🌿 Dry matter of sludge, biowaste, soil and waste — drying at 105 °C (method A) or Karl Fischer titration (method B)

Environment PN-EN 15934

Overview

The standard specifies methods of calculating the dry matter fraction in sewage sludge, treated biowaste, soil and waste — wherever the results of other determinations are to be converted to dry matter. Depending on the nature and the origin of the sample, the calculation is based on the determination of the dry residue (method A) or of the water content (method B). Scope: samples containing more than 1 % by mass of dry residue or more than 1 % by mass of water. Method A concerns sludge, treated biowaste, soil and solid waste; method B — liquid waste and samples which are suspected or known to contain volatile substances other than water.

The definitions in the standard are precise and it is worth watching them in the test report. The dry residue is the mass fraction of the sample remaining after drying at 105 °C under defined conditions. The water content is the mass fraction of water determined by the method of drying at 105 °C or by Karl Fischer titration. The dry matter fraction is the mass fraction of the sample excluding water, calculated from the determination of the dry residue or of the water content.

The principle of method A: the sample is dried to constant mass at 105 °C. The method concerns solid samples and those which become solid in the course of drying. For multiphase samples (waste) the standard requires homogenisation; where homogenisation is impossible, the phases are separated according to EN 15002 and analysed separately. The preparation of the laboratory sample is described by EN 16179.

Practice from the application note of a manufacturer of balances: liquid sewage sludge settles quickly, so samples of liquid structure must be mixed before the test and a homogeneous portion taken; the remaining sludges are dried in the state in which they occur. The weighing vessels are prepared with a glass rod and about 15 g of pre-dried quartz sand, and a sample of about 5 g is mixed with the sand with the rod, which is left in the vessel — the sand as a support prevents the formation of a crust on the surface of the dried sample, which would trap the water inside. The mass of the sample is determined on a balance with an accuracy of 0.1 mg. The reference method for the determination of the dry matter of sludge is PN-EN 12880; moisture analysers with an infrared radiator are sometimes used as an accelerated method, but they require validation against the reference method.

Status of the standard: PN-EN 15934:2013-02 has been withdrawn by the Polish Committee for Standardization and replaced by PN-EN ISO 11465:2026-03. Laboratories which have the old standard in their scope of accreditation should check whether the new edition changes anything in their procedure and prepare a justification for the transitional period. The description below corresponds to the content of the 2012 edition, which we read in the preview; we have not seen the newer edition.

Why this matters: the result of every other test of a sludge — metals, nitrogen, phosphorus, parasites — refers to a kilogram of dry matter. An error in the dry matter is carried over proportionally into all those results, and it is a determination apparently trivial and therefore often done carelessly.

THE SCALE OF CITATIONS (read on 23.09.2026, the working copy of the accreditation-scope database). Matching by the BEGINNING of the string, i.e. the way the "Laboratories" tab searches: **99 entries at 41 laboratories**. By all forms of the core: 101 at 42 — the record "PN EN 15934:2013-02", without the hyphen in the PN element, is added. Sixteen different forms, and their distribution says more about the method than the number itself: the bare form "PN-EN 15934:2013-02" occurs 35 times, but right after it come records with a CHOICE OF VARIANT — "metoda A" [method A] 22 times, "Metoda A" 15, "z wyłączeniem metody B" [excluding method B] 10, ", metoda A" 3. So half of the laboratories that have this standard indicate in their scope which of its methods they use — and when comparing offers this is more important information than the number of the standard itself.

The ratio of entries to laboratories here is 2.4, i.e. the standard is dispersed: many laboratories cite it, each in two to three lines of the scope. This is the reverse of concentrated standards, where several hundred entries fall on a few laboratories — with those, the number of entries alone would mislead the reader.

Method principle

Method A: a weighed portion of the sample is dried to constant mass at a temperature of 105 °C, and the dry residue is calculated as the ratio of the mass after drying to the mass of the weighed portion. The method concerns solid samples and those which in the course of drying become solid — in practice dewatered sludge, soil, treated biowaste and solid waste. Method B: the water content is determined by direct Karl Fischer titration; this variant is applied to liquid waste and to samples in which the presence of volatile substances other than water would falsify the result of drying (during drying they would evaporate together with the water and overstate the loss of mass). From the dry residue or the water content determined, the dry matter fraction is calculated, to which the results of all the other tests of the sample are converted. Multiphase samples are homogenised; where this is not possible, the phases are separated according to EN 15002 and analysed separately. The preparation of the laboratory sample is carried out in accordance with EN 16179. In the gravimetric variant the weighing vessel is prepared with a glass rod and pre-dried quartz sand (about 15 g), with which the weighed portion (about 5 g of semi-liquid sludge) is mixed, so as to prevent the formation of a crust; the weighing is carried out on a balance with an accuracy of 0.1 mg.

Applications

• Sewage sludge — converting the results for metals, nitrogen, phosphorus and parasitological tests to a kilogram of dry matter
• Treated biowaste and composts — process control and the documentation of the handing over
• Soil and ground — the basis of the conversions in contamination testing
• Solid and multiphase waste — determination after homogenisation or after separation of the phases according to EN 15002
• Liquid waste and samples with volatile substances other than water — method B (Karl Fischer)
• Control of the concentration of the activated sludge in a treatment plant — routine measurement of the dry matter

Key parameters

Standard

Standard number

PN-EN 15934:2013-02 (EN 15934:2012)

Title (PL)

Osady ściekowe, uzdatnione bioodpady, gleba oraz odpady — Oznaczanie suchej masy poprzez oznaczanie zawartości suchej pozostałości lub zawartości wody

Title (EN)

Sludge, treated biowaste, soil and waste — Calculation of dry matter fraction after determination of dry residue or water content

Step-by-step procedure

1. Preparation of the laboratory sample

   Prepare the sample in accordance with EN 16179. Mix liquid sludges thoroughly immediately before the portion is taken — the settling is rapid and an unmixed sample gives a result too low or too high depending on the place of sampling. Homogenise multiphase samples; where this is impossible, separate the phases according to EN 15002 and analyse them separately.

2. Preparation of the vessel

   Weigh the weighing vessel together with the glass rod and the pre-dried quartz sand (about 15 g). Record the mass to an accuracy of 0.1 mg.

3. The weighed portion

   Place in the vessel a portion of the sample (for semi-liquid sludge about 5 g), mix it with the sand with the rod and leave the rod in the vessel. Weigh again and determine the actual mass of the weighed portion.

4. Drying (method A)

   Place the vessels with the sample in a drying oven heated to 105 °C and dry to constant mass. Repeat the successive weighings until a difference is obtained which falls within the criterion of constant mass adopted in the procedure.

   🌡 Temperature: 105 °C

5. Cooling and weighing

   Cool the vessels in a desiccator to room temperature and weigh immediately after taking them out — a dried sample takes up moisture from the air.

6. The Karl Fischer variant (method B)

   For liquid waste and for samples with volatile substances other than water, determine the water content by direct Karl Fischer titration instead of drying — drying would also remove those substances and overstate the result.

7. Calculation of the dry matter fraction

   From the dry residue (method A) or the water content (method B) calculate the dry matter fraction of the sample. Record by which method it was determined, because for the same sample the results of the two variants may differ.

8. Conversion of the other results

   Convert all the other test results for this sample to dry matter. In the test report give both the converted result and the dry matter fraction on the basis of which the conversion was made.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Sewage sludge is infectious material — gloves, a laboratory coat, avoiding contact with the face; disinfection of the working place after the work.
• Hot vessels from the drying oven are to be handled with tongs only; a vessel with sand keeps its temperature for a long time.
• The drying of sludge releases troublesome and irritating vapours — the drying oven should work with an extraction system or in a ventilated room.
• The Karl Fischer reagent contains methanol and is toxic — work under a fume hood, collect the waste separately.
• Do not dry samples suspected of containing volatile flammable substances in a drying oven without protection — use method B.

Frequently asked questions