Engineering char production from mushroom bag log waste

Oyster mushrooms are one of Indonesia's most widely consumed horticultural commodities, which consequently generates large quantities of spent mushroom substrate (baglog waste) that may cause environmental pollution if not properly managed. One promising utilisation pathway is carbonisation into char, which offers added value as both an energy source and a substrate for mushroom cultivation. This study aimed to produce char from oyster mushroom baglog waste and to evaluate its characteristics. The waste was collected from mushroom farmers in Indralaya Utara, Ogan Ilir, and sun-dried for one to three days. Carbonisation was carried out in a drum kiln at 300–350 °C for two hours. The resulting char was assessed for quality parameters, including moisture content, ash content, volatile matter, fixed carbon, and calorific value. The results indicated that three days of drying (T3) produced the lowest moisture content (20.5%), although with less consistent yield. Post-carbonisation, moisture content decreased significantly to 2.05–2.64% (adb) compared to the raw substrate (50.84%). Ash content increased to approximately 48.10% (adb), with T2 recording the lowest value (45.34%) and T3 the highest (50.80%). Volatile matter remained relatively high, yet T2 exhibited the lowest level (27.10% adb) and the highest fixed carbon content (25.51%). The calorific value ranged between 1960 and 2645 kcal/kg; T2 achieved the highest value (2645 kcal/kg), exceeding that of the raw substrate (2009 kcal/kg). Overall, oyster mushroom baglog waste demonstrates considerable potential to be converted into high-quality char, with T2 showing the most favourable performance as an alternative solid fuel.