ISO 11733:2004规定了测定需氧微生物对有机化合物的消除和生物降解性的方法。所描述的条件模拟废水处理厂。可以使用两种测试系统:活性污泥设备或多孔罐。测试可以任选地在硝化和反硝化以及单元偶联的条件下进行。 本方法适用于在试验条件下为 在测试浓度下可溶于自来水，如果确定除消除外还会发生生物降解，预计不会转化为不溶性代谢物；水溶性差，但可令人满意地分散在水中并允许用合适的分析手段(例如有机碳测量)检测；非挥发性的，或在测试条件下具有可忽略的蒸气压；在为试验选择的浓度下对试验微生物无抑制作用。在该测试中使用的浓度下具有抑制作用的化合物可以在低于其EC20值的浓度下进行测试，然后在适应一段时间后以更高的实际浓度进行测试。 该方法还可用于测量废水中溶解有机化合物（在该方法中也称为“测试化合物”）的生物降解和消除。

ISO 11733:2004 specifies a method for the determination of the elimination and the biodegradability of organic compounds by aerobic micro-organisms. The conditions described simulate a wastewater treatment plant. Two test systems can be used: activated sludge plants or porous pots. The tests can optionally be performed under conditions of nitrification and denitrification and coupling of the units. The method applies to organic compounds which, under the conditions of the test, are

1. soluble in tap water at the test concentration and not expected to be transformed to insoluble metabolites if biodegradation, in addition to elimination, is determined;
2. poorly water-soluble, but which are satisfactorily dispersible in water and allow detection with suitable analytical means (e.g. organic carbon measurements);
3. non-volatile, or which have a negligible vapour pressure under the test conditions;
4. not inhibitory to the test micro-organisms at the concentration chosen for the test. Compounds inhibitory at concentrations used in this test may be tested at concentrations less than their EC₂₀ value, followed by higher practical concentrations after a period of acclimatization.

The method can also be used to measure the biodegradation and elimination of dissolved organic compounds in waste water (also called "test compound" in the method).