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The EU-funded circular economy project MUBIC transformed low-value agricultural waste into high-value products – one of which is used to grow mushrooms, whose cultivation the partners set out to revolutionize.
This product is a new type of mushroom substrate, the material on which the mushrooms are grown. ‘Along with other outputs, such as fuel pellets, organic fertilizer and pre-treated feedstock for faster biogas production, the process shaped in MUBIC also delivers substantial sustainability gains,’ says project coordinator Peter Damgaard Nielsen of Danish SME Advanced Substrate Technologies (AST).
It increases the biogas yield from agricultural biomass wastes like straw, deep litter or horse bedding by about 30 %, through the prior cutting and grinding of this biomass. The ability to process wet straw, meadow grass and similar material is a particular plus point: the MUBIC process for these challenging types of feedstock also involves pretreatment with ammonia to break down the lignin in the stalks, Nielsen explains.
Profitable, circular, green
‘Using the AST concept, you get more biogas, and you get it faster says Nielsen. The ammonia used for this pre-treatment is recovered through the drying of the fiber fraction from digestate – the residues after biogas production.
The ammonia is extracted from the digestate in facilities designed as add-on to the biogas plants themselves or integrated part of an AST plant serving more biogas plants. As of July 2020, commercial scale operations have begun at the first such plant in Denmark. The plant can process about 10 tons of 30% dry matter (DM) digestate from a biogas plant per hour.
In the MUBIC project, the digestate starts out as biomass supplied by the partners. ‘Our lorries take feedstock to the biogas plant and digestate back to the AST plant, where we process it,’ Nielsen continues.
The treated digestate is then converted into a variety of products. Along with the mushroom substrate, these outputs include growing media for plants and fuel pellets that are significantly more sustainable than competing products because they are derived from waste that is a residue of locally-sourced biomass.
The AST process delivers a substrate – loose, compacted or pelletized with dry matter content in the range of 70 to 85 %. This is much higher than that of conventional substrates, which typically average about 34 % DM. Furthermore, the share of volatile solids (VS) is considerably higher (85-90% of DM) in the AST substrate compared with ~ 70% of DM in traditional mushroom substrate. Thus, AST substrate provides far more mushroom feed per m³ than competing products, Nielsen explains. Due to its high dry-matter content, it can be stored and does not require cooling during transport over longer distances – unlike conventional mushroom substrates, which are useless when it gets too hot.
AST substrate complements another innovation developed in the project: a system by which mushrooms grown on trays move past pickers on a conveyor belt, as opposed to pickers having to move through the shelves in mushroom farms. This particular innovation was perfected by Dutch SME Panbo Systems, the second partner involved in the project, as a way to reduce harvesting costs. The first 2000 tons a year mushroom production Panbo plant is being built in Germany and will start operating in 2021. This process will change the mushroom industry from a labour-intensive production to a semi-automated production.
An alternative to peat
MUBIC, which ended in January 2020, was funded via a Horizon 2020 programme specifically designed to help SMEs prepare their innovations for commercialisation. Without this support, the straw-to-substrate concept and the automated mushroom production plant would have been shelved, says Nielsen, who emphasizes that the funding enabled the partners to bring their idea to life.
AST had initially considered selling entire add-on plants, but eventually decided to focus on the products generated throughout the process instead: income is generated at several steps, from converting cheap raw material to a high value product for biogas production and from digestate to high value sustainable products.
Spent substrate from mushroom production is one such residue, and a perfect example of the proposed circular approach. In the AST process, it is recovered as feedstock for the production of biogas, and the digestate left over from this process is used to make fresh substrate.
Another positive element of the project is that the AST substrate can be used at a substitute for peat. AST is participating in a research project finding alternatives to peat for growing media, and the positive results of adding AST substrate to growing media have already resulted in the first big order for substrate for horticulture.
The growing media industry have for decades been trying to reduce the use of peat with little success. None of the alternatives have proven as effective as peat, in many cases have they hindered plant growth. The AST substrate have proven effective in up to 100% without inhibiting plant growth.
The growing media consumption is predicted to grow rapidly as the production of food and plant in green houses is seen as a more sustainable production method that conventional plant production because it uses the resources (water, fertilizer energy) much better. This means that the growing media industry will be needing vast amounts of raw material and with peat being a scarce resource we have to find alternatives. ASP substrate has already proven to be an economic and effective alternative to peat.
Both the new mushroom cultivation system and the various products from AST’s circular value chain have been met with interest, with new partnerships enabling the project partners to take these developments forward, Nielsen concludes.