Municipal WWTP Digester Cleanout - Jekyll Island, Georgia - Case Study
Coastal Georgia's Jekyll Island Stale Park, a popular vacation destination, is also home to about 750 permanent residents. John Day, Superintendent of the Water and Wastewater plants, operates the Jekyll Island Authority's I MGD wastewater treatment plant. Structural modifications and improvements to the plant's two anaerobic digesters were scheduled for early 2004. The job was publicly bid and awarded, however it was the responsibility of the treatment plant personnel to empty the digesters before the contractor could begin the modifications.
To remove 360,000 gallons of sludge from the primary digester and 180.000 gallons from the secondary digester in the shortest amount of time while keeping costs at a minimum and to accomplish this task with plant personnel.
Consulting Engineer, Ron Kolat of Carter and Sloope, recommended Geotubes as the cost effective solution to the problem. Initially, three 45* circumference x 101' long Geotubes were placed in three of plant's existing sand drying beds. Bench tests were conducted to determine the optimum polymer and dosage to dewater the thick solids. A high molecular weight cationic polymer was chosen to create the optimum floe which binds the particles together and releases water. Originally, the plan was to gravity feed the sludge into the Geotubes, however due to the heavy feed solids, 4.5%-5%, plus rags, hair and other debris, it was nearly impossible to gel adequate mixing of the polymer into the sludge stream. To correct this situation, a pump was added to provide consistent flow and the sludge was bulked up with water to achieve optimum mixing of the polymer solution. By doing this, the dewatering was much more efficient, improving both volume reduction and cake solids. At times, clean effluent water was pouring from the Geotubes so fast that the drying bed couldn't handle it A sump pump had to be placed into the bed to pump off excess water and bypass the sand drying bed underdrain system.