Codigestion
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Anaerobic digestion is a process where bacteria break down organic matter, such as manure, in the absence of oxygen. The anaerobic digestion process generates biogas that is composed mostly of methane, which can be used as an energy source (e.g., heat or electricity generation). Codigestion refers to the simultaneous anaerobic digestion of multiple organic wastes in one digester. Codigestion is used to increase methane production from low-yielding or difficult to digest materials (i.e., feedstocks). For the codigestion process, care must be taken to select compatible feedstocks that enhance methane production (and to avoid materials that may inhibit methane generation). In addition, an existing anaerobic digester system must be able to handle the significant increase in methane output that is common with codigestion.
In agriculture, codigestion is often used to increase methane production from the anaerobic digestion of manure. There are multiple choices for codigestion feedstocks, including restaurant or cafeteria food wastes; food processing wastes or byproducts; fats, oil and grease (FOG) from restaurant grease traps; energy crops; crop residues; and others. Codigestion of various organic feedstocks may enhance the biogas and methane production from an anaerobic digester. The Codigestion Fact Sheet (PDF) (3 pp, 422K) discusses factors that should be considered when selecting a feedstock.
AgSTAR also has compiled resources for those interested in pursuing a codigestion anaerobic digestion system. Use the information below to determine the feasibility of a codigestion system for your facility. Additionally, AgSTAR has a discussion of permitting requirements on the Permitting Practices page.
- Methods for Testing Potential Codigestion Feedstocks
- Information on Carbon to Nitrogen (C:N) Ratios
- Laboratories that Conduct Testing of Anaerobic Digester Feedstocks
Methods for Testing Potential Codigestion Feedstocks
- Biochemical Methane Potential (BMP): BMPs give a prediction of the amount of biogas and/or methane production that can occur from the codigestion substrate. While laboratory BMPs provide preliminary information on a codigestion substrate, additional research following the BMP work is necessary because BMPs typically overpredict the amount of biogas and/or methane produced. Some possible BMP methods for use include the following:
ASTM Standard E2170 – 01 (2008), Standard Test Method for Determining Anaerobic Biodegradation Potential of Organic Chemicals Under Methanogenic Conditions. ASTM International,
West Conshohocken, PA.ISO 11734:1995 Water quality – Evaluation of the "ultimate" anaerobic biodegradability of organic compounds in digested sludge - Method by measurement of the biogas production. International Standards Organization.
Additional BMP protocols are listed in the following papers:
Moody, L., R. Burns, W. Wu-Haan, and R. Spajić. (2009). Use of biochemical methane potential (BMP) assays for predicting and enhancing anaerobic digester performance. In Proceedings of The 4th International and 44th Croatian Symposium of Agriculture. Optija, Croatia.
Gunaseelan, V.N. (1997). Anaerobic digestion of biomass for methane production: a review. Biomass & Bioenergy, 13:83-114.
Owen, W., D. Stuckey, J. Healy Jr., Young, and P. McCarty. (1979). Bioassay for monitoring biochemical methane potential and anaerobic toxicity. Water Research, 13:485-492.
Faivor, L., and D. Kirk. (2011). Statistical verification of a biochemical methane potential test. In Proceedings of American Society of Agricultural and Biological Engineers, Louisville, Kentucky.
- Anaerobic Toxicity Assays (ATA): ATAs typically show the potential ability of a codigestion substrate to inhibit biogas production and/or methane production. Some possible ATA methods for use include the following:
ISO 13641-1:2003 Water quality - Determination of inhibition of gas production of anaerobic bacteria - Part 1: General test. International Standards Organization.
ISO 13641-2:2003 Water quality - Determination of inhibition of gas production of anaerobic bacteria - Part 2: Test for low biomass concentrations. International Standards Organization.
Owen, W., D. Stuckey, J. Healy Jr., Young, and P. McCarty. (1979). Bioassay for monitoring biochemical methane potential and anaerobic toxicity. Water Research, 13:485-492.
- Total Solids and Volatile Solids
SM 2450B. Solids. Total Solids Dried at 103-105°C. Standard Methods for the Examination of Water and Wastewater, 22nd edition. Washington D.C.: American Public Health Association.
SM 2540E. Solids. Fixed and Volatile Solids Ignited at 550°C. Standard Methods for the Examination of Water and Wastewater, 22nd edition. Washington D.C.: American Public Health Association.
SM 2540G. Solids. Total, Fixed, and Volatile Solids in Solid and Semisolid Samples. Standard Methods for the Examination of Water and Wastewater, 22nd edition. Washington D.C.: American Public Health Association.
EPA Method 160.4. Water. Residue, Volatile (Gravimetric, Ignition at 550°C). U.S. Environmental Protection Agency.
- Alkalinity or pH
ISO 10523:2008 Water quality - Determination of pH. International Standards Organization.
SM 2320B. Alkalinity. Titration Method. Standard Methods for the Examination of Water and Wastewater, 22nd edition. Washington D.C.: American Public Health Association.
ASTM D1067 - 11 Standard Test Methods for Acidity or Alkalinity of Water. ASTM International,
West Conshohocken, PA, 2011. - Chemical Oxygen Demand (COD)
EPA Method 410.4 Water. The Determination of Chemical Oxygen Demand (COD) by Semi-Automated Colorimetry. U.S. Environmental Protection Agency.
Information on Carbon to Nitrogen (C:N) Ratios
Basics of Energy Production through Anaerobic Digestion of Livestock Manure (PDF) (6 pp, 926 KB),
Characteristics of raw materials for on-farm composting,
Materials and methods to ensure quality compost: carbon-nitrogen relationships,
The Carbon/Nitrogen Ratio,
A Balancing Act (Carbon-Nitrogen Ratios),
Laboratories that Conduct Testing of Anaerobic Digester Feedstocks
| Organization | Contact | Phone |
|---|---|---|
| Cornell University Manure Management Program * | Curt Gooch (cag26@cornell.edu) | 607-255-2088 |
| Iowa State University Agricultural Waste Management Laboratory | Dan Andersen (dsa@iastate.edu) | 515-294-4167 |
| Marquette University Water Quality Center | Dan Zitomer (Daniel.zitomer@mu.edu) | 414-288-5733 |
| Michigan State University Anaerobic Digestion Research and Education Center | Dana Kirk (kirkdana@msu.edu) | 517-432-6530 |
| Ohio State University Bioproducts and Bioenergy Research Laboratory | Yebo Li (li.851@osu.edu) | 330-263-3855 |
| University of California-Davis Bioenvironmental Engineering Research Laboratory | Ruihong Zhang (rhzhang@ucdavis.edu) | 530-754-9530 |
| University of Wisconsin-Platteville | Tim Zauche (zauchet@uwplatte.edu) | 608-342-1678 |
*Research laboratory, testing for public on case-by-case basis