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 (aka Magnetic Head Pulley or Over Band Magnet) 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.
Commons Sources Material of Contaminants
How raw materials are received at your facility will determine what contaminants will need to be addressed before deciding how your recycling system will be organized.
Loose Material:
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 them.
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 by several times. If you intend to grind vacuum-packed leaves you should first put the leaves through a compost screen to remove the dirt.