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Impact of bottom ash addition on Pleurotus ostreatus cultivation on coffee ground substrate

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Overview

Hnydiuk-Stefan and colleagues tested the feasibility of using coal-fired power plant bottom ash as an amendment to spent coffee grounds for Pleurotus ostreatus cultivation, assessing elemental composition of substrates and resulting fruiting bodies. The addition of 1 to 5% bottom ash did not cause fruiting body cadmium to exceed the EU ML of 0.15 mg/kg for Pleurotus ostreatus. Fruiting bodies from pure coffee grounds (control) contained approximately 0.063 mg/kg cadmium; a similar concentration was obtained with 15 g bottom ash per 300 g coffee grounds. No fruiting bodies grew on the pure bottom ash substrate (Mix V). Chromium was of note given the high bottom ash chromium content (68.89 mg/kg), though chromium in fruiting bodies was low.

Key numbers

Raw material cadmium content (Table 2, mg/kg):

  • Spent coffee grounds: cadmium (Cd) 0.05 ± 0 mg/kg, chromium (Cr) 2.29 ± 0.02 mg/kg, nickel (Ni) 2.99 ± 0.39 mg/kg, lead (Pb) 3.85 ± 0.01 mg/kg.
  • Straw: Cd 0.05 ± 0 mg/kg, Cr 3.33 ± 0.02 mg/kg, Ni 6.09 ± 0.78 mg/kg, Pb 6.39 ± 0.02 mg/kg.
  • Bottom ash: Cd 0.736 ± 0.02 mg/kg, Cr 68.89 ± 71 mg/kg, Ni 40.91 ± 5.29 mg/kg, Pb 81.26 ± 0.3 mg/kg.

Fruiting body cadmium (from text, mg/kg):

  • Mix I (pure coffee grounds): approximately 0.063 mg/kg.
  • Mix II (coffee grounds + 3 g bottom ash): approximately 0.063 mg/kg.
  • Mix III (coffee grounds + 15 g bottom ash): approximately 0.05 mg/kg.
  • EU ML for Pleurotus ostreatus (EU 2021/1323): 0.15 mg/kg fresh weight.

Methods (brief)

ICP-OES (ICPE-9800, Shimadzu) for metals and metalloids; flame emission photometry for macronutrients; CHNS elemental analysis. Mineral processing with HNO3, H2O2, and HF (mushroom samples: HNO3 plus H2O2 only). Recovery 93 to 111% for metals. Certified reference materials BCR-482 and AlfaAlfa B2273 used. Three experimental replications.

Evidence fitness

Substrate-safety study in a closed-loop recycling context; directly relevant to commercial Pleurotus cultivation on coffee grounds. Cadmium values in fruiting bodies on control substrate (pure spent coffee grounds) are the principal contamination-profile contribution. Limitation: exact individual fruiting-body cadmium values reported from text narrative rather than a table; no confidence intervals on the narrative values. Bottom ash content above 10% inhibited growth, limiting the contamination scenario to lower amendment levels.

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