Anaerobic Digestion of Spent Compost and Peat from the Cultivation of Mushroom

ABSTRACT. For mushroom producers, compost is a fundamental resource representing the main cultivation substrate, but it also represents a cost at the end of each production cycle. This study reports the results of a pilot scale experiment of anaerobic digestion (AD) of spent mushroom cultivation substrate composed of compost and peat. The tests were performed utilizing a specific bag-type anaerobic reactor with high efficiency hydraulic mixing (AD Bag®, Demetra Group, Italy), at 38°C. The process was quite proficient, as indicated by the concentration of methane in biogas (53%) and acidity/alkalinity ratio (0.28). Biogas yields resulted 26.30 l/kg of raw material, 66.34 l/kg of total solids (TS) and 110.22 l/kg of volatile solids (VS); methane yields resulted of 13.93 l/kg, 35.13 l/kgTS and 58.37 l/kgVS. These values are lower than those of more conventional feedstocks but are compelling and unexpected, in that the input products are typically considered stable. AD could provide energy to the mushroom production with a contribution to the environmental sustainability of the sector. Digestate could be composted on a bed of straw to produce the mushroom cultivation substrate (i.e. compost), a perfect example of circular economy. These results could introduce innovative integration perspectives between AD and composting.