ASTM D6731 Standard Test Method for Determining the Aerobic, Aquatic Biodegradability of Lubricants or Lubricant Components in a Closed Respirometer
1. Scope
1.1 This test method covers a procedure for determining the degree of biodegradability of lubricants or their components in an aerobic aqueous medium on exposure to an inoculum under controlled laboratory conditions. This test method is an ultimate biodegradation test that measures oxygen demand in a closed respirometer.

1.2 This test method is suitable for evaluating the biodegradation of volatile as well as nonvolatile lubricants or lubricant components.

1.3 This test method is applicable to lubricants and lubricant components which are not toxic and not inhibitory to the test microorganisms at the test concentration.

1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. Specific hazards are given in Section 10.

2. Referenced Documents
2.1 ASTM Standards:
D1129 Terminology Relating to Water
D1193 Specification for Reagent Water
D1293 Test Methods for pH of Water
D4175 Terminology Relating to Petroleum, Petroleum Products, and Lubricants
D4447 Guide for Disposal of Laboratory Chemicals and Samples
D6384 Terminology Relating to Biodegradability and Eco-toxicity of Lubricants
E943 Terminology Relating to Biological Effects and Environmental Fate

2.2 ISO Standards:
ISO 4259:1992(E) Petroleum Products - Determination and Application of Precision Data in Relation to Methods of Test
ISO 6107-2:1997 Water Quality - Vocabulary - Part 2
ISO 8192:1986 Water Quality - Test for Inhibition of Oxygen Consumption by Activated Sludge
ISO 9408:1999 Water Quality - Evaluation of Ultimate Aerobic Biodegradability of Organic Compounds in Aqueous Medium by Determination of Oxygen Demand in a Closed Respirometer

2.3 OECD Standards:
OECD 301F:1992 Ready Biodegradability-Manometric Respirometry

2.4 APHA Standards:
2540B Total Solids Dried at 103-105°C
9215 Heterotrophic Plate Count

3. Terminology
3.1 Definitions:
3.1.1 Definitions of terms applicable to this test method appear in the Compilation of ASTM Standard Definitions and the following terminology standards: D1129, D4175, D6384, E943, and ISO 6107-2:1997.

3.1.2 activated sludge, n - the precipitated solid matter, consisting mainly of bacteria and other aquatic microorganisms, that is produced at a domestic wastewater treatment plant and is used primarily in secondary sewage treatment to microbially oxidize dissolved organic matter in the effluent.

3.1.3 aerobic, adj - (a) taking place in the presence of oxygen; (b) living or active in the presence of oxygen.

3.1.4 biochemical oxygen demand (BOD), n - the mass concentration of dissolved oxygen consumed under specified conditions by the biological oxidation of organic or inorganic matter, or both.
3.1.4.1 Discussion - BOD determination is performed using empirical tests employing standardized laboratory procedures. These tests measure oxygen utilization during a specified incubation period for the biochemical degradation of organic material (carbonaceous demand) in water.

3.1.5 biodegradation, n - the process of chemical breakdown or transformation of a test material caused by microorganisms or their enzymes.
3.1.5.1 Discussion - Biodegradation is only one mechanism by which materials are removed, transformed, or both, in the environment.

3.1.6 lag phase, n - the period of diminished physiological activity and cell division following the addition of microorganisms to a new culture medium.

3.1.7 log phase, n - the period of growth of microorganisms during which cells divide at a positive constant rate.

3.1.8 pre-adaptation, n - the incubation of an inoculum in the presence of the test material which is done prior to the initiation of the test and under conditions similar to the test conditions.
3.1.8.1 Discussion - The aim of pre-adaptation is to improve the precision ofthe test method by decreasing variability in the rate of biodegradation produced by the inoculum. Pre-adaptation may mimic the natural processes which cause changes in the microbial population of the inoculum leading to more rapid biodegradation of the test material but is not expected to change the overall extent of biodegradation of the test material.

3.1.9 pre-condition, n - the pre-incubation of an inoculum under the conditions of the test in the absence of the test material.

3.1.10 sludge, n - a water-formed sedimentary deposit.

3.1.11 suspended solids (of an activated sludge or other inoculum samples), n - solids present in activated sludge or other inoculum samples that are not removed by settling under specified conditions.