Characteristics of a new solid olive-mill by-product ("alperujo") and its suitability for composting

The technology for olive oil extraction in Spain has recently changed to a new, two-phase centrifugation system which produces a semisolid, humid, aci d and polluting by-product called "alperujo", its production being estimate d as no less than 2,500,000 t per year. Alperujo is rich in organic matter and lignin, abundant in water-soluble carbohydrates and fats and has good c ontents of N and K. To study the suitability of alperujo composting, it was mixed with cotton waste to adjust its C/N ratio and improve the porosity o f the mixture. By monitoring the composting process, a rather low biodegrad ation of organic matter and a clear reduction in C/N ratio, total fats, wat er-soluble carbohydrates and phenols were observed as composting advanced. The compost was rich in organic matter, had an acceptable content of nutrie nts and showed values of humification and stability indices which allow us to recommend its use for crop production as a non-toxic, soil organic ferti liser.