Examples of value chains

There is scope for a more diversified use of side streams from the fisheries industry and for the production of more valuable products from them. An example of the use of fish side stream is the processing of rainbow trout trimmings into raw materials for the food industry or directly into consumer products. Hydrolysis-based processing can produce not only protein hydrolysate, but also fish gelatin, fish meal, fish oil and minerals from fish side streams. Potential markets for oil, hydrolysate, gelatin and minerals include the food industry, pet food, dietary supplements, cosmetics and pharmaceuticals. Side streams from rainbow trout production are currently mainly used as feed for fur animals and the price is relatively low (about 0.20 €/kg, Setälä et al. 2024).

As in other value chain examples, the sustainability and economic analysis was conducted as a hotspot analysis strictly limited to the processing of the side stream itself. The amount of side stream considered (2 500 tons per year) would be formed from 10 000 tons of rainbow trout, of which almost 7 500 tons of fish would be supplied for food use. In addition, a buffer stock of 10% of the fish side stream would be set aside to cover possible supply disruptions and uninterrupted processing. The value chain does not include transportation of raw materials, as processing could take place at the production site.

The emissions from processing the rainbow trout side stream would be 0.9 kg CO2 eq/kg value added (for all value fractions combined). The main emissions are from the need for heating energy (75%) and electricity (25%). Heat was assumed to be produced from natural gas and electricity was assumed to be average Finnish electricity. In this example, both increasing energy efficiency and choosing a renewable and low-emission energy source would significantly reduce emissions from processing.

The profitability of rainbow trout side stream processing can be assessed on the basis of a study on salmonids (Setälä et al. 2024). A processing plant of this size would require an investment of 3 700 000 €, assuming a 20 % subsidy (European Maritime and Fisheries Fund). Two thirds of the revenue will come from protein hydrolysate and fish oil. Fish gelatin represents a very small proportion of the product volume, but its selling price is higher than that of other fractions. The estimated prices of protein hydrolysate (4.00 €/kg), fish oil (1.30 €/kg) and raw material have the greatest impact on the profitability of production. Based on the assumptions made, the investment is profitable (payback period 3.9 years).

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Approximately one third of Finland's arable land is grassland. Grasses contribute to soil carbon sequestration, improve soil structure and water retention, and thus reduce nutrient runoff. However, grassland cultivation is regionally concentrated in the cattle farming areas of Northern Savo and the four counties of Ostrobothnia. It would therefore be important to include grass in the crop rotation in areas such as intensive pig production in Southwest Finland.

Grass silage as such is not suitable for pig feed, but it can be processed into a protein-rich liquid fraction, also known as grass juice, which would improve the availability of feed for pig farms. In general, the possibility to use the grass yield would increase the motivation of pig farmers to include grass in their crop rotation. The dry fraction produced as a by-product of pressing could be used as a co-feedstock for the farm's biogas plant, increasing gas production and improving nutrient recycling.

An example of a grass biorefinery was assumed for a farm with 5 000 fattening pigs per year and feeding 2.5 L of grass juice /pig/day to the pigs. The profitability analysis took into account the benefits to the pig farm of both the feed used to feed the pigs and the dry fraction used as co-feedstock for the biogas plant. However, it should be noted that the main input to the biogas plant on the farm is pig slurry and the dry fraction from the grass is only an additional feed. The profitability of the process is affected by both the price of the raw material and the price of the final products. The production costs of grass silage and the value of the grass juice in the feed do not vary as much as the income from biogas.

The climate emissions of the liquid fraction extracted from the grass silage are 0.1 kg CO₂ eq/kg (liter) of grass juice. The emissions were fully allocated to the grass juice, as the dry fraction from the grass silage pressing is considered as a zero-emission waste to be used as an co-feedstock for biogas production. The majority of the emissions from grass juice (93%) are from grass grown on mineral soils. Climate emissions from grass cultivation depend on the cultivation practices, e.g. mineral soils are heavily fertilized. In this study, grass grown on mineral soils was assumed to be fertilized with low-emission digestate from a biogas plant instead of mineral fertilizers (Rasi et al. 2019). Emissions can be further reduced by, for example, using biomethane as a fuel for machinery. Furthermore, the emissions do not take into account the positive effects of grassland cultivation on soil carbon sequestration. Further research is needed to determine the significance of this for emissions from cultivation. For example, the carbon footprint of grass juice has been found to be lower than that of barley meal (0.45 kg CO2 eq/kg (excluding production equipment and infrastructure), Hietala et al. 2022). However, the comparison is not straightforward as barley and grass juice are very different feeds.

In a situation where biogas is used to produce electricity and heat on the farm, the higher the proportion of energy used on the farm, the better the profitability. The selling price of electricity produced in excess of the farm's own electricity needs is only about half of the price the farm has to pay when buying electricity. In addition, if heat is produced in excess of the farm's own heating needs, the excess heat can rarely be sold. For a pig farm of the size of the example (5,000 pigs per year), the income from the end product was estimated to be about the same as the cost of producing the grass juice. Therefore, the main benefit to the farm is in terms of improved nutrient cycling and cannot be directly quantified in monetary terms.

If the farm is able to process the biogas into biomethane for transportation fuel, the dry fraction of the grass silage will be a valuable addition to the biogas process, and overall the production of grass juice will be clearly profitable.

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More than 75 000 tons of carrots are produced in Finland each year, of which about 30% end up as side stream. Currently, the carrot side stream is mainly used for the production of fertilizer products and renewable energy through anaerobic digestion or composting. The use of carrot side stream as animal feed is limited by its poor shelf life and seasonal production period.

An alternative for the utilization of carrot straw is based on the fractionation of the material by compression into dry and liquid fractions. The liquid fraction could, in an optimal case, even be suitable for direct food use. The dry fraction could be further fermented as cattle feed, similar to grass silage. Fermentation is a cost and resource efficient preservation method that maintains the characteristics and homogeneity of the feed.

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In addition to renewable energy, the biogas process produces nutrient-rich digestate. The digestate is suitable as fertilizer on its own, but in centralized plants the transport distances for the often very watery digestate can be long and the nutrient needs of the fields vary. Therefore, in some cases it is worthwhile to process the digestate into fertilizer products that are easier to transport and have different nutrient ratios.

The recycling of nutrients and organic matter is at the heart of the value chain of downstream digestate processing. The model assumed an annual input of 20 000 tons to the biogas plant, with pig slurry as the main input (60%). The biogas was used for electricity and heat production.

The considered digestate treatment process is based on centrifuge separation, which separates the mass into solid and liquid fractions. The solids are dried and crushed, resulting in a dried fertilizer granule as an end product. The liquid fraction is evaporated to produce a nutrient concentrate. The resulting water is reused in the process as process water. During the centrifuge separation process, the nutrients in the digestate are separated into solid and liquid fractions, with the solid fraction containing proportionally more phosphorus and the liquid fraction containing proportionally more nitrogen than the original digestate. Similarly, the fertilizer granule contains more phosphorus and the nutrient concentrate contains more nitrogen in the final products.

The climate emissions of the proposed digestate processing are 1.8 kg CO₂ eq/kg N for soluble nutrient concentrate and 7.5 kg CO2 eq/kg P for fertilizer granulate. The climate emissions were only due to the electricity produced from the biogas and its consumption (The evaporation and drying technologies selected consume only electricity and no heat). The main source of emissions was the evaporation of nutrient concentrate (used as nitrogen fertilizer) and the drying of the fertilizer granulate (used as phosphorus fertilizer). By improving the energy efficiency of the processing, emissions would be reduced. The fractions are intended to replace mineral fertilizers in agriculture. In comparison, the emissions from the production of mineral nitrogen fertilizer (5.3 kg CO2 eq/kg N) are higher than for the nutrient concentrate that replaces it.

Further processing of the digestate on this scale would require an investment of 1 200 000 €, assuming a 30% subsidy (Rural Enterprise funding). The investment is profitable (payback period 2.3 years) if the price of the recycled fertilizer products; fertilizer granulate and nutrient concentrate, is estimated on the basis of their nutrient content. However, if the price is estimated based on the farmers' willingness to pay, the investment is not profitable (Anttila 2020, Appendix 6b).

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