This interview with Donata Chiari, Policy Officer at the EBI, aims to provide key insights into promoting sewage sludge-based biochar in the European Union.

As traditional feedstocks like wood chips become increasingly expensive, and other sources such as agricultural waste have increasingly well-established recycling pathways, sewage sludge emerges as a promising yet underutilised material for biochar production.

As use of sewage sludge as a feedstock gains traction, it is important to differentiate between the qualities of sewage sludges, as not all are suitable for agricultural use. Some sludges, due to the presence of heavy metals, will never find their way into agriculture. In these cases, biochar can still be produced through pyrolysis, but the resulting chars will be directed towards other applications, such as in certain materials or even incineration. In some instances, pyrolysis may serve as just one step in the treatment process.

This article highlights how this process can not only eliminate contaminants but also supports nutrient recovery and resource efficiency. Biochar from sludge can enhance soil fertility, water retention, and nutrient availability, while aiding to reduce and remove atmospheric emissions. Moreover, sewage sludge biochars that don’t fit the agricultural purpose can be used for other applications, such as in materials.

We highlight current blockages whilst providing key insights as to how this novel treatment method offers a chance to turn waste into a valuable resource, generating revenue and fostering economic sustainability, all while adhering to the EU’s various regulatory ambitions. 

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‍Paul: Hi Donata, would you please introduce yourself and the work you do at the European Biochar Industry Consortium?  
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Donata: Hello Paul, my name is Donata Chiari, I am a Policy Officer at the European Biochar Industry Consortium (EBI) where I am in charge of promoting informed decision-making for policy changes related to biochar.

As a members organisation, the EBI acts as a representation for the European biochar sector, fostering growth and sectoral collaboration. We seek to bridge the gap between market innovation, policy-making and research to promote the growth of the biochar industry. 

Paul: There’s a growing interest in the topic of manure and sewage sludge as a feedstock for biochar production. In your opinion, what are the main factors motivating this development? 
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Donata: I believe the drive towards the thermochemical conversion of sludges is primarily driven by the increasing cost of waste management, with some Waste Water Treatment Plants paying up to €200/ton for the disposal. Moreover, as sewage sludge will always be present - and increasingly more as our population grows - we need to find cost-effective and value-adding upcycling methods for this abundantly present resource. Finally, traditional treatment methods like sludge incineration, which often result in added emissions, become increasingly scrutinised to make place for alternative treatments that can reduce, and remediate our environmental impact. 

Looking at it from a policy perspective, the introduction of sludge pyrolysis and biochar production offers a pathway to promote the elimination of the contaminants of concern in sewage sludges. Pyrolysis operates under high temperatures, which can eliminate a wide range of harmful substances, including heavy metals, pathogens, pharmaceuticals, and persistent organic pollutants like PFAS (per- and polyfluoroalkyl substances) and PAHs (polycyclic aromatic hydrocarbons).

By immobilising or fully breaking down these contaminants, the pyrolysis process transforms sewage sludge into a safer material that can either be repurposed for agricultural biochar or redirected to other uses, such as in construction materials. This approach not only mitigates the risks associated with contaminant leakage but also supports resource efficiency by recovering essential nutrients like phosphorus, contributing to the circular economy. Indeed, critical materials such as Phosphorus (P), a non-renewable resource with an essential role in modern agricultural systems as a plant nutrient, are becoming increasingly scarce. The adoption of technologies that can recover these materials, like certain pyrolysis processes that can recover up to 100% of phosphorus in sludge, are therefore gaining increased attention. 

However, pyrolysis is not a one-size fits all solution, as Nitrogen (N) is volatised during the process. Certain technologies can be used for Nitrogen recovery in sewage sludge, though only few of these methods are common practice in the industry. However, it is possible to extract the N before a feedstock is pyrolysed to avoid nutrient losses.

Hence, the thermochemical conversion (i.e. pyrolysis) of sewage sludge can serve to reduce the EU’s dependence for the sourcing of critical resources and is therefore in line with the EU nutrient recovery policy. 

Finally, it is increasingly well-known that biochar offers notable agronomic advantages such as the enhancement of soil fertility, water retention, and nutrient availability for plants. The conversion of sewage sludge into biochar therefore presents an opportunity to transform waste into a valuable resource, potentially generating revenue streams whilst also holding great potential in addressing agricultural challenges. The climate-postive effects of sewage sludge biochar are becoming increasingly valuable as it also aids in carbon sequestration, mitigating greenhouse gas emissions, and promoting soil health and biodiversity. 
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Image: A sewage sludge to biochar facility by Next Generation Elements GmbH in Germany

Paul: Despite this growing mountain of evidence favoring the treatment of sewage sludge through pyrolysis, many policy-makers continue to express their concerns of possible contamination concerns on sewage sludge biochar, even excluding it from the list of eligible feedstocks for “Pyrolysis and gasification materials” (CMC14).

‍Donata: There are high risks of sewage sludge containing pathogens, LAS (Linear alkylbenzene sulfonate), DEHP (Bis(2-ethylhexyl) phthalate), nonylphenols, PCBs (Polychlorinated biphenyl), pharmaceuticals, PFAS (polyfluoroalkyl substances), PAHs (Polycyclic aromatic hydrocarbon) and heavy metals. Such risks make it important that we ensure product safety by eliminating contaminants through advanced treatment, with clearly well-defined process parameters. However, depending on national regulations, much of today’s sewage sludge is sent to landfills, spread on agricultural fields or incinerated. 

As of 2019, the EU’s Fertilising Products Regulation (Regulation (EU) 2019/1009) Component Material Category 14 defines Pyrolysis as a thermochemical conversion process with a requirement that it occur under oxygen-limiting conditions in such a way that a temperature of at least 180 °C for at least two seconds is reached in the reactor at temperatures. 

The EBI on the other hand finds that pyrolysis should be done at temperatures of a minimum of 550 - 600°C for a minimum duration that ensures full carbonisation. Research finds that the process conditions of pyrolysis are much harsher and can be effective at removing or immobilising contaminants when compared to currently approved sterilisation conditions for sewage sludge.

We found that the pyrolysis temperature plays an important role in determining the effectiveness of sewage sludge treatment. For example, microplastics can be entirely degraded when the pyrolysis temperature reaches 450 °C, temperatures of 600-650 °C have been shown to eliminate all  PFAS compounds found in sewage sludge. Target temperatures range have been identified for other contaminants as well, such as PAH’s. 

We believe that there’s enough recent scientific evidence to alleviate claims regarding uncertainties as to whether contaminants are eliminated.

‍Paul: What is the EBI’s position on the correct treatment method for sewage sludge for the production of high-quality, environmentally friendly biochar?

Donata: Earlier this year, with the European Biochar Initiative (EBI) we released a position paper advocating for a minimum pyrolysis temperature of 550-600 degrees Celsius. The residence time is not specified as the required time depends on different plant process design.

Paul: So these findings aren’t considered in policy? Are there no regulatory frameworks that govern the production and application of biochar from sludge at the EU-level, or in its member states?

Donata: The EU holds the authority to set standards for safety and quality within the single market, meaning regulations such as the Fertilising Product Regulation’s CMC 14 regulates the levels of pollutants in biochar - to ensure safe applications in soils. It’s also critical that all producers analyse their production, to know its composition and ensure it is safe for its intended use. 

However, as of now, the CMC14 does not include sewage sludge in the positive list of feedstock for pyrolysis and gasification materials. We believe this should be revised, and even propose to impose stricter requirements for sewage sludge pyrolysis if needed. We believe there’s a huge market opportunity here, to reduce treatment costs (and even generate incomes), sequester carbon and promote healthy soil ecosystems.

Despite the lack of a EU regulatory framework, four member states currently allow for the use of sewage sludge-based biochars in agricultural soils: the Czech Republic, Finland, Denmark and Sweden. This opens the possibility to sell such biochar produced in other EU countries in these member states.

However, each country has a different procedure. 

• The Czech Republic allows sewage sludge to achieve an end-of-waste status following an approval by regional authorities, this entails an approval for both the end-product and production plant. 

• In Sweden, permission needs to be obtained through the Swedish Chemical Agency (KEMI) where the product's composition is assessed for its compliance with their requirements.

• In Denmark, the regulation was adopted in 2022 already. They consider pyrolysis to be an effective treatment method if the process achieves 500°C for a minimum of 3 minutes, the resulting biochar then reaches the end-of-waste status.

• In Finland the regulation was only adopted last October, in 2023, there the authorities also focused on the process - requiring temperatures to reach 500°C for 5 minutes to reach end-of-waste status. They did go a step further by also looking at the biochar’s composition, H/Corg values must be less than 0.7, and PAH’ lower than 6mg/kg of PAH16 dry matter, this is in alignment with the EU’s Fertilising Product Regulation. 

Other member states, such as Austria and Switzerland, favor the incineration of sewage sludge but are strict with regards to the spreading of the resulting ashes on fields. In Italy biochar must be plant based, whilst in Spain there’s no mention of biochar in this field. In the United Kingdom its private companies that are actively considering the pyrolysis of sludge, probably for economic gains. 

In general, the EU fears sewage sludge due to the risks associated with contaminants such asPFAS (persistent synthetic chemicals linked to health and environmental risks), as current treatment methods do not always address this issue. However, pyrolysis offers a promising solution. Through the high-temperature process, pyrolysis can effectively break down and destroy PFAS, preventing their accumulation in the environment. By targeting these persistent chemicals, pyrolysis provides a way to safely treat sewage sludge and reduce the risks associated with PFAS contamination, offering a more robust alternative to traditional methods.

‍Paul: So in your experience, having spoken to different sector representatives and government authorities, how would you categorise the different perspectives of the different stakeholders? 

Donata: Seeing as biochar is still considered to be a novel product, we actively engage with different stakeholders—such as policymakers, industry leaders, and agricultural professionals—to raise awareness and provide in-depth education on the critical issues surrounding sewage sludge treatment. 

We focus on explaining the benefits of pyrolysis not only for sanitation purposes but also for biochar’s potential in soil remediation, carbon sequestration, nutrient recovery, and its broader environmental impacts. By sharing scientific evidence, case studies, and best practices, we aim to build trust and promote informed decision-making about the adoption and application of biochar in various sectors.

The scientific community remains deeply interested in the topic, with their findings consistently supporting previous claims about environmental benefits, particularly regarding how this process degrades pollutants like PAHs and immobilises metals, making them less likely to leak, while also looking into the breaking down of contaminants such as plastics, pharmaceuticals, and PAHs. 

Similarly, much attention has been given to the composition of the biochar. Once more, the suggested temperature range of 550-600°C also proved vital to produce inertinite biochar - meaning it is not susceptible to microbial degradation relevant for climate periods for BCR. This helped promote biochar as an effective, durable, carbon removal tool. Similarly, such work has helped promote biochar as a fertilising product that, for example, enhances the soil’s cation exchange capacity (CEC - the total capacity of a soil to hold exchangeable cations influencing its ability to retain essential nutrients and provides a buffer against soil acidification). Similar research also highlighted its benefits for effective arsenic remediation and PFAS absorption in soils.

We’ve gained similar attention from operators of wastewater treatment plants (WWTP), mainly because biochar can help reduce sludge disposal costs (which can reach upwards of €200/tonne in some countries). Pyrolysis of sludge can represent a solution to turn this cost into a revenue, by selling/using thermal energy, biochar and possibly even carbon credits. As the growing quantities of sludge produced across Europe, biochar production would therefore represent a significant opportunity for these operators.

Fertilising agencies also recognise pyrolysis as an effective solution for nutrient recovery, aiming to reclaim valuable nutrients like Phosphorus (P). This aligns with the EU’s ambition to reduce its dependence on foreign countries for such vital, often non-renewable, nutrients. Producing organic fertilisers from sludge offering environmental and economic benefits. In fact, sludge pyrolysis can help recover 80-100% of the total P content of sludge. 

Similarly, biochar filters are emerging as an alternative to activated carbon for waste-water treatment. Currently such products are largely sourced from China, this would be another opportunity to  reduce our dependence on imported materials, further highlighting biochar’s relevance.

Based on these findings, the EU is beginning to reassess its stance on nutrient recovery, potentially including it in new delegated acts. Some countries have already integrated biochar into their regulations, reflecting its growing acceptance and application in sustainable practices.

That said, the widespread presence of existing incineration plants, coupled with the limited number of pyrolysis installations, presents a logistical challenge when considering a transition to pyrolysis. While incineration facilities are well-established, expanding pyrolysis infrastructure will require significant investment and development to reach comparable scale. Additionally, the preference toward classic fertilising products, limited public knowledge, and potential fear of new technologies pose challenges to the wide-scale adoption of this treatment process. There is also a need for a European-level study on component material categories to support this transition. The European Commission is currently seeking stakeholder suggestions and recommendations on fertilising products and nutrient recycling legislations, making it an appropriate moment to develop regulations or amendments.

Paul: Thank you very much for participating in this interview and sharing your insights with us!