Marshall Municipal Utilities - Wastewater - Wastewater Treatment - Treatment Process

Sludge Treatment and Removal

Return Activated Sludge
Pump Building

Sludge at the final clarifiers is divided into two classes, return activated sludge (RAS), and waste activated sludge (WAS). The return activated sludge pump building houses three 12-inch Fairbanks pumps, variable frequency drives (VFDs), flow level sensing devices, and overhead hoist system. The RAS pumps move activated sludge from the final clarifiers back to the aeration basins for further treatment.

Sludge Holding Basins

Waste activated is transferred from the final clarifiers to the sludge holding basins by gravity flow. Sludge is stored at the Sludge Holding Area until spread on area farms. Currently, this will hold approximately 45 days of sludge.

Sludge Holding Area

The Wastewater Treatment Plant has adopted DNR's beneficial use of municipal biosolids program (land application). We actually began our application program in 1972, which is before the state began to regulate it in the mid-eighties. During 2002, we land applied 952 dry tons of sludge to 1,131 acres of farm land following federal regulations (40 CFR 502). We currently have 2,360 acres available during the year.

Filter Building

The building is used for dewatering sludge for our land application program. This building houses two Rex Belt filter presses. Final treatment of the sludge to be used on farms is done here.

Per 40 CFR 503, each farm where we spread sludge is required to have a soil test. We usually get this done through the Farm Service Agency (FSA). The soil tests are for pH, phosphorus, potassium, calcium, magnesium, organic matter, neutralizable acidity, and cation exchange capacity. Soil tests for each farm can be used for a 5-year period.