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Date: October 31, 2011 

To: Rachel Schmeltz, U.S. EPA 

From: Jeff Coburn, RTI International 

Subject: Review of Anaerobic Biodegradability Tests of Determining Degradable Organic 

Content of Solid Waste Materials 

Purpose 

This memorandum documents the review of anaerobic biodegradability test methods which may 

be used to assess the degradable organic carbon (DOC) content of solid wastes. 

Background 

On July 12, 2010, EPA promulgated mandatory GHG reporting requirements for a variety of 

sources including industrial waste landfills. On August 4, 2011, EPA proposed amendments to 

the mandatory GHG reporting requirements for industrial waste landfills (as well as other 

sources). EPA received numerous public comments on the proposed amendments, including 

comment that the determination of DOC based on the volatile solids content of the waste would 

overestimate the amount of degradable carbon in the waste when plastics or coke are present in 

the waste material. The commenter suggested that anaerobic biodegradability tests, such as 

those used to develop the default DOC values and the DOC-volatile solids correlation, be 

allowed to estimate DOC values of wastes as an alternative to the method in the rule. 

Findings 

A limited literature search was conducted and a number of test methods from consensus standard 

organizations were identified. Relevant test methods identified during this search include: 

ASTM D5511-11. Standard Test Method for Determining Anaerobic Biodegradation of Plastic 

Materials Under High-Solids Anaerobic-Digestion Conditions. 

ASTM D5526-94. (Reapproved 2011). Standard Test Method for Determining Anaerobic 

Biodegradation of Plastic Materials Under Accelerated Landfill Conditions. 

ASTM E2170-01. (Reapproved 2008). Standard Test Method for Determining Anaerobic 

Biodegradation Potential of Organic Chemicals Under Methanogenic 

Conditions. 

ISO 11734 (1995) Water quality - Evaluation of the Ultimate Anaerobic Biodegradability of 

Organic Compounds in Digested Sludge - Method by Measurement of the 

Biogas Production 
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OECD Test No. 311. Anaerobic Biodegradability of Organic Compounds in Digested Sludge: 

By Measurement of Gas Production. Adopted 23 March 2006. 

OPPTS 835.3400 Anaerobic Biodegradability of Organic Compounds. (EPA 712-C-98-090) 

OPPTS 835.3420 Anaerobic Biodegradability of Organic Compounds in Digested Sludge: By 

Measurement of Gas Production. (EPA 712-C-08-007) 

Only the abstract/introductory sections of ASTM D5511, ASTM D5526, and ISO 11734 were 

reviewed as these methods were not specifically purchased. The complete test methods of the 

other methods listed above were reviewed. ASTM E2170, OECD Test No. 311, and OPPTS 

835.3420 were all nearly identical; OPPTS 835.3420 specifically states that it is based on OECD 

Test No. 311. All of these test methods state that triplicate test samples should be prepared. 

ASTM E2170 clearly states that three blanks are also required, but that only one reference 

compound sample may be used. The language in OECD Test No. 311 and OPPTS 835.3420 

suggests that triplicate blanks and triplicate reference samples must be tested. All three test 

methods indicate that the test is valid if more than 60 percent biodegradation of the reference 

compound is achieved. All three of these test methods indicate that the standard deviation of 

replicate samples is generally less than 20 percent. 

The earlier OPPTS test method (835.3400) does not include the same level of detail in the testing 

with respect to the number of samples to be tested. It also does not include analysis of the water 

for inorganic carbon (as “[m]uch of the CO2 produced will be dissolved in the liquid phase or 

transformed into carbonate or hydrogen carbonate under the conditions of the test”), so it may 

have a low bias for the results. This test method suggested that degradation of the reference 

compound should exceed 50% for a valid test. 

As an exhaustive literature review has not been conducted, there may be other applicable test 

methods like OPPTS 835.3400 that do not have specific number of samples or recovery 

requirements. At a minimum, the biodegradation test should have a control sample with a 

known test substrate that demonstrates a minimum level of biodegradation (like 50 percent) to 

ensure the anaerobes are sufficiently active. It may also be reasonable to correct the results of 

the waste sample biodegradability for the fraction of the control sample biodegraded. Similarly, 

a target precision between duplicate or triplicate samples should be used to ensure the validity of 

the test results. If triplicate test sample analyses are not required in the test method, then 

duplicate test samples should be used as a minimum. 

One concern regarding these test methods is how well they will perform for solid, low solubility 

materials that degrade slowly. It is uncertain how well these methods will predict the 

biodegradability of wood, for example. The test methods suggest that solvents may be used to 

increase the solubility of the organic test compound in water, but this may not be appropriate for 

solid waste material. For solid materials, it is recommended that the material be finely ground to 

provide the anaerobes easy access to all of the solid material within the test vessel. Also, the test 

should be conducted for as long a period of time as possible (most of the methods reviewed 

suggest a maximum test period of 60 days) so that slowly degrading materials will show 

degradation over the test period. Given the high concentration of anaerobes used in these tests, it 
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is expected that a 60-day test should provide an accurate estimate of the amount of carbon in the 

test material that can be anaerobically biodegraded. 

Finally, it should be noted that, in Equation TT-1, the amount of carbon that is ultimately 

anearobically biodegraded in the landfill is actually the product of DOC and the fraction of DOC 

dissimilated (DOCF). In Equation TT-1, it is assumed that DOCF has a fixed default value of 0.5. 

Therefore, the amount of carbon degraded per mass of waste sample as determined during the 

biodegradability tests should be multiplied by two to calculate a DOC value appropriate for 

Equation TT-1. By doing so, the gas generation quantity projected by Equation TT-1 will match 

the gas generation quantity (per unit of waste disposed) determined in the biodegradability tests.