Changes in physical, chemical, and microbiological properties during the two-stage co-composting of green waste with spent mushroom compost and biochar

• Spent mushroom compost (SMC) and/or biochar (BC) were added to green waste composting.
• Physico-chemical and microbiological properties explained the rapid decomposition.
• Particle sizes, microorganisms, enzymes, nitrification, and nutrients were optimized.
• Combination of 35% SMC and 20% BC reduced two-stage co-composting time to 24 days.
• Two-stage co-composting enhanced the humification and decomposition of organic wastes.

This research determined whether the two-stage co-composting can be used to convert green waste (GW) into a useful compost. The GW was co-composted with spent mushroom compost (SMC) (at 0%, 35%, and 55%) and biochar (BC) (at 0%, 20%, and 30%). The combined addition of SMC and BC greatly increased the nutrient contents of the compost product and also improved the compost quality in terms of composting temperature, particle-size distribution, free air space, cation exchange capacity, nitrogen transformation, organic matter degradation, humification, element contents, abundance of aerobic heterotrophs, dehydrogenase activity, and toxicity to germinating seeds. The addition of 35% SMC and 20% BC to GW (dry weight % of initial GW) and the two-stage co-composting technology resulted in the production of the highest quality compost product in only 24 days rather than the 90–270 days required with traditional composting.