A measurement of compost stability is needed for several reasons. It aids in assessing whether the composting process has proceeded sufficiently far to allow the finished compost to be used for its intended application. A different compost stability may be required for different applications of the compost.

A measurement of compost stability also is needed to verify whether a composting plant is processing the waste to previously agreed levels of stability. This measurement is useful in the commissioning of composting plants and the verification of whether plant operators are satisfying permit requirements.

The level of compost stability also will indicate its potential to cause odors if the compost is stored without aeration, as well as the level to which it has been hygienized and how susceptible the compost is to renewed bacterial and possible pathogenic activity. Compost stability is an important parameter with regard to phytotoxicity and plant tolerance of the compost.

The determination of compost stability will allow the selection of well performing composting technologies, as well as the safe application of compost in its various markets. The method indicates a degree of stability, but does not necessarily indicate that one level is preferable over another level of stability.

1.1 This test method covers the stability of a compost sample by measuring oxygen consumption after exposure of the test compost to a well-stabilized compost under controlled-composting conditions on a laboratory scale involving active aeration. This test method is designed to yield reproducible and repeatable results under controlled conditions that resemble the end of the active composting phase. The compost samples are exposed to a well-stabilized compost inoculum that is prepared from municipal solid waste or waste similar to the waste from which the test materials are derived. The aerobic composting takes place in an environment where temperature, aeration, and humidity are monitored closely and controlled.

1.2 This test method yields a cumulative amount of oxygen consumed/g of volatile solids in the samples over a four-day period. The rate of oxygen consumption is monitored as well.

1.3 This test method is applicable to different types of compost samples including composts derived from wastes, such as municipal solid waste, yard waste, source-separated organics, biosolids, and other types of organic wastes that do not have toxicity levels that are inhibitory to the microorganisms present in aerobic composting systems.

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 There is no similar or equivalent ISO method.

1.6 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 hazard statements are given in Section 8.