ATB in Pots­dam does pion­eer­ing work: Arti­fi­cially pro­duced hum­ic sub­stances for agriculture

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 hum­i­fic­a­tion. 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” 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”.

“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, 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 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, 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.

A list of the related pub­lic­a­tions can be found on the ATB Insti­tute’s homepage.