What is activated carbon: structure, production and key parameters
Activated carbon is porous carbon with a surface area of up to 1,500 m² per gram. An overview of production, pore classes, iodine number and use in drinking water.
Activated carbon is porous carbon with a very large internal surface area. Depending on the grade, data sheets state 500 to 1,500 m² per gram. The substance has the number 7440-44-0 in the Chemical Abstracts Service (CAS). In the European Inventory of Existing Commercial Chemical Substances (EINECS), it is listed under 231-153-3. The list of the Umweltbundesamt (German Environment Agency) names 2 forms: granules according to DIN EN 12915-1 and powder according to DIN EN 12903. In 2024, Germany imported 83,897 tonnes and exported 53,041 tonnes.
This guide explains the structure, raw materials and the 2 steps of production. It also covers the 3 pore classes according to the 2015 report and the values stated on a data sheet. The final section shows where authorities regulate its use.
Carbon with 1,500 m² per gram
Activated carbon consists almost entirely of carbon, the element with atomic number 6 and the symbol C. It has no fixed molecular formula, because the carbon is amorphous. Amorphous means that the atoms form a loose framework instead of a crystal lattice. Within the framework lies a labyrinth of extremely fine cavities. These cavities create the surface to which substances attach.
A football pitch measures 105 by 68 metres, i.e. 7,140 m². Five grams of activated carbon at 1,500 m² each add up to 7,500 m². That is the surface area in one teaspoon of powder.
The same substance goes by 5 names. Technical papers use active carbon or AC. Medicine packs say medicinal charcoal or Carbo medicinalis. Vegetable carbon refers to the variant made from plant-based raw materials. It is approved as the food colour E 153. For this, the EU requires at least 95% carbon, calculated on the dry, ash-free mass.
Raw materials from hard coal to coconut
Almost any material containing carbon is suitable as a starting material. The European Food Safety Authority (EFSA) names 5 groups for vegetable carbon. These include wood from pine and oak, coconut shells, bamboo, peat and wood pellets. For technical grades, hard coal, lignite and nutshells are added. Alb Filter obtains its carbon from the renewable raw material lignin. Lignin is found in lignified plant cells.
The raw material shapes the name of the finished product. Tradition has given rise to 3 terms that still appear in the trade today.
| Name | Starting material | Current use |
|---|---|---|
| Vegetable carbon | Wood, shells, bamboo | Colour E 153, soil additive |
| Blood charcoal | Animal blood | formerly in sugar factories |
| Sugar charcoal | carbonised sugar | Laboratory |
When choosing, 2 factors count: origin and yield. Coconut and lignin are renewable. Hard coal remains a fossil raw material. With every method, the yield is well below the input weight. The reason: when heated, part of the carbon escapes as gas.
Carbonisation at 450 to 1,300 degrees
Two steps lead from the raw material to activated carbon. In the first, the material is carbonised in the absence of oxygen. The technical term for this step is pyrolysis. Depending on the raw material, EFSA gives 450 to 1,300 °C for this. What remains is a framework of almost pure carbon instead of ash.
The second step gives the substance its name. During activation, heat opens up the framework and exposes the pores. There are two methods to choose from.
| Method | Agent | Evidence from the EFSA text | What happens |
|---|---|---|---|
| Gas | Steam, carbon dioxide | above 800 °C, 1 to several hours | part of the carbon gasifies, pores remain |
| Chemical | Phosphoric acid | cited as an alternative to steam activation | the acid dries out the framework, then steam follows |
After activation, the material is washed with hydrochloric acid. This is followed by neutralisation with water or caustic soda, drying and grinding. For vegetable carbon used in food, the mean particle size is then 154 to 673 nm.
Pores below 2 nm do the work
The International Union of Pure and Applied Chemistry (IUPAC) divides pores into 3 classes according to their width. The authoritative report was published in 2015 in Pure and Applied Chemistry, volume 87, pages 1051 to 1069.
| Class | Width | Role |
|---|---|---|
| Micropores | up to about 2 nm | Main storage, the pore space fills up |
| of which narrow | below 0.7 nm | narrowest range, for small molecules |
| of which wide | 0.7 to 2 nm | Transition |
| Mesopores | 2 to 50 nm | Transport route, attachment to the wall |
| Macropores | above 50 nm | Access into the grain, fast transport |
Older guides give other limits, such as 1 nm and 25 nm. The 2015 IUPAC version remains authoritative. Anyone comparing 2 data sheets should therefore first check what the figures are based on.
The distribution of the pores determines the effect. A carbon with a high proportion of micropores binds small molecules well. Large molecules need mesopores. If these are missing, the molecules remain stuck at the entrance.
Adsorption binds substances to the surface
Adsorption refers to foreign substances attaching to a surface. Absorption refers to uptake into a body, just as a sponge soaks up water. Both words go back to the Latin sorbere, meaning to suck in. Activated carbon works by adsorption. Dissolved substances adhere to the walls of the pores and accumulate there.
In worksheet W 239, the Deutscher Verein des Gas- und Wasserfaches (DVGW, German Technical and Scientific Association for Gas and Water) defines 22 terms. Five of them describe how long a carbon keeps working.
| Term | Meaning |
|---|---|
| Loading | Mass of bound substance per mass of carbon |
| Capacity | Amount a carbon takes up at equilibrium |
| Breakthrough curve | Change in concentration in the outflow over time |
| Competition | 2 or more substances occupy the same sites |
| Contact time (EBCT) | Bed volume divided by the flow rate |
The capacity of a carbon is finite. Once the surface is occupied, the value in the outflow rises. The filter then reaches breakthrough. In the household, this means the cartridge is due for replacement. How often it needs changing is explained in the guide on water filter cartridges.
The iodine number measures 1 gram against 0.02 mol
The iodine number is the most common value on a data sheet. DIN EN 12902 defines it as the mass of iodine in mg that 1 gram of carbon binds from solution. The reference point: 0.02 mol per litre remains in the filtrate. At 0.02 mol, there is mathematically a single layer of molecules on the carbon. The iodine number is therefore regarded as an indication of the surface area per gram.
The values in the table come from a tender issued by Stadtwerke Düsseldorf on 28.05.2025. They show what a water supplier actually requires.
| Value | What it measures | Standard | Requirement |
|---|---|---|---|
| Iodine number | Uptake of iodine per gram | DIN EN 12902 | at least 200 mg/g on acceptance, at least 750 mg/g after reactivation |
| Grain size | Particle size range | DIN EN 12915-1 | 8 x 30 mesh, i.e. 0.6 to 2.36 mm |
| Undersize | Proportion of grains that are too fine | DIN EN 12915-1 | up to 5% |
| Oversize | Proportion of grains that are too coarse | DIN EN 12915-1 | up to 15% |
| Ball-pan hardness | Abrasion in the bed | DIN EN 12915-1 | above 90 |
| Tamped density | Mass per volume, compacted | DIN EN 12902 | around 530 kg/m³ |
| Bulk density | Mass per volume, loose | DIN EN 12902 | around 460 kg/m³ |
| Ash | Mineral residue | DIN EN 12902 | up to 15% |
| Water | Moisture on delivery | DIN EN 12902 | up to 5% |
| BET surface area | Surface area per gram according to Brunauer, Emmett and Teller (BET) | DVGW W 239, section 3.9 | Manufacturer's specification |
The iodine number comes with a caveat. The Chair of Water Technology at the University of Duisburg-Essen has recorded a finding on this. Deviations in the double-digit range occur between the analyses of different laboratories, even though the method is standardised. Anyone comparing 2 carbons should therefore obtain the values from the same laboratory.
37 carbons tested: the iodine number explains little
A 2025 screening shows how far data sheets and practice diverge. Roman Wiget and 2 experts from Membratec tested 37 powdered activated carbons made from wood, hard coal and coconut. The work was published on 05.12.2025 in Aqua & Gas. The iodine number explained only a fraction of the measured removal of a micropollutant; the coefficient of determination was 0.08. For the BET surface area, the authors found an inverse relationship with a coefficient of determination of 0.36. The gap between the best and the weakest carbon was more than 80%.
For substances that are difficult to bind, the iodine number therefore reaches its limits. Annex A of worksheet W 239 additionally describes the isotherm and the nitrobenzene number. Both measure the uptake of the actual substance instead of iodine.
Powder, granules and block follow 3 standards
Four types are available on the market. For drinking water, 3 of them are standardised.
| Type | Particle size | Standard | Typical location |
|---|---|---|---|
| Powder | Ultrafine powder | DIN EN 12903 | Dosing into water, wastewater treatment plant, food |
| Granules, virgin | 0.6 to 2.36 mm | DIN EN 12915-1 | Bed in the waterworks |
| Granules, reactivated | 0.6 to 2.36 mm | DIN EN 12915-2 | Bed after reprocessing |
| Block, pressed or sintered | solid body | Manufacturer's specification | Household cartridge |
In a filter jug, the water flows around loose granules instead of passing through them. A pressed block forces the water through fine channels. It therefore retains more. The guide Activated carbon filters for water compares the household types in detail. Why filter jugs bring their own hygiene issues is explained in the article on the risk of germ growth in jug filters. An overview of the fixed types can be found under drinking water filters.
Barbecue charcoal needs 75%, E 153 as much as 95%
The difference between charcoal and activated carbon lies in a single step. Charcoal undergoes carbonisation. Activated carbon additionally undergoes activation. Only then does the pore system form. The figures in the respective standards make the gap visible.
| Substance | Production | Regulation | Carbon content |
|---|---|---|---|
| Barbecue charcoal | Carbonisation | DIN EN 1860-2:2023 | at least 75%, with DINplus 80% |
| Barbecue briquettes | Carbonisation, pressed | DIN EN 1860-2:2023 | at least 60%, with DINplus 65% |
| Vegetable carbon E 153 | Carbonisation, activation | EU requirement | at least 95% of the dry, ash-free mass |
| Activated carbon for drinking water | Carbonisation, activation | DIN EN 12915-1, DIN EN 12903 | at least 90%, ash up to 10% |
Barbecue charcoal therefore binds little from water or air. Its surface area remains far below that of an activated carbon. Vegetable carbon in soil serves yet another purpose. There, it stores water and nutrients.
§ 20 of the German Drinking Water Ordinance names 2 forms
Anyone treating drinking water may only use listed substances. The list is kept by the Umweltbundesamt. It was published in the Bundesanzeiger (Federal Gazette) on 27.01.2023 and corrected on 27.08.2024. In Part I b, activated carbon appears as granules in position 1 and as powder in position 2.
| Specification | Granules | Powder |
|---|---|---|
| Position in Part I b | 1 | 2 |
| CAS number | 7440-44-0 | 7440-44-0 |
| EINECS number | 231-153-3 | 231-153-3 |
| Purpose | Adsorption, binding chlorine and ozone, biological filtration, binding particles | Adsorption |
| Purity | DIN EN 12915-1, Tables 1 and 2 | DIN EN 12903, Tables 1 and 2 |
| Dosing limit | unrestricted | unrestricted |
How a waterworks uses carbon is governed by worksheet W 239 in the version of October 2021. It replaces the edition of March 2011. It covers planning, operation, reactivation, purchasing and testing. It was drawn up by the Sorption project group in the joint committee of DIN and DVGW.
In the waterworks, the carbon mainly retains organic substances. These include halogenated hydrocarbons and residues of pesticides. It also binds chlorine and ozone. Substances that shape odour, taste and colour are also retained. Limescale, on the other hand, remains in the water. Calcium and magnesium are present as ions and bind poorly to carbon. What this means at the tap is explained in the article on limescale in water. The guide to the Drinking Water Ordinance lists which substances are limited by law.
Treatment plants serving 150,000 or more inhabitants are upgrading
The EU Urban Wastewater Treatment Directive requires a 4th treatment stage. It targets traces of substances that pass through the 3 stages. The Umweltbundesamt summarised the current status on 25.02.2026. For this stage, 2 processes are at the forefront: activated carbon and ozone.
| Rule | Contents |
|---|---|
| Article 8(1) | Mandatory for all plants from 150,000 population equivalents (p.e.) |
| Article 8(2) | Mandatory from 10,000 p.e. in areas at risk |
| List of areas | by the end of 2030, first update in 2033, then every 6 years |
| Article 9 | at least 80% of the costs borne by the pharmaceutical and cosmetics industries |
| Reason | 92% of the harmfulness of the measured micropollutants comes from these 2 sectors |
The upgrade targets precisely the substances that pass through the 3 stages. These include residues of medicines, as well as residues from cosmetics. The article on pharmaceutical residues shows which active substances can be measured in German tap water. The guide to per- and polyfluoroalkyl substances covers the second major group in the debate.
WHO list 2025, food colour E 153
The World Health Organization (WHO) includes activated carbon in its list of essential medicines. The 24th edition was published in September 2025. It lists the substance under section 4.1 as an antidote for poisoning. The carbon binds poison in the gut before the body absorbs it.
In food, vegetable carbon bears the number E 153. On 28.01.2026, EFSA presented an assessment of it in the EFSA Journal, volume 24, issue 1. In it, the current limits and the authority's advice are set out side by side.
| Size | Current limit | EFSA advice |
|---|---|---|
| Carbon | at least 95% | confirmed |
| Ash | up to 4.0% | confirmed |
| Water | up to 12% | confirmed |
| Lead | up to 2 mg/kg | lower |
| Arsenic | up to 3 mg/kg | lower |
| Mercury | up to 1 mg/kg | lower |
| Cadmium | up to 1 mg/kg | lower |
| Benzo[a]pyrene | below 50 µg/kg | lower, measured up to 37.1 µg/kg |
Two further findings concern the particle size. In all samples, 40 to 87% of the particles were below 250 nm. The proportion below 100 nm was 4 to 24%. EFSA calls for a separate entry for this in the specification. It also recommends a sum value for 4 polycyclic aromatic hydrocarbons.
In the kiln, 600 degrees suffice instead of 900
Spent activated carbon ends up in the kiln instead of in the waste. During reactivation, the bound substances evaporate and decompose. The pores open up again. The Opt-Aktiv-C project, reference AiF 20617N, examined the process from March 2019 to May 2022. The DVGW and the University of Duisburg-Essen were involved.
| Finding | Value |
|---|---|
| Tests in the rotary kiln | 52 in total, 26 per type |
| Carbon from the waterworks | about 600 °C is enough |
| Carbon from the wastewater treatment plant | 900 °C almost sufficient |
| Greatest influence | Heating rate and duration |
| Minor influence | Proportion of steam and carbon dioxide |
The quality of the result is again checked using the iodine number. For reactivated material, DIN EN 12915-2 applies as the product standard. The Düsseldorf tender requires 750 mg per gram after reactivation. The operator rejects carbon with an iodine number below 200 mg per gram on acceptance.
Trade data provides information on the quantities. In the United Nations Comtrade database, activated carbon is listed under the number 3802 10. In 2024, Germany imported 83,897 tonnes and exported 53,041 tonnes. In 2017, imports stood at 74,180 tonnes. Imports therefore grew by around 13% in 7 years.
Related to this topic
Alb Filter FUSION – activated carbon from renewable lignin
The FUSION under-sink drinking water filter works with a sintered activated carbon block made from the renewable raw material lignin. It binds chlorine, microplastics, hormones and heavy metals and leaves the minerals in the water – permanently installed, without electricity and without waste water.
Frequently asked questions
What is activated carbon good for?
As a means of filtering and purifying, activated carbon covers 3 fields. In the waterworks, it binds organic substances, chlorine and pesticide residues. In medicine, the WHO has listed it as an antidote for poisoning since the 24th edition of 2025. For air, it is used in filters for cabins and extractor hoods.
What is activated carbon made of?
The main component is amorphous carbon. For vegetable carbon used as the colour E 153, the EU requires at least 95% carbon, calculated on the dry, ash-free mass. Raw materials include wood, coconut shells, bamboo, peat, hard coal and lignin.
What is the difference between charcoal and activated carbon?
The difference lies in the second production step. Both substances undergo carbonisation. Only activated carbon additionally undergoes activation with steam or chemicals. Only then does the pore system form. Barbecue charcoal according to DIN EN 1860-2 needs at least 75% carbon, whereas vegetable carbon E 153 needs 95%.
How large is the surface area of activated carbon?
Depending on the grade, one gram reaches an internal surface area of 500 to 1,500 m². Five grams at 1,500 m² each add up to 7,500 m². A football pitch measures 105 by 68 metres, i.e. 7,140 m².
What does the iodine number tell you?
The iodine number indicates how many mg of iodine 1 gram of carbon binds from a solution. The reference point: 0.02 mol per litre remains in the filtrate. It is regarded as an indication of the surface area per gram. For drinking water, reactivated carbon must reach 750 mg per gram.
How large are the pores of activated carbon?
Since its 2015 report, IUPAC has divided pores into 3 classes. Micropores measure up to about 2 nm, mesopores 2 to 50 nm and macropores over 50 nm. Older sources give 1 nm and 25 nm as the limits.
Is activated carbon harmful?
In medicine and food, the substance is considered to cause little irritation. In food, however, it also binds vitamins and minerals. On 28.01.2026, EFSA advised lowering the limits for lead, arsenic, mercury, cadmium and benzo[a]pyrene.
Is activated carbon flammable?
Yes. Activated carbon consists almost entirely of carbon and is flammable. When used as a filter, it stays moist or cool. It is therefore safe there.
Can activated carbon remove odours?
Yes. Substances that smell are usually organic molecules. These are exactly what activated carbon binds well. Worksheet W 239 names better odour, taste and colour values as the first purpose in the waterworks.
What is sintered activated carbon?
Sintered activated carbon is a form compacted under heat and pressure. Sintering increases the number of pores and thus the capacity. A block of sintered carbon retains more than loose granules. Minerals remain in the water.
How often does activated carbon need to be replaced?
The service life depends on the loading. Once the surface is occupied, the filter reaches breakthrough. The value in the outflow then rises. For household use, manufacturers specify an interval in litres or months. In the waterworks, the breakthrough curve determines when the carbon is replaced.
Sources
- List of approved treatment substances under § 20 TrinkwV, Umweltbundesamt — Bundesanzeiger of 27.01.2023, corrected on 27.08.2024, Part I b, positions 1 and 2
- DVGW worksheet W 239 (A) of October 2021 — on the use of activated carbon in waterworks, with 22 terms in section 3
- Physisorption of gases, IUPAC Technical Report 2015 — in Pure and Applied Chemistry 87, pages 1051 to 1069, with the limits of 2 nm and 50 nm
- Characterisation of activated carbon using the iodine number, University of Duisburg-Essen — on the definition according to DIN EN 12902 and on deviations between laboratories
- Activated carbon qualification system, Stadtwerke Düsseldorf, 28.05.2025 — with iodine number, grain size, hardness, density and ash
- Opt-Aktiv-C project, AiF 20617N, 2019 to 2022, DVGW — with 52 tests at 600 and 900 degrees
- Assessment of the specification of vegetable carbon E 153, EFSA, 28.01.2026 — in the EFSA Journal, volume 24, issue 1, with limits and particle size
- WHO Model List of Essential Medicines, 24th edition, September 2025 — with activated carbon under section 4.1 as an antidote
- Questions and answers on the Urban Wastewater Treatment Directive, Umweltbundesamt, as of 25.02.2026 — with the thresholds of 150,000 and 10,000 p.e.
- DIN EN 1860-2:2023 on barbecue charcoal and briquettes — with 75% and 60% carbon
- DIN EN 12915-1:2009 on virgin granular carbon — and Part 2 on reactivated material
- Screening of powdered activated carbon for drinking water treatment, Aqua & Gas, 05.12.2025 — with 37 carbons tested and coefficients of determination of 0.08 and 0.36
- United Nations Comtrade, commodity code 3802 10, Germany 2024 — with imports of 83,897 tonnes and exports of 53,041 tonnes
