By Jessica Lietze
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. In particular, fertile soil contains about 3% humic acids, while peat contains about 3%–10%.
The advantages of humic substances are that 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 and fertilize less, and the soil restores itself within a few years. Humic substances also act as a pH buffer, and nitrogen, for example from fertilizers, 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 about 85% humic substances and is a precursor to lignite.
In recent decades, numerous companies have specialized 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 its utilization 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 humification. In a high-pressure reactor, we mix the biomass with water in an approximate ratio of 0.1 to 0.4. The fiber components, cellulose, hemicellulose, and lignin are then broken down under high pressure (between 6 to 60 bar) and at a high temperature (between 160°C 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 color between brownish to black."
Dry carbonization, 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" with distinction (suma cum laude). Shortly afterwards, he and his colleagues from Germany and Iran published two papers in the Biofuel Research Journal.
"In terms of content, we—colleagues from selected research institutes around the world—are asking: Which starting biomass materials can be artificially humified? Which process parameters have the most significant effect on the production of humic substances? How can we engineer the characteristics of our products?
"Of course, besides 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 microfertilizer is one of our starting points.
"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 phosphorous.
"A project in the historic Sanssouci Park in Potsdam, Germany, 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 year-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 utilize the great potential of this technology, including a recent article published in Biochar. "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 valorize 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 fertilizers as a slow-release biofertilizer."
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