Mobility of trace metals and microbiological pollution from dredged sediments to the Gulf of Gabes, Tunisia.

Sediments are periodically dredged from the major ports in the Gulf of Gabes (GG) during maintenance operations. These sediments are dumped near the coats of Sfax and Gabes cities. In the present study, 6 trace metals (Cd, Cu, Cr, Ni, Pb, and Zn) concentrations were assessed in both sediments and column water taken from the different basins of Sfax port. This study is the first to focus on the microbial and microalgae contaminations of Sfax port sediments. The spatial distributions of trace metals in dredged sediments from the different basins of Sfax port show that the maximum concentrations of Cd (13.75 µg/g), Cu (892.5 µg/g), and Zn (1447 µg/g) exceeded the Geode standard thresholds. The same elements, also detected in the water column, exceeded the toxicity thresholds for phytoplankton, shellfish, and algae (Cd 0.095 µg/l, Cu 4.52 µg/l, and Zn 37 µg/l). The presence of coliforms, indicators of sewage pollution, as pathogenic germs (Pseudomonas), was shown through microbiological examinations of the sediments and water column. The microalgae enumeration showed the abundance of dinoflagellate cysts (stressed form) which attests to the presence of severe conditions in Sfax port. Different toxic species were identified as Prorocentrum lima and Alexandrium minutum. The same trace metal sources and abundance in Sfax port and GG sediments suggest the hypothesis of their transfer from their disposal sites in coastal areas to deeper depths in the GG and until Boughrara lagoon (BL). As trace metals, microalgae species were also transferred by hydrodynamic currents inside the GG where they found suitable conditions to their proliferation causing the seawater coloration phenomenon, eutrophication, and degradation of the aquatic system.

Modelling the mechanical strength development of treated fine sediments: a statistical approach.

Sediments valorization (recycling) has revealed limitations due to different restrains and practical difficulties. When it comes to different recovery methods, the possibility of valuing diverse types of sediments still needs to be defined. Using a statistical approach, the present study aims to quantitatively estimate the mechanical resistance of stabilized sediments. A database that included 22 fine sediments is selected and assembled from the literature. These sediments were treated with distinct types and quantities of additives (fillers and/or binders). The present study includes two parts. On one hand, using multivariate linear regression tool of XLstat software, an analytical model that highlights the effects of various parameters influencing the mechanical resistance of treated sediments after 28 days is obtained. This model showed that organic matter content and plasticity index are the most significant factors of sediments characteristics, while cement is the best mechanical strength booster. On the other hand, the evolution of treated sediments mechanical resistance over time is modelled by an exponential relationship using a least square regression method. Both models showed acceptable accuracies compared to a panel of selected experimental values.