Wood & Yard Waste
Recycling

Equipment Application Guide

By

Powell Clinton

EarthSaver Equipment, Inc.

TABLE OF CONTENTS

PLANNING THE OPERATION

DESCRIPTION OF EQUIPMENT

RECYCLABLE WOOD AND YARD WASTE

MARKETABLE PRODUCTS

NON-WOODY MATERIALS

REVIEW OF MACHINE APPLICATIONS

PLANNING THE OPERATION

The purpose of the following document is to help you understand the different phases of wood and yard waste recycling and identify the equipment presently being used for recycling these materials into marketable products. We begin by asking questions that must be answered before organizing a recycling facility, and then discuss the machinery.

What wood and yard waste materials will be recycled?

Yard trimmings – grass, leaves, and shrub prunings
Tree limbs
Tree stumps
Pallets
Construction wood

What non-woody materials (contaminants) should be expected?

Paper and Plastic
Ferrous Metals
Aluminum
Dirt and Rock

What marketable products will be produced?

Landscape Mulch
Soil Amendment
Boiler Fuel
Sewage Sludge Bulking Agent

What equipment is needed to produce the desired products?

Following is a list of the most common equipment currently being used for recycling wood and yardwaste materials. Depending on the size of the operation you may see all of the equipment listed or only a few pieces. After we’ve reviewed the equipment, we’ll discuss specific applications and how the equipment fits into a complete recycling system.

DESCRIPTION OF EQUIPMENT

MATERIAL HANDLING

Rubber Tired Loader:

This is the most common type loader found at recycling facilities. It is used for loading raw materials into the equipment and moving finished products around the site. It should be able to dump materials over 10’ high and ideally should be able to load finished products into 13’6” high trailers. Smaller loaders will require that you build a ramp next to your equipment. If you process pallets or crating materials there will be a lot of nails around the site so tires will have to be foam filled.

Track Type Loader:

This machine is used like a rubber-tired loader plus it can be used for crushing raw material before the shredding or grinding process. By pre-breaking the raw materials with a track machine the shredder or grinder will produce a much higher volume of finished products. Small machines will require that you build a ramp next to your equipment. The disadvantage of this machine when compared to a rubber tired loader is that it cannot move as quickly over longer distances, cannot operate on paved surfaces and there are more wear parts.

Optional Bucket for Rubber Tired or Track Type Loader:

Either of the above described loaders can utilize a special light materials bucket commonly referred to as a high-lift or roll-out bucket.  Basically the bucket is desiged so that it will lift and dump 3-4 feet higher than a standard bucket; this allows you to use a medium size loader to load semi-trailers from flat ground without building a permanent ramp.  This bucket is mentioned because in conjunction with the Rubber Tired or Track Loader it is one of the most cost efficient tools you can own in a wood recycling facility.

Track Mounted Excavator with Grapple:

This machine consists of an operator’s cab and a long boom (usually 25’) with a grapple on the end, mounted on top of a rotating platform and Caterpillar style tracks. It can be used to crush raw material, pile raw material, sort raw material, and feed raw material to the grinding equipment. It is mobile so can also be used for many other support activities such as shearing stumps and logs using an optional shear attachment. It is not practical for handling final products that are normally small in size.

Knuckleboom Loader with Grapple:

This machine consists of an operator’s cab and a long boom (usually 25’) with a grapple on the end and mounted on top of a rotating platform. It is usually installed on a hammermill grinder or a shredder and is used for self-loading raw materials into the equipment. A benefit of knuckleboom loaders is that they can be used to sort through mixed materials and remove large items you don’t want to process, such as large stumps or tires prior to putting them in the machine. Don’t plan on using a knuckleboom to sort out small items; the operator is usually looking through a dusty window and visibility is not that good. Anytime a knuckleboom is used the operator station should be mounted high enough so that the operator can see into the infeed hopper of the shredder or grinder. This allows the operator to see and remove undesirable items, or shut down the machine, before they have a chance to damage the grinding mechanism. Also, it is helpful if the operator station rotates with the boom so that the operator is always facing the work area; this will reduce operator fatigue and improve safety.

Knuckleboom loaders are rated by the length of the boom, the lift capacity at 8’ or 10’, and at full extension.

SIZE REDUCTION

Stump Shear:

Use to reduce the size of large logs and stumps to a size more easily handled by a hammermill grinder, normally under 18” diameter, and to loosen any dirt or rock attached to stumps. It is normally mounted on a track type backhoe in place of the bucket, and can handle dirt without excessive wear.

Slow Speed Shredder:

Use for reducing the size of large diameter wood and stumps to a size more easily handled by a secondary grinder, and to loosen any dirt or rock attached to stumps. Although the name shredder is used to describe all slow turning machines that are used to shred materials, they are not all alike. One type is designed with close tolerances and is used to shred finely sized materials, 1” and less, and therefore can’t handle dirt without excessive wear. Another type, designed to shear, tear and rip, is not intended to produce particles smaller than 3” to 4” in length and can therefore accept dirt and small rocks with little adverse effect. For wood and yard waste applications we only recommend using a machine design that produces large particles, ones that must be processed a second time through a hammermill grinder.

Hammermill Grinder:

Use for grinding all woody materials. Hammermill grinders normally include horizontal feed grinders and tub type grinders. Do to the high rotation speed of the grinding mechanism they can be set up to produce a wide variety of finished size material and are commonly used to produce landscape mulch or boiler fuel products. They are not as tolerant of dirt and rock contamination as slow speed shredders and small amounts of non-woody materials substantially increase wear to the grinding mechanism. Due to the high production rates experienced with hammermill grinders some non-woody contamination and the extra repair expense it causes is often considered acceptable.

The two most popular styles of hammermill grinders are Tub Type and Horizontal Feed, and they are quite different in design and operation:

Tub Type grinders have been used in green waste recycling operations since the early 1980’s and are a dependable means of processing a wide variety of materials and sizes. The infeed hopper is basically a large tub, normally 10’-14’ in diameter that is easily loaded from the top with a front-end loader or grapple, and doesn’t necessitate the machine operator arranging raw material in any particular fashion for proper feed or operation. The operator can basically fill the tub and then leave to do something else while the machine is grinding, it isn’t necessary for him to watch the machine all the time. Tub Type grinders can normally handle material in lengths up to 15 feet and 3 feet in diameter. A disadvantage to this style machine is that due to the large open top tub and exposed grinding mechanism materials can be ejected back out of the machine if the tub is not kept full of material. This is a safety hazard if the machine is not located in an area that can be kept clear. A distinct advantage of tub type machines is in the way material is fed to the grinding mechanism; it is gravity feed, as opposed to force feed, and often the machine can be shut down for removal of unwanted materials such as a steel bar or large rock prior to any damage occurring to the grinding mechanism. On most Tub Type machines the tub can be raised to the vertical position for hammermill maintenance and for emptying the tub of its contents if necessary.

Horizontal feed grinders have become popular in the last few years as an option for operating in areas where it is not acceptable for material to be ejected out of the machine during normal operation; the grinding mechanism is not exposed in a way that will allow material to escape out of the machine. Another feature is that the feed mechanism is normally of force-feed design, resulting in a higher rate of production in certain materials when compared to other types of grinders. A disadvantage is the feed hopper itself; material needs to be arranged somewhat better, as compared to the tub grinder, in order for material to feed into the smaller opening leading to the grinding mechanism. Another disadvantage, resulting from the force-feed design, is that the operator has little opportunity to remove non-woody material such as a steel bar or large rock prior to it coming into contact with the grinding mechanism, resulting in higher wear and tear.

SCREENING

Flat Shaker Screen (Vibratory):

Used in conjunction with a Stump Shear to remove dirt and rock before the chunks of wood are processed through a hammermill grinder. It is normally fed with a rubber-tired loader following the shearing operation. Also used occasionally for final sizing of shredded wood products.  Shaker screens are designed to work primarily with rock and dirt so are normally not suitable for shredded wood products.  There are a few exceptions to this but generally they are more prone to plugging (blinding) when loaded with shreaded wood.

Flat shaker screens are sized by length and width.

Disc Screen & Star Screens:

A Disc or Star Screen is comprised of a long box with screening discs (or stars) mounted on rolling shafts that are installed close together and across the box. Pre-chipped material is put in at one end of the box and exits at the other end with the small acceptable size material falling down between the rolling shafts onto a product removal conveyor. When used following a hammermill grinder this kind of screen should effectively remove 95% of all contaminants such as plastic, paper, ferrous metals and aluminum cans from the shredded wood product and produce a reasonably clean wood chip product that can vary in size from a fine sawdust up to a maximum of 3” long by 1/2” in width. For this type sizing screen to be effective on material contaminated with paper and plastic the hammermill grinder must use product sizing screens with holes no smaller than 3” in diameter, otherwise the particles of paper and plastic will be too small for the disc or star screen to separate them properly. Acceptable size wood chips should make up approximately 90% of the total flow and rejected wood chips approximately 10%. A Disc or Star screen is sized by the width and length of the screen box, plus the number of shafts within the box.

Trommel Screen: 

A Trommel Screen is a rolling drum screen where material is put in at one end of the drum and flows through to the other end of the drum; during this action the acceptable size material passes through the wire mesh on the rolling drum and is carried away by a conveyor; oversized material passes out the other end of the drum and is usually carried away by another conveyor. The most common use of a Trommel is screening finished compost or mulch materials into two or more sizes. Trommels are the most popular screen to use when processing shredded materials that are wet or sticky because the trommel is self-cleaning and does not plug (blind) like is possible with a flat screen, and is capable of screening material to smaller unform sizes than either the Disc or Star screen.

A Trommel Screen is also effective at removing other contaminants such as paper and plastic when using screen cloth with holes smaller than 3/8”, but is ineffective removing paper and plastic if the screen holes are larger. There is a spearing action that takes place inside a trommel which will occasionally force plastic though the screen with the acceptable end product, so plan to keep all raw material free of contaminants if you are using a screen cloth with larger holes.

Trommel Screens need to be sized by the square footage of usable screen cloth installed on the drum. The length and diameter of a drum is not always the correct indicator of production capability.

COMPOSTING

Windrow Turners:

A windrow turner is used to aerate windrows of shredded and compostable materials. It works like an above ground roto-tiller to mix air and water into the windrow. Windrow turning is required in order to maintain microbial action within the windrow and to cause decomposition of the shredded material. There are a number of windrow tuners available which work with varying degrees of efficiency. The largest machines are self-contained, have their own power supply and are operated from an operators cab on the machine. Less expensive machines are pulled by a farm style tractor and powered by an engine mounted on the turner or by the tractors PTO. The appropriate size for a compost turner will be dictated by the size of your operation; the size of your property, how tall you want to make your piles and how much material you will have at any one time. The compost turner’s efficiency will dictate how often you must aerate the windrows and how many times you must turn them before composting is completed. Some machines turn an entire windrow in one pass while others turn one-half of the windrow per pass.

Compost turners are identified by the size of the windrow they’ll turn, the length of the rotating drum in the middle of the machine and how many cubic yards per hour they turn.

Water Application System:

Compost needs a lot of water and a water application system will be necessary. Common systems may include one of the following: a water tank pulled by the turner; a water truck to spray or dump water on the windrow prior to turning the windrow; long hoses that run more or less continuously on the windrows; and more elaborate systems including permanent but mobile overhead watering.

RECYCLABLE WOOD AND YARD WASTE

The following items are common to wood and yard waste recycling operations. Because of the amount of equipment required to recycle all of these items you may see many operators who limit their recycling to only one or two items listed.

What wood and yard waste materials will be recycled?

Yard trimmings are the easiest to process of all the materials listed and make up for approximately 15% of the total solid waste stream in the US. They are by far the largest portion of recyclable wood and yard waste materials available. They are generally small in size, less than 2” in diameter, less than 4’ long, and are easy to handle. They consist of grass, leaves, brush and tree trimmings. Hammermill grinders have proven to be the most efficient machines available for processing these materials into smaller particle sizes and into final products.

Tree Limbs:

Long tree limbs are difficult to handle and require grinders with large infeed openings to accommodate them. Tree limbs are normally mixed with yard trimmings so if you accept one you will normally get the other. Tub type and Horizontal feed hammermill grinders have proven to be very efficient machines for processing tree limbs into smaller particle sizes. If you have no control over the length of material you receive then you will need a grinder with a large infeed opening. If you have control over the length then you can get by with a smaller machine. You can waste a lot of time and money trying to put long material into a grinder with a small infeed opening. Long lengths of course are relative to the machine in question; 10’ long is okay if the machine is 12’ wide at the infeed opening, 8’ long is okay if the machine is 10’ wide, etc. If you use a tub type machine with an infeed opening smaller than your materials length the material will constantly bridge across the infeed opening and production rate will be less than anticipated. If you have a horizontal feed machine the longer lengths are not a problem, although organizing tree limbs to fit in a horizontal machine can be. Some customers control the length of material coming into their facilities by requiring that it be cut to shorter lengths. They are then able to save money by utilizing a smaller machine (by smaller I don’t mean lighter duty, just a smaller infeed opening).

 
Tree Stumps:

It requires an extraordinary amount of work to reduce tree stumps down to chips and remove contaminants, but the small chips do make excellent landscape products. For shredding large diameter wood and stumps you will need either a slow speed shredder or a shear mounted on a large track type excavator. This equipment is used to break up large diameter wood and stumps (over 18” diameter) into sizes which can be processed more efficiently by a hammermill grinder. Since hammermills don’t work economically with rock and dirt you will need to run the broken and sheared chunks of wood across a screen which is capable of removing most of the dirt and gravel previously attached to the stumps. This can me accomplished with either a heavy-duty trommel screen or a flat shaker screen. And finally, you can process the cleaned chunks of wood into small marketable products with a hammermill grinder.

Pallets & Construction Wood:

Pallets and construction wood make up approximately 7% of the total solid waste stream in the US and are second to yard trimmings in the amount of raw woody material available for recycling. They are usually processed through a tub grinder along with yard trimmings and recycled into landscape mulch, boiler fuel or sewage sludge bulking agents. Normally, the wood is not large but it can sometimes can be long, over 10’. Most grinders handle this kind of wood very easily. The big problem with pallets and construction wood is the amount of non-woody materials that are associated with them and that must be removed from your finished products. Also, wood that is nailed together such as pallets and crates slow down the grinding operation because they create a lot of air space within the infeed hopper. When recycling pallets and crates it is very helpful to pre-grind the material by crushing it with a track-type loader or excavator.

Marketable Products

What products will be produced?

Landscape Mulch:

Mulch has been one of the main products of wood and yard waste recycling operations. It is a shredded product that is generally 2” or less in length, ½” or less in diameter (or width), and by volume will contain less than 10% particles as fine as sawdust. It is normally aged for a few months or until it acquires a uniform dark brown color. To make marketable mulch you need material that has been reduced in size, aged and all contaminants must be removed.

Mulch (unmarketable): I want to mention here that many customers produce an unmarketable mulch product that is used for public convenience such as landfill cover, highway right-of-ways, etc., uses that do not require uniform size or quality. Depending on the application, not all contaminants or oversized wood chips may need to be removed.

Soil Amendment:

Composting shredded wood and yard waste produces soil amendment. It is a fibrous wood product that helps improve the condition of any soil and is competitive with peat moss as a soil additive. Soil amendment particles are normally less than ½” in length, no larger than 1/16” in diameter, and are primarily fine particles similar to sand and dirt.

There are several methods of composting; in-vessel systems that require high tech equipment and a large up front investment, and windrow composting that is basically low tech and utilizes less expensive equipment. We will only deal with the windrow composting method here.

To operate a windrow composting facility you need pre-processed raw material that has been reduced in size through the shredding and/or grinding process to particles 4” long or less that 1” diameter and less and all contaminants removed. You then need land; space for your windrows, water and a method for adding it to the windrows, a rubber tired loader for moving materials, a compost turner for aerating the windrows and a compost screen for sizing your final products.

A compost facility can be indoors or out depending on the size and location of the project. There are earthy odors associated with composting that some individuals find objectionable so find a location with adequate space around it and isolate yourself from neighbors as much as possible.

Boiler Fuel:

Waste wood particles have long been used for firing boilers in the forest industry and now many wood fired power plants have been constructed for burning waste wood generated in the municipal sector. Boiler fuel made in a recycling operation is a shredded product, normally 1” to 3” in length and ¼” to 1” in diameter. Wood fired power plants can’t accept leaves, grass or sawdust from recycling operations because these items contain too much dirt. If you want to make boiler fuel from waste wood materials you will normally be required to screen out all contaminants and remove any fines less than ¼” in size. The fines will often have a market as a low quality landscape product, and can be composted to improve the quality.

Sewage Sludge Bulking Agent:

Wood chips are an excellent bulking agent for sewage sludge composting operations. Some sludge composting facilities are deigned to use chips the same size as is used for boiler fuel but will accept them with the fines (sawdust and dirt) mixed in, other operators want just the fines and no large chips. Those facilities that use the larger chips will compost them with the sludge and then used a trommel screen to separate out whatever is left of the wood chips at the end of the compost process. The remainder of the old chips are then combined with new chips and used to form a new compost pile. This system is a cycle: old chips deteriorating away and new chips being added. Those facilities that use only sawdust as a bulking agent normally compost it all down to dirt and there is nothing left to separate.

Non-Woody Materials
“Contaminants”

What common non-woody material (contaminants) can you expect will be mixed with the wood and yardwaste you receive?

You may not expect to have non-woody contaminants mixed in with the wood and yardwaste you’re recycling, but if you don’t you’ll be the exception. Experience has shown that there is always some percentage of non-woody items mixed with wood and yard waste in the municipal waste stream. You can probably guess that there will be at least a little plastic and paper, and we know from experience that there is usually ¼ to ½ pound of ferrous metal mixed with each ton of yardwaste, and more in pallets or construction wood. Sound unbelievable? Believe it! You will have to deal with this problem because unsightly paper and plastic, roofing nails, razor blades, pocket knives, garden tools, metal banding, etc. in your raw material can absolutely ruin the finished product and ruin any chance of a successful recycling program. It is imperative that a plan, or system, be developed for preventing contaminants from becoming mixed with your recyclable raw materials, and for removing the ones that you are unable to keep out. Be assured, whoever uses your products will expect them to be of the highest quality regardless of price, and completely free of any hazardous materials.

Paper and Plastic:

Paper in your product may or may not be a problem but plastic will most certainly render your product unmarketable. You will have to remove all the plastic that comes into your recycling facility either manually as it arrives, or mechanically as a part of your recycling operation. If all your material is received in paper or plastic bags, then manual separation may be too overwhelming a job to be an option and a mechanical separator will be required.

If you are composting and leave paper and plastic mixed in your material throughout the composting process, thinking to remove it in the final screening, then you’ll need a plan on how to control it from blowing all over your site and perhaps into the adjoining neighborhood. Blowing plastic has caused many compost operators problems with environmental agencies.

Ferrous Metals:

Large pieces of ferrous metal must be removed manually prior to grinding; small pieces must be removed after grinding. You cannot see small pieces such as razor blades, knifes and wire, especially if your material has been compacted or is in plastic bags, and you cannot economically remove nails that are attached to lumber so these items must go through the grinding process before they can be removed. After grinding, the ferrous metals can be removed with magnetics on the grinder’s product stacking conveyor or by magnetics in the next processing stage, screening.

Aluminum:

Soft drink cans always find their way into your recyclable wood and yard waste. There are normally not enough of them to justify the high tech equipment required to remove them mechanically, so the next best method is manually. It is fairly easy to see and remove them prior to grinding, unless your material is in bags. If a disc screen is being used after grinding to remove paper and plastic, it will normally remove aluminum cans as well.

Will your product be usable if it contains contaminants?

If your product contains contaminants then it most likely will not be salable, and you may not be able to give it away. Very few consumers, if any, will accept landscape mulch, soil amendment, or even boiler fuel that contains contaminants. About the only use for contaminated material is daily cover at the local landfill.

Will there be liability exposure due to use of your products?

We cannot give legal advice but you may be liable if someone is hurt by ferrous metal, etc. found in your products.

The following questions regarding contaminants in your material need to be addressed before deciding how your recycling system will be organized.

How are raw materials received at your recycling facility?

Loose:

Landscapers, gardeners, homeowners and some municipal public works departments will pick up loose wood and yard waste materials for transport to a disposal facility. In this case you can visually inspect the load for contaminants. It will be easy to see paper and plastic, but you will need to look closely for wire-tied bundles, garden tools, etc. You will be able to remove some of the contaminants but it will be impossible for you to see and remove all of them.

Packer Trucks:

Tightly packed material will grind much faster than loose material but when material is packed tightly together it is very difficult to determine if there are any undesirable materials hidden within the load, and there will be. If you are receiving packer loads you can expect to experience more wear and tear on your grinder; there will be dirt, concrete, bricks, garden tools, etc. in the load and you won’t be able to see them. If packer trucks are bringing in material that is also in plastic bags it will be packed and intertwined too tightly for you to separate the plastic. The point here is not to refuse packer loads; just that you will need to be much more observant when you are grinding material that has come from packer trucks.

Vacuum Trucks:

Normally used to pick up leaves, they also pick up huge amounts of dirt. Grinding leaves from vacuum trucks goes fast but the high content of dirt will increase wear and tear of your grinder be several times. If you intend to grind vacuum-packed leaves you should first put the leaves through a compost screen to remove the dirt.

Review of Machine Applications

Your selection of machinery will depend on which raw materials you process, your desired end products and the contaminants you have to remove. Following is a review of the machines required and the order in which they might be used.

Front end Loader (rubber tired or tracks):

Can be used to load unprocessed wood and yard waste into the machinery and for moving stockpiles of finished material.

Grapple Loader (normally optional):

Can be used to load unprocessed wood, yard waste and stumps into the machinery (you will still need a front end loader for moving stockpiles of material).

Shredder:

Reduces any material over 18” in diameter to smaller sizes but will not make finished products.

Shear:

Mounted on an excavator and used for the same purpose as a shredder.

Primary Screen (disc, trommel or shaker):

Remove high concentrations of dirt before using a hammermill grinder (normally only needed when processing stumps or leaves).

1st Grind with Hammermill Grinder:

Reduces wood and yard waste into small shredded chips.

If there were no contaminants in your raw material you could process it down to the size you need as a finished product the first time through the machine. However, there are always contaminants that you don’t see and that will have to be removed. You therefore should protect your grinder by coarse grinding your raw materials down to particles approximately 6” long and less by 1” in diameter or less. By coarse grinding; contaminants are passed through the grinder more easily and with less wear and tear on the grinder.

Secondary Screen (disc or trommel):

The use a disc or trommel screen to separate contaminants and improperly sized wood chips from your acceptable product

2nd Grind with Hammermill Grinder:

After contaminants and improperly sized chips have been separated you can re-grind all the improperly sized chips to the size you need as your finished product.

A Composting Facility will need the following equipment:

Compost Turner:

For turning the windrows of composting material. The machine can be either self-propelled or pulled and powered by a farm tractor.

Water Application System:

Compost requires a lot of water and a system for adding water will be required.

Compost Screen (trommel or disc):

For screening the finished compost into a high quality soil amendment or landscape mulch.