Practical treatment system for polluted sea water and soil by tributyltin

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In order to restore the deteriorated marine environment by Tributyltin (TBT), the integrated research was initiated by the group of "Practical treatment system for polluted sea water and soil by tributyltin" at the field and laboratory in 2004 and 2005. The roles of the group members were as follows : Kenji Jinno and Yoshinari Hiroshiro planed the entire scheme and the practical plant setup to separate the TBT contaminated sea water from the dredged marine sediment. The separation was successfully done by applying the coagulant named PSI-100,and then the series infiltration consisted of fiber sheet, sand and activated carbon. To release the treated water back to the sea nearby the plant, TBT concentration was carefully checked. It was confirmed that the proposed series of treatment plant was able to reduce the dissolved TBT with 1,200-1,450ng/L in the turbid water to 3ng/L which is admissible release level. Beside such establishment of the proposed system, the evaluation method for the … More cost performance was investigated. So far, it was shown that the optimal designing scheme for the proposed treatment system to remove TBT was applicable for the present treatment system and the optimal combination of the fiber sheet, sand and activated carbon for infiltration was determined considering the cost of materials.Yuji Oshima and Tsuneo Honjo carried out toxicity bioassay of TBT in nauplii, copepodite and adult stages of marine harpacticoid copepod, Tigriopus japonicus which shows different sensitivities to chemicals, and evaluated on practical use of this bioassay. In the bioassay, the toxicity of TBT was examined by observations of hatching ratio, survival in the each stage, fecundity, and sex ratio. The results suggested that the bioassay test has a potential to evaluate risk of chemicals in various life stages of this copepod less than 16 days.Kazutoshi SAEKI investigated the time-changes in butyltin compounds (BTs), dibutyltin (DBT) and monobutyltin (MBT) in the sediment treated with various conditions (light (UV, sunlight and light exclusion), moisture (air-drying and water saturation) and heated-drying at 40℃ for 12 hrs at every 7day) in order to evaluate the behavior of BTs compounds together with various changes of the sediment condition occurred in the process. Consequently, the dehydrating and sunlight drying treatments for the sediment were expected possibly to enhance the slight degradation of TBT in the sediment. However an attention is required for the expansion of the contamination to an ambient environment because these treatments could accelerate wind scattering of the sediment particles.Kouki Zen investigated the effect of cement-mixing and dehydration method (CMD) on the elusion control of heavy metals, tri-butyl tin (TBT) and tri-phenyl tin (TPT) in a contaminated marine bottom sediment. The elusions of both TBT and TPT are affected by the pH of pore water and they decrease as the pH comes to the neutrality. The use of low pH cement in the CMD has, therefore, an advantage to the elusion control of TBT and TPT from treated sediment.Akihide Tada and his colleagues from the commercial companies applied the strip dredging machine developed for the marine sediment digging. This device is able to vacuum up the surface sediment polluted by TBT or other toxic chemicals which are usually adsorbed on the surface organic soil. The excavated area in Nagasaki and Hakata bays extended approximately 700〜800m^2. It was demonstrated in these bays that only fine silty clay was dredged effectively resulting in the low remediation cost.Honda Katsuhisa investigated, in field examination, the detoxification of dioxins and organotin compounds in the precipitate and supernatant separated from the dredged marine sediment, and proposed that an addition of chemical agent such as iron oxide (Fe_3O_4) is useful for the detoxificating contaminants. About 5% addition of iron oxide per weight of precipitate degradated about 20% of dioxins burden in the sediment. About 5% addition of iron oxide per weight of precipitate or supernatant occurred adsorption and/or degradation of organotin compounds : TBT and TPT burdens declined, respectively, about 30% and 40%, which resulted in higher detoxification ratios of the contaminants than amounts of chemical additives.In conclusion, the conducted research entitled on "Practical treatment system for polluted sea water and soil by tributyltin" confirmed to be applicable for the polluted sea water and sediment by TBT and other toxic chemicals. The conventional plants are integrated to separate sea water and sediment through coagulations, infiltrations, cementing, degrading and the bio-assay monitoring schemes. Until now, there is little practical research on the polluted marine sediment except for the expensive and huge scale systems. The group members are confident that present research can highlight the silent but polluted marine sediment. Less