Fast, controlled and from residual materials: Leibniz Institute for Agricultural Engineering and Bioeconomy (ATB) is driving forward global research into the artificial production of humic substances and its beneficial use in agriculture. The new process called hydrothermal humification makes it possible to fully exploit biological waste.

Every farmer and every allotment gardener knows that humus is good for plant growth. But why? Humus contains humic substances. These substances have numerous advantages for the soil. Particularly fertile soil contains around 3% humic acids, while peat contains around 3 - 10%. The advantages of humic substances: they bind moisture and beneficial minerals in the soil, promoting a healthy ecosystem for microorganisms that convert biomass into nutrient-rich biostimulants to support plant growth. Farmers need to water less, fertilise less and the soil restores itself within few years. Humic substances also act as a pH buffer and nitrogen, for example from fertilisers, tends to remain in the soil, which protects the groundwater.

Humic substances are found in nature and are formed over many years through biological processes, releasing many greenhouse gases. The best-known example of this is composting. Humic substances are found in large quantities in soft lignite. It consists of around 85% humic substances and is a precursor to lignite. In recent decades, numerous companies have specialised in the complex extraction and careful processing of humic substances in order to make them available for agriculture, for example. However, these resources are finite, and coal mining and utilisation are considered harmful to the environment and climate. 

ATB therefore relies on a hydrothermal process. With resounding success. Dr Nader Marzban, post-doctoral researcher at ATB and an expert in biochar and humic substances, puts it like this: "What nature can do in years with the help of microorganisms, we can do in minutes to hours in a controllable process with heat, pressure and water. In agriculture, but also in landscape conservation or private households, a lot of organic waste is produced. We were able to prove that many of these are ideally suited for humification⁸. In a high-pressure reactor, we mix the biomass with water in an approximate ratio of 0.1 to 0.4. The fibre components, cellulose, hemicellulose, and lignin are then broken down under high pressure (between 6 to 60 bar) and at a high temperature (between 160 and 240°C). Depending on the pH value and temperature in the reactor, we obtain either more hydrochar or artificial humic acid. Both are solids that range in colour between brownish to black.” 

Dry carbonisation, also known as pyrolysis, has been used by charcoal burners for centuries. In contrast, hydrothermal conversion, in particular hydrothermal humification, is still very new. However, research and its use in practice are currently gathering pace. Many parameters are still unclear. “Here at ATB, we have done pioneering work in recent years! Only a handful of research institutes around the world have looked into this type of humic production in any depth," says Dr Marzban. 

At the end of 2023, Marzban defended his doctoral thesis "From hydrothermal carbonization to hydrothermal humification of biomass: The role of process conditions”¹³ with distinction (suma cum laude). Shortly afterwards, he and his colleagues from Germany and Iran published two papers in the internationally renowned "Biofuel Research Journal".^4,5

"In terms of content, we – colleagues from selected research institutes around the world – are asking: Which starting biomass materials⁸ can be artificially humified? Which process parameters have the most significant effect¹ on the production of humic substances? How can we engineer the characteristics of our products? Of course, beside to agricultural impact we ask about the environmental impact. How much carbon can we permanently store in the soil if we add humic substances? And finally, what success can we achieve? A new type of humic-based microfertiliser is one of our starting points3. The initial results showed that adding just 0.01% of hydrothermal humification products to soil could significantly increase the germination index and support plants in uptaking more nutrients, such as phosphorous⁴. 

A project in the historic Sanssouci Park in Potsdam, Germany, which was funded by Brandenburg's Ministry of Science, is also particularly illustrative. The old trees there have been struggling with years of drought, losing vitality and becoming susceptible to disease. The park operators are making great efforts to preserve the trees. In a joint project with the Max Planck Institute of Colloids and Interfaces, Professor Markus Antonietti, and the Prussian Palaces and Gardens Foundation, we tried to save a 150-160 years old beech tree there. To do this, we produced artificial humic substances and applied them to the soil around the tree. The first application was in 2022 and the initial results are impressive! The beech is doing very well compared to untreated trees. Of course, we are running parallel trials on around 100 small trees to verify the results," says Dr Marzban. 

He is currently working on several project proposals to further advance its research and utilise the great potential of this technology: “Hydrothermal humification can also facilitate other processes. At ATB, for example, we use bioconversion processes to produce high quality lactic and succinic acid or the energy source biogas with the help of microorganisms. Humification enables us to completely valorise residual materials. In biogas production, for example, carbohydrates are difficult to break down and lignin inhibits the process. However, if we add artificial humification, we can humify up to 37% of the dry matter from biogas fermentation residues. This produces by-products such as soluble organic compounds in the process liquid. If we add these again to the anaerobic process during biogas production, we can double the methane yield. In addition, humus-rich digestate is produced, which can replace chemical fertilisers as a slow-release biofertiliser.”

For Dr Marzban, the future viability of this process is obvious. "We are closing cycles and replacing fossil resources in line with a sustainable and circular bioeconomy. If we ensure that our humic acids are in no way inferior to natural deposits in terms of quality and benefits - and we can prove this, we have a fast, controllable process that utilises renewable raw materials and enables cascading, i.e. multi-stage, use of this biomass. I think hydrothermal humification will significantly contribute to the bioeconomy through the integrated residue management and sustainable transformation of agriculture. By integrating hydrothermal humification into biorefineries, solid and liquid residues can be converted into humic substances, advancing zero-waste efforts and sequestering carbon in soil," summarises Dr Marzban.

Contact

Dr Nader Marzban
Scientist for Thermochemical Conversion, ATB
Phone: +49 331 5699-339
E-Mail: nmarzban@spam.atb-potsdam.de 

Jessica Lietze
Officer for Public Relations, ATB
Phone: +49 331 5699-819
E-Mail: presse@spam.atb-potsdam.de

List of related publications

1. Marzban, N.; Libra, J.A.; Rotter, V.S.; Herrmann, C.; Ro, K.S.; Filonenko, S.; Hoffmann, T.; Antonietti, M. (2024): Maximizing the value of liquid products and minimizing carbon loss in hydrothermal processing of biomass: an evolution from carbonization to humification. Biochar 6, 44. https://doi.org/10.1007/s42773-024-00334-1.
2. Marzban, N.; Libra, J.A.; Ro, K.S.; Moloeznik Paniagua, D.; Rotter, V.S.; Sturm, B.; Filonenko, S. (2024): Hydrochar stability: understanding the role of moisture, time and temperature in its physiochemical changes. Biochar 6, 38. https://doi.org/10.1007/s42773-024-00329-y.
3. Ischia, G.; Berge, N.D.; Bae, S.; Marzban, N.; Román, S.; Farru, G.; Wilk, M.; Kulli, B.; Fiori, L. (2024): Advances in Research and Technology of Hydrothermal Carbonization: Achievements and Future Directions. Agronomy 14, 955. https://doi.org/10.3390/agronomy14050955.
4. Ghaslani, M.; Rezaee, R.; Aboubakri, O.; Sarlaki, E.; Hoffmann, T.; Maleki, A.; Marzban, N. (2024): Lime-assisted hydrothermal humification and carbonization of sugar beet pulp: Unveiling the yield, quality, and phytotoxicity of products. Biofuel Research Journal. https://doi.org/10.18331/BRJ2024.11.1.4
5. Volikov, A.; Schneider, H.; Tarakina, Nadezda V.; Marzban, N.; Antonietti, M.; Filonenko, S. (2024): Artificial Humic Substances as Sustainable Carriers for Manganese: Development of a Novel Bio-based Microfertiliser. Biofuel Research Journal. https://doi.org/10.18331/BRJ2024.11.1.3
6. Tkachenko, V.; Ambrosini, S.; Marzban, N.; Pandey, A.; Vogl, S.; Antonietti, M.; Filonenko, S. (2024): Fulvic acid modification with phenolic precursors towards controllable solubility performance. RSC Sustainability. : p. 1-11. Online: https://doi.org/10.1039/D3SU00295K
7. Marzban, N.; Libra, J.; Rotter, V.; Ro, K.; Moloeznik Paniagua, D.; Filonenko, S. (2023): Changes in Selected Organic and Inorganic Compounds in the Hydrothermal Carbonization Process Liquid While in Storage. ACS Omega. (4): p. 4234-4243. Online: https://doi.org/10.1021/acsomega.2c07419
8. Tkachenko, V.; Marzban, N.; Vogl, S.; Filonenko, S.; Antonietti, M. (2023): Chemical Insight into the Base-Tuned Hydrothermal Treatment of Side Stream Biomasses. Sustainable Energy & Fuels. : p. 769-777. Online: https://doi.org/10.1039/D2SE01513G
9. Kohzadi, S.; Marzban, N.; Godini, K.; Amini, N.; Maleki, A. (2023): Effect of Hydrochar Modification on the Adsorption of Methylene Blue from Aqueous Solution: An Experimental Study Followed by Intelligent Modelling. Water. (18): p. 3220. Online: https://doi.org/10.3390/w15183220
10. Kohzadi, S.; Marzban, N.; Zandsalimi, Y.; Godini, K.; Amini, N.; Harikaranahalli Puttaiah, P.; Lee, S.; Zandi, S.; Ebrahimi, R.; Maleki, A. (2023): Machine learning-based modelling of malachite green adsorption on hydrochar derived from hydrothermal fulvification of wheat straw. Heliyon. (11): p. 21258. Online: https://doi.org/10.1016/j.heliyon.2023.e21258
11. Sarlaki, E.; Ghofrani-Isfahani, P.; Ghorbani, M.; Benedini, L.; Kermani, A.; Rezaei, M.; Marzban, N.; Filonenko, S.; Peng, W.; Tabatabaei, M.; He, Y.; Aghbashlo, M.; Kianmehr, M.; Angelidaki, I. (2023): Oxidation-alkaline-enhanced abiotic humification valorises lignin-rich biogas digestate into artificial humic acids. Journal of Cleaner Production. (5 January 2024): p. 140409. Online: https://doi.org/10.1016/j.jclepro.2023.140409   
12. Marzban, N.; Libra, J.; Hosseini, S.; Fischer, M.; Rotter, V. (2022): Experimental evaluation and application of genetic programming to develop predictive correlations for hydrochar higher heating value and yield to optimise the energy content. Journal of Environmental Chemical Engineering. (6): p. 108880. Online: https://doi.org/10.1016/j.jece.2022.108880
13. Marzban, N. (2023): From hydrothermal carbonization to hydrothermal humification of biomass: The role of process conditions. Online: https://doi.org/10.14279/depositonce-20983

Background

Leibniz Institute for Agricultural Engineering and Bioeconomy is a pioneer and a driver of systemic-technological bioeconomy research.

We create the scientific foundation for the transformation of agricultural, food, other industrial and energy systems into a sustainable bio-based circular economy. We develop, deploy and integrate technologies, techniques, processes and management strategies, strategically integrate a variety of bioeconomic production systems within a comprehensive system approach and manage them in a knowledge-driven, adaptive and extensively automated way using converging technologies.

We conduct research in dialogue with society, policymakers, industry and other stakeholders - knowledge-driven and application-inspired.