Steelmaking slag came to be used in a marine environment and safety issue of slag material is a matter of concern. We are trying to provide the safety information of the slag material. Experimental ...facility with mesocosm aquarium tank, which integrated tidal flat area and shallow area, was constructed in order to evaluate the environmental impact. The facility consists of two aquarium tanks, one is the experimental unit using slag materials as dredged soil improver, called CaO-improver, and another is the control unit not using slag materials. Long-term operation over the five years from 2012 to 2017 was carried out to evaluate the long-term safety of slag materials. We observed not only the changes of water quality but also the acute and chronic toxicity assessment using three kinds of aquatic marine organisms such as bioluminescent bacteria, micro algae and copepod for seawater in the aquarium tanks. As a result of the long-term experiment, stabilization of bottom sediment by CaO-improver could be confirmed, but on the other hand, influence of alkali elution from slag was estimated. Furthermore, as a result of three bioassays, it was judged that there was no effect of acute toxicity and chronic toxicity on organisms caused by slag material within the range examined.
To evaluate the effectiveness of soft CaO-improved soil as tidal flat and shallow sediment material, we conducted a comparative experiment using mesocosm tanks. The soft CaO-improved soil is composed ...of dredged soil and converter steelmaking slag, which is a byproduct of steelmaking. It is a mixed soil that has been improved by adjusting the particle size and the percentage of the converter steelmaking slag to enable benthic organisms to live in it. In this study, a two-year long-term evaluation using a tidal flat/shallow integrated mesocosm was conducted before application to actual coastal areas. In each experimental tank, soft CaO-improved soil was laid as an experimental site, and dredged soil was laid as the control site. The macrobenthos was observed in the sediments of both the experimental and control sites. More eelgrasses grew in the experimental site, where the light environment was improved as a result of stabilizing the sediment, than in the control site. These results show the utility of the soft CaO-improved soil as the sediment for eelgrass beds and benthic organisms.
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