Freeze-thaw conditioning of RBC (Rotating Biological Contactor) sludge was tested using a pilot-scale freezing bed placed in a mobile freezer 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 8 layers of 10 cm thick. Approximately 4 months after the first layer of sludge was added, the pilot unit was removed from the freezer and thawed at ambient temperatures. After one day of thawing, the solids concentration increased from 2.6% to 16.2%. The final cake solids concentration was 21%. Melt water had increasing turbidity, COD, TSS, VSS, nitrogen and phosphorus concentrations during the thawing period. Freeze-thaw conditioning also decreased the initial densities of fecal coliforms and Salmonella in sludge. 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 and remote regions.

Freeze-thaw conditioning of RBC sludge was tested using a pilot-scale freezing bed placed in a mobile freezer unit operated at -10ºC. 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 26ºC 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. INTRODUCTIONSludge dewatering is one of the most challenging processes during sludge treatment. Particularly in cold climates, sludge dewatering becomes a major problem for treatment plants because mechanical equipment such as centrifuges and filter presses are difficult to maintain and operate. The equipment ices up often, skilled operators are scarce, treatment plants are in remote locations and large amount of chemicals are needed to condition the sludge.