| Sludge management is a major technical issue at both water and wastewater treatment facilities. Typically, process sludges contain 90 to 99% water. In most cases, direct disposal of these very dilute sludges is unacceptable because of the cost of transportation of the water. Commonly used sludge dewatering methods include filter presses, horizontal belt filters, centrifugation, vacuum filtration, drying beds and lagoons. Treatment of large volumes of sludge in cold regions, selection of an effective and economical year round dewatering method can be especially challenging.;The freeze-thaw method was studied to dewater the sludge without chemical addition. Sludges from three different sources with solids content ranging from 2.2 to 37.0% were tested. The samples were frozen under controlled temperature boundary conditions using constant temperature baths. Drainage test was performed for both the freeze-thaw conditioned sludge and never frozen sludge. Based on these test results, the improvement of dewaterability of the sludge after freeze-thaw was examined. Rapid volume separation (70 to 90%) occurred in the first hour of the drainage test for the freeze-thaw conditioned sludge. This improvement in dewatering rate is effective on all sludges. The released filtrate was also collected and tested. Its quality is sludge specific and normally can not be discharged directly into the receiving environmental.;Canada is a northern nation where cold climate is experienced by most locations. The water and wastewater treatment facilities in these areas can take advantage of the cold climate to assist in dewatering sludges by the freeze-thaw method. A sludge dewatering model called the freezing bed is reviewed, the study shows that freeze-thaw is a simple, efficient, and economic method for sludge dewatering within the cold regions. |
