IS 13933 : 1995 Method of test for ready biodegradability of surface active agents (Modified sturm test)

1 Scope

1.1 This standard prescribes the method of test for readybiodegradability of Surface Active Agents.

1.2 Outline of the Method

In this test, test organisms are inoculated into a chemicallydefined microbial growth medium containing the test material.Carbon dioxide-free air is bubbled through the contents and theamount of carbon dioxide produced is estimated by its absorption inbarium hydroxide solution. The biodegradability is judged by theamount of carbon dioxide generated by the test material as apercentage of the theoretical amount that would be produced by thematerial.

1.3 Principle

Aerobic micro-organisms utilising an organic substrate as acarbon and energy source convert the molecule into new cells,carbon dioxide and water. Further, when the available substrate isexhausted, some bacteria die and are subsequently metabolised bythe surviving cells. By measuring the amount of carbon dioxideproduced and comparing the quantity with the theoretical yield,calculated from the substrate carbon content, a measure of theultimate biodegradability can be made. The test duration is limitedto 28 days.

Note - It has been found by experience that materials degradingextensively in this period are readily degraded under practicalconditions. Hence, a result regarded as positive by this testprocedure indicates that the substance tested is readily andultimately biodegradable.