists recommend mowing frequently enough so that the short clippings filter through the growing grass and return their nutrients to the soil. Contrary to popular belief, this practice does not contribute to thatch. If the clippings are collected, they can be incorporated in moderate amounts in back yard composting piles or used as a garden mulch.

Since grass clippings are still green when collected, they are relatively higher in nitrogen, moisture content, and readily degradable organic material than leaves collected in autumn. They therefore decompose more rapidly, have a higher oxygen demand, and quickly go anaerobic. Since grass clippings often have a strong smell by the time they are delivered to a composting site, it is especially important to properly implement (and strictly enforce) the odour control measures discussed. Additional precautions, such as enlarging the buffer zone, also may be necessary.

Grass clippings should be incorporated into a leaf windrow before the end of the delivery day. A 50:40 ratio of leaves to grass clippings provides an optimal carbon to nitrogen ratio. (Until experience is gained, a higher ratio of leaves to grass can be used to reduce odour problems). Thorough mixing is essential: this can be done with a front-end loader combining 20-30 bucketfuls of material at a time, then forming a windrow with the mixture. Once the material has been mixed in this way, no further odour problem is expected. The partially composted leaves act as a bulking agent to improve penetration of oxygen to the grass clippings. The grass in turn speeds the decomposition of the leaves by providing needed nitrogen. The end result is a higher quality compost product ready within a shorter period of time. However, these benefits must be balanced against the increased potential for odour problems. Green weeds can be considered identical to grass clipping for the purposes of composting, but large quantities of diseased plant wastes should be excluded from compost windrows.

A common concern about using grass clippings for composting is the potential inclusion of lawn chemicals in the finished product. While there is some debate on this topic, University of Saskatchewan horticulturists indicate that most commonly used lawn pesticides degrade in six to eight weeks. Therefore, compost made from yard waste will be free of significant quantities of lawn chemicals. Further, concerns about the toxicity of materials used in agriculture usually centre on the uptake of heavy metals by plants grown in treated soil. Finished compost made from yard waste typically contains extremely low levels of heavy metals.

Woody Materials
Wood tends to decompose very slowly, making composting impractical in most cases. These woody materials should not be intentionally incorporated into yard waste composting windrows, although small amounts of incidental branches and twigs pose little problem.

Tree trunks and large branches can be cut and given away or sold as firewood, while smaller diameter woody materials can be chipped to produce a useful mulch. Communities can use wood chips as mulch or bedding for municipal landscaping, park pathways, and school playgrounds. Residents will appreciate free wood chips for use in their own yards. As well, wood chips are valuable at the compost site to form roads and all-weather work surfaces. Accidental inclusion of small quantities of wood chips into the windrow will not adversely affect the quality of the final product.

Pine Needles
Pine needles can be successfully composted if they are mixed with grass and leaves. However, since pine needles decompose very slowly, the formation of windrows containing almost exclusively pine needles should be avoided. Christmas trees should be treated as woody materials.

Go to top of page

Facility Siting and Preparation

Site selection for a municipal yard waste composting program is an extremely important decision that should be made only after careful consideration. Siting the facility should take into account factors such as proximity to residences and streams, prevailing winds, traffic patterns, and travel distance and its effect on collection equipment and labour costs.

Area Requirements
A minimum of one hectare per 1600-2100 cubic meters (one acre per 3000-4000 cubic yards) of yard waste is required for the actual composting operation in addition to a buffer zone. Volume reduction and the time required to complete the composting process are variables which influence the area required for an adequate site.

Buffer Zone
A buffer zone between the site activities and neighbouring areas will minimize possible odour, noise, dust and visual impacts. There are no hard and fast rules on the size of the buffer zone needed for composting but it is prudent to provide at least 50 meters between the composting operation and the property line. According to SERM, a minimum of 500 meters must be allowed between the compost site and any sensitive neighbouring land uses, such as residences, restaurants, hotels/motels, schools, churches or public buildings. The buffer zone may include a berm, consisting in part of finished compost, to serve as a visual barrier, help control vehicle access, and reduce noise levels off-site. A landscaping plan will enhance the appearance of the facility.

A centralized area will reduce transportation time and costs, although such sites are not always available, or practical. If residents are to bring materials to the site, the location should be convenient to encourage their participation. Often an area at the local landfill serves as an ideal site for composting, keeping in mind that access on uncrowded, non-residential, hard surface roads is preferable.

Slope and Grading
Steep slopes on site are unsatisfactory because of problems with erosion, vehicle access, and equipment operation. However, a gentle slope of about 2 per cent is desirable to prevent ponding of rainwater and runoff. Initial site preparation usually requires grading; yearly maintenance should include regrading where necessary. Windrows should run up and down rather than across slopes to allow runoff to move between windrows instead of through them. Care should be taken so that leachate does not run off into nearby streams or lakes.

An ideal composting site will have moderate soil percolation, so that ponding will not be a problem. Where percolation is poor, or where an impervious surface is used, particular care must be taken to prevent ponding. An impervious surface such as a paved site offers advantages in terms of vehicle access, equipment operation, and groundwater protection, but these advantages must be weighed against the loss of direct contact between composting materials and soil microorganisms, as well as the difficulties in managing runoff.

Water Supply
Water is essential for yard waste composting. Windrows should be formed with flat or slightly indented tops to maximize the collection and infiltration of precipitation. Water can also be supplied by using a hose from a fire hydrant or by pumping from a nearby lake, stream or well. For smaller operations, use of a water truck is practical, depending on the amount of yard waste composted.

Vehicle access to the site must be controlled to prevent illegal dumping of materials as well as vandalism. A gate across the entrance road is the minimum precaution. In some cases the entire site will have to be fenced, although pre-existing features such as streams, trees and embankments may provide partial security: an ideal site will have natural barriers on three sides. Since permanent chain link fencing can interfere with site operations, replaceable snow fencing is suggested, while a berm consisting of earth and finished compost can serve in place of a fence at other points.

On-Site Roads
Because of heavy truck traffic during the collection period, a limited road network within the site (paved, gravel, or covered with wood chips) may be desirable to improve all-weather access. A circular traffic flow pattern is advantageous at heavily used sites. The purpose of the on- site roads is to facilitate drop-off of materials and to prevent trucks from getting stuck in muddy conditions, so an extensive road network is not required. (If gravel roads are used, contamination of windrows with gravel should be avoided).

Safety Considerations
Safety measures common to any heavy machine operation should be exercised. Road layout should be designed with safety in mind, restricting public access unless citizens are to drop off materials. A ready supply of water and delivery capacity, initial wetting of leaves, and aisles between windrows are good fire precautions. Normally, a windrow of yard waste will burn poorly since the interior is wet. Thus, while vandals may be able to ignite the dry surface leaves, a major fire is unlikely.

One relatively new concern with leaf composting is the release of spores of the fungus "A Spergillus fumigatus". These spores can produce an allergic response in some individuals and can, in a few cases, cause infection in individuals with a weakened immune system, who are taking antibiotics or adrenal cortical hormones, or have a punctured eardrum. Workers having such conditions should not be assigned to the composting operation (as well as any other tasks putting them at similar elevated risk), unless a health specialist is consulted.

Public Acceptance
An acceptable site location is important in gaining public support for the project. Composting operations will be noisy at times due to the truck traffic and heavy equipment involved. Odours, flies, dust and other nuisances may occur if the operation is mismanaged, or if equipment problems cause the operation to be temporarily suspended. Consequently, the site should be located in non-residential and non- recreational areas. Communities often locate composting operations at existing or closed waste handling facilities such as landfills, transfer stations and sewage treatment plants. Public acceptance will be enhanced by an effective public information campaign.

Go to top of page

Use of Finished Compost

A plan for the distribution of the end product should be developed early in the setup of the composting facility. Centralized composting systems require that the yard waste be transported to the processing site and that the finished product be transported off site to provide room for the processing of the next batch.

While the nutrient content of yard waste compost is too low for it to be considered a fertilizer, it is a valuable soil conditioner and organic amendment which improves the physical, chemical and biological properties of the soil. Most Saskatchewan soils will benefit considerably from the increase in organic matter which compost can provide. Demand for finished compost is dependent on a number of interrelated factors: product quality, assured supply, cost, and consumer education.

Product quality involves product appearance, uniform consistency, level of impurities (foreign objects such as stones, sticks, glass, plastics, metals), and chemical composition (nutrients and heavy metals). To a large extent, product appearance is dependent on the level of impurities found in the incoming yard waste and the level of processing done to it. Grass and leaves that are free of brush and other impurities can be processed into a good quality compost using minimal technology with an adequate composting period.

Shredding and screening can be used to improve appearance, remove impurities and improve consistency, as well as reduce the length of the processing period. Assured supply is essential if finished compost is to be used on a regular basis by agencies and institutions.

Price is primarily a function of supply and demand, although it also reflects the costs embodied in the processing and marketing of the product. There is the attitude that "you get what you pay for," so if a product is free it may be considered to have no value. Poorly processed compost has little value compared to its principal competition (black dirt, peat and similar soil amendments). The closer finished compost approaches the quality, uniformity and consistency of the competition, the higher its relative value.

Consumer education is the final component of demand. As with any other product, the quality, availability and price of compost mean little if it is unknown to the consumer. Advertising through various media is needed to raise consumer awareness about composting in general.

Municipal Use
Use of compost in municipal applications will result in a cost savings to offset some of the expenses of collecting and composting yard waste. Some specific applications for compost are:

Compost also may be blended with poor soils to produce a good quality topsoil.

For most Saskatchewan communities, especially in rural and agricultural areas, it is unrealistic to expect to make any direct revenue from the sale of yard waste compost. For these communities, compost will have value in reducing municipal costs and rewarding residents for their participation in the program. Potential markets for yard waste compost include:

Giveaway Programs
Giveaway programs are usually directed at the general public and require the public to go to the composting site or to a more central location to pick up the finished compost. People are normally required to bring their own containers and equipment for loading the compost: some people bring specialized equipment to further shred the compost before loading it. Occasionally compost is left; this material is generally allowed to continue composting until the next distribution season. Some finished compost should be retained as a starter for incoming wastes.

Cost for giveaway programs is minimal, primarily involving the hiring of a site monitor whose principal duty is to control illegal dumping of incoming materials. Programs which ship finished compost to centrally located distribution sites will incur additional transportation costs.

Go to top of page

For more information on municipal composting, contact:
Saskatchewan Waste Reduction Council
#203 - 115 2nd Ave N.
Saskatoon, SK S7K 2B1
(306)931-3242, fax (306)665-2128

Last modified: December 3, 1997