Advanced treatment of wastewater from maritime activities through in-tegrated catalytic processes

Wastewater generated by maritime activities are characterized by a complex composition containing both oils and emulsifying agents, corrosion inhibitors, bactericides and other chemical compounds, strongly facing the limits of acceptability and purifi-cation of any depurator plant. Hence, the combination of appro-priate techniques is nowadays considered imperative to conceive technically and economically feasible wastewater treatment. Therefore, the present work aims to assess the practicability of the exploitation ofcatalytic wet air oxidation (CWAO) process, incorporated with chemical-physical technologies (i.e. filtration, sedimentation, clarification), for the treatment of shipyard wastewater. The catalytic oxidation process has been investigated with both “simulated” water samples containing recalcitrant probe molecules and “real” wastewaters collected from shipyard activities, using a model catalyst. Furthermore, the tests’ execu-tion in a relevant environment of the Augusta (Italy) city harbor provided the technological validation of the innovative integrat-ed process, aiming to bring the technology at industrial level. Then, the depuration grade reached with the multistage treatment layout proposed fell within the limits set for surface and sewer effluents, allowing the direct emission in the sewer network or as surface water. In particular, Total Organic Carbon (TOC) and Chemical Oxygen Demand (COD) load of “real” shipyard wastewater sample were reduced from 310000 and 560000 mg/l to 15 and 24 mg/l, respectively, proving the integrated treatment efficiency for the purification of highly polluted wastewaters. Moreover, from techno-economic analysis, the estimated total operating costs of the whole treatment process resulted to be ca. 25 €/m3, with the energy needed for reactor heating and the costs of coagulants representing almost the 99% of the net costs. However, the global cost of treatment may drop considerably if the volume of wastewater is reduced. Because of the exothermic character of the catalytic process, in fact, a greater concentration of the polluting load can balance the energy required to maintain reactor temperature. In conclusion, the catalytic technology can improve the efficien-cy and the performance of the low cost biological oxidation, ei-ther as pre-treatment for enhancing the biodegradability of toxic and refractory molecules or as final wastewaters cleaning step, growing the global efficiency of depuration and the water recy-clability.