Environmental assessment of compost for Agaricus bisporus production: an Irish case study

Abstract

There has been a considerable rise in cultivated edible mushroom production since 1997, with mushrooms now a major component of diets worldwide. Button mushroom (Agaricus bisporus) production accounts for a significant portion of global production and even more in Europe and North America. The cultivation of A. bisporus relies on the production of a compost (also known as substrate) designed specifically for A. bisporus’ cultivation requirements. Previous studies have shown compost as a potentially important hotspot in the mushroom cultivation life cycle, yet few studies have assessed it as its own product. It is important to carefully evaluate the processes involved in compost production as it is strongly linked with other agricultural activities. This research conducts a life cycle assessment (LCA) on the production of mushroom compost using an Irish system as a case study. The ingredients for compost production (e.g. wheat straw) as well as some production processes themselves (e.g. composting) are highlighted as hotspots. The LCA shows that materials from other agricultural processes can contribute highly to the overall emissions of the compost. For example, wheat straw contributes 36% to ‘climate change’ impact category, and 94% and 95% to ‘freshwater eutrophication’ and ‘marine eutrophication’ categories, respectively. However, the allocation method has a significant impact on the extent of contribution from these agricultural co-products. A mass based allocation increases the contribution of wheat straw in most impact categories compared to an economic allocation. Furthermore, economic allocation produces different impacts depending on the jurisdiction in question and its legislative support of waste reuse and the circular economy. This research demonstrates how the impact of compost production can vary across jurisdictions due to the value given to ‘waste’ products. This has significant importance to the mushroom industry in terms of understanding their emissions and reaching climate-net zero targets.