RAW MATERIAL MIXING USING COMPOST MIXERS

Revision Date: 9/03
Process Code: Navy/Marines: N/A; Air Force: N/A; Army: N/A
Usage List: Navy: Medium; Marines: Medium; Army: Low; Air Force: Low
Alternative For: N/A
Compliance Impact: Low
Applicable EPCRA Targeted Constituents and CAS Numbers: N/A
Overview: Compost mixers are used to mix raw materials such as food, yard waste, paper, and sewage sludge uniformly before composting. Mixing is an important step to distribute the carbon and nitrogen materials evenly and to assure fast, clean smelling decomposition. For materials such as food waste and sewage sludge, mixers can be used to incorporate bulking agents such as wood chips that add carbon to the mix and break up wet clumps.

Mixers are large containers with mobile paddles that are used to mix compostable materials. They are used for larger composting operations where (1) mixing with a loader is impractical, or (2) compost recipes require precise mixtures of carbon and nitrogen. The four auger mixer is the most common compost mixers. The unit may be stationary or mobile, and may be powered electrically or by diesel engine.

Compost reduces the amount of waste to be disposed. Complete recovery of yard waste will reduce the amount of waste disposed in landfills by an average of 12% (U.S. EPA, 2000).
Compliance Benefit: Composting will help facilities meet the requirements of Executive Order (EO) 13101, which call for executive agencies (e.g., Department of Defense) to incorporate waste prevention and recycling into their daily operations. Using compost mixers in the composting process may also help facilities to meet the environmentally beneficial landscaping requirements outlined in EO 13148.

States and/or localities may have additional regulations applicable to composting that should be followed. The compost mixers may increase the quantity of fuels on site which may increase a facility's need to comply with SARA Title III (40 CFR 355, 370) and EO 13148 reporting requirements as well as spill plan requirements under 40 CFR 112. In addition, the mixers may also contribute to a facility's need for an air permit (40 CFR 70 or 71). If electric mixers are used, additional electricity will be used at the facility. Under EO 13123, federal facilities are required to be as energy efficient as possible.

The compliance benefits listed here are only meant to be used as general guidelines 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.
Materials Compatibility:


 No materials compatibility issues were identified.


Safety and Health: Safety issues for using compost mixers deal with the operation of power equipment. Operators should be specifically trained in the proper operation of the mixer. Machinery should not be used if workers are on medication. Proper personal protective equipment including gloves, eye protection, and hearing protection should be used if needed.

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


Benefits:
  • Thorough mixing speeds up the composting process by making nutrients available to microorganisms.
  • Fast, efficient mixing of compost materials compared to mixing with a loader.
  • Can handle a large volume of materials.
  • Breaks up clumps of material that can become anaerobic and odorous in the compost pile.


Disadvantages: None identified.


Economic Analysis: Compost mixers cost from $70,000 to $180,000 for units that process from 20 to 40 tons/hr. Maintenance costs are approximately $500/yr excluding labor. Compost mixers are available as either stationary units with an electric motor or mobile units with a diesel engine. The economic analysis presented is based on an aerated static pile compost operation. The capital costs include compost pads with air lines, blowers, a tub grinder, compost mixer, trommel screen, front end loaders, and offices.

Assumptions:

  • Process 25,000 tons/yr of wood and yard waste
  • Produce 15,000 tons/yr of finished compost.Capital Costs: $3,000,000
  • Solid waste disposal costs: $13/ton
  • Operating costs (labor & maintenance): $25/ton
  • Avoided topsoil purchases: $50/ton
  • Hauling to landfill: $5/ton
  • Hauling to composting facility: $2/ton

Table 1. Annual Operating Cost Comparison for Diversion and Disposal Using a Composting Facility

 
Diversion
Disposal
Operational Costs:    
Labor & maintenance: $625,000 $0
Landfill costs: $0 $325,000
Hauling costs: $50,000 $125,000
Total Operational Costs: $675,000 $450,000
Total Recovered Income: $750,000 $0
Net Annual Cost/Benefit: $75,000 -$450,000

Economic Analysis Summary:

  • Annual Savings for Composting Facility: $525,000
  • Capital Cost for Diversion Equipment/Process: $3,000,000
  • Payback Period for Investment in Equipment/Process: < 6 years

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Approving Authority: Appropriate authority for making process changes should always be sought prior to procuring or implementing any of the technologies identified herein.


NSN/MSDS: None identified.


Points of Contact: For more information
Vendors: This is not meant to be a complete list, as there may be other manufacturers of this type of equipment.

McLanahan Corporation
P.O. Box 229
200 Wall Street
Hollidaysburg,  PA   16648
Phone: (814) 695-9807 
FAX: (814) 695-6684
  Detcon
P.O. Box 2249
Farmingdale,  NJ   07727
Phone: (732) 938-2211 
  Kuhn Knight Inc.
PO Box 167
Brodhead,  WI   53520
Phone: (608) 897-2131 
FAX: (608) 897-2561

Double T Equipment Manufacturing Limited
P.O. Box 3637
Airdrie, AB T4B 2B8    CANADA
Phone: (403) 948-5618 
FAX: (403) 948-4780
Related Links: Composting -- June 2002, Air Force Center for Environmental Excellence/Environmental Quality (AFCEE/EQ)


Sources: Detcon, September 2002.
U.S. EPA, Municipal Solid Waste in the United States: 2000 Facts and Figures.
Mr. John Comstock, Naval Facilities Engineering Service Center, May 1999.
The F. B. Leopold Company, Inc., March 1995.
The McLanahan Corporation, March 1995.
Knight Industrial Division, March 1995.