Economic and Environmental Manure Solutions

ANAEROBIC DIGESTION

Technology Description (from Wright, 2001)
Anaerobic digestion is the breakdown of complex organic material by microorganisms in the absence of oxygen.  The end products of anaerobic digestion of manure include biogas that is comprised of methane, carbon dioxide, and some trace gases; and stabilized organic matter.  Anaerobic digestion may be a viable manure treatment and handling method for dairy farms of a particular size.  There are several types of anaerobic digesters being employed on dairy farms for manure digestion including plug flow digesters, mixed digesters, and fixed film digesters.  The most appropriate digester type depends primarily upon incoming biomass and manure characteristics and manure management goals.

Advantages of anaerobic digestion include ability to generate electricity and heat (through the combustion of the biogas), odor control, reduction of pathogens, ability to use digested (separated) solids as bedding, and the ability to spread digested (separated) liquid effluent at different times and different places than was previously socially acceptable. 

The primary disadvantages of anaerobic digestion include high capital and operating costs.  It is a general rule that the larger the farm, the greater the economic feasibility of anaerobic digestion.  Studies indicate that the minimum dairy farm size for anaerobic digestion may be between 500 and 800 cows (Jewell et al. 1997 and Wright 2001).

An additional area of interest in regards to anaerobic digestion is co-digestion of food wastes along with the dairy manure.  Co-digestion of food wastes and manure leads to increase biogas and energy production and increased revenue associated with tipping fees.

Sources of Additional Information
Case studies and posters on several active dairy farm anaerobic digestion projects in NY State can be found on the www.manuremanagement.cornell.edu website

Guidebooks on anaerobic digestion including “Anaerobic Digestion for Dairy Farms” (ABEN 458) and “Evaluation of Anaerobic Digestion Options for Dairy Farms in Upstate New York” (ABEN 97) can be purchased through NRAES at www.nraes.org

A Guide to Technology Providers (including digester designers and project developers) can be found at the USEPA AgStar website:  www.epa.gov/agstar

References
Jewell, W.J., P.E. Wright, N.P. Fleszar, G. Green, A. Safinski, and A. Zucker.  “Evaluation of Anaerobic Digestion Options for Groups of Dairy farms in Upstate New York.” 1997.  Department of Agriculture and Biological Engineering, Cornell University, Ithaca, NY  14853.

Wright, P. E..  “Overview of Anaerobic Digestion Systems for Dairy Farms.”  Proceedings from “Dairy manure Systems:  Equipment and Technology” Rochester, NY  March 20-22, 2001  NRAES Publication No. NRAES-143  pp. 93-109.

Click on the picture to enlarge.

Cornell University

Department of Biological and Environmental Engineering

Ithaca, NY 14853

Fax: 607.255.4080