Factors governing adsorption and distribution of copper in Samut Prakarn coastal sediment, Thailand

Performance of electrokinetic remediation system for mercury contaminated marine sediment: Roles of electrode spacing and electrode configuration

Understanding mercury (Hg) species existing after electrokinetic remediation (EK) for marine-sediment remediation is limited. Herein, the Hg fraction removal of EK from contaminated marine sediment was investigated appertaining to bipolar electrode settings along with the effects of electrode spacing and configuration considered. Based on the selective sequential Hg extractions (Hg SSE), much of the Hg in the sediment originated from F5 (i.e., HgS) and F4 (i.e., HgO). The F5 fraction removed by EK was about 30 %, while the F4 fraction had a slight increase of about 34 %. When it comes to electrode configuration, a hexagonal pattern has a higher Hg removal performance than that of a rectangular shape. The addition of anodes increases the remediation surface area, thus allowing superior Hg removal. This study indicates that the electrode spacing significantly affects the mercury removal and the remediation time. Determining suitable spacing enhances the electrical potentials in the migration flux.

Effects of cathode coating materials and operational time on the mercury removal performance of electrokinetic remediation system for marine sediment

Electrokinetic remediation (EK) is a promising in-situ technique for removing mercury (Hg) from contaminated sites; yet it demands long operational periods when conventional electrodes are used. Herein, we investigate the effectiveness of lab-prepared cathodes (Cu foam coated with reduced graphene oxide (rGO) or manganese oxide (MnO₂)) to enhance Hg removal rates from sediment by EK. Although short term (2 h) Hg removal rates were insignificantly different (p-value > 0.05) when using the uncoated and coated Cu foam cathodes, long term (60 h) operations saw greater Hg removal by coated Cu foam cathodes over pure Cu foam, probably owing to the time required for Hg to migrate towards the electrodes from sediment. The highest Hg removal at the cathode was achieved when an αMnO₂-coated Cu foam cathode was used with a strong-base anion exchange membrane (AEM) in the system. Using H₃PO₄, as a cathodic electrolyte resulted in a higher Hg removal efficiency than using NaCl and HCl electrolytes. Electromigration was found to be the dominant Hg-ions (e.g. HHgO₂^-, Hg²⁺) transport mechanism in the marine sediment during remediation. Overall, this research demonstrates that employing enhanced electrodes and AEMs can enhance Hg removal by EK processes in relatively shorter operating times than conventional EK processes.

Mineral and chemical changes of sediments after Cu sorption and then desorption induced by synthetic root exudate

Understanding the fate of anthropogenically introduced copper in sediments is important to comprehend the biogeochemical processes; consequently, beneficial utilization of Cu-rich materials can be proposed (e.g. soil amendment). Therefore, we address the behavior of copper and other metals at the liquid-solid interface of different grain sizes in lake sediments. Initially, the sediment fractions were characterized for mineralogy (XRD), chemical structure (FTIR), physicochemical parameters (mainly pH, cation exchange capacity, and electric conductivity), organic content, and chemical composition (AAS). Then, solutions of varying Cu concentrations were added to the fractions; the Cu concentrations of the sorption experiment were chosen according to the exchangeable cations of each fraction. A desorption experiment by synthetic root exudate was followed. The physicochemical parameters, functional groups, and mineralogy were noted before and after the two experiments. The sorption and desorption of Cu, Ca, Mg, K, and Na were also studied. The sediment fractions had similar mineralogy and chemical structure, yet the physicochemical composition and metal contents were different. The Cu sorption experiment showed that surface Ca and embedded Mg were the main cations that were exchanged with Cu, as shown by linear and logarithmic trends, respectively. The copper-sediment interaction mainly occurred at the organic interface. Finally, synthetic root exudate was able to restore part of the initial chemical structure of the sediments, indicating exchangeable Cu sorption on the organic part of the sediments. The various grain sizes had an insignificant influence on the behavior of metal sorption and desorption.

Trace Elements in Marine Sediment and Organisms in the Gulf of Thailand

This review summarizes the findings from studies of trace element levels in marine sediment and organisms in the Gulf of Thailand. Spatial and temporal variations in trace element concentrations were observed. Although trace element contamination levels were low, the increased urbanization and agricultural and industrial activities may adversely affect ecosystems and human health. The periodic monitoring of marine environments is recommended in order to minimize human health risks from the consumption of contaminated marine organisms.