Enhancement of Microbial and plant Biodiversity by Restoration of degraded soils in Mediterranean Areas through marine Compost and zeolites Exploitation (EMBRACE project)

The endemic seagrass species of the Mediterranean Sea, Posidonia oceanica (L.) Delile, appears to be highly effective in C storage and its decline, due to direct anthropogenic activities and indirect disturbances, unbalances C sequestration dynamics. In addition, high amounts of P. oceanica litter deposit along the coasts of the Mediterranean Sea every year after leaves detaching from the rhizome during Autumn. Notwithstanding the fundamental ecological role of such deposits against coastal erosion, the use of beaches for tourism purposes currently implies the removal of these deposits, which are negatively considered by stakeholders. At the same time, fishing activities, comprising industrial and small-scale fishing, are responsible for high necromass production that also turn as an undesirable bio-waste. In the last few years, valorisation of P. oceanica litter throughout anaerobic digestion and aerobic stabilization processes has been proposed as a valid alternative to landfill or incineration disposal, although the presence of sea salts can negatively affect these processes. Zeolite-rich rocks, working as ionic exchanger of NH4+, can be useful to reduce its content during anaerobic digestion process and loss of ammonia, via NH3 generation, in atmosphere during the composting process. The moderate affinity of zeolites for Na+ would also lower the salinity of the suspension marine waste/anaerobic sludge with presumable positive effects on both anaerobic digestion process efficiency and final properties of the marine compost originated from the aerobic stabilization of the digestate. Moreover, the natural zeolites can improve the properties of compost and of receiving soils, in terms of cation exchange capacity (CEC), porosity, aeration and water holding capacity. In this general frame, EMBRACE project (PRIN 2022 PNRR) aims at reaching two major objectives, represented by i) valorisation (in terms of both energy and matter) of a marine bio-waste and of a natural zeolite-rich quarry dust; ii) use of the obtained products (quality compost with natural zeolites) in restoring degraded soils of Mediterranean coastal areas (in terms of increase of both above- and belowground biodiversity). This contribution provides the preliminary results about the chemical and mineralogical characterization of selected zeolite-rich rocks coming from abandoned quarry of Neapolitan Yellow Tuff Formation (i.e., ex Cava Suarez, Naples, Italy). This raw material shows a total zeolite content of ca. 40 wt.% mainly consisting of phillipsite and chabazite, and sporadic analcime. The amount of low-ordered and amorphous phases, that also could contribute to ion exchange processes, is estimated up to 29 wt.% whereas non-sorbent minerals are formed by feldspars (mainly sanidine), and subordinately clinopyroxene and micas. The total CEC values is ca. 2.5 mEq/g (0.95 mEq/g for Ca2+, 0.83 mEq/g for K+, 0.60 mEq/g for Na+ and 0.13 mEq/g for Mg2+).