oSIST prEN ISO 15936:2025
(Main)Soil, waste, treated biowaste and sludge - Determination of total organic carbon (TOC) by dry combustion (ISO/DIS 15936:2025)
Soil, waste, treated biowaste and sludge - Determination of total organic carbon (TOC) by dry combustion (ISO/DIS 15936:2025)
Specifies a method for the determination of the total carbon content in soil after dry combustion. The organic carbon content is calculated from this content after correcting for carbonates present in the sample. If carbonates are removed beforehand, the organic carbon content is measured directly. Applicable to all types of air-dried soil samples.
Boden, Abfall, behandelter Bioabfall und Schlamm - Bestimmung des gesamten organischen Kohlenstoffs (TOC) mittels trockener Verbrennung (ISO/DIS 15936:2025)
Sols, déchets, biodéchets traités et boues - Dosage du carbone organique total (COT) par combustion sèche (ISO/DIS 15936:2025)
La présente Norme internationale prescrit une méthode de dosage du carbone organique et du carbone total du sol après combustion sèche. La teneur en carbone organique est déterminée à partir de cette dernière valeur après correction en raison des carbonates présents dans l'échantillon. Si ces derniers sont éliminés au préalable, on effectue le dosage du carbone organique directement. La présente Norme internationale est applicable à tous les types d'échantillons de sol séchés à l'air.
Tla, odpadki, obdelani biološki odpadki in blato - Določanje celotnega organskega ogljika (TOC) s suhim sežigom (ISO/DIS 15936:2025)
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Standards Content (Sample)
SLOVENSKI STANDARD
01-november-2025
Tla, odpadki, obdelani biološki odpadki in blato - Določanje celotnega organskega
ogljika (TOC) s suhim sežigom (ISO/DIS 15936:2025)
Soil, waste, treated biowaste and sludge - Determination of total organic carbon (TOC)
by dry combustion (ISO/DIS 15936:2025)
Boden, Abfall, behandelter Bioabfall und Schlamm - Bestimmung des gesamten
organischen Kohlenstoffs (TOC) mittels trockener Verbrennung (ISO/DIS 15936:2025)
Sols, déchets, biodéchets traités et boues - Dosage du carbone organique total (COT)
par combustion sèche (ISO/DIS 15936:2025)
Ta slovenski standard je istoveten z: prEN ISO 15936
ICS:
13.030.20 Tekoči odpadki. Blato Liquid wastes. Sludge
13.080.10 Kemijske značilnosti tal Chemical characteristics of
soils
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
DRAFT
International
Standard
ISO/DIS 15936
ISO/TC 190/SC 3
Soil, waste, treated biowaste and
Secretariat: DIN
sludge — Determination of total
Voting begins on:
organic carbon (TOC) by dry
2025-10-02
combustion
Voting terminates on:
ICS: 13.080.10
2025-12-25
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
PUBLISHED AS SUCH.
This document has not been edited by the ISO Central Secretariat.
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Reference number
ISO/DIS 15936:2025(en)
DRAFT
ISO/DIS 15936:2025(en)
International
Standard
ISO/DIS 15936
ISO/TC 190/SC 3
Soil, waste, treated biowaste and
Secretariat: DIN
sludge — Determination of total
Voting begins on:
organic carbon (TOC) by dry
combustion
Voting terminates on:
ICS: 13.080.10
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
PUBLISHED AS SUCH.
This document has not been edited by the ISO Central Secretariat.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
© ISO 2025
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
STANDARDS MAY ON OCCASION HAVE TO
ISO/CEN PARALLEL PROCESSING
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Published in Switzerland Reference number
ISO/DIS 15936:2025(en)
ii
ISO/DIS 15936:2025(en)
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
4.1 Method A (indirect procedure) .2
4.2 Method B (direct procedure) .2
5 Interferences . 2
6 Reagents . 3
7 Apparatus . 4
8 Sample pre-treatment . 4
9 Procedure – Method A (indirect method) . 4
9.1 Determination .4
9.1.1 General .4
9.1.2 Determination of the TC .4
9.1.3 Determination of the TIC .5
9.2 Calibration .5
9.3 Control measurements .5
9.4 Calculation and expression of results .6
10 Procedure Method B (direct method) . 7
10.1 Determination .7
10.1.1 General .7
10.1.2 Removal of the inorganic carbon and determination of the TOC . .7
10.2 Calibration .7
10.3 Control measurements .7
10.4 Calculation and expression of results .8
11 Performance data . 8
12 Expression of results . 8
13 Test report . 9
Annex A (informative) Repeatability and reproducibility data .10
Annex B (informative) Factors influencing dry combustion methods .13
Bibliography .16
iii
ISO/DIS 15936:2025(en)
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.
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).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 190, Soil quality, Subcommittee SC 3, Chemical
and physical characterization.
This edition cancels and replaces ISO 10694:1995, which has been technically revised.
The main changes are as follows:
— the content of EN 15936:2022 and ISO 10694:1995 has been merged;
— the scope has been widened to include treated biowaste, waste and sludge;
— clause 9.2 "Calibration" and 9.3 "Control measurements" have been technical revised;
— the text has been editorially revised.
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
DRAFT International Standard ISO/DIS 15936:2025(en)
Soil, waste, treated biowaste and sludge — Determination of
total organic carbon (TOC) by dry combustion
1 Scope
This document specifies two methods for the determination of total organic carbon (TOC) in sludge, treated
biowaste, soil and waste samples containing more than 0,1 % carbon in relation to the dry matter (dm).
This document is validated for several types of matrices as indicated in Table 1 (see also Annex A for the
results of the validation). The results in this document are expressed in % C in relation to the dry matter (dm).
Table 1 — Matrices for which this document is applicable and validated for
Matrix Materials used for validation
Sludge Municipal sludge
Biowaste Compost, Fresh Compost
Soil Sludge amended soil, Agricultural soil
Waste Filter cake, Bottom ash,
Electro-plating sludge, Dredged sludge,
Rubble
NOTE This method can also be applied to other environmental solid matrices, provided the user has verified the
applicability.
WARNING — Persons using this document should be familiar with usual laboratory practice. This
document does not purport to address all of the safety problems, if any, associated with its use. It is
the responsibility of the user to establish appropriate safety and health practices.
IMPORTANT — It is absolutely essential that tests conducted according to this document be carried
out by suitably trained staff.
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 terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
total carbon
TC
quantity of carbon present in the sample in the form of organic, inorganic and elemental carbon
ISO/DIS 15936:2025(en)
3.2
total inorganic carbon
TIC
quantity of carbon that is liberated as carbon dioxide by acid treatment
Note 1 to entry: Typically, the TIC represents the carbonates present in a sample.
3.3
total organic carbon
TOC
quantity of carbon that is converted into carbon dioxide by combustion and which is not liberated as carbon
dioxide by acid treatment
4 Principle
4.1 Method A (indirect procedure)
In this procedure, the TOC is obtained by the difference between the results of the measurements of TC and TIC.
The total carbon (TC) present in the sample is converted into carbon dioxide by combustion in an oxygen-
containing gas flow free of carbon dioxide. To ensure complete combustion, catalysts and/or modifiers
can be used. The released amount of carbon dioxide is measured e.g. by infrared spectrometry, thermal
conductivity detection, or other suitable techniques.
The TIC is determined separately from another sub-sample by means of acidification and purging of the
released carbon dioxide. The carbon dioxide shall be measured by one of the techniques mentioned above.
4.2 Method B (direct procedure)
In this procedure, the TIC present in the sample are previously removed by treating the sample with acid. The
carbon dioxide released by the following combustion step is measured by one of the techniques mentioned
in 4.1 and indicates the TOC directly.
NOTE The quality of results of Method B is dependent on experience and practice, especially regarding the steps
before the determination of TOC. Use of automatic dispensing units regarding removal of TIC prior to determination of
TOC can improve the performance of Method B.
5 Interferences
Depending on the laboratory experience with samples containing high amounts of TIC, the procedures can
lead to unreliable TOC results if the TIC to TOC ratio is very high (e.g. ≥ 10).
Depending on the detection method used, different interferences can occur, for instance:
— the presence of cyanide can interfere with the coulometric detection of TIC by modifying the pH value
(dissolution of HCN);
— high content of halogenated compounds can lead to an overestimation of TOC when coulometric detection
is used; in some cases the classical silver or copper trap can be insufficient to absorb all halides.
Method B can lead to incorrect results in the following cases:
— Volatile organic substances (e.g. volatile hydrocarbons from sludge of oil separators) can be lost during
sample preparation especially during the acidification. If necessary, the carbon content resulting from
volatile organic substances shall be determined separately.
— side reactions between the sample and the acid take place (e.g. decarboxylation, volatile reaction
products).
ISO/DIS 15936:2025(en)
When present, elemental carbon, carbides, cyanides, cyanates, isocyanates, isothiocyanates and thiocyanates
are determined as organic carbon using the methods described in this document. An interpretation of the
measured value can therefore be problematic in cases where the sample contains relevant levels of the
above-mentioned components. If needed, these components shall be determined separately by means of a
suitable validated method and be recorded in the test report.
Depending on the method of detection used, reagents and/or catalysts may be required for reduction,
oxidation, removal and/or fixing of combustion gases which interfere with the analysis. These reagents and/
or chemicals are to be used according to the manufacturer's instruction.
6 Reagents
Use only reagents of recognized analytical grade, unless otherwise specified.
Hygroscopic substances shall be stored in a desiccator.
6.1 Calcium carbonate, CaCO .
6.2 Sodium carbonate, Na CO , anhydrous.
2 3
6.3 Tetrasodium ethylenediamine tetraacetate-tetra-hydrate, Na -EDTA ∙ 4 H O (C H N O Na ∙ 4
4 2 10 12 2 8 4
H O), heated at 80 °C for 2 h.
Other forms of Na -EDTA hydrates may be used if the water content is exactly known. In these cases, the
composition of the control mixtures shall be recalculated accordingly (see also 6.10 and 6.11).
6.4 Potassium hydrogen phthalate, C H O K.
8 5 4
6.5 Acetanilide, C H NO.
8 9
6.6 Atropine, C H NO .
17 23 3
6.7 Spectrographic graphite powder, C.
6.8 Sodium salicylate, C H O Na.
7 5 3
6.9 Aluminium oxide, Al O , neutral, granular size < 200 µm, annealed at 600 °C.
2 3
6.10 Control mixture A, prepared from sodium carbonate (6.2), Na -EDTA ∙ 4 H O (6.3) and aluminium
4 2
oxide (6.9) in a mass ratio of 2,34 : 1,00 : 7,28.
The mixture shall be homogenized. It shall contain 2,5 % TIC and 2,5 % TOC (e.g. 22,06 g of sodium carbonate,
9,41 g Na -EDTA ∙ 4 H2O, 68,53 g of aluminium oxide).
6.11 Control mixture B, prepared from sodium salicylate (6.8), calcium carbonate (6.1), Na -EDTA · 4 H O
4 2
(6.3) and aluminium oxide (6.9) in a mass ratio of 1,00 : 4,36 : 1,97 : 8,39.
The mixture shall be homogenized. It shall contain 3,3 % TIC and 6,6 % TOC (e.g. 6,36 g of sodium salicylate,
27,78 g of calcium carbonate, 12,50 g of Na4-EDTA · 4 H2O, 53,36 g of aluminium oxide).
6.12 Non-oxidizing mineral acid, used for carbon dioxide expulsion, e.g. phosphoric acid H PO (w = 85 %).
3 4
NOTE Due to potential corrosion by hydrochloric acid, phosphoric acid is preferred for TIC determination in
Method A (9.1.3). Due to potential formation of P O during combustion, hydrochloric acid is preferred for removal of
4 10
inorganic carbon in Method B (10.1.2).
ISO/DIS 15936:2025(en)
6.13 Carrier gas, e.g. synthetic air, nitrogen, oxygen or argon, free of carbon dioxide and organic impurities
in accordance with the manufacturer's instructions.
7 Apparatus
7.1 Precision balance, accurate to at least 0,5 % of test portion weight.
7.2 Equipment for determination of carbon in solids, with relevant accessories.
7.3 Purging unit for TIC determination, for Method A only.
7.4 Vessels, made of e.g. ceramic, silica, quartz, silver or platinum.
NOTE Tin and nickel vessels are not acid-resistant. Tin vessels are suitable only for Method A.
8 Sample pre-treatment
Moist or paste-like waste samples may be mixed with aluminium oxide (6.9) until granular material is
obtained and then be ground or crushed to a maximum particle size (D ) < 250 μm. In this case, the ratio of
aluminium oxide to sample shall be considered in the calculation of TOC (according to 9.4 or 10.4).
Note 1 For waste samples, the homogeneity is important and often the aluminium oxide step is helpful. More
information is given in Annex B.
All other samples should be pre-treated according to EN 16179 or EN 15002 or ISO 11464 or ISO PWI 21744,
if not otherwise specified. The maximum particle size (D ) shall be < 250 μm. Foreign bodies or material
that can’t be ground or crushed should be separated from the sample and the weight and nature of the
material should be recorded.
Samples shall be dried. If moist or paste-like waste samples contain – depending on the accuracy requested
for the method – negligible amounts of volatile compounds except water, the samples shall be also dried. The
drying temperature should not exceed 40 ˚C. The drying method shall be recorded.
NOTE 2 The drying method can affect the result.
9 Procedure – Method A (indirect method)
9.1 Determination
9.1.1 General
The mass of the test portion shall be as large as possible and shall be chosen so that the liberated quantity of
carbon dioxide lies within the working ran
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