Pile Composting of Two-phase Centrifuged Olive Husks: Bioindicators of the Process

Abstract

Composting is a process largely used to solve the organic material disposal problem, but composting of the olive husks produced by two-phase technology remains largely unknown. Because of their high content of salts, polyphenols, fatty acids and tannins, husk utilisation as fertiliser is not possible. Composting of the husks could permit the reduction of salt content and conversion of phenolic compounds into humic substances, but the knowledge about conditions of starting up, running the plant, degradation and microbiological characteristics of the cured compost has to be improved. Trials were carried out with uninoculated (A), and inoculated (B) piles and the process was monitored by ATP content and a pool of enzyme activities. The results showed that the performance of the process improved from pile A to pile B and ATP and mainly a pool of enzyme activities (alkaline phosphatase, esterase, esterase-lipase, phosphoamidase, β-galactosidase, β-gluco-sidase) showed effectiveness in the description of process. Finally, the molecular methods used to detect faecal contaminants in the cured compost resulted to be reliable.