ISO 18749:2004 specifies a screening test method for the determination of the degree of adsorption of substances on to the activated sludge or primary sludge in a waste water treatment plant.

The conditions described in this International Standard normally correspond to the optimum conditions for the adsorption to occur at the chosen activated-sludge concentration and water hardness during the test period.

The method applies to substances for which an analytical method with sufficient accuracy is available and which, under the conditions of the test and at the test concentration used,

1. are water-soluble;
2. or, if only slightly water-soluble, allow sufficiently stable suspensions, dispersions or emulsions to be prepared;
3. are not significantly removed from the test solution during the test by known abiotic processes such as stripping or foaming;
4. do not deflocculate activated sludge;
5. are not readily biodegradable.