The objectives of the respiration inhibition tests may be defined by the interests of the user, but the test method is designed primarily for examination of the inhibition response with operating microbial systems such as an activated sludge process treating domestic or industrial wastes.

Different apparatus exist that facilitate continuous or continual measurement of respiration in microbial systems and each may be used as the tool to observe respiration in this test method.

Respirometry may utilize any apparatus and technique that will achieve the determination of respiration rate. A number of devices are presented in Appendix X1. Equivalency in the experimental capability of each device is not implied. The analyst should select the respirometric approach that best suits his needs.

The inhibitory effect of a test candidate is identified more completely by examining inhibition over a range of concentrations, such as determining the EC₅₀. The use of aerated containers permits concurrent management of a series of cell suspensions. A respirometer for each cell suspension might also be used.

1.1 This test method covers a batch procedure that evaluates the impact of selected wastewaters, materials, or specific compounds on the respiration rate of an aqueous microbial culture, such as activated sludge.

1.2 Alternative procedures for measurement of microbial activity, such as adenosine 5` triphosphate (ATP), specific substrate utilization, etc. are not within the scope of this test method.

1.3 The results obtained are based on comparisons in a specific test series that examines a range of concentrations of the potentially inhibitory test candidate using batch methods in a laboratory. Results are completed in a short time frame (a few hours).

1.4 The test results are specific to the microbial culture used. Microbial culture from different wastewater treatment plants will differ in kinds and numbers of organisms, and performance capability. Thus, there is no basis for comparing results for microbial cultures from different treatment facilities.

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.