The production of spent mushroom medium (SMM) from oyster mushroom industry is increasing every year parallel to the increment of the market demand. SMM is considered solid waste and conventionally collects and dumps into the landfill without any pre-treatment. SMM contains major beneficial organic elements with the potential to be converted into valuable compost with appropriate conditions. This research aims to study the potential of several types of microbial inoculum to compost the SMM with dried sludge from bio-ethanol waste and chicken manure in the aerobic composting process for 12 days. Three composting beds of 3 kg each were composted with different types of microbial inoculum; EM-1, tempeh fermented liquid, and food waste fermented liquid. The initial carbon-to-nitrogen (C/N) ratio and moisture for each composting bed were 23.42 and 55% respectively. The temperature, moisture content, pH, and total organic matter (TOM) were measured for each composting bed. All the composting beds reached the maximum temperature at the thermophilic phase (>40 °C) after 24 h of the composting being started. Similar trends were recorded for pH, moisture, and total organic matter (TOM) for all the composting beds. The commercial microbial inoculum (EM-1) recorded the highest degradation rate of TOM (0.0225 day−1) which followed the first-order kinetic reaction (R2 = 0.9556) compared to the tempeh and food waste fermented liquid. However, the results shown by tempeh and food waste fermented liquid were comparable to EM-1 microbial inoculum and thus feasible to substitute EM-1 for the composting of SMM.
