Composting of Posidonia oceanica and its use in agriculture

The extraordinary accumulation of deposits of the seaweed Posidonia oceanica on the beaches of Sardinia has given rise to a series of problems linked to its disposal. Leafy deposits of Posidonia oceanica are treated as refuse and disposed of in waste dumps. This is an enormous waste of organic material. Bearing this in mind, some composting experiments have been carried out using washed Posidonia oceanica, sludge and woody residues. The selected substrates were categorised and then mixed homogeneously, according to the previously established parameters, to obtain different mixtures which would satisfy the preliminary physical and chemical conditions for correct composting. The experiment was conducted using an open system with natural ventilation. The final assessment of the chemical parameter values of the compost showed a good carbon, nitrogen and phosphorus content and a balanced ON ratio. The degree of humification was raised appreciably, which indicated that the material had reached a high level of stability. The parameters for the physical characteristics (porosity, apparent density, easily available water and reserve water, etc.) were within the acceptable limits. No pathogenic microorganisms were found, which indicates that the compost was healthy, and the heavy metal content, in particular that of thallium, cadmium, chromium and lead, was below the levels established by law. These results offer an innovative solution to the disposal of Posidonia oceanica which would otherwise be taken to waste dumps, and offers undoubted advantages for the coastal communities interested in this problem.