1

Date: October 31, 2011 To: Rachel Schmeltz, U.S. EPA From: Jeff Coburn, RTI International Subject: Review of Anaerobic Biodegradability Tests of Determining Deg radable 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 o f sources including industrial waste landfills. On August 4, 2011, EPA proposed amendments to the mandatory GHG reporting requirements for industrial waste landfills (a s 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 ar e present in the waste material. The commenter suggested that anaerobic biodegradabil ity 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 r ule. 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 sear ch include: ASTM D5511-11. Standard Test Method for Determining Anaerobic Biodegradation of Pla stic

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 Biodegrada bility of

Organic Compounds in Digested Sludge - Method by Measurement of the Biogas Production2

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: B y

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 tes t 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 i s based on OECD Test No. 311. All of these test methods state that triplicate test samples shoul d be prepared. ASTM E2170 clearly states that three blanks are also required, but that only one r eference 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 t ested. All three test methods indicate that the test is valid if more than 60 percent biodegradation of the ref erence compound is achieved. All three of these test methods indicate that the standard deviati on 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 analysi s of the water for inorganic carbon (as “[m]uch of the CO 2 produced will be dissolved in the liquid phase or transformed into carbonate or hydrogen carbonate under the conditions of the test”), s o it may have a low bias for the results. This test method suggested that degradation of the re ference compound should exceed 50% for a valid test. As an exhaustive literature review has not been conducted, there may be other applica ble 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 wit h a known test substrate that demonstrates a minimum level of biodegradation (like 50 perc ent) 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 biodegra ded. 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 i n 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 sol id, low solubility materials that degrade slowly. It is uncertain how well these methods will pr edict the biodegradability of wood, for example. The test methods suggest that solvents may be us ed to increase the solubility of the organic test compound in water, but this may not be appropr iate for solid waste material. For solid materials, it is recommended that the mat erial 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, it3

is expected that a 60-day test should provide an accurate estimate of the amount of c arbon 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 (DOC F ). In Equation TT-1, it is assumed that DOC F has a fixed default value of 0.5. Therefore, the amount of carbon degraded per mass of waste sample as determine d during the biodegradability tests should be multiplied by two to calculate a DOC value appropri ate for Equation TT-1. By doing so, the gas generation quantity projected by Equation TT-1 will m atch the gas generation quantity (per unit of waste disposed) determined in the biodegrada bility tests.