Anaerobically digested food waste in compost for Agaricus bisporus and Agaricus subrufescens and its effect on mushroom productivity

Background: Source-separated food waste is increasingly being treated by means of hygienisation followed by anaerobic digestion. The fibrous digester residue (digestate) is a potential mushroom substrate, while heat from the biogas can provide steam for the cultivation process. Using bag experiments the present study explored digestate as a full substitute for chicken manure conventionally used in mushroom composts. Results: After mixing, a rapid temperature development in the compost was stimulated by a small amount of chicken manure, as aerobic microbial seeding. Mechanical elimination of lumps was essential for full mycelial colonisation. Three straw digestate composts had Agaricus bisporus mushroom yields above 370gkg^-1 substrate. The optimal compost water content was 600gkg^-1 at inoculation, and high digestate content (up to 500gkg^-1 by dry weight) did not affect yield for this species. High yields of A. subrufescens (200gkg^-1) were related to drier composts of lower digestate content (more straw) and lower pH values at inoculation. Conclusion: Digestate successfully substituted chicken manure in straw composts without affecting mushroom yields for both species. There were no clear differences between straw digestate and control composts in terms of mushroom dry matter, size, nitrogen or ash content.