Charcoal Filter|Activated Charcoal

Charcoal is a fairly easy material. It binds water and nutrients, filters and cleans. We use them in our self-sufficient vehicle in the green sewage treatment plant and in the litter of the bio-toilet. Again and again we come across the term “activated carbon”. huh We wanted to get to the bottom of the mystery: what exactly is activated carbon? How is it created and what is different from “normal” and vegetable charcoal?

Charcoal, biocharcoal, activated charcoal - isn't it all the same?

no Well, all three contain a lot of carbon, some of which originally comes from plants. And all three are black. But otherwise they are quite different!

Coal is formed, similar to oil, when plant residues are deposited and compressed in the ground over millions of years. Most of the time it is lignite or hard coal, which is mined and burned with huge machines. This creates electricity, for example. Incidentally, almost 30% of global energy consumption is still covered by coal. Another 28% is then petroleum. But we'll talk about the madness another time. In any case: "Normal" mined coal: CO2 centrifuge, not very sympathetic.

Biocharcoal is clearly easier because it is made from renewable raw materials such as straw and helps with soil improvement, fertilization and composting, for example, as an addition to the compost. During composting, the coal is enriched with nutrients. Your humus will be upgraded and can store even more water and nutrients in the future, some studies even say that the yield will be increased by up to 50%. That may be a bit exaggerated, but in any case you have to water and fertilize less and actively bind CO2 in the soil, which is good for the plants and the climate.

Activated charcoal is biocharcoal that is produced under special circumstances and is even more porous than biocharcoal. It can therefore also be used as a water filter, for example, but it is also 5-10 times more expensive!

What is so unique about activated charcoal?

Activated carbon consists of an intricate labyrinth of ultra-fine pores that binds pollutants. Activated carbon does this job so well because there is a lot of space for it: One gram has an inner surface of 500-1500 m2 . In other words, a teaspoon of activated charcoal is the size of a soccer field!

In comparison: biocharcoal provides 300 m2 per gram, still plenty of space for particles of all kinds, so the filter and storage capacity is also there, just less. Not ideal as a water filter, but ideally suited for upgrading the soil!

How is activated charcoal made?

Activated charcoal and biocharcoal are quite similar here. In both cases, the starting material is burned in the absence of oxygen. But activated carbon is only created through activation!

1. Charring

The starting material is wood, peat, lignite, fruit kernels such as olive kernels, coconut shells, etc. They all contain a lot of carbon. First, the raw material is charred, i.e. burned without oxygen supply. The process is also called "pyrolysis". Almost everything that isn't carbon gets rid of, and space is created for an intricate tunnel system of fine pores.

Oxygen would cause the carbon to burn completely and escape as a gas or turn to ash. Incidentally, this also happens during normal combustion in a campfire – only a fraction of the carbon remains from the starting material. That's why it's better without oxygen, because we want to use the carbon!

2. Activating Activated Charcoal

In the subsequent activation, a distinction is made between gas activation and chemical activation.

Gas activation : A very, very hot gas stream (700-1000°C) of water vapour, carbon dioxide and air converts part of the material into carbon monoxide and hydrogen, which escape as gases. What remains is a highly active, porous carbon framework with a huge inner surface.

Chemical activation: Not quite as hot (“only” 400-800°C), but with a lot of chemicals, porous activated carbon is also created here, directly from the uncharred starting material. The chemicals are recovered and reused.

What does activated charcoal do?

Activated charcoal cleans, and pretty well too! The decisive process here is called adsorption. Dirt from air and water accumulates on the walls of the pore labyrinth. The pores differ in diameter and thus absorb dirt particles of different sizes. Not all particles fit into every pore. Many pores in different sizes ensure a particularly good filter effect.

What makes a powerful filter?

The type of dirt - does your dirt fit into your pores?

PH value, temperature – optimal framework conditions?

Time – how long is the activated carbon in contact with the contaminated medium