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

Abstract

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: [Figure not available: see fulltext.].