Wood wastes can be reused in home heating or construction. Although this diversion strategy is cost-free, it is often difficult to reuse all of the waste products. If the wood wastes cannot be reused or taken offsite by a recycler, the next viable diversion step is size reduction. Grinding is the most common method used to reduce the size of wood wastes. Wood tub grinders are used to reduce wood wastes into smaller particles. No screening is necessary. The larger-sized output material from the tub grinder can be used as a biomass fuel or as a bulking agent to balance high nitrogen loads in composting operations. The smaller-sized material can be composted or used as mulch. However, according to the Naval Facilities Engineering Service Center, it is not recommended to grind or compost wood covered with lead based paint. During grinding this paint will generate a toxic dust cloud , where the lead can leach into the compost. Wood wastes that are chipped or ground will decompose more readily. Composted wood wastes can be used as a soil amendment or fertilizer. The reduced wood wastes can also be used as mulch and help grow grass at municipal and commercial landscape applications, such as highway projects and golf courses. Mulch can also be used to control weed growth.

Wood tub grinders are not limited in opening size like smaller chippers or shredders. The grinders can process large and odd shaped wood including stumps, pallets, and waste lumber. Material that is pressure treated, chemically treated, or creosote contaminated should not be composted. Such wood contains chemicals that inhibit plant growth or are toxic to the environment. Avoid plywood or particle board since they contain glues which might be hard on machinery, difficult to compost, and contain undesirable chemicals for land application.

The compliance benefits listed here are only meant to be used as a general guideline and are not meant to be strictly interpreted. Actual compliance benefits will vary depending on the factors involved, e.g. the amount of workload involved.

Consult your local industrial health specialist, your local health and safety personnel, and the appropriate MSDS prior to implementing this technology.

• Produces usable products such as landscape mulch, fuel, and compost agents.
• Wood wastes can be ground to a fine, even texture that will compost quickly.
• The wood tub grinder can process large trees and finished lumber.
• Reusing or composting wood waste will result in a reduction of disposed waste.
• Composted wood waste can be used as a soil amendment on base, possibly reducing the need for purchased supplies.
• Cost savings are achieved from reduced landfill disposal fees.

• Requires an initial capital cost for the purchase of a wood tub grinder (or a fee for a recycling company to perform on-site recycling services).
• Increased costs associated with labor and operation and maintenance of the equipment.

Assumptions:

• Process 1,000 tons/yr of wood waste at 10 tons/hr
• Produce: 1,000 tons/yr of mulch
• Tub grinder operated for 100 hrs/yr
• Green waste disposal costs: $13/ton
• Labor: 100 hrs/yr at $30/hr
• Maintenance: 20 hrs at $30/hr
• Engine rating: 110 hp
• Heating value of diesel: 137,000 Btu/gal
• Price of diesel: $1.50/gal
• Mulch value: $25/ton
• Diversion produces minimal effect on labor for solid waste collection.

Economic Analysis Summary

Annual Savings for Wood Recycling: $34,090
Capital Cost for Diversion Equipment/Process: $44,000
Payback Period for Investment in Equipment/Process: < 2 years

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