Hort2thefuture project partner Vlaco visited the Magic Factory, a Norwegian company processing food waste into digestate and mixing it with green waste, developing a compost used for growing tomato plants.
The Magic Factory: A Large-Scale Anaerobic Digestion Plant in Sem, Norway
The Magic Factory is a large-scale anaerobic digestion plant located in Sem, Norway. It is co-owned by Lindum and Greve Biogass – companies in eastern Norway whose largest shareholders are intermunicipalities. The plant collects 70,000 tonnes of biowaste from 1.2 million people and processes it at the biogas facility in Sem. This biowaste is mixed with 47,000 tonnes of liquid biowaste from industry and 73,000 tonnes of manure.
The biowaste is mixed with water, manure, and liquid industrial biowaste, then shredded and pressed through an 8mm sieve. This process yields a liquid food waste slurry (6% Dry Matter – DM) and a relatively large reject material (16%). The reject is pressed again to extract even more slurry and is then dried for incineration – although The Magic Factory is considering pyrolysis for its future treatment.
Before anaerobic digestion of the slurry, it is essential to remove mineral fractions, such as sand. This is achieved using a cyclone. The input is then thickened to 12-15% DM and transferred to a hydrolysis tank before passing through one of three hygienisation tanks for a minimum of 1 hour at 70°C.
The digestion step is mesophilic wet digestion and takes approximately 30 days. The raw digestate is separated in a screw press (with a 0.5mm screen), resulting in:
- 3% w/w fibre product (still contaminated with plastics)
- 97% w/w biofertiliser with 3 to 4% DM. This biofertiliser is transported to be stored in satellite tanks before being used in agriculture and horticulture.
R&D to Further Improve the Processing Site
The operators of The Magic Factory heavily invest in research and development (R&D) for various system improvements:
- Purification of Biowaste: The current de-packaging plant for extracting plastics and other impurities from biowaste is quite primitive. An R&D project is underway to find a better, potentially robotic, system.
- Treatment of Rejects: The treatment of rejects from the pre-treated waste represents a significant cost and environmental impact for the facility. An ongoing R&D project is exploring pyrolysis as a method to treat this reject material.
- Optimisation of Biofertiliser: Further treatment of the liquid fraction (‘biofertiliser’) using reverse osmosis or evaporation is currently under study. The heat required for this purpose will be produced by pyrolysis in the future.
- Useful Applications of CO2: Biogas is upgraded to biomethane using a water scrubber, with CO2 (mixed with air) as a by-product. This CO2 is only partly utilised by injecting it into greenhouses. Investing in alternative biogas upgrading technologies could yield purer CO2 suitable for food production or other industrial applications.
Circular Food Production
The Magic Factory works closely with Reklima, an agricultural company, notably utilising the biofertiliser from The Magic Factory. They are dedicating considerable effort to researching, improving, and mainstreaming an agri-/horticultural system that integrates biowaste cycles from households, agriculture, and industry.
At another site, the fibre product from the biogas plant is biologically dried and screened. Afterwards, 10 to 20% of this digestate fibre is mixed with green waste, papermill residues, and clay, and then composted in a vermicomposting plant. The ultimate aim is to grow tomatoes on the resulting substrate. To this effect, Reklima is experimenting with tomatoes in their greenhouse. According to literature, 40% compost is the maximum for growing plants, but the shift to vermicompost has been a breakthrough in waste-based organic growing systems. This system is also known as ‘digeponics’.
The vermicompost is mixed with additional dried digestate fibres and earthworms. The earthworms in the vermicompost substrate help to close the nutrient cycle by nitrifying the organic nitrogen in both the substrate and the added fertilisation. This fertilisation consists of The Magic Factory’s biofertiliser (the liquid fraction of digestate) combined with potassium sulphate. Special spray nozzles have been installed in the greenhouse to distribute the nutrient-rich water over the boxes containing the tomato plants.
In the future, Reklima aims to scale up this system in other greenhouses. However, profitability currently remains a challenge. While the tomatoes are very tasty, their yield is relatively low. At present, a robust marketing system is also lacking. With some financial support for circular production, they believe it is possible to make it profitable.
Separate collection of biowaste: Same challenges in Norway as in other European countries
In Norway, biowaste is also collected door-to-door, and it presents a significant challenge to ensure the purity of the collected material. This purity is crucial because it directly leads to high-quality compost. The Magic Factory plant receives three types of collection bags:
- Green ordinary plastic bags from Oslo: These bags are distributed free of charge in grocery shops across the city. Oslo citizens can place different types of waste in various coloured bags (green for biowaste, blue for plastics, etc.) within a single bin. The waste from this bin is then collected, and the bags are sorted optically. The Magic Factory’s experience indicates that this waste stream is quite polluted.
- Biodegradable bags: Biowaste collected in biodegradable bags is of a better quality. However, these bags are not biodegradable during digestion, which can cause mechanical problems within the facility.
- Paper bags in a separate bin: The best solution for biowaste collection is using paper bags in a dedicated biowaste bin.
In addition to door-to-door collected biowaste from households, biowaste from supermarkets is also collected (a requirement in Norway since 2023). Supermarkets typically use large plastic bags for this collection.
Other End-Products
Currently, a total of 110,000 tonnes of digestate derived from food waste and manure are recycled. Most of this leaves the plant as biofertiliser, which is returned to farms to produce new food. Another main product is the biogas, which is upgraded to biomethane. The biomethane produced is sold to Air Liquide Skagerrak AS, which owns the natural gas network and biomethane refuelling stations for buses and garbage trucks. A portion of it is also liquefied for marine shipping purposes.