ISO 13975:2012
(Main)Plastics — Determination of the ultimate anaerobic biodegradation of plastic materials in controlled slurry digestion systems — Method by measurement of biogas production
Plastics — Determination of the ultimate anaerobic biodegradation of plastic materials in controlled slurry digestion systems — Method by measurement of biogas production
ISO 13975:2012 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.
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
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INTERNATIONAL ISO
STANDARD 13975
First edition
2012-05-01
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 13975:2012(E)
©
ISO 2012
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ISO 13975:2012(E)
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© ISO 2012
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ii © ISO 2012 – All rights reserved
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ISO 13975:2012(E)
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 . 4
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 . 5
8.3 Calculation of percentage biodegradation . 6
9 Expression and interpretation of results . 6
10 Validity of results . 6
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
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ISO 13975:2012(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 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 13975 was prepared by Technical Committee ISO/TC 61, Plastics, Subcommittee SC 5, Physical-
chemical properties.
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ISO 13975:2012(E)
Introduction
Biological recycling (biorecycling) is a viable option, together with mechanical recycling and chemical recycling,
for the recovery of plastic waste. This International Standard 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 International Standard is a biodegradation test method for plastic materials in a controlled
anaerobic slurry system, and differs from ISO 15985 which uses high-solids anaerobic digestion conditions
and ISO 14853 which uses an aqueous system in an anaerobic environment.
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INTERNATIONAL STANDARD ISO 13975:2012(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 International Standard 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
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced document
(including any amendments) applies.
ISO 14853:2005, Plastics — Determination of the ultimate anaerobic biodegradation of plastic materials in an
aqueous system — Method by measurement of biogas production
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
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
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ISO 13975:2012(E)
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 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 an
4 2
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
NOTE 1 to entry: It is measured in days.
3.9
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 1 to entry: It is measured in days.
3.10
plateau phase
time from the end of the biodegradation phase until the end of the test
NOTE 1 to entry: It is measured in days.
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ISO 13975:2012(E)
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 measured. A
2 4
considerable amount of CO will also be dissolved in the digested sludge or dissociated to hydrogen carbonate
2
ion and carbonate ion under the conditions of the test. This dissolved inorganic carbon (DIC) is measured at
the end of the test. The amount of biogas produced is calculated from the volume of biogas collected and the
amount of DIC formed in excess of blank values.
The percentage biodegradation is calculated as the ratio of the sum of the net increase of produced biogas
and DIC to the theoretical amount of evolved biogas (ThBiogas). The biodegradation curve can be followed by
making intermediate measurements of biogas production.
5 Test and reference materials
5.1 Test material: The test material is normally added directly as solids to give a concentration of volatile
solids in the range of 7 g/l to 10 g/l. The test material should preferably be used in powder form or as film.
5.2 Reference material: TLC (thin-layer chromatography) grade microcrystalline cellulose with a particle
size <
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