Freeze-Thaw Treatment of RBC Sludge: A Sustainable Option for Sludge Dewatering in Cold Regions

Freeze-thaw conditioning of RBC sludge was tested using a pilot-scale freezing bed placed in a mobile freezer unit operated at −10°C. Sludge samples from a remote mining exploration facility were flown in every 2 weeks, and added to the freezing bed in layers approximately 10 cm thick. A total of 8 layers of sludge were added to the pilot unit over 3 months. The total volume of sludge added was 290 L and the average solids concentration was 2.6%. Approximately 4 months after the first layer of sludge was added, the pilot unit was removed from the freezer and thawed at ambient temperatures that varied between 17.5 and 26°C during the time of the thawing. After 10 days of thawing, 250 L of meltwater was collected through simple drainage. Meltwater had increasing turbidity, COD, TSS, VSS, nitrogen and phosphorus concentrations during the thawing period, but predominantly within the first 4 days. During the first week of thawing, the cake solids concentration increased from 2.6% to 18.4% solids, and after an additional month of thawing, the cake solids concentration was 21%. Freeze-thaw conditioning also resulted in approximately a one-log decrease in the densities of fecal coliforms and Salmonella. The results of this study showed that freeze-thaw technology successfully dewatered RBC sludge without the need for mechanical equipment, and is a sustainable option for sludge dewatering in cold regions. The final quality of the sludge cake, in this case, makes soil application feasible.