ISO 13975:2019

INTERNATIONAL ISO
STANDARD 13975
Second edition
2019-04
Plastics — Determination of the
ultimate anaerobic biodegradation
of plastic materials in controlled
slurry digestion systems — Method by
measurement of biogas production
Plastiques — Évaluation de la biodégradabilité anaérobie ultime
des matériaux plastiques dans des systèmes de digestion de boue
contrôlés — Méthode par mesurage de la production de biogaz
Reference number
©
ISO 2019
© ISO 2019
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ii © ISO 2019 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 3
5 Test and reference materials . 3
6 Apparatus . 3
7 Procedure. 4
7.1 General . 4
7.2 Preparation of inoculum . 4
7.3 Start-up of the test . 5
7.4 Measurement of biogas produced (see Annex A) . 5
7.5 Test duration . 5
7.6 Measurement of dissolved inorganic carbon (see Annex B) . 5
8 Calculation and expression of results . 5
8.1 Amount of biogas produced . 5
8.2 Amount of dissolved inorganic carbon . 6
8.3 Calculation of percentage biodegradation . 6
9 Expression and interpretation of results . 7
10 Validity of results . 7
11 Test report . 7
Annex A (informative) Examples of test systems . 8
Annex B (informative) Example of apparatus for measurement of biogas dissolved in slurry .10
Annex C (informative) Example of a biodegradation curve .11
Annex D (informative) Table of water vapour pressures at various temperatures .12
Bibliography .13
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
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ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
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on the ISO list of patent declarations received (see www .iso .org/patents).
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URL: www .iso .org/iso/foreword .html.
This document was prepared by Technical Committee ISO/TC 61, Plastics, Subcommittee SC 14,
Environmental aspects.
This second edition cancels and replaces the first edition (ISO 13975:2012), which has been technically
revised. The main changes compared to the previous edition are as follows:
— at least following numbers of test vessels have been provided;
— three test vessels for the test mixture;
— three vessels for blank controls;
— three vessels for checking inoculum activity using a reference material;
— the Clausius-Clapeyron equation has been collected (see Formula D.1).
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/members .html.
iv © ISO 2019 – All rights reserved

Introduction
Biological recycling (biorecycling), together with mechanical recycling and chemical recycling,
is a viable option for the recovery of plastic waste. This document specifies a method of evaluating
the anaerobic biodegradability of such waste in a controlled anaerobic slurry system. This is a
representative anaerobic digestion test method and system for biodegradable plastic waste.
The production of a biogas is observed under anaerobic conditions suitable for the growth of
thermophilic or mesophilic microorganisms. The biogas is collected in a bag under atmospheric
pressure, and the biogas volume is measured with a syringe or a gas burette. The biodegradability of
the test material is evaluated from the sum of the amount of carbon dioxide dissolved in the supernatant
and the cumulative quantity of evolved biogas. This document describes a biodegradation test method
for plastic materials in a controlled anaerobic slurry system. It differs from ISO 15985 which uses high-
solids anaerobic digestion conditions, and ISO 14853 which uses an aqueous system in an anaerobic
environment.
INTERNATIONAL STANDARD ISO 13975:2019(E)
Plastics — Determination of the ultimate anaerobic
biodegradation of plastic materials in controlled slurry
digestion systems — Method by measurement of biogas
production
WARNING — Sewage sludge and other organic waste might contain potentially pathogenic
organisms. Therefore, appropriate precautions should be taken when handling such materials.
Digestion of organic materials produces flammable gases that present fire and explosion
risks. These gases also contain toxic chemicals, including hydrogen sulfide and ammonia, in
substantial concentrations. Appropriate safety measures, such as the use of a draft chamber,
gas masks and/or well-ventilated laboratory facilities, should be taken. Toxic test chemicals and
chemicals whose properties are not known should be handled with care and in accordance with
safety instructions. Care should be taken when transporting and storing quantities of organic
matter undergoing digestion.
1 Scope
This document specifies a method of evaluating the ultimate anaerobic biodegradability of plastic
materials in a controlled anaerobic slurry digestion system with a solids concentration not exceeding
15 %, which is often found for the treatment of sewage sludge, livestock faeces or garbage. The test
method is designed to yield a percentage and rate of conversion of the organic carbon in the test
materials to carbon dioxide and methane produced as biogas.
The method applies to the following materials, provided they have a known carbon content:
— natural and/or synthetic polymers, copolymers or mixtures;
— plastic materials that contain additives such as plasticizers, colorants, or other compounds;
— water-soluble polymers.
It does not apply to materials which exhibit inhibitory effects on the test microorganisms at the
concentration chosen for the test.
NOTE Inhibitory effects can be determined by an inhibition test (e.g. ISO 13641-1 or ISO 13641-2).
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https: //www .iso .org/obp
— IEC Electropedia: available at http: //www .electropedia .org/
3.1
ultimate anaerobic biodegradation
breakdown of an organic compound by microorganisms in the absence of oxygen into carbon dioxide,
methane, water and mineral salts of any other elements present (mineralization) plus new biomass
3.2
digested sludge
mixture of the settled sewage and activated sludge which has been incubated in a mesophilic or
thermophilic anaerobic digester to reduce the biomass and odour and to improve the dewaterability of
the sludge
Note 1 to entry: Digested sludge contains an association of anaerobic fermentative and methanogenic
microorganisms producing carbon dioxide and methane.
3.3
slurry
watery mixture of insoluble matter
Note 1 to entry: The suspended-solids concentration of a slurry might be as high as around 15 %, but slurry is
fluid and pumpable.
3.4
dissolved inorganic carbon
DIC
carbon dioxide dissolved in water or transformed into carbonic acid, hydrogen carbonate ion and
carbonate ion
3.5
total dry solids
amount of solids obtained by taking a known volume of test material or inoculum and drying at about
105 °C to constant mass
3.6
volatile solids
amount of solids obtained by subtracting the residue of a known volume of test material or inoculum
after incineration at about 550 °C from the total dry solids (3.5) of the same test portion
Note 1 to entry: The volatile-solids content is an indication of the amount of organic matter present.
3.7
theoretical amount of evolved biogas
ThBiogas
maximum theoretical amount of biogas (CH + CO ) which will evolve after complete biodegradation of
4 2
an organic compound under anaerobic conditions
Note 1 to entry: ThBiogas is calculated from the molecular formula and expressed as litres of biogas evolved per
gram of test material under the standard conditions.
3.8
lag phase
time from the start of an anaerobic digestion test until adaptation and/or selection of the degrading
microorganisms is achieved and the degree of biodegradation of a chemical compound or organic
matter has increased to about 10 % of the maximum level of biodegradation (3.11)
Note 1 to entry: It is measured in days.
3.9
biodegradation phase
time from the end of the lag phase (3.8) of a test until about 90 % of the maximum level of biodegradation
(3.11) has been reached
Note 1 to entry: It is measured in days.
2 © ISO 2019 – All rights reserved

3.10
plateau phase
time from the end of the biodegradation phase (3.9) until the end of the test
Note 1 to entry: It is measured in days.
3.11
maximum level of biodegradation
degree of biodegradation of a chemical compound or organic matter in a test, above which no further
biodegradation takes place during the test
Note 1 to entry: It is measured in percent.
4 Principle
This test method is designed to determine the biodegradability of plastic materials under anaerobic
conditions in a slurry system. The methanogenic inoculum is obtained from an anaerobic digester
operating on sewage sludge or, alternatively, on organic waste such as livestock faeces or garbage.
The test material mixed with the inoculum is anaerobically incubated in a test vessel at a pre-selected
temperature for a period normally of 60 days. The test period may be shortened or extended until a
plateau phase is reached, but the total period shall not exceed 90 days. The digestion temperature
shall be (55 ± 5) °C in order to simulate thermophilic anaerobic digestion. Alternatively, the digestion
temperature may be set at (35 ± 3) °C in order to simulate mesophilic anaerobic digestion.
The volume of the gases produced in the test vessel, carbon dioxide (CO ) and methane (CH ), is
2 4
measured. A considerable amount of CO will also be dissolved in the digested sludge or dissociated
to hydrogen carbonate ion and carbonate ion under the conditions of the test. This dis
...