Biocul can reduce certain environmentally hazardous substances - but monitoring is necessary if agriculture wants to use it.
Økologisk NuThe government's ambitions to distribute large quantities of biochar on agricultural land have created a need for further investigations into the presence of environmentally hazardous substances in biochar and the effects of the pyrolysis process. An ongoing research project led by the Technical University of Denmark (DTU) has shown that in many cases, the pyrolysis process reduces the content of several organic environmental pollutants compared to the original raw materials. This includes PFAS and several other industrial chemicals. The experiments also indicate that biochar generally releases fewer of these substances into the environment than the raw materials from which it is made. DTU announced this in a press release. This is significant because the raw materials currently used are applied directly to farmland without any proper pre-treatment. Particularly, sewage sludge can contain organic contaminants such as PFAS, pharmaceutical residues, and other hazardous substances, as well as several heavy metals, which can be released into the environment and leach into groundwater. Authorities have warned about these risks. In Denmark, biochar is produced from straw, residual fibers from biogas production, and sewage sludge. This occurs in pyrolysis plants where biomass is heated in the absence of oxygen, preventing combustion, and instead breaking down into gas, oil, and charcoal. The solid, carbon-rich residue is called biochar. The Danish Environmental Protection Agency previously warned that biochar produced through pyrolysis could contain carcinogenic and hormone-disrupting substances. There is also uncertainty regarding the degradation, leaching, and bioavailability of harmful substances in biochar, as well as which toxic compounds are formed during the pyrolysis process. The content can vary depending on the type of biomass used and the pyrolysis conditions. Jyllands-Posten has previously reported on residents in Vendsyssel, where Denmark’s first large pyrolysis plant is located, who complain of dizziness, headaches, blisters, and rashes. In another project—Danish Biochar LTE—researchers are investigating the long-term effects of biochar on agricultural soils. DTU’s ongoing study shows clear differences between raw materials. Straw generally produces the cleanest biochar with low levels of both heavy metals and organic pollutants. Residual biogas fibers are at an intermediate level, while sewage sludge is the most challenging type, with higher contents of especially heavy metals and many organic hazardous substances. The results also show that biochar from Danish pyrolysis plants contains only very low levels of PAHs, also called tar substances, which can form during pyrolysis. However, some samples from industrial plants showed elevated levels of tar substances. Some substances can concentrate in the biochar. Although many organic pollutants are reduced during pyrolysis, this does not apply to all types of substances. Heavy metals and metalloids, such as cadmium, nickel, copper, and arsenic, do not break down during pyrolysis and can therefore become concentrated in the biochar. Many of these metals are strongly bound within the structure of the biochar and are only released in limited amounts. However, the long-term environmental effects are not yet fully understood. “Our results suggest that pyrolysis can be an effective technology for reducing the content of a range of organic hazardous substances found in biomass. At the same time, they show that the quality of biochar depends on both the raw material and the production conditions. Therefore, control and clear frameworks are necessary if biochar is to be used on a larger scale,” says senior researcher Wolfgang Stelte from DTU Chemical Engineering. Need for regulation and control Overall, the results indicate that biochar from Danish pyrolysis plants often has a lower emission of hazardous substances than the raw materials it is made from, but not all biochar is suitable for application on farmland. Biochar produced from raw materials with high levels of environmental contaminants can contain excessively high concentrations of, for example, heavy metals or other unwanted substances, and there is considerable variation between raw materials and production conditions. This underscores the need for quality control and strict regulation if biochar is to be widely used in agriculture, especially considering that imported biochar with an unknown risk profile could enter the Danish market, Stelte explains. “There are already certification schemes, such as the European Biochar Certificate, which require documentation and analysis of biochar. Our results support the need for clear standards, ongoing control, and continued research,” he adds. The ongoing project continues to explore other key environmental aspects of pyrolysis, including emissions from the process and potential risks associated with handling and storing large quantities of biochar. The research findings have been submitted to the Danish Environmental Protection Agency, and a summary of the results is publicly available in DTU’s research database under the title: 'Investigation of environmental issues related to the production and use of biochar - Executive summary of feedstock and biochar analysis.' The project’s results are also being prepared for publication in peer-reviewed scientific journals.
The government's ambitions to spread large quantities of biochar on agricultural land have created a need for further investigations into the content of environmentally hazardous substances in biochar and the effects of the pyrolysis process.
Now, an ongoing research project led by the Technical University of Denmark shows that the pyrolysis process in many cases reduces the content of a range of organic environmentally hazardous substances compared to the original raw materials. This includes, among others, PFAS and several other industrial chemicals.
The experiments also show that biochar generally releases fewer of these substances into the environment than the raw materials from which it is produced. This is stated by DTU in a press release.
This is significant because the raw materials used today are spread on agricultural land without any real pretreatment. Particularly wastewater sludge can contain organic pollutants such as PFAS, medicine residues, and other environmentally hazardous substances, as well as several heavy metals, which are released into the environment and can seep into the groundwater.
Agency has warned about risks
In Denmark, biochar is produced from straw, residual fibers from biogas production, and wastewater sludge. This occurs in pyrolysis plants where the biomass is heated without oxygen, so it does not burn but instead decomposes into gas, oil, and charcoal. The solid carbon-rich residue is called biochar.
The Environmental Protection Agency has previously warned in a note that biochar created through pyrolysis can contain both carcinogenic and hormone-disrupting substances. There is also uncertainty regarding the degradation, leaching, and bioavailability of harmful substances in biochar, as well as which harmful substances are formed during the pyrolysis process. The content can vary depending on which biomass is used and the conditions under which it is processed.
Jyllands-Posten has previously reported on residents in Vendsyssel, where Denmark's first large pyrolysis plant is located, who complain of dizziness, headaches, blisters, and rashes.
In another project - Danish Biochar LTE - researchers are investigating the long-term effects of biochar on agricultural soils.
DTU's ongoing study shows clear differences between the raw materials. Straw generally produces the cleanest biochar with low levels of both heavy metals and organic pollutants. Residual fibers from biogas production are at an intermediate level, while wastewater sludge is the most challenging type, with higher contents of especially heavy metals and many organic hazardous substances.
The results also show that biochar from Danish pyrolysis plants contains only very low levels of PAHs, also called tar substances, which can form during the pyrolysis process. However, some samples from industrial plants showed elevated values of tar substances.
Some can be concentrated in biochar
Although many organic pollutants are reduced during pyrolysis, this does not apply to all types of substances. Heavy metals and metalloids, such as cadmium, nickel, copper, and arsenic, do not degrade during pyrolysis and can therefore be concentrated in the biochar.
Many of these metals are strongly bound within the structure of the biochar and are only released to a limited extent. The long-term effects in the environment, however, are not yet fully clarified.
”Our results indicate that pyrolysis can be an effective technology to reduce the content of a range of organic hazardous substances found in biomass. At the same time, they show that the quality of biochar depends on both the raw material and the production conditions. Therefore, there is a need for control and clear frameworks if biochar is to be used on a larger scale,” says senior researcher Wolfgang Stelte from DTU Chemistry.
Need for control
The results overall show that biochar from Danish pyrolysis plants often has a lower emission of hazardous substances than the raw materials from which it is produced, but at the same time, not all biochar is suitable for spreading on agricultural land. Biochar made from raw materials with a high content of environmental contaminants can contain excessively high concentrations of, for example, heavy metals or other unwanted substances, and there is considerable variation between both raw materials and production conditions.
This emphasizes the need for quality control and strict regulation if biochar is to be widely used in agriculture, also considering that foreign biochar with an unknown risk profile may enter the Danish market, explains Wolfgang Stelte.
”There are already certification schemes, such as the European Biochar Certificate, which set requirements for documentation and analysis of biochar. Our results support the need for clear standards, ongoing control, and continued research,” he says.
The ongoing project continues to shed light on other key environmental aspects of pyrolysis, including emissions from the pyrolysis process and potential risks associated with handling and storing biochar on a large scale.
The research results have been submitted to the Environmental Protection Agency, and a summary of the findings is publicly available in DTU’s research database under the title: 'Investigation of environmental issues related to the production and use of biochar - Executive summary of feedstock and biochar analysis'.
The project's results are also being prepared for publication in peer-reviewed scientific journals.