Reduction Characteristics of the Purified Water Sludge and Its Stabilization Effect under the Optimum Moisture Content
Mikio YAMADA, Hiroaki SANO, Tomohiro INAZAWA and Eiji MORIKUNI
Abstract:Sludge treatment at the water purification plant is classified into solar drying and pressure dehydration. Compared with the latter, the former can reduce an expense required for a device and facilities. On the other hand, the former has disadvan-tages in that the retrievement of sludge is after approximately one year because the drying rate of sludge including a large quantity of water depends on a season or the weather. We firstly performed a simple loading test to promote the water-reducing of sludge which was dried in the sun. In this experiment, we laid the sludge of nearly 460% water content onto geotextile fixed in a container of 100mm inside diameter,and added the normal stress of 0.10MN/m2 from 0.05MN/m2 for 24 or 48 hours. Water contents after the unloading have decreased to about 260% due to synergy of load and geotextile for the drainage promotion. This difference of the water con-tent was almost corresponding to three months solar drying period. We secondly examined the bearing capacity and strength characteristics of specimens made by adding stabilizers into the sludge which was dried to nearly optimum water content. The results of California Bearing Ratio test, unconfined compression test and box shear test indicated that CBR value, un-confined compressive strength and shear strength all increased with lapse of the days, regarding the specimens cured in wa-ter upon the neck of air. The consequence that the strength developed in proportion to the common logarithm of curing days was also obtained, from the unconfined compression test of specimens cured only in air for 90 days.As above, it can be considered that shortening a solar drying period to heighten the desludging frequency contributes to an improvement in the operating ratio of air drying bed and a cyclic utilization of resources. Key Words:Purified water sludge, Air drying bed, Geotextile, Water-reducing, Optimum water content, Stabilization, CBR value, Unconfined compressive strength, Strength parameter