Unidirectional freezing of waste-activated sludges: Effects of freezing speed
Journal
Environmental Science and Technology
Journal Volume
30
Journal Issue
7
Pages
2391-2396
Date Issued
1996
Author(s)
Abstract
In this work, we employ unidirectional freezing of waste-activated sludge to investigate the effects of freezing speed on the sludge performance including filterability, zone settling, and floc density versus size relationships. With a high freezing speed, no global particle migration occurs, but the sludge filterability is markedly improved. However, the floc density and the floc morphology are only slightly changed; therefore, the zone settling characteristics are those of the original sludge. With a low freezing speed, however, global particle migration occurs. Consequently, both the sludge filterability and settleability are enhanced. The floc density and the morphology are changed significantly. With an intermediate freezing speed, a gradual transition of sludge characteristics occurs between the two extremes, resulting from an average behavior ortho constituting flocs. No precise definition for the critical freezing speed can thereby be defined. If improvement of sludge filterability is the only concern, a high freezing speed is acceptable. Furthermore, a low freezing speed is necessary if both sludge settleability and bound-water content must be changed.In this work, we employ unidirectional freezing of waste-activated sludge to investigate the effects of freezing speed on the sludge performance including filterability, zone settling, and floc density versus size relationships. With a high freezing speed, no global particle migration occurs, but the sludge filterability is markedly improved. However, the floc density and the floc morphology are only slightly changed; therefore, the zone settling characteristics are those of the original sludge. With a low freezing speed, however, global particle migration occurs. Consequently, both the sludge filterability and settleability are enhanced. The floc density and the morphology are changed significantly. With an intermediate freezing speed, a gradual transition of sludge characteristics occurs between the two extremes, resulting from an average behavior of the constituting flocs. No precise definition for the critical freezing speed can thereby be defined. If improvement of sludge filterability is the only concern, a high freezing speed is acceptable. Furthermore, a low freezing speed is necessary if both sludge settleability and bound-water content must be changed.
Type
journal article