kSIST FprEN 18256:2026
(Main)Digestate - Determination of the residual biogas potential
- Abstract
This document specifies a method for the determination of the residual biogas potential in digestate in an anaerobic environment.
NOTE This method has been validated in an interlaboratory study with specific products that were present on the market during the study (as included in Annex B, being solid digestate).
- Status
- Not Published
- Public Enquiry End Date
- 19-Dec-2025
- Technical Committee
- KAT - Soil quality
- Current Stage
- 5020 - Formal vote (FV) (Adopted Project)
- Start Date
- 13-Oct-2026
- Due Date
- 01-Dec-2026
- Mandate
- M/XXX - M/XXX
kSIST FprEN 18256:2026 is SIST’s publication of draft European Standard prEN 18256 from CEN. It specifies a laboratory method for determining the residual biogas potential (RBP) of digestate in an anaerobic environment. In practice, it is used to measure how much biogas can still be produced from a digestate sample after digestion.
What does kSIST FprEN 18256:2026 specify?
kSIST FprEN 18256:2026 specifies a test method for digestate RBP and organizes it as a full laboratory procedure, from principle to validation. The document covers clauses 1 to 11, followed by two informative annexes.
It excludes sampling itself from the method and points users to the sampling standard for soil improvers and growing media. The method is built around controlled sample preparation, inoculum preparation, gas measurement, calculation and reporting.
| Annex | What it covers |
|---|---|
| A (informative) | An example RBP reaction-vessel setup, shown with a figure of the vessel and its main parts. |
| B (informative) | Performance characteristics from an interlaboratory study, including the material tested and repeatability/reproducibility data. |
What are the key requirements of kSIST FprEN 18256:2026?
Clause 4 states that the test is run under anaerobic, temperature-controlled conditions in sealed reaction vessels. Biogas accumulates in the headspace and is measured by either a manometric or volumetric method. This matters because leaks, temperature drift, or the wrong measurement principle can change the result.
Clause 5 sets the main equipment: a temperature-controlled test facility, gastight reaction vessels, pressure or volume measurement devices, a barometer, a mixing device, a balance, a pH meter and sieves. The method expects tight control of vessel size, pressure measurement and mixing, because the result depends on gas capture and stable incubation.
Clause 6 specifies the reagents and media, including water of defined conductivity, NaOH, HCl, trace elements stock solution, complete nutrient solution, nitrogen gas and microcrystalline cellulose. The nutrient solution is used to support the microbial activity in the test, while microcrystalline cellulose is the reference substance for checking performance.
Clause 7 says sampling is not part of this method and refers users to EN 12579:2024. It also stresses that the laboratory sample must remain representative and unchanged during transport and storage. In practice, this is important because a degraded or unrepresentative sample can give a misleading RBP.
Clause 8 gives the core procedure. The sample is characterized for total solids (TS) and volatile solids (VS), the inoculum is pre-digested and checked for suitability, and the reaction vessel is prepared with an inoculum-to-sample ratio of 2 on a VS basis. The blank vessel, inert-gas flushing, pH control and daily gas recording are all part of the setup, so the test can separate sample gas from background gas.
Clause 8.4 allows two measurement routes:
- manometric measurement, based on pressure change at constant volume
- volumetric measurement, based on gas volume at constant pressure
The test runs for 28 days, with the end pH still required to be in range. The method also expects periodic equipment checks and a blank production limit, which helps confirm that the system is behaving properly.
Clause 9 standardizes the measured gas to standard conditions and calculates the RBP after blank correction, with an additional correction if the inoculum masses differ between test and blank vessels. This is the calculation step that turns raw gas readings into a comparable RBP value in litres of biogas per gram of VS.
Clause 10 defines what the test report has to contain: sample identification, replicates, mean RBP, temperature, duration, gas method and any optional or non-standard work cycles. That makes the result traceable and usable for quality records or product comparison.
What terms does kSIST FprEN 18256:2026 define?
Biogas is the gas mixture mainly made of methane (CH4) and carbon dioxide (CO2) that forms when organic material breaks down without oxygen.
Inoculum is the active biological material that contains anaerobic microorganisms and starts or supports the degradation process.
Working volume is the usable volume in the reaction vessel that is occupied by inoculum, sample, nutrients and water.
Headspace is the remaining volume in the sealed vessel where the produced biogas collects.
Total solids (TS) is the solids content of the sample used for preparation and calculation.
Volatile solids (VS) is the organic fraction used to express the gas potential per gram of organic matter.
Residual biogas potential (RBP) is the amount of biogas still obtainable from digestate under the test conditions, reported in litres of biogas per gram of VS.
Who uses kSIST FprEN 18256:2026?
Laboratories use kSIST FprEN 18256:2026 to measure digestate stability and compare batches under a common method. Digestate producers, biogas plant operators and quality teams use it to check whether a product may still generate gas during storage.
It is also relevant for organizations working with soil improvers, growing media and organic fertilizers, because the introduction links digestate to those product sectors. Annex B also places the method in the context of European standardization work supporting the European Fertilising Product Regulation.
Which standards are used with kSIST FprEN 18256:2026?
CEN/TS 17732:2022 provides the terminology used in the document. EN 12579:2024 covers sampling.
prEN 13039:2025 provides the method for determining organic matter content and ash, which is used here for VS. prEN 13040-1:2025 covers sample preparation, transport, reception and storage conditions, and EN 45501 supports the weighing step.
What does the kSIST FprEN 18256:2026 document contain?
The document contains a principle, apparatus list, reagent recipes, sampling guidance, a detailed test procedure, calculation formulas, reporting requirements and method validation. It also includes an example reaction-vessel figure in Annex A and interlaboratory performance data in Annex B.
Annex B reports the validation work on solid digestate and summarizes the repeatability and reproducibility results from the interlaboratory study. The bibliography points to related work on digestate testing and gas-production calculations, which helps readers understand the background behind the method.
Relations
- Effective Date
- 28-Jan-2026
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Frequently Asked Questions
kSIST FprEN 18256:2026 is a draft published by the Slovenian Institute for Standardization (SIST). Its full title is "Digestate - Determination of the residual biogas potential". This standard covers: This document specifies a method for the determination of the residual biogas potential in digestate in an anaerobic environment. NOTE This method has been validated in an interlaboratory study with specific products that were present on the market during the study (as included in Annex B, being solid digestate).
This document specifies a method for the determination of the residual biogas potential in digestate in an anaerobic environment. NOTE This method has been validated in an interlaboratory study with specific products that were present on the market during the study (as included in Annex B, being solid digestate).
kSIST FprEN 18256:2026 is classified under the following ICS (International Classification for Standards) categories: 65.080 - Fertilizers. The ICS classification helps identify the subject area and facilitates finding related standards.
kSIST FprEN 18256:2026 has the following relationships with other standards: It is inter standard links to SIST EN ISO 24025-2:2020. Understanding these relationships helps ensure you are using the most current and applicable version of the standard.
kSIST FprEN 18256:2026 is associated with the following European legislation: EU Directives/Regulations: 2003/2003, 2019/1009; Standardization Mandates: M/564, M/564 AMD 1, M/564 AMD 2, M/588, M/XXX. When a standard is cited in the Official Journal of the European Union, products manufactured in conformity with it benefit from a presumption of conformity with the essential requirements of the corresponding EU directive or regulation.
kSIST FprEN 18256:2026 is available in PDF format for immediate download after purchase. The document can be added to your cart and obtained through the secure checkout process. Digital delivery ensures instant access to the complete standard document.
Standards Content (Sample)
SLOVENSKI STANDARD
oSIST prEN 18256:2025
01-december-2025
Digestat - Določanje potenciala bioplina, ki se še lahko sprosti iz digestata (RBP)
Digestate - Determination of the residual biogas potential
Gärrest - Bestimmung des Restbiogaspotentials
Digestat - Détermination du potentiel de production de biogaz résiduel
Ta slovenski standard je istoveten z: prEN 18256
ICS:
65.080 Gnojila Fertilizers
oSIST prEN 18256:2025 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
oSIST prEN 18256:2025
oSIST prEN 18256:2025
DRAFT
EUROPEAN STANDARD
prEN 18256
NORME EUROPÉENNE
EUROPÄISCHE NORM
October 2025
ICS 65.080
English Version
Digestate - Determination of the residual biogas potential
Digestat - Détermination du potentiel de production de Gärrest - Bestimmung des Restbiogaspotentials
biogaz résiduel
This draft European Standard is submitted to CEN members for enquiry. It has been drawn up by the Technical Committee
CEN/TC 223.
If this draft becomes a European Standard, CEN members are bound to comply with the CEN/CENELEC Internal Regulations
which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.
This draft European Standard was established by CEN in three official versions (English, French, German). A version in any other
language made by translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC
Management Centre has the same status as the official versions.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
Recipients of this draft are invited to submit, with their comments, notification of any relevant patent rights of which they are
aware and to provide supporting documentation.
Warning : This document is not a European Standard. It is distributed for review and comments. It is subject to change without
notice and shall not be referred to as a European Standard.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2025 CEN All rights of exploitation in any form and by any means reserved Ref. No. prEN 18256:2025 E
worldwide for CEN national Members.
oSIST prEN 18256:2025
prEN 18256:2025 (E)
Contents Page
European foreword . 3
Introduction . 4
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 5
4 Principle . 6
5 Apparatus . 6
6 Reagents . 6
7 Sampling . 7
8 Procedure . 7
8.1 Storage and preparation of sample . 7
8.2 Sampling, storage and preparation of inoculum . 8
8.3 Starting the procedure . 8
8.4 Measurement methods . 9
9 Calculation . 9
10 Test report . 11
11 Validation of the method . 11
11.1 Validation in accordance with ISO 5725-2. 11
11.2 Performance characteristics. 11
Annex A (informative) Specific information on RBP - test . 12
Annex B (informative) Performance characteristics of the method . 13
Bibliography . 15
oSIST prEN 18256:2025
prEN 18256:2025 (E)
European foreword
This document (prEN 18256:2025) has been prepared by Technical Committee CEN/TC 223 “Soil
improvers and growing media”, the secretariat of which is held by NEN.
This document is currently submitted to CEN Enquiry.
This document has been prepared under a standardization request addressed to CEN by the European
Commission. The Standing Committee of the EFTA States subsequently approves these requests for its
Member States.
oSIST prEN 18256:2025
prEN 18256:2025 (E)
Introduction
Anaerobic digestion is a biological process leading, in absence of oxygen, to the degradation of organic
carbon and to the production of biogas, a gas mixture composed mainly by methane (CH ) and carbon
dioxide (CO ). The degradation process is carried out by a wide range of mesophilic or thermophilic
microorganisms and applied on an industrial scale as an exploitation strategy to produce added-value
products from crops, livestock manure, agro-industrial by-products, biowaste and sludges. The digestate
obtained is a stabilized, nutrient-rich material, and a suitable component for soil improvers, growing
media and other organic fertilizers.
When the organic material is not efficiently converted into biogas, the digestate coming out from the plant
is unstable and continues to produce biogas in the final storage tank.
The assessment of the digestate’s stability can be carried out through the residual biogas potential (RBP)
test which represents the amount of biogas that could still be produced from the organic material present
at the end of the anaerobic digestion process.
oSIST prEN 18256:2025
prEN 18256:2025 (E)
1 Scope
This document specifies a method for the determination of the residual biogas potential in digestate in
an anaerobic environment.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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.
CEN/TS 17732:2022, Soil improvers and growing media — Terminology
EN 12579:2024, Soil improvers and growing media — Sampling
prEN 13039:2025, Soil improvers and growing media — Determination of organic matter content and ash
prEN 13040-1:2025, Soil improvers and growing media — Sample preparation — Part 1: Sample
preparation for chemical and physical tests, determination of dry matter content, moisture content and
laboratory bulk density
EN 45501, Metrological aspects of non-automatic weighing instruments
3 Terms and definitions
For the purposes of this document, he terms and definitions given in CEN/TS 17732:2022 and the
following 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
biogas
mixture of gases mainly composed of CH (methane) and CO (carbon dioxide) and produced by the
4 2
anaerobic degradation of organic material
3.2
inoculum
biological material with active anaerobic microorganisms able to initiate and enhance the degradation
process
3.3
working volume
usable volume within a reaction vessel taken up by inoculum, sample, nutrients solution and water
3.4
headspace
remaining volume within the reaction vessel obtained by subtraction of the working volume, occupied by
the biogas
oSIST prEN 18256:2025
prEN 18256:2025 (E)
4 Principle
The test is carried out under anaerobic conditions and in a temperature-controlled environment. Closed
reaction vessels are filled with adjusted quantities of inoculum, sample and a nutrient solution. The
biogas is cumulated within the headspace of the reaction vessel and its amount and composition are
measured by manometric or volumetric methods. The residual biogas potential (RBP) is referred to the
standard conditions of pressure and temperature and to the amount of organic matter (volatile solids)
added to the reaction vessel.
5 Apparatus
5.1 Test facility, temperature controlled room, climate cabinet or water bath, mesophilic temperature
adjustable to 38 °C ± 2 °C.
The laboratory may carry out the analysis in thermophilic temperature 52 °C ± 1 °C.
5.2 Reaction vessels, glass or steel gastight vessels (with a volume of 0,5 l to 2,5 l).
5.3 Pressure transducer, operating range of 0 kPa to 50 kPa and a maximum uncertainty set lower
than 1,5 % of the full scale.
5.4 Volume displacement devices, liquid displacement gasometers, lubricated gas syringes and gas
counters.
5.5 Barometer, to measure atmospheric pressure.
5.6 Mixing device, shaking Table 120 rpm ± 20 rpm or magnetic stirring unit.
5.7 Balance, meeting EN 45501 class II tolerances with a scale interval of 0,01 g.
5.8 pH meter, with slope adjustment and temperature control.
5.9 Sieves, 5 mm square aperture size or smaller.
6 Reagents
6.1 Water with a specific conductivity not higher than 0,2 mS/m at 25 °C, free from the elements to be
determined.
6.2 NaOH (0,5 mol/l)
6.3 HCl (0,5 mol/l)
6.4 Trace elements stock solution
Dissolve the following masses of chemical compounds in 1000 ml water (see 6.1):
— 0,05 g of MnCl · 4H O;
2 2
— 0,005 g of H BO ;
3 3
— 0,005 g of ZnCl ;
— 0,003 g of CuCl ;
oSIST prEN 18256:2025
prEN 18256:2025 (E)
— 0,001 g of Na MoO4 · 2H O;
2 2
— 0,1 g of CoCl · 6H O;
2 2
— 0,01 g of NiCl · 6H O;
2 2
— 0,005 g of Na SeO .
2 3
6.5 Complete nutrient solution
Dissolve the following masses of chemical compounds in 1000 ml water (see 6.1):
— 0,27 g of KH PO ;
2 4
— 1,12 g of Na HPO · 2H O;
2 4 2
— 0,53 g of NH Cl;
— 0,075 g of CaCl · 2H O;
2 2
— 0,10 g of MgCl · 6H O;
2 2
— 0,02 g of FeCl · 4H O;
2 2
— 10 ml of trace elements stock solution (see 6.4).
Adjust the pH of the medium, if necessary, with dilute mineral acid or alkali to 7 ± 0,2 (see 6.2 and 6.3).
6.7 N gas
6.8 Microcrystalline cellulose (CAS 9004-34-6)
7 Sampling
Sampling is not part of the method specified in this document. Follow EN 12579:2024 dealing with soil
improvers and growing media. It is important that the laboratory receives a sample that is representative
of the product under consideration. The sample should not have been damaged or changed during
transport or storage.
8 Procedure
8.1 Storage and preparation of sample
Transportation, reception and storage of samples shall be determined according to prEN 13040-1:2025,
Clauses 6 and 7; samples preparation shall follow Clauses 9.2.1, 9.3 and 9.4. The sample shall be
characterized by the following parameters: total solids (TS) according to prEN 13040-1:2025 for dry
matter and volatile solids (VS) according to prEN 13039:2025 for organic matter. Volatile solids shall be
submitted to the preparation procedure within 24 hours after sampling. Otherwise, the sample shall be
stored (max. 1 month) at 3 °C ± 2 °C under anaerobic/anoxic condition.
+
NOTE For further characterization of the sample, the determination of pH, ammonium content (N-NH ),
volatile fatty acid profile (VFA) and the chemical oxygen demand (COD) is applicable.
oSIST prEN 18256:2025
prEN 18256:2025 (E)
8.2 Sampling, storage and preparation of inoculum
The inoculum (3.2) should come from a biogas digester working at mesophilic (or thermophilic)
condition; it shall be sieved with a maximum square aperture size of 5 mm to remove the particles
retained and then pre-digested without the addition of any nutrients and carbon sources
...