Quality definition for field biomass in the circular bioeconomy

Authors: Eliisa Punttila & Mikko Rahtola

Straw and reed canary grass are examples of field biomasses, that could be utilized in various of circular bioeconomy solutions. In BioCarbonValue project, funded by Business Finland, they were studied as potential raw material for biocarbon used in high-value applications by VTT and LAB. (Punttila 2024a; Punttila 2024b.) In LAB, reed canary grass in biogas production value chain is also studied in Just Transition Fund programme funded project KUPELA (Utilization of bedding material residues in biogas production and as biofertilizer).

The need of quality criteria

The challenge in Nordic conditions is the quality variation of the field biomass, due to uncertain weather conditions in where the biomass is collected and transported. Currently there are not yet common quality criteria defined for field biomasses utilized in circular bioeconomy. From the point of view of the industry, the required or preferred quality depends on the industrial process. From the point of view of the supplier, once the field biomass, e.g. straw, is collected, supplier is willing to sell all bales despite of the quality variation.

Defining the quality criteria would be needed for several reasons. The quality criteria should be included in the supply contract. The criteria and quality monitoring should be understandable for each part of the supply chain and harmonized​. Quality may also have impact on prizing, if the prize is connected to the utilization value of the biomass. Utilisation of biomass in all qualities would be beneficial for the profitability of the supply chain. (Punttila et al 2021, 26-27.)

Existing quality definitions for straw

How the required quality is defined, depends on the application. Examples on how quality of straw is defined in different cases in the Table 1 illustrate the problem of creating common quality criteria. High moisture content is common quality aspect for different applications, since it causes a risk for growth of mold, bacteria and fungi during the storage. Moisture also increases fire risk during the storage, since tight bales in high moisture content (over 18-20%) may start to burn by themselves due to fermentation process (Pelastustoimi 2023). As bedding material, pelletised straw has good hygienic quality since the temperature in the process eliminates the bacteria (Seinäjoki UAS 2023; Hevostietokeskus 2015).

Application	Quality aspect	References
Bedding	Moisture Mold, bacteria and fungi Dust Good hygienic quality of pelletized straw	Hevostietokeskus 2015; Seinäjoki UAS 2023
Animal feed	Moisture Mold and mycotoxins Fungi Bacteria and yeast Chemicals Soil, weeds, foreign objects, carcasses Dust Nutrient value	Heinonen 2018; Hevostietokeskus 2022
Energy production	Moisture Chemical content (especially Ca, K, Cl) Ash content Grey straw is preferred	Alakangas et al 2016; Skøtt et al 2021
Biorefinement	Valuable fractions: lignin, cellulose and hemicellulose Inorganic compouds, eg. Si	Passoth & Sandgren 2019

Table 1. Quality aspects of straw in different applications

In Finland the assumption is, that straw is collected in autumn as soon the moisture content is suitable for baling. However, in energy production, it is preferred to use grey, “weathered” straw exposed to lot of rain, since it contains less chlorine and alkali and is then less corrosive for boilers (Alakangas et al 2016, 133; Skøtt et al 2021, 12-13).

Which the quality criteria for e.g. straw could be from the point of view of biocarbon production, were discussed during the BioCarbonValue project with the company partners. Important properties of raw materials to consider are especially moisture, which is essential from the pyrolysis point of view. Another is the yield, i.e. how much biocarbon is gained from the raw material in the process. Also, the fixed carbon is important aspect, as well as the contents of metals, alkalis and pyrolysis emissions.

Impact of cultivation practises on biorefinement quality

On farm level, two factors make the biggest difference in the quality of straw – the cultivation method used and whether the cereal on the field has lodged down due weather conditions. The use of plant protection products and growth regulators used in conventional farming can leave residues that affect the use of straw as feed or in other processes. In particular, fungicides can affect the use of straw in microbiological processes. Findings of concentrations exceeding the limit values are rare, while monitoring analyses has also been very limited. A maximum residue level (MRL) is the highest level of a pesticide residue that is legally tolerated in or on food or feed when pesticides are applied correctly (Good Agricultural Practice). The European Commission fixes MRLs for all food and animal feed. The MRLs for all crops and all pesticides can be found in the MRL database on the Commission website. Table 2 illustrates the amount of different permitted pesticides. (European Union Reference Laboratory (EURL) 2024).

Number or pesticides permitted for cereals
Insecticides (pest control)	26 different
Herbicides (weed control)	23 different
Fungicides (fungal disease control)	20 different
Acaricides (mite control)	10 different

Table 2. Number or pesticides permitted for cereals (modified from European Union Reference Laboratory 2024)

These residues are generally not present in straw from organic production. On the other hand, the higher number of weeds in organic fields can affect the usable quality of straw. Microbiological quality is affected by whether conditions and if the plant has lodged down. In wetter growing conditions, the amount of mold and microbes easily increases.

In addition to straw, another key field biomass that can be utilized and is available in larger quantities in biological processes is reed canary grass. With this plant, pesticides are used significantly less than in cereals. Plant biomass is also harvested in its entirety, unlike cereals, where a large part of the mass is utilized specifically as grains. However, excessive weeds and high moisture, can also threaten the quality of reed meadows. (Pahkala et al 2005)

Potential quality classification

In the BioCarbonValue project it was also discussed, is it possible to create classification for raw material quality in case of biocarbon production. The classification could be applied in prizing in the field biomass supply chain. The quality classification could be, for example:

1. Poor quality: not suitable for biocarbon production
2. Suitable quality: suitable for biocarbon production
3. High quality: suitable for high-quality biocarbon production

If rough division to poor and suitable quality would be used, the monitoring could be based on visual evaluation and moisture measurement. In addition, the supply contract could include the required practises related to harvest and collection of field biomass, to minimise the amount of soil or vegetation in bales.

However, to create detailed definition for high-quality, there should be information on the minimum requirements for the raw materials in the case of high value biocarbon properties. The challenge is in defining the threshold values for each class, especially since they may depend on each biocarbon application. Defining the threshold values would require also further research and optimisation with each application. Also, monitoring of the high-quality would require additional technology for analysing the chemical properties already on the field. For example, Near Infrared Spectroscopy (NIR) was studied in the BioCarbonValue as a potential solution.

Another essential question is, in which part of the supply chain the quality criteria should be applied. There can be two business approaches. If the business case if to produce biocarbon for certain application, the final product or application defines the quality requirements for the raw material, and company is interested only in raw material of certain quality. The second business case is that the company receives biomass of any kind of quality, from which it can then produce biochar of different quality or direct it to other processes, for example to energy production.

References

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European Union Reference Laboratory (EURL). (2024). EUPT-CF18: Proficiency test on pesticide residue in wheat straw – Final report. Technical University of Denmark (DTU). Cited 28 March 2025. Available at https://www.food.dtu.dk/english/-/media/institutter/foedevareinstituttet/publikationer/pub-2024/eupt-cf18_proficiency-test-on-pesticide-residue-wheat-straw_final-report_version1_241218.pdf

Heinonen, N. 2018. Pellolta talliin – Opas hevosen karkearehuruokintaan. Hygieeninen laatu. Savonia-ammattikorkeakoulu. Cited 9 December 2024. Available at https://pelloltatalliin.wordpress.com/hygieeninen-laatu/

Hevostietokeskus. 2015. Kuivikkeen laatu ja käyttö. Cited 4 December 2024. Available at https://hevostietokeskus.fi/i/talliymparisto/kuivitus/kuivikkeen-laatu-ja-kaytto

Hevostietokeskus. 2022. Hevosille soveltuvista oljista. Cited 9 December 2024. Available at https://hevostietokeskus.fi/i/talliymparisto/kuivitus/hevosille-soveltuvista-oljista

Pahkala, K., Isolahti, M., Partala, A., Suokannas, A., Kirkkari, A.-M., Peltonen, M., Sahramaa, M., Lindh, T., Paappanen, T., Kallio, E. & Flyktman, M. 2005. Ruokohelven viljely ja korjuu energian tuotantoa varten (2. korjattu painos). Helsinki: MTT. Maa- ja elintarviketalous 1. Cited 28 March 2025. Available at http://www.mtt.fi/met/pdf/met1b.pdf

Pahkala, K. & Kontturi, M. 2008. Korsibiomassojen laatu bioetanolin raaka-aineena. Suomen maataloustieteellisen seuran tiedote nro 23 : Maataloustieteen päivät 2008.  Cited 28 March 2025. Available at https://doi.org/10.33354/smst.75872

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Pelastustoimi. 2023. Heinä- ja olkipaalit voivat syttyä palamaan itsestään. Cited 4 December 2024. Available at https://pelastustoimi.fi/-/heina-ja-olkipaalit-voivat-syttya-palamaan-itsestaan

Punttila, E., Luste, S., Tuominen, K. & Suomi, H. 2021. Oljen toimitusverkon perustamisen reunaehdot – Case: Heinolan biojalostamo. Lahti: LAB-ammattikorkeakoulu. LAB-ammattikorkeakoulun julkaisusarja, osa 34. Cited 4 December 2024. Available at https://urn.fi/URN:ISBN:978-951-827-389-2

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Authors

Eliisa Punttila works as an RDI Specialist in the Faculty of Technology in the LAB University of Applied Sciences. In the BioCarbonValue project she worked as the project manager.

Mikko Rahtola works as an RDI Specialist in the Faculty of Technology in the LAB University of Applied Sciences and as a project manager in the KUPELA project.

Illustration: https://pixabay.com/fi/photos/olki-pudota-olkipaaleja-maatalous-1649857/ (Pixabay Licence)

Reference to this article

Punttila, E. & Rahtola, M. 2025. Quality definition for field biomass in the circular bioeconomy. LAB Pro. Cited and date of citation. Available at https://www.labopen.fi/lab-pro/quality-definition-for-field-biomass-in-the-circular-bioeconomy/