天日乾燥浄水汚泥の縮減性と最適含水比条件下での安定処理効果

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 disadvantages 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 content 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, unconfined compressive strength and shear strength all increased with lapse of the days, regarding the specimens cured in water 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.