Comparative performance of inoculation strategies for garden waste composting: implications for biodegradation,...

The transition towards a circular economy requires efficient and sustainable composting technologies. This study compared three inoculation strategies for garden waste composting: (i) mature compost, (ii) a commercial microbial preparation "Compost Plus", and (iii) a modified "Compost Plus" enriched with 1% glucose. Composting was conducted in 400 L pilot-scale reactors and evaluated through microbial, chemical and technological indicators. The inoculation materials differed significantly in microbial composition and metabolic activity. Mature compost contained the highest abundance of aerobic heterotrophs and actinomycetes, whereas the commercial preparation exhibited the highest initial dehydrogenase activity and abundance of cellulolytic microorganisms. Mature compost achieved the highest thermophilic temperature (58 °C), indicating high sanitization potential, while the commercial preparation reached a maximum temperature of only 43.5 °C. Glucose stimulated initial microbial growth but did not improve compost quality. Both mature compost and the unmodified commercial preparation produced high-quality products (Fertility Index ≥ 3.50; Clean Index ≥ 4.00). As an exploratory laboratory assay, nanodiamond treatment increased the proportion of metabolically active Penicillium griseofulvum spores by 4.7-fold, highlighting the potential of nanodiamond-assisted fungal stimulation for future composting applications. Overall, the results demonstrate that indigenous mature compost represents the most cost-effective and operationally sustainable inoculation strategy for garden waste composting.