製鋼スラグによる底泥中硫化水素抑制の実海域試験

摘要

Hydrogen sulfide is generated through sulfate reduction under anaerobic condition in enclosed coastal seas. It is highly toxic, depletes oxygen and generates blue tide. To evaluate the sulfide reduction effect of steelmaking slag, we carried out field experiments in Fukuyama inner harbor, where the people there have suffered from odor caused by gasses including hydrogen sulfide generated from the sediments. We placed the steelmaking slag on the sediments, and monitored the water quality of interstitial water in the sediments and the overlying water of the sediments as well. Hydrogen sulfide gas was also collected and measured.The results showed that dissolved sulfide concentrations in interstitial water in the control plots ranged from 100 to 350 mgS/L, on the other hand, those in the steelmaking slag construction area were suppressed, being below 5 mgS/L. The reduction effect of dissolved sulfide by steelmaking slag has lasted for about two years. It was supposed that Fe ions eluted from steelmaking slag may have reacted with sulfide. Species number and individual numbers of macro benthos increased in the experimental area.The results imply that capping the deteriorated sediments with steelmaking slag can effectively improve the water and sediment quality of coastal areas.%閉鎖性海域では，水の滞留時間が長く，有機物の分解によって貧酸素化し，還元的な環境になることで硫酸還元菌によつて硫化水素が発生する。硫化水素は毒性が高く，生物生息を困難にするだけでなく，異臭の主要因となる。日本で年間約4,000万t発生する鉄鋼スラグは，100%近く再利用が図られており，製銑工程で年間2，500万t発生する高炉スラグについては既に付加価値の高い利用がなされている。しかし，製鋼工程において年間約1,500万t発生する製鋼スラグについては，道路用，土木用が60%を占めており，物性や組成を活用した付加価値の高い利用技術は充分確立されていない。