Full scale composting of food waste and tree pruning: How large is the variation on the compost nutrients over time?

The aim of the study was to evaluate if a composting unit on a commercial scale can produce, during 15 months, an organic compost according to the guarantees and tolerance margins required by Brazilian legislation for its nutrient content. For this, a food and tree pruning waste compost produced in a composting unit located in Belo Horizonte (Brazil) was evaluated. Noncompliance regarding tolerance margins for nitrogen, phosphorus and potassium were 3, 17 and 28% on a dry matter basis and 19, 31 and 33% on a fresh matter basis. Noncompliance can be mainly attributed to difference in the initial condition among piles (mass used in the piles preparation, proportion of food and pruning waste, initial nutrient content in the mixture, etc.) and differences in the operational activities among the piles. Together, these factors explained 64 to 86% of the variation in the nutrient content of the compost.