Olive mill wastewater-evaporation ponds long term stored: Integrated assessment of in situ bioremediation strategies based on composting and vermicomposting.

During the last two decades, the method most widely used to manage olive mill wastewater (OMW) derived from olive oil production has been its disposal in evaporation ponds. Long-term storage of OMW leads to the accumulation of toxic sediments (OMWS) rich in recalcitrant compounds with phytotoxic and antimicrobial properties, which limit their use for agronomic purpose. The aim of this study was to compare the effect of two in situ bioremediation strategies (composting and a combination of composting followed by vermicomposting) to remove the potential toxicity of the sediments derived from long-term stored OMW. The results obtained showed that the composting method assisted with the earthworms enhanced the depletion of phenolic compounds and OMWS ecotoxicity more than composting, especially during the maturation stage. Moreover, vermicomposting was more effective in the reduction of the OMWS salinity. However, a pre-composting process to the OMWS is necessary prior to vermicomposting to provide the suitable conditions for earthworms survival and activity. Furthermore, the final compost showed a phytostimulating effect. Therefore, these in situ bioremediation strategies can be considered potential tools for decontamination and recovery of long-term stored OMWS in evaporation ponds, which currently poses an unsolved environmental problem.

The Posidonia oceanica marine sedimentary record: A Holocene archive of heavy metal pollution.

The study of a Posidonia oceanica mat (a peat-like marine sediment) core has provided a record of changes in heavy metal abundances (Fe, Mn, Ni, Cr, Cu, Pb, Cd, Zn, As and Al) since the Mid-Holocene (last 4470yr) in Portlligat Bay (NW Mediterranean). Metal contents were determined in P. oceanica. Both, the concentration records and the results of principal components analysis showed that metal pollution in the studied bay started ca. 2800yr BP and steadily increased until present. The increase in Fe, Cu, Pb, Cd, Zn and As concentrations since ca. 2800yr BP and in particular during Greek (ca. 2680-2465cal BP) and Roman (ca. 2150-1740cal BP) times shows an early anthropogenic pollution rise in the bay, which might be associated with large- and short-scale cultural and technological development. In the last ca. 1000yr the concentrations of heavy metals, mainly derived from anthropogenic activities, have significantly increased (e.g. from ~15 to 47µg g(-1) for Pb, ~23 to 95µg g(-1) for Zn and ~8 to 228µg g(-1) for As). Our study demonstrates for the first time the uniqueness of P. oceanica meadows as long-term archives of abundances, patterns, and trends of heavy metals during the Late Holocene in Mediterranean coastal ecosystems.