SIST ISO 18749:2010

INTERNATIONAL ISO
STANDARD 18749
First edition
2004-02-15
Water quality — Adsorption of
substances on activated sludge — Batch
test using specific analytical methods
Qualité de l'eau — Adsorption des substances sur la boue activée —
Essai de lot utilisant des méthodes analytiques spécifiques

Reference number
©
ISO 2004
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Contents Page
1 Scope . 1
2 Terms and definitions . 1
3 Principle . 2
4 Reagents and materials . 2
5 Apparatus . 4
6 Test environment . 5
7 Procedure . 5
8 Calculation . 7
9 Validity of the test . 9
10 Test report . 9
Bibliography . 10
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ISO 2004 – All rights reserved iii

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International
Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 18749 was prepared by Technical Committee ISO/TC 147, Water quality, Subcommittee SC 5, Biological
methods.
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iv ISO 2004 – All rights reserved

Introduction
This test is used as a screening test to determine the degree of adsorption of substances on activated sludge
or primary sludge in waste water treatment plants. General information on the adsorption and desorption of test
compounds may also be obtained by other tests (see e.g. Reference [5] in the Bibliography).
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ISO 2004 – All rights reserved v

.
vi
INTERNATIONAL STANDARD ISO 18749:2004(E)
Water quality — Adsorption of substances on activated
sludge — Batch test using specific analytical methods
WARNING — Activated sludge and sewage contain potentially pathogenic organisms. Take appropriate
precautions when handling them. Handle with care toxic test compounds and those whose properties
are unknown.
1Scope
This International Standard 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,
a) are water-soluble;
b) or, if only slightly water-soluble, allow sufficiently stable suspensions, dispersions or emulsions to be
prepared;
c) are not significantly removed from the test solution during the test by known abiotic processes such as
stripping or foaming;
d) do not deflocculate activated sludge;
e) are not readily biodegradable (for a discussion of biodegradability, see ISO/TR 15462).
An important parameter that can influence the reliability of the test results is the stability of the test compound
during the test. If no information on the stability is available, it is recommended that this be checked before the
test. If any transformation (e.g. due to hydrolysis) is observed, it is recommended that the degree of adsorption
of the transformation products be determined, if possible. Since biodegradability of the test compound may also
lead to an incorrect assessment of the degree of adsorption, it is recommended that the biodegradability be
investigated in advance using standard biodegradation tests which are preferably based on oxygen
consumption or on carbon dioxide production and in which adsorption has no influence on the test result. If
biodegradation cannot be excluded, sterilized sludge may be used (see Clause 7). There is generally no need
to carry out adsorption tests on substances which are readily biodegradable as they are sufficiently removed
biologically in waste water treatment plants. Substances which are easily adsorbed on activated sludge in waste
water treatment plants are preferably removed by adsorbing them in sludge digesters and degrading them
anaerobically. For such substances, high adsorption may be a reason for carrying out anaerobic biodegradation
tests. An overview of standardized biodegradation tests is given in ISO/TR 15462.
The test compound concentrations used in this method are usually very low and therefore no negative effects
are to be expected on the capacity of the activated sludge to adsorb even toxic test compounds. When there is
any doubt, it is recommended that microscopic investigations of the flocs and suitable toxicity tests such as that
specified in ISO 8192 be carried out.
2 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
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ISO 2004 – All rights reserved 1

2.1
activated sludge
biomass and inert matter produced in the aerobic treatment of waste water by the growth of bacteria and other
microorganisms in the presence of dissolved oxygen
2.2
degree of adsorption on activated sludge
percentage of a test compound eliminated by any process except biodegradation and stripping under the
conditions of a specific aqueous batch test by activated or primary sludge, determined by comparing the
concentration at the beginning of the test with that at the end
2.3
distribution coefficient
the ratio of the concentration of a test compound in the sludge to its concentration in the aqueous phase
2.4
concentration of suspended solids in an activated sludge
amount of solids obtained from a known volume of activated sludge by filtration or centrifugation under specified
◦
conditions and drying at about 105 C to constant mass
3Principle
The method determines the degree of adsorption, and, optionally, the distribution coefficient and mass balance,
of water-soluble organic substances on activated or primary sludge using an aqueous batch-test system. The
test mixture usually comprises an inorganic-salt test medium, activated sludge and the test compound. The
hardness of the test medium, the concentration of suspended solids in the activated sludge and the amount of
test compound added are specified to simulate real conditions of waste water treatment plants. Thus, the initial
concentration of the test compound is usually as low as possible within the sensitivity range of the analytical
methods available.
The concentration of the test compound is measured using substance-specific analytical methods at the
beginning, during and at the end of the test (normally 24 h). The measured values are used as the basis for
calculating the degree of adsorption and, optionally, the distribution coefficient and the mass balance. The
measurement of elimination in the test vessels generally allows no direct differentiation between adsorption and
other elimination mechanisms such as complex formation, flocculation, precipitation, sedimentation or
biodegradation. More information can be obtained by using an abiotic elimination control without activated
sludge, sterilized sludge and/or by determining biodegradation of the test compound with appropriate tests.
4 Reagents and materials
Use only reagents of recognized analytical grade.
4.1 Water
Use distilled or de-ionized water containing less than 1mg of dissolved organic carbon (DOC) per litre.
4.2 Test medium
4.2.1 Preparation of solution A
Anhydrous potassium dihydrogen phosphate (KH PO ) 8,5 g
2 4
Anhydrous dipotassium hydrogen phosphate (K HPO ) 21,75 g
2 4
Disodium hydrogen phosphate dihydrate (Na HPO ·2H O) 33,4 g
2 4 2
Dissolve in water (4.1) and make up to 1 000 ml
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2 ISO 2004 – All rights reserved

It is recommended that this buffer solution be checked by measuring its pH. If it is not about 7,4± 0,5, prepare
a new solution.
4.2.2 Preparation of solution B
Dissolve 12,3 g of magnesium sulfate heptahydrate (MgSO ·7H O) in water (4.1) and make up to 1 000 ml.
4 2
4.2.3 Preparation of solution C
Dissolve 29,4 g of calcium chloride dihydrate (CaCl ·2H O) in water (4.1) and make up to 1 000 ml.
2 2
4.2.4 Preparation of solution D
Dissolve 22,4 g of sodium hydrogen carbonate (NaHCO ) in water (4.1) and make up to 1 000 ml.
4.2.5 Preparation of test medium
The test medium is prepared at the beginning of each test by adding the correct amounts of stock solutions A to
D to the test compound as described in Clause 7. It is important to follow the instructions in Clause 7 to avoid
precipitation of the salts. The hardness of the test medium is adjusted to a value which will depend on the usual
water hardness in the region concerned or on the purpose of the test. Mixing 10 ml of each of solutions A to D
2+ 2+
and making up to 1 000 ml with water (4.1) will give a hardness of 2,5 mmol/l (80 mg/l of Ca , 12 mg/l of Mg )
–
and a hydrogen carbonate (HCO ) concentration of 162 mg/l, which is typical for many waste waters. If
required, another hardness may be used. In this case, change the amounts of solutions B and C added, bearing
2+
in mind that an extra 1 ml of solution B corresponds to an increase in Mg concentration of 0,05 mmol/l and an
2+
extra 1 ml of solution C to an increase in Ca concentration of 0,2 mmol/l. Indicate the hardness used and the
Ca/Mg ratio clearly in the test report.
If a test compound influences the pH of the mixture significantly at the chosen concentration (e.g. if the pH is
outside 6,0 to 9,0), an increase in the buffer capacity of the test medium may be required. In such cases, add
more of solution A, e.g. 100 ml instead of 10 ml.
Solutions A to D may be stored for up to 6 months in the dark at room temperature.
4.3 Preparation of stock solutions of test compound and reference material
Dissolve the test compound in water (4.1) or in test medium (4.2) at a suitable concentration. Suitable means a
concentration which simulates real environmental conditions (e.g. of waste water), but which is high enough to
allow a sufficiently accurate quantitative determination of the test compound remaining at the end of the test to
be made, using the intended analytical procedure, even after elimination of about 90 % by adsorption. In the
case of substances which are toxic to activated sludge and might for this reason influence the adsorptive
capacity of the sludge and hence the test result (see Clause 1), the concentration shall be low enough to avoid
this effect. The concentration may also be governed by the intended purpose of the test, for example the
simulation of an exposure scenario at a given environmental concentration. If there is no special request or
other information, a concentration of 1 mg/l to 5 mg/l is appropriate for substance-spec
...