Unidirectional Freezing of Waste-Activated Sludges:  Effects of Freezing Speed

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 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.

Enhancement of waste activated sludge dewaterability using calcium peroxide pre-oxidation and chemical re-flocculation

“…Generally, the higher the D F always means the more irregular surface of the sludge. A floc with a D F close to 3 indicates a close interior packing, and an extremely loose packing feature appears at a D F close to 1 (Hung et al, 1996). Eriksson and Alm found that higher charge-density coagulants interact strongly with negatively charged surfaces, and thus it would have a flat adsorption conformation.…”

Multiscale structures of biological flocs

“…Freezing and thawing tests were conducted in an air-cooling room of −17 • C. The sludge sample was placed in a container of diameter 3:5 cm and height 3 cm (Lee and Hsu, 1994;Hung et al, 1996). Complete freezing was achieved in 2 h of freezing.…”

Correlation of physicochemical properties and sludge dewaterability under chemical conditioning using inorganic coagulants

“…Generally, the higher the dimension is the more irregular the surface of the sludge is. Generally, a floc with a D F close to 3 indicates a close interior packing, and an extremely loose packing feature appears at a D F close to 1 (Hung et al, 1996).…”