Bioremediation of port environments: efficiency and evaluation of different approaches

ABSTRACT Bioremediation of port environments: efficiency and evaluation of different approaches Elvira Chiesa This PhD research evaluated microbial bioactivators as a bioremediation strategy for improving the environmental quality of organically impacted harbour sediments and waters, using the Porto Antico of Genoa as a model urban marine system. The study followed a three-year, multi-scale pathway integrating environmental characterization, laboratory microcosm experiments, field-scale validation, ecotoxicological assessment and the development of an operational protocol. Seasonal monitoring of three harbour sectors revealed a clear spatial gradient controlled by hydrodynamic confinement, sediment texture, external inputs and sediment–water interactions. The most confined areas showed greater accumulation of organic matter and contaminants, stronger microbiological pressure and more pronounced signs of reduced sediment conditions, providing the environmental basis for subsequent experimental work. Two laboratory microcosm phases were then used to compare four bioactivator formulations and to investigate the influence of dose, sediment contact and oxygen availability. The experiments showed that the indigenous microbial community was already metabolically active and that bioactivation mainly acted by supporting and modulating endogenous organic-matter transformation. Treatment performance depended on the interaction between formulation, substrate accessibility and environmental conditions rather than on a single operational factor. On the basis of the integrated response of water and sediment matrices, the SM formulation was selected for field validation. The field experiment was conducted over 120 days in the Porto Antico. The selected treatment was associated with changes in sedimentary organic-matter quality, including a marked late decrease in sediment proteins at the treated sub-stations, while no persistent deterioration of the water column was detected. A transient perturbation observed during the experiment affected both treated and untreated sectors and was therefore interpreted as environmental forcing rather than a treatment effect. Metabarcoding indicated a reorganization of the indigenous sediment microbial community without an evident decline in alpha diversity. Ecotoxicological assays further supported the environmental compatibility of the treatment, with no new or persistent toxicity signal attributable to the bioactivator. Overall, the research demonstrates that field bioremediation in urban harbour environments must be site-specific, adaptive and supported by integrated monitoring. The principal outcome is a preliminary Standard Operating Protocol that links site diagnosis, treatment application, environmental safety assessment and monitoring-based operational adjustment, providing a transferable framework for the management and restoration of comparable organically impacted port environments.