Scope: 

The ASTM D6139 is a standard test method for determining the aerobic aquatic biodegradation of lubricants or their components using the Gledhill shake flask. This test method is an ultimate biodegradation test that measures carbon dioxide (CO₂) evolution. This test method is intended to specifically address the difficulties associated with testing water-insoluble materials and complex mixtures such as are found in many lubricants. This test method is designed to be applicable to all nonvolatile lubricants or lubricant components that are not toxic and not inhibitory at the test concentration to the organisms present in the inoculum. 

Test procedure:

For the ASTM D6139 test, biodegradable lubricant or its component(s) is calculated by collecting and measuring CO₂ produced when the lubricant or component is exposed to microorganisms in a controlled aerobic aquatic environment. This value is then compared to the theoretical amount of CO₂ that could be produced if all of the carbon in the test material was converted to CO₂. Carbon dioxide is a byproduct of aerobic microbial metabolism of carbon-containing materials, and thus is a direct measure of the test material’s ultimate biodegradation. The CO₂ is captured in a Ba(OH)₂ or other alkaline solution, and the amount of CO₂ absorbed is calculated by titrating the remaining hydroxide in the solution. 

Another appropriate test method is used in ASTM D6139 to estimate the carbon content of the test material, and the theoretical CO₂ is computed from that measurement. Because of the complexity of the mixture of compounds included in lubricants, it is important to directly measure the carbon content of the test sample rather than computing this amount. Biodegradability is measured as the proportion of CO₂ generated in theory. 

Video 01: Explanation of the aerobic digestion process

Specimen size:

Lubricants are used as test specimens in the ASTM D6139 test procedure.

Data:

As per the ASTM D6139, the percent of theoretical CO₂ evolved (Pi) for the “i”th replicate is  calculated as shown below:

Pi= (Cti / Xi) × 100 

where: 

Cti = total amount of CO₂ calculated by summing the CO₂ produced at each titration interval for  a given test or reference material for the “i”th replicate

Xi = theoretical CO₂ produced from a given material for the “i”th replicate

Conclusion:

The ASTM D6139 is a standard test method for determining the aerobic aquatic biodegradation of lubricants or their components using the Gledhill shake flask.