Microwave vacuum pyrolysis conversion of waste mushroom substrate into biochar for use as growth medium in mushroom cultivation

Abstract BACKGROUND Spent mushroom substrate (SMS), largely produced as an agriculture waste from mushroom cultivation, was transformed into biochar via microwave vacuum pyrolysis under different ratios of SMS to microwave absorbent (1:1, 1:2, and 1:3). The biochar was then examined for its potential to be re‐used in mushroom cultivation as a growth medium added to conventional mushroom baglog (plastic bag with mushroom seeds and culture substrates containing rice straw, sawdust, lime and water), with emphasis on its ability to form mycelium – a fungus that grows into mushroom from its seeds. RESULT The pyrolysis generated up to 36 wt% biochar yield with a large adsorption area (up to 215 m 2 g ‐1 ) and less water (4 wt%), indicating that many adsorption sites are available on which mushroom seeds, nutrient and water can be adsorbed onto in order to form mycelium (and subsequently mushroom). The biochar added to grow mushroom in baglog recorded a higher water retention percentage (up to 59%), a higher mycelium colonization length in 8 days (6.3 cm), coverage area (up to 259 cm 2 ) and total mycelium growth volume (317 cm 3 ), and resulted in a higher yield of mushroom (200 g month ‐1 ) than that recorded for the conventional baglog without biochar (160 g month ‐1 ). CONCLUSION The results indicated that biochar produced from SMS using microwave vacuum pyrolysis shows great potential in retaining water and nutrient that in turn promotes the formation of mycelium that leads to increased growth of mushroom in its cultivation. © 2018 Society of Chemical Industry