Cultivation of Pleurotus ostreatus Mushroom on Substrates Made of Cellulose Fibre Rejects: Product Quality and Spent Substrate Fuel Properties

Waste and Biomass Valorization https://doi.org/10.1007/s12649-020-01311-y ORIGINAL PAPER Cultivation of Pleurotus ostreatus Mushroom on Substrates Made of Cellulose Fibre Rejects: Product Quality and Spent Substrate Fuel Properties Alejandro Grimm1 · Lill Eilertsen1,2 · Feng Chen1 · Renyuan Huang3 · Lars Atterhem4 · Shaojun Xiong1 Received: 15 November 2019 / Accepted: 18 November 2020 © The Author(s) 2020 Abstract This paper explores an alternative valorisation method for high-moisture content waste streams from the pulp and paper industry. Cellulose fibre rejects from industrial-scale recycling/pulping of waste paper was used as an ingredient in substrates for cultivation of Pleurotus ostreatus, commonly known as oyster mushroom. Three substrates with 40, 60, and 80 wt% fibre rejects were tested, and a conventional substrate formula based on birch (Betula ssp.) sawdust was used for comparison. The spent mushroom substrate (SMS) fuel characteristics were assessed through ashing procedures. Mycelium growth was faster on substrates based on fibre rejects. The average biological efficiencies of the first flush of fruit bodies were between 29 and 36% compared to 42% for birch sawdust substrates. The fruit bodies had good nutritional values, i.e., crude protein (22–25 wt% d.b.), crude fat (3–3.5 wt% d.b.), crude fibre (8–10 wt% d.b.), and carbohydrates (57–62 wt% d.b.). The concentrations of heavy metals, 5–10 µg/kg Pb, 19–28 µg/kg Cd, 5–6 µg/kg Hg, and 26–53 µg/kg As were well below the limit values for food products set in EU regulations. The SMS could be used as fuel for direct combustion or co-combusted with other biomasses. Graphic Abstract Keywords Edible fungus · Nutritional values · Heavy metals · Fuel characterization · Circular economy Statement of Novelty * Alejandro Grimm 1 Department of Forest Biomaterials and Technology, Swedish University of Agricultural Sciences, 901 83 Umeå, Sweden 2 Department of Forest Genetics and Plant Physiology, Umeå Plant Science Center, Swedish University of Agricultural Sciences, 901 83 Umeå, Sweden 3 Swedfungi AB, 907 40 Umeå, Sweden 4 Biosteam AB, 937 93 Burträsk, Sweden Many different types of biowaste materials contain components that can be converted into high value-added biobased products before being used for energy purposes. This study is meant to show how cellulose-rich fibre rejects (‘secondary wastes’) from industrial-scale recycling/pulping of waste paper (‘primary wastes’) can be used as an ingredient in substrates for cultivation of edible mushrooms, and how the spent substrates (‘tertiary wastes’) can be used as solid 13 Vol.:(0123456789) Waste and Biomass Valorization biofuel. Today, fibre rejects are mostly disposed of in landfills or, to a lesser extent, used as fuel in waste-to-energy plants. To the author’s knowledge, the information about the suitability of fibre rejects for combined production of edible mushrooms and biofuels is scarce. Introduction According to the International Council on Clean Transportation [1], approximately 225 Mt of diverse residues including, e.g., waste paper, wood, food, and plant materials are annually generated in Europe. Wastes generated during the recycling/pulping of waste paper, so-called ‘rejects’, are considered a problematic material from both the environmental and economic point of view. As much as 15–25 wt% of the raw waste paper can end up as rejects during the pulping process [2]. The rejects can be subdivided into different types according to their composition [3], and some of these can be seen as an interesting raw material for the development of a circular economy. Rejects that contain a high amount of cellulose fibre, not suitable for the production of paper, could be used to cultivate high value-added biobased products such as edible mushrooms. The latter are the fruit bodies of basidiomycetes with a saprotrophic lifestyle. These basidiomycetes are divided into primary, secondary, and tertiary decomposers [4, 5]. Primary decomposer fungi such as the Pleurotus spp., Lentinula edodes, and Grifola frondosa, have the ability to degrade and use plant material components such as cellulose, hemicellulose, and lignin as carbon sources. Edible mushrooms are cultivated and consumed worldwide, e.g., Pleurotus spp. and Lentinula edodes, with a protein content of about 30 wt% and 18 wt% d.b., respectively [6], are two of the most popular on the global market. Many species have also a health-promoting effect [7], and some are used for extraction of bioactive compounds [8, 9]. According to Royse et al. [10], the world annual production of cultivated edible mushrooms is about 34 Mt with a 30-fold increase since 1978, which corresponds to a value of 34 billion USD. China is today the largest producer and exporter (with 80% of the world market) of cultivated edible mushrooms, while the EU and America stand for approximately 10% of the global production. Cultivation of primary decomposer mushroom results in considerable quantities of spent substrate (SMS). The latter can be used as a component of substrates for mushrooms that grow on composts, but not always in sufficient quantities to solve the problem of their accumulation in producing areas where they represent a pollution risk [11, 12]. In a wellmanaged mushroom industry, approximately 70 wt% d.b. of the initial substrate may remain as SMS [13, 14]. Disposal of SMS is also costly due to the high transportation volumes 13 [15]. This emphasizes a necessity for the development of smart solutions to reduce environmental problems and costs tied to the production process. Mushrooms such as Pleurotus spp. are cultivated on substrates made of various lignocellulosic wastes [14, 16–19], and to a lesser extent on different types of waste paper or cellulose-rich materials [20–24]. This paper evaluates the suitability of fibre rejects (‘secondary waste’) from industrial-scale recycling/pulping of waste paper (‘primary waste’) as an ingredient in substrates for cultivation of Pleurotus ostreatus mushroom, and the possibility of using spent substrates (‘tertiary waste’) as fuel for the generation of the heat necessary for the substrate pasteurization and mushroom cultivation processes. The main goal is to promote the establishment of an integrated production model to achieve almost zero-waste development. Materials and Methods Substrate Raw Materials Mushroom substrate ingredients included: (a) Light coarse fibre rejects, which consists mainly of cellulose fibre and impurities such as limestone and different silicates, was collected from SCA Obbola, Umeå, Sweden; (b) Sawdust (particle size < 2 mm), generated during the processing of birch (Betula ssp.) timber, was collected from a sawmill in the province of Västerbotten, Sweden; and (c) Wheat bran (Lantmännen Lantbruk, Sweden) was used as a nutrient source in the substrates to promote productivity. Produced Substrate Compositions Substrate ingredients were mixed on a (...truncated)