Holding/Settling Sludge Tank

Waterloo, IL

Surrounded by rich farmland east of the Mississippi River, the City of Waterloo is located within 30 minutes of downtown St. Louis. The city built a new 2.086 MGD (organic design loading rate of 4588 lbs of BOD) waste water treatment plant on the east side of town with a start up date of September 2007. The WWTP lead man Jim Straub, PE, can not say enough good things about the 59×24 450,000 gallon Aquastore tank designed as a holding/ settling tank for the sludge process on its way to the belt filter press. “The Aquastore tank gives us the flexibility that other waste water treatment plants do not have. We have choices. We can either press or store the biosolids in the Aquastore tank. We can store up to 100 days with out pressing. When the weather is right to haul the solids for field application, we first decant the clear material in the Aquastore tank back to the front of the WWTP for further processing. This gives us a smaller volume required to be separated. We are averaging 5% solids going to the belt filter press. The Aquastore tank is equipped with a JetMix™ system consisting of 2 rotatable nozzles and a chopper pump to keep the remaining material in suspension. We now press when it works best for us; when manpower, weather and resources are available. We went all last winter with out starting up the press. When we are not pressing, we can use the truck used to haul the pressed solids for other tasks.”

How would the plant run without the Aquastore holding/ settling tank?
Typically on other waste water treatment plants using a solids press of some kind, sludge is wasted from the aerobic digesters and sent to the belt filter press on a daily basis. The solids would be around 1% to 2% solids so you are working with a lot more volume. The daily running of the belt filter press would also require that you have a truck available to move the material to a sludge drying beds, land application or field application. The solids truck would be dedicated and parked under the solids conveyor 24/7.