The combination of raw animal skin manufacturing processes involves the use of large amounts of chemicals, resulting in the generation of complex and highly polluted tannery wastewater. In this context, the high concentration of chloride in tannery wastewater represents a crucial bottleneck. Indeed, sodium chloride, commonly used in tannery industry to prevent skin rot, increases the concentration of chlorides up to 50 %. At the same time, most of the advanced oxidation processes usually employed in tannery wastewater treatment to remove recalcitrant COD involve the use of conditioning agents, thus increasing the overall concentration of chlorides in the treated effluent. The aim of this study was to evaluate the electrochemical peroxidation process (ECP) efficiency in the treatment of tannery wastewater without changing pH, to improve Fenton technology by avoiding the use of chemicals. The influence of different electric currents on COD and color removal was investigated. The characterization of the produced sludge was conducted through FTIR, SEM and XRD analysis, exploring the morphology and composition of precipitate, depending on the applied current. Although an electrical current of 750 mA yields the highest COD and color removal efficiency (69.7 % and 97.8 %, respectively), 500 mA can be considered the best compromise because of energy consumptions. Iron oxides and hydroxides were generated during the ECP process, playing the role of coagulants through the absorption of organic and inorganic contaminants. The consumption of energy increased as a function of time and applied current; however, cost analysis showed that the electrodes contributed the most to the total cost of the process. In authors' knowledge, the application of ECP process as a tertiary treatment for the removal of recalcitrant COD in tannery wastewater represents a novelty in the literature and the results obtained can be considered as the basis for scaling up the process in future research.

In this study, a Life Cycle Assessment (LCA) was conducted on a project to clean up a heavy metals-contaminated site located in central Italy (Tuscany) in order to define the less impactful solution. The study evaluated the contamination in the soil, derived from the leaching of backfill materials composed of quarry aggregates and sintered granules referred to as “Keu”, a waste derived from the pyrolization of sewage sludge from the Tuscan tannery district, rich in chromium. Three action scenarios were compared, namely the no-action scenario, an excavation and landfill disposal scenario, and a permanent material capping and sealing scenario. The LCA results show the lowest impact for soil capping operations due to the high impacts of heavy metal emissions and landfilling of materials for the first and third scenarios. The third scenario has the lowest impact for ten of the eleven categories analyzed by the CML-IA baseline method. The only exception is the ozone layer depletion category due to the binder synthesis process used for the pavement to protect the membrane. Future studies could be devoted to the study of Keu, through extensive characterization, as well as a study of the fate of this material in landfills to define an appropriate process for future LCA analysis.