Thaw Period

The time required to thaw the frozen sludge can be calculated using Equation 9.2 and the appropriate thawing index. Frozen sludge will drain quite rapidly. In field trials with wastewater sludges in New Hampshire, solids concentrations approached 25% as soon as the material was completely thawed (Reed et al., 1984). An additional 2 weeks of drying produced a solids concentration of 54%. The sludge particles retain their transformed characteristics, and subsequent rainfall on the bed will drain immediately, as indicated by the fact that the solids concentration was still about 40% 12 hours after an intense rainfall (4 cm) at the New Hampshire field trial (Reed et al., 1984). The effects for a variety of different sludge types are reported in Table 9.9.

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