oSIST prEN 18256:2025

SLOVENSKI STANDARD
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
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

DRAFT
EUROPEAN STANDARD
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.

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

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.
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.
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
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 ;
— 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.
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 at test
temperature at least for 5 days, in order to reduce background gas production and to decrease the
influence of the blank control. The inoculum shall be characterized, after pre-digestion period, by TS and
VS.
To check the suitability of inoculum, it is required a pH range between 7,0 to 8,5, a VFA
+
concentration < 1 g HAc eq/l, an N-NH concentration < 5 g/l and alkalinity > 3 g CaCO eq/l, according
4 3
to process monitoring in biogas plants [3].
8.3 Starting the procedure
For the preparation of each reaction vessel (5.2) it is necessary to calculate masses of the sample (8.1)
and the inoculum (8.2) as well as the volumes of the complete nutrient solution (6.5) and the dilution
water
...