Optimizing alperujo composting strategies for acceleration and quality enhancement

Alperujo (AL), the main byproduct of olive oil production, holds promise for circular economy applications, particularly as a soil amendment. However, composting AL faces challenges, including small-scale facilities and lengthy processes often exceeding four months, increasing costs and limiting capacity. This study evaluated thirteen treatments to accelerate and enhance composting, using AL at seventy percent wet weight mixed with olive leaf as a bulking agent along with various activators and accelerators, including manures, biochar, ash, olive pomace, wood vinegar, and four commercial products with microorganisms. The composting mixture comprised 30 kg wet weight of materials. Temperature, moisture, pH, total organic matter, total nitrogen, phosphorus, potassium, C/N ratio, phytotoxicity, and germination were monitored. Composting duration ranged from twenty-seven to eighty-four days, with chicken manure and ash mixtures achieving the shortest times, between twenty and twenty-seven days. Initial pH and its daily increase were key factors in optimizing composting efficiency, correlating with shorter durations (r between −0.65 and −0.70). The highest-quality composts were obtained with cow, goat, and chicken manure, all surpassing two percent total nitrogen and exhibiting C/N ratios ranging from 14.6 to 26.1. Mean sunflower and pea biomass production and nitrogen use efficiency were between 1.43 to 1.87 times and 1.96 to 4.12 times higher, respectively, for compost enriched with microorganisms, demonstrating their effectiveness in supporting plant development. Composts, except those with ashes, met regulatory limits for heavy metals and polyphenols, confirming their safety and suitability as organic fertilizers. Optimized AL composting mixtures can produce high-quality, eco-friendly amendments, shorten composting times, and improve plant growth. • Mixtures containing chicken manure and woody ash showed the shortest composting time. • Initial pH and its daily increase are key factors in optimizing the composting process. • Blends with cow, goat, or chicken manure and alpeorujo achieved the highest quality. • Compost with microorganisms increased sunflower NUE to 15–22 %. • All produced composts (except with ash) are suitable as organic fertilizers.