Application Example of a Volume Reduction System for Dredged Sludge by Screw Decanter Centrifuge

In order to transport high-moisture sludge dredged in the sea area to a waste disposal site, it is essential to reduce the moisture content ratio of dredged sludge. Therefore, we devised a volume reduction system for high-moisture sludge and applied it at Dokai Bay located in Kitakyushu City. The volume reduction system consisted of a two-step process, a dewatering process and a cement reforming process. The moisture content ratio (w_n) of the dredged sludge was more than 200%, and the moisture content ratio (w_n) of the dehydrated cake discharged from the screw decanter centrifuge was about 100%. As a result of adding an appropriate amount of cement-based solidifying agent according to the moisture content ratio of the dehydrated cake, it was possible to transport the treated soil in a dump on the day after dehydration. The reforming dredged sludge cured in the temporary storage yard satisfied the required quality (cone index q_c ≧ 400 kN/m²). The actual dredging amount was 17,157 m³ and the reformed soil volume after the addition of the cement-based solidifying agent was 6072 m³. By applying a volume reduction system, the volume reduction rate of dredged sludge was achieved at 35.4%.