Co-composting of olive husks with high moisture contents: Organic matter dynamics and compost quality

As the adoption of new generation, two-phase olive oil extraction systems becomes more widespread, there is an increasing need to evaluate the feasibility of co-composting processes to treat the resulting olive husk by-products that often present particularly elevated moisture contents with respect to traditional two-phase systems. The present work compares process parameters, organic matter dynamics and compost quality during the co-composting of two olive husks having different initial moisture contents, with the adoption of agricultural organic residues as bulking/absorbent agents and forced aeration. Despite the elevated moisture content, the co-composting conditions adopted were effective in reducing the elevated contents of water soluble organic matter, phenolic and lipidic compounds as well as reducing the extreme phytotoxicity of the experimental husk. Organic matter evolution during composting showed that the stabilization process in the two husks was comparable, and final compost quality was adequate in both cases.

► Co-composting of olive husks with elevated moisture contents is a new challenge.
► Composting conditions adopted were effective in reducing phytotoxicity of these husks.
► Degradation of soluble organic compounds led to an effective stabilization process.
► Good compost quality was obtained from an environmental and agronomical point of view.
► All parameters established by Italian law were met by the composts obtained.