Circular management of beached waste: recovery of posidonia oceanica

Posidonia oceanica (PO) is a marine plant endemic to the Mediterranean Sea that forms extensive underwater seagrass beds providing essential ecosystem services. During winter, PO dead leaves are carried ashore by currents, forming accumulations known as “banquettes.” These deposits are often perceived as a problem, leading to their removal and landfilling, which has serious consequences for environment (Escandell-Westcott, et al., 2023; Dentamare, et al., 2024). The "Circular Management of Beached Waste" project investigates two alternatives for the valorization of PO waste: 1) the production of sustainable cement mortars and 2) the biogas production via anaerobic digestion. Laboratory tests were conducted for the assessment of the physical and mechanical properties (e.g., workability and compressive/flexural strength) of the cement mortar obtained with the addition of PO waste in varying fractions (from 0% to 17,5%) at different water/cement ratios (0,5 and 0,7). Results showed a reduction in compressive strength proportional to the percentage of PO waste, with an average value of approximately 20 MPa. The mechanical characterization of samples (conducted both at 28 and 90 days of curing time) suggests that PO waste fibers represent a sustainable reinforcement for mortars. For the second area of research, BMP (Biochemical Methane Potential) tests were performed according to standard protocols, which involve monitoring of anaerobic batch reactors for a testing period of 35 days at 37 °C (Holliger, et al., 2016). PO waste were washed with tap water, dried at 50 °C and shredded; the fraction < 2 mm was fed in AD reactor at different concentrations: 8, 16, 32 and 64 gVS/L (in accordance with De Sanctis & Di Iaconi, 2019). The results show increasing methane yields with organic load and the specific methane production range between 0 and 31 NmlCH4/gVS (below the range determined in De Sanctis & Di Iaconi, 2019 of 29 – 62 NmlCH4/gVS). Further mix optimization could enhance biogas production, promoting energy recovery from this organic substrate. The project results can contribute to reducing pollution in marine environment and recovering secondary raw materials from beached waste. However, further studies are needed to evaluate the scalability and economic feasibility for large-scale waste management applications.