🌿 Loss on ignition (550 °C) of sludges, biowaste, soil and waste — gravimetric method
In short
Ignition of a weighed portion of the sample (0. 5–5 g) in a furnace at a temperature of 550 ± 25 °C to constant mass and calculation from the difference of masses of the loss on ignition referred to the dry matter (in accordance with EN 15934); the result is treated as an approximate measure of the content of organic matter. The test is performed according to PN-EN 15935:2022-01; Ignition temperature: 550 ± 25 °C. The procedure comprises 6 steps; it is used for: Characterisation of sewage sludges (stabilisation, content of organic substance) in treatment plants and waterworks laboratories, Assessment of composts and treated biowaste and of waste before landfilling or recovery, Testing of soils and bottom sediments — the approximate content of organic matter.
At a glance
- Standard: PN-EN 15935:2022-01
- Category: Environment
- Procedure steps: 6
- Ignition temperature: 550 ± 25 °C
- Weighed portion: 0.5–5 g (more where complete combustion is ensured), to 1 mg
- Time: at least 2 h at 550 °C (a dried sample); at least 1 h for undried samples after slow ignition; re-ignition ≥ 1 h where there are residues of carbon
Overview
The earlier edition was PN-EN 15935:2013-02.
EN 15935:2021 specifies a method for the determination of the loss on ignition (LOI) at 550 °C; the dry matter is determined in accordance with EN 15934. The method is applied to bottom sediments, sewage sludges, treated biowaste, soil and waste. The loss on ignition is often used as an estimate of the content of organic matter, although under the conditions of the reaction inorganic substances and products of decomposition (H₂O, CO₂, SO₂, O₂) are also released or taken up, and some inorganic compounds are volatile. The 2021 edition replaced EN 15935:2012 and EN 15169:2007; in Poland PN-EN 15935:2022-01 is in force (previously PN-EN 15935:2013-02), applied among others in accredited waterworks laboratories for the testing of sewage sludges and waste. The method was worked out within the European "Horizontal" project as a common analytical module for sludges, bottom sediments, soil and waste.
The LOI is an empirical parameter, so formally there are no interferences, but in interpreting it as organic matter it must be borne in mind that elemental carbon, chemically bound water and the transformations of inorganic compounds enter into the result; iron and other metals in a low oxidation state are oxidised (a negative contribution), sulfides pass into sulfates (negative), a violent ignition throws the residue out of the crucible (positive), and calcium hydroxide or oxide (limed sludges) binds SO₂ and CO₂ and lowers the result — this is prevented by gradual heating, ventilation of the furnace and a layer of sample no thicker than 5 mm.
SCALE OF CITATIONS — A MEASUREMENT ON THE DATABASE OF ACCREDITATION SCOPES (read on 23-09-2026, matching on the BEGINNING of the notation "PN-EN 15935", i.e. the way the "Laboratories" tab of this entry searches): 134 entries at 64 laboratories.
Method principle
A weighed test portion is ignited in a furnace to constant mass at a temperature of 550 ± 25 °C, and the difference of masses before and after the ignition is used for the calculation of the loss on ignition. The determination is carried out on a dried sample, on an air-dry sample or directly on an undried sample (with a drying stage or with reference to the dry matter in accordance with EN 15934); it may be combined with the determination of the dry residue at 105 ± 5 °C in the same crucible. Constant mass means a change of mass within a further hour of heating of no more than 0.5 % (m/m) or 2 mg (whichever is the greater); the mass after at least 2 h at 550 °C is taken to be constant. The loss on ignition referred to the dry matter: w_LOI = (mc − md)/(mc − ma)·100 [%], where ma is the mass of the empty crucible, mc the mass of the crucible with the dried sample and md the mass of the crucible with the sample after ignition. If black particles of carbon are visible in the residue (some substances burn slowly at 550 °C), the residue is moistened with a few drops of a solution of ammonium nitrate (10 g NH₄NO₃ in 100 ml of water) and ignited further for at least 1 h, with slow heating.
Applications
- Characterisation of sewage sludges (stabilisation, content of organic substance) in treatment plants and waterworks laboratories
- Assessment of composts and treated biowaste and of waste before landfilling or recovery
- Testing of soils and bottom sediments — the approximate content of organic matter
- Control of the processes of digestion and of drying of sludges, mass balances
- A method applied in the scopes of accreditation of laboratories testing sewage sludges and waste
Key parameters
| Parameter | Value |
|---|---|
| Ignition temperature | 550 ± 25 °C |
| Weighed portion | 0.5–5 g (more where complete combustion is ensured), to 1 mg |
| Time | at least 2 h at 550 °C (a dried sample); at least 1 h for undried samples after slow ignition; re-ignition ≥ 1 h where there are residues of carbon |
| Constant mass | a change of ≤ 0.5 % (m/m) or 2 mg within 1 h; after the third ignition without constant mass — take the last result and record it |
| Formula | w_LOI = (mc − md)/(mc − ma)·100 % |
| Preparation of the sample | comminution to < 200 µm; air drying at ≤ 40 °C; pasty samples with aluminium oxide (to be taken into account in the calculation); the layer in the crucible ≤ 5 mm |
Standard
- Standard number
- PN-EN 15935:2022-01
- Title (PL)
- Gleba, odpady, uzdatnione bioodpady oraz osady ściekowe — Oznaczanie strat podczas prażenia
- Title (EN)
- Sludge, treated biowaste, soil and waste — Determination of loss on ignition
Step-by-step procedure
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Preservation and preparation of the sample
Immobilise biologically active samples (freezing or air drying); prepare them in accordance with EN 15002 or EN 16179: comminute solid waste to a powder of < 200 µm (air drying at ≤ 40 °C only where there are no volatile substances), mix moist or pasty samples with aluminium oxide, homogenise liquid samples immediately before weighing out. Separate, weigh and describe any foreign bodies (nuts, bolts, scrap).
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Crucible
Ignite the empty crucible in the furnace at 550 ± 25 °C for at least 20 min, cool it preliminarily on a metal plate, finish the cooling in a desiccator to ambient temperature and weigh it to 1 mg (ma). Where it is combined with EN 15934 the crucible is dried at 105 ± 5 °C.
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Weighed portion
Weigh out into the crucible 0.5–5 g of the sample (dried, air-dry or after the determination of the dry matter at 105 °C in the same crucible) to 1 mg; larger masses are permissible where complete combustion is ensured. For undried samples protect them against the loss of volatile components until they are weighed.
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Ignition
Dried sample: put the crucible into the furnace, raise the temperature to 550 ± 25 °C and maintain it for at least 2 h. Undried sample or one rich in volatile components: remove most of the volatile components in a fume cupboard at ambient temperature (flammable ones — set light to them and let them burn away in the fume cupboard), put the crucible into a cold furnace, heat it slowly until ignition (for paper and demolition wood gradually up to 250 °C over 50 min), then 550 ± 25 °C for at least 1 h.
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Cooling and weighing
Stand the hot crucible for a few minutes on a metal plate, transfer it to a desiccator while still warm, cool it to ambient temperature and weigh it immediately to 1 mg (md). If black particles of carbon are visible, moisten the residue with a few drops of the NH₄NO₃ solution, heat it slowly (without losses from the steam) and ignite it further for ≥ 1 h at 550 °C; repeat until constant mass, and after the third ignition without constant mass take the last result and record it.
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Calculation
Calculate w_LOI = (mc − md)/(mc − ma)·100 % referred to the dry matter (with an undried sample — using the dry matter in accordance with EN 15934, method B where there are volatile substances). Take into account the addition of aluminium oxide. In the test report give the variant (dried/undried sample), the foreign bodies and any failure to attain constant mass.
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| Crucible with a flat bottom, 50–70 mm | of nickel, platinum, porcelain or quartz, resistant to 550 °C | — |
| Muffle furnace | maintaining 550 ± 25 °C, with sufficient ventilation | — |
| Metal plate | preliminary cooling of the crucibles after taking them out of the furnace | — |
| Desiccator with an active drying agent (e.g. silica gel) | cooling to ambient temperature | — |
| Precision balance | accuracy of at least 1 mg | — |
| Drying oven at 105 ± 5 °C | determination of the dry residue in accordance with EN 15934 in the same crucible | — |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| Solution of ammonium nitrate (10 g of analytical grade NH₄NO₃ in 100 ml of distilled or demineralised water) | — | moistening of a residue with residues of carbon before an additional ignition |
| Aluminium oxide | — | mixing with moist or pasty samples to obtain a granular material (the ratio to be taken into account in the calculation) |
Health and safety (OHS)
- Samples with solvents, waste oils or a high content of organic matter may ignite violently (deflagration) — evaporate the volatile components in a fume cupboard, put them into a cold furnace and heat them slowly
- Take the crucibles out of the furnace at 550 °C wearing heat-resistant gloves and using tongs; hot crucibles on a metal plate, not on the bench
- Sewage sludges and biowaste are biologically active material — occupational hygiene, gloves; comminute the dusts of waste in a fume cupboard
Frequently asked questions
Which standard describes this test?
The test is performed according to PN-EN 15935:2022-01 — “Sludge, treated biowaste, soil and waste — Determination of loss on ignition”.
How does this method work?
A weighed test portion is ignited in a furnace to constant mass at a temperature of 550 ± 25 °C, and the difference of masses before and after the ignition is used for the calculation of the loss on ignition. The determination is carried out on a dried sample, on an air-dry sample or directly on an undried sample (with a drying stage or with reference to the dry matter in accordance with EN 15934); it may be combined with the determination of the dry residue at 105 ± 5 °C in the same crucible.
What is the measuring range and accuracy?
Ignition temperature: 550 ± 25 °C; Weighed portion: 0.5–5 g (more where complete combustion is ensured), to 1 mg; Time: at least 2 h at 550 °C (a dried sample); at least 1 h for undried samples after slow ignition; re-ignition ≥ 1 h where there are residues of carbon; Constant mass: a change of ≤ 0.5 % (m/m) or 2 mg within 1 h; after the third ignition without constant mass — take the last result and record it.
How long does the test take?
The procedure comprises 6 steps. The standard does not give a duration for every stage — the laboratory's own procedure decides.
What equipment is required?
Crucible with a flat bottom, 50–70 mm, Muffle furnace, Metal plate, Desiccator with an active drying agent (e.g. silica gel), Precision balance, Drying oven at 105 ± 5 °C.
Where is this test used?
Characterisation of sewage sludges (stabilisation, content of organic substance) in treatment plants and waterworks laboratories; Assessment of composts and treated biowaste and of waste before landfilling or recovery; Testing of soils and bottom sediments — the approximate content of organic matter; Control of the processes of digestion and of drying of sludges, mass balances; A method applied in the scopes of accreditation of laboratories testing sewage sludges and waste.
What safety precautions apply?
Samples with solvents, waste oils or a high content of organic matter may ignite violently (deflagration) — evaporate the volatile components in a fume cupboard, put them into a cold furnace and heat them slowly; Take the crucibles out of the furnace at 550 °C wearing heat-resistant gloves and using tongs; hot crucibles on a metal plate, not on the bench; Sewage sludges and biowaste are biologically active material — occupational hygiene, gloves; comminute the dusts of waste in a fume cupboard.
Which laboratory can perform this test?
The test is performed by laboratories accredited to ISO/IEC 17025. On LabCoda you can find them by the standard number PN-EN 15935.