Gas and Water Treatment with Biochar

Gas and Water Treatment with Biochar

Biochar is a powerful filter material. It can already replace fossil activated carbon in various filter applications. Read more about advantages and technological status quo.

Advantages of Activated Carbon from Biochar 

  • Lower to equal adsorption costs (chromium, zinc, lead, copper) compared to conventional activated carbons1Hashim A. Alhashimi, Can B. Aktas, Life cycle environmental and economic performance of biochar compared with activated carbon: A meta-analysis, Resources, Conservation and Recycling, Volume 118, 2017, Pages 13-26, ISSN 0921-3449, https://doi.org/10.1016/j.resconrec.2016.11.016
  • Same cleaning power compared to hard coal-based activated carbon
  • Reduction of fossil resource use and thus positive climate effect

Activated carbon has long been used for the filtration of water as well as for steam, air and gas cleaning. The large inner surface of more than 800 qm per gram is crucial for this, as it gives the hard coal-based activated2Tschuden, Niklas 2019. VERSUCHE ZU PHOSPHATENTFERNUNG AUS ABWASSER MITTELS PFLANZENKOHLE.  Masterarbeit an der Universität für Bodenkultur Wien. Aufgerufen am 31.August 2022 von https://forschung.boku.ac.at/fis/suchen.hochschulschriften_info?sprache_in=de&menue_id_in=107&id_in=&hochschulschrift_id_in=19825 carbon a high adsorption power. Through various heat or chemical treatments or coatings, activated carbon filters out chlorine, medicinal residues3Hashim A. Alhashimi, Can B. Aktas, Life cycle environmental and economic performance of biochar compared with activated carbon: A meta-analysis, Resources, Conservation and Recycling, Volume 118, 2017, Pages 13-26, ISSN 0921-3449, https://doi.org/10.1016/j.resconrec.2016.11.016 and phosphorus from water and wastewater, among other things. On the other hand, e.g., ozone, BTEX, toluene, odorous substances and hydrogen sulphide can be removed from gases. 

Fossil activated carbon can also be replaced by biochar that is derived from renewable resources such as wood, coconut fibres or nutshells. However, due to a higher ash content and therefore a higher mineral content, the physical properties are different from those of hard coal. Biochar is softer and usually achieves between 300-400 qm/g porosity. Yet, as far as biochar has a medium porosity, it can be targeted for versatile purposes through specific coating.4Tschuden, Niklas 2019. VERSUCHE ZU PHOSPHATENTFERNUNG AUS ABWASSER MITTELS PFLANZENKOHLE.  Masterarbeit an der Universität für Bodenkultur Wien. Aufgerufen am 31.August 2022 von https://forschung.boku.ac.at/fis/suchen.hochschulschriften_info?sprache_in=de&menue_id_in=107&id_in=&hochschulschrift_id_in=19825 The lower porosity and softness yet limits the areas of application of biochar-based activated carbon to adsorption in the water phase and biogas desulphurisation. Specific treatment can increase the pore surface area.

Biochar can adsorb heavy metals with the same efficiency and a smaller environmental footprint if the biochar used is designed for the task in the best possible way. This is shown by a meta-study by Alhashimi and Aktas from 2017, which includes 80 individual studies.5Hashim A. Alhashimi, Can B. Aktas, Life cycle environmental and economic performance of biochar compared with activated carbon: A meta-analysis, Resources, Conservation and Recycling, Volume 118, 2017, Pages 13-26, ISSN 0921-3449, https://doi.org/10.1016/j.resconrec.2016.11.016

At the same time, the biochar acts as a carbon sink, which means that the biochar lowers the carbon dioxide content in the atmosphere by sequestering carbon for a long time.

Degree of Development

Activated carbon from biochar is already available as standard on the European market, but is not yet widespread. According to Alb-Filter, a maximum of one fifth of the activated carbon used worldwide is produced from regenerative resources. These include wood, sawdust, coconut fibers and shells, ear of maize, lignin, bamboo, fruit pits, nut shells and seeds.

Activated carbon from regenerative materials is mostly used for water treatment and only rarely for adsorption of pollutants in a gas phase. This is due to the increased mineral content (1.5-2%), which results in a softer carbon, which in turn remains stable longer in a water phase.

For the production of highly porous, comparatively durable activated carbons from plant materials, input materials with a high density are necessary. Hardwoods such as Beech wood, fruit kernels and nut shells are suitable for this purpose. In Poland and Germany, there are small and larger industrial production plants, mostly with rotary kilns, that process beech wood into activated carbon. Activated carbon from coconut is mostly produced in Asia, as the coconut can be processed fresh and uncarbonised directly into activated carbon. Finished biochar is almost exclusively processed into activated carbon by chemical activation – because other processes that use heat reduce the stability of the biochar.

An interesting aspect is that the biogenic feedstock for the production of biochar is not critical for the adsorption of coated biochar. An example of targeted coating is biochar based on cherry and apricot pits, which has been loaded with a magnesium layer and thus adsorbs phosphorus from treated wastewater.6Tschuden, Niklas 2019. VERSUCHE ZU PHOSPHATENTFERNUNG AUS ABWASSER MITTELS PFLANZENKOHLE.  Masterarbeit an der Universität für Bodenkultur Wien. Aufgerufen am 31.August 2022 von https://forschung.boku.ac.at/fis/suchen.hochschulschriften_info?sprache_in=de&menue_id_in=107&id_in=&hochschulschrift_id_in=19825

Activated carbon made from biochar is available as pellets, granules, powder or tissue, depending on the intended use.

Approval & Certification

The certification depends on the intended use. This in turn requires targeted production and specific finishing (mostly surface treatment). For the use of biochar as activated carbon, certification according to EBC-BasicMaterial or EBC-ConsumerMaterial is recommended.

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