SIST EN ISO 9408:2000

SLOVENSKI STANDARD
SIST EN ISO 9408:2000
01-januar-2000
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Water quality - Evaluation of ultimate aerobic biodegradability of organic compounds in
aqueous medium by determination of oxygen demand in a closed respirometer (ISO
9408:1999)
Wasserbeschaffenheit - Bestimmung der vollständigen aerobiologischen Abbaubarkeit
organischen Stoffe im wäßrigen Medium über die Bestimmung des Sauerstoffbedarfs in
einem geschlossenen Respirometer (ISO 9408:1999)
Qualité de l'eau - Evaluation de la biodégradibilité aérobieultime des composés
organiques, en milieux aqueux, par détermination de la demande en oxygene dans un
respirometre ferméometre fermé (ISO 9408:1999)
Ta slovenski standard je istoveten z: EN ISO 9408:1999
ICS:
13.060.70 Preiskava bioloških lastnosti Examination of biological
vode properties of water
SIST EN ISO 9408:2000 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN ISO 9408:2000

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SIST EN ISO 9408:2000

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SIST EN ISO 9408:2000

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SIST EN ISO 9408:2000
INTERNATIONAL ISO
STANDARD 9408
Second edition
1999-08-01
Water quality — Evaluation of ultimate
aerobic biodegradability of organic
compounds in aqueous medium
by determination of oxygen demand
in a closed respirometer
Qualité de l'eau — Évaluation, en milieu aqueux, de la biodégradabilité
aérobie ultime des composés organiques par détermination de la demande
en oxygène dans un respiromètre fermé
A
Reference number
ISO 9408:1999(E)

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SIST EN ISO 9408:2000
ISO 9408:1999(E)
Contents Page
1 Scope .1
2 Terms and definitions .1
3 Principle.3
4 Test environment.3
5 Reagents.4
6 Apparatus .5
7 Procedure .5
8 Calculation and expression of results.8
9 Validity of results.10
10 Test report .11
Annex A (informative) Example of calculation of theoretical oxygen demand.12
Annex B (informative) Correction of oxygen uptake for interference by nitrification.14
(informative)
Annex C Example of a biodegradation curve .16
Annex D (informative) Closed respirometer .17
Bibliography.18
©  ISO 1999
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic
or mechanical, including photocopying and microfilm, without permission in writing from the publisher.
International Organization for Standardization
Case postale 56 • CH-1211 Genève 20 • Switzerland
Internet iso@iso.ch
Printed in Switzerland
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SIST EN ISO 9408:2000
© ISO
ISO 9408:1999(E)
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 3.
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.
International Standard ISO 9408 was prepared by Technical Committee ISO/TC 147, Water quality, Subcommittee
SC 5, Biological methods.
This second edition cancels and replaces the first edition (ISO 9408:1991), which has been technically revised.
Annexes A to D of this International Standard are for information only.
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SIST EN ISO 9408:2000

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SIST EN ISO 9408:2000
INTERNATIONAL STANDARD  © ISO ISO 9408:1999(E)
Water quality — Evaluation of ultimate aerobic biodegradability
of organic compounds in aqueous medium by determination
of oxygen demand in a closed respirometer
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.
1 Scope
This International Standard specifies a method, by determination of the oxygen demand in a closed respirometer, for
the evaluation in aqueous medium of the ultimate biodegradability of organic compounds and waste waters at a given
concentration by aerobic microorganisms.
The method applies to organic compounds which
a) are water-soluble under the conditions of the test;
b) are poorly water-soluble under the conditions of the test, in which case special measures may be necessary to
achieve good dispersion of the compound (see for example, ISO 10634);
c) do not reach and react with the CO absorbent;
2
d) are volatile, provided that a suitable respirometer or suitable conditions (e.g. a smaller ratio of volume head
space to volume liquid medium) are used;
e) are not inhibitory to the test microorganisms at the concentration chosen for the test. The presence of inhibitory
effects can be determined as specified in 7.3, or by using any other method for determining the inhibitory effect of
a compound on bacteria (see, for example, ISO 8192).
NOTE The conditions described in this International Standard do not always correspond to the optimal conditions for
allowing the maximum degree of biodegradation to occur. For alternative biodegradation methods, see ISO 15462.
2 Terms and definitions
For the purposes of this International Standard, the following terms and definitions apply.
2.1
ultimate aerobic biodegradation
breakdown of a chemical compound or organic matter by microorganisms in the presence of oxygen to carbon
dioxide, water and mineral salts of any other elements present (mineralization) and the production of new biomass
2.2
primary biodegradation
structural change (transformation) of a chemical compound by microorganisms, resulting in the loss of a specific
property
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SIST EN ISO 9408:2000
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2.3
activated sludge
biomass produced in the aerobic treatment of wastewater by the growth of bacteria and other microorganisms in the
presence of dissolved oxygen
2.4
concentration of suspended solids of an activated sludge
amount of solids obtained by filtration or centrifugation of a known volume of activated sludge and drying at about
105 °C to constant mass
2.5
biochemical oxygen demand
BOD
mass concentration of dissolved oxygen consumed under specified conditions by the aerobic biological oxidation of
a chemical compound or organic matter in water
NOTE It is expressed in this case as milligrams oxygen uptake per milligram (or gram) test compound.
2.6
chemical oxygen demand
COD
mass concentration of oxygen equivalent to the amount of a specified oxidant consumed by a chemical compound
or organic matter when a water sample is treated with that oxidant under defined conditions
NOTE It is expressed in this case as milligrams oxygen consumed per milligram (or gram) test compound.
2.7
theoretical oxygen demand
ThOD
theoretical maximum amount of oxygen required to oxidize a chemical compound completely, calculated from the
molecular formula
NOTE It is expressed in this case as milligrams oxygen required per milligram (or gram) test compound.
2.8
dissolved organic carbon
DOC
that part of the organic carbon in the water which cannot be removed by specified phase separation
–2
NOTE Examples of specified phase separation are centrifugation at 40 000 m{s for 15 min or by membrane filtration
using membranes with pores of 0,2 mm to 0,45 mm diameter.
2.9
lag phase
time from the start of a test until adaptation and/or selection of the degrading microorganisms are achieved and the
biodegradation degree of a chemical compound or organic matter has increased to about 10 % of the maximum
level of biodegradation
NOTE It is expressed in days.
2.10
maximum level of biodegradation
maximum biodegradation degree of a chemical compound or organic matter in a test, above which no further
biodegradation takes place during the test
NOTE It is expressed in percent.
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SIST EN ISO 9408:2000
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ISO 9408:1999(E)
2.11
biodegradation phase
time from the end of the lag phase of a test until about 90 % of the maximum level of biodegradation has been
reached
NOTE It is expressed in days.
2.12
plateau phase
time from the end of the biodegradation phase until the end of the test
NOTE It is expressed in days.
2.13
pre-exposure
pre-incubation of an inoculum in the presence of the test chemical compound or organic matter, with the aim of
enhancing the ability of this inoculum to biodegrade the test material by adaptation and/or selection of the
microorganisms
2.14
preconditioning
pre-incubation of an inoculum under the conditions of the subsequent test in the absence of the test chemical
compound or organic matter, with the aim of improving the performance of the test by acclimatization of the
microorganisms to the test conditions
3 Principle
Determination of the biodegradation of organic compounds by aerobic microorganisms is carried out using a static
aqueous test system. Organic compounds in the context of this International Standard include waste waters. The
test mixture contains an inorganic medium, the organic compound as the sole source of carbon and energy at a
mass concentration of normally 100 mg/l organic carbon [but its theoretical oxygen demand (ThOD) shall be at least
100 mg/l], and a mixed inoculum obtained from a waste-water treatment plant or from another source in the
environment.
The mixture is agitated in a closed test vessel and the consumption of oxygen is determined either by measuring
the amount of oxygen required to maintain a constant gas volume in the respirometer vessel, or by measuring the
change in volume or pressure (or a combination of the two) in the apparatus. The evolved carbon dioxide is
absorbed in a suitable substance in the test vessel.
The degradation is followed over a period of 28 d, or longer if necessary, by determining the consumption of oxygen
either automatically or manually. The amount of oxygen consumed by the organic compound (after correction by
comparison with blank control) is expressed as a percentage of either the theoretical oxygen demand (ThOD),
calculated from the formula of the compound, or the chemical oxygen demand (COD).
For sufficiently water-soluble compounds, removal of dissolved organic carbon (DOC) may be determined
(optionally) by measuring the concentration of DOC at the beginning and the end of incubation to obtain additional
information on the ultimate biodegradability. If a substance-specific analytical method is available, information on the
primary degradability may be obtained.
4 Test environment
o o
Incubation shall take place in the dark or in diffused light, at a temperature within the range 20 C to 25 C which
o
shall not vary by more than ± 1 C during the test.
3

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SIST EN ISO 9408:2000
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ISO 9408:1999(E)
5 Reagents
Use only reagents of recognized analytical grade.
5.1 Water
Distilled or deionized water containing less than 1 mg/l DOC.
5.2 Test medium
5.2.1 Composition
5.2.1.1 Solution a)
Dissolve
anhydrous potassium dihydrogenphosphate (KH PO ) 8,5 g
2 4
anhydrous dipotassium hydrogenphosphate (K HPO ) 21,75 g
2 4
.
disodium hydrogenphosphate dihydrate (Na HPO 2H O) 33,4 g
2 4 2
ammonium chloride (NH Cl) 0,5 g
4
water (5.1), in quantity necessary to make up to 1000 ml
In order to check this buffer solution, it is recommended to measure the pH, which should be at about 7,4. If this is
not the case prepare a new solution.
5.2.1.2 Solution b)
Dissolve 22,5 g magnesium sulfate heptahydrate (MgSO {H O) in water (5.1), quantity necessary to make up to
4 2
1000 ml.
5.2.1.3 Solution c)
Dissolve 36,4 g calcium chloride dihydrate (CaCl {2H O) in water (5.1), quantity necessary to make up to 1000 ml.
2 2
5.2.1.4 Solution d)
Dissolve 0,25 g iron(III) chloride hexahydrate (FeCl {6H O) in water (5.1), quantity necessary to make up to
3 2
1000 ml. Prepare this solution freshly before use, or add a drop of concentrated hydrochloric acid (HCl) to avoid
precipitation
5.2.2 Preparation of the test medium
For 1000 ml of test medium, add to about 800 ml of water (5.1):
 10 ml of solution a);
 1 ml of each of the solutions b) to d).
Make up to 1000 ml with the water (5.1). Prepare the test medium freshly before use. The solutions a) to c) may be
stored up to 6 months in the dark at room temperature.
5.3 Carbon dioxide absorber
Potassium hydroxide solution (about 10 mol/l), soda lime pellets or other suitable absorbent.
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SIST EN ISO 9408:2000
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5.4 Mercury chloride solution
Dissolve 1 g of mercury(II) chloride (HgCl ) in 100 ml of the water (5.1).
2
5.5 Sodium hydroxide solution
Dissolve sodium hydroxide (NaOH) in the water (5.1) to obtain a solution of concentration 0,1 mol/l to 0,5 mol/l.
5.6 Hydrochloric acid solution
Dilute concentrated hydrochloric acid (HCl) in the water (5.1) to obtain a solution of concentration 0,1 mol/l to
0,5 mol/l.
6 Apparatus
Ensure that all glassware is thoroughly cleaned and free from organic or toxic matter.
6.1 Closed respirometer
The principle of a closed respirometer is given in annex D. The respirometer contains test vessels allowing oxygen
supply and stirring, including tubing nonpermeable to oxygen and carbon dioxide. The respirometer vessels are
located in a constant temperature room or in a thermostatically controlled water-bath. When testing volatile
compounds, the apparatus used shall be appropriate or adapted to this particular purpose. Care shall be taken that
there is no loss of compound due to the apparatus.
6.2 Water-bath or constant temperature room (to comply with clause 4)
6.3 Equipment for measurement of dissolved organic carbon
Instrument of sufficient sensitivity for the measurement of dissolved organic carbon (DOC) (optional).
)
6.4 Device for determining chemical oxygen demand (COD) (optional
6.5 Centrifuge or device for filtration
The centrifuge shall be capable of producing an acceleration of 4 000 g.
The filtration apparatus shall be equipped with membrane filters (nominal aperture diameter of 0,2 mm to 0,45 mm
pore size) which do not adsorb or release organic carbon.
6.6 pH meter (usual laboratory equipment)
7 Procedure
7.1 Preparation of the test solutions
7.1.1 Test compound
Prepare a stock solution of a sufficiently water-soluble test compound in the test medium (5.2) and add a suitable
amount of this solution to the test vessels to obtain a final mass concentration of 100 mg/l test compound, but
equivalent to at least 100 mg/l ThOD. Depending on the properties of the test compound (e.g. toxicity) and the
purpose of the test, other concentrations may be used. Add compounds of low water-solubility directly into the test
vessels. Determine the added amount exactly. Determine, if required, the COD of the test compound using e.g.
ISO 6060.
NOTE For more details on handling poorly water-soluble compounds, see ISO 10634.
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SIST EN ISO 9408:2000
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7.1.2 Solution of the reference compound
Use as reference compound an organic compound of known biodegradability, such as aniline or sodium benzoate
which have degradation degrees >60 %. Prepare a stock solution of the reference compound in the test medium
(5.2) in the same way as with a water-soluble test compound (7.1.1), in order to obtain a final mass concentration of
100 mg reference compound per litre test medium.
7.1.3 Solution to check inhibition
If required (e.g. when no information on the toxicity of test compound is available), prepare a solution containing, in
the test medium (5.2), both the test compound (7.1.1) and the reference compound (7.1.2) preferably at mass
concentrations of 100 mg/l for each.
7.2 Preparation of the inoculum
7.2.1 General
Prepare the inoculum, using preferably activated sludge or the following sources (7.2.2 to 7.2.4) or a mixture of
these sources, to obtain a microbial population that offers sufficient biodegradative activity. Check the activity of the
inoculum by means of the reference compound (7.1.2 and clause 9). The BOD of the blank shall fulfil the validity
criteria (see clause 9). To reduce the influence of the blank, it may be helpful to precondition the inoculum, e.g. by
aerating it, up to one week before use. Use a suitable volume for inoculation.
NOTE Normally the inoculum should not be pre-exposed to the test compound, to allow a general prediction of the
degradation behaviour in the environment. In certain circumstances, depending on the purpose of the test, pre-exposed inocula
may be used, provided that this is clearly stated in the test report (e.g. percent biodegradation = x %, using pre-exposed
inocula) and the method of pre-exposure is detailed in the test report. Pre-exposed inocula can be obtained from laboratory
biodegradation tests conducted under a variety of conditions [e.g. Zahn-Wellens test (ISO 9888) and SCAS test (ISO 9887)] or
from samples collected from locations where relevant environmental conditions exist (e.g. treatment plants dealing with similar
compounds or contaminated areas).
Based on experience, suitable volume means:
 sufficient to give a population which offers enough biodegradation activity;
 degrades the reference compound by the stipulated percentage (see clause 9);
3 6
 gives between 10 to 10 colony-forming units per millilitre in the final mixture;
 gives not greater than the equivalent of 30 mg/l suspended solids of activated sludge in the final mixture;
 the quantity of dissolved organic carbon provided by the inoculum should be less than 10 % of the initial
concentration of organic carbon introduced by the test compound;
 generally 1 ml to 10 ml of inocu
...