The City of Beaver Dam (Wis.) water and wastewater utilities are pulling closer together, in part thanks to a dewatering system that now handles lime slurry from the water treatment plant but will eventually handle wastewater biosolids, too.

In July 2008, a 1.7-meter skid-mounted belt filter press from Bright Technologies went to work at the wastewater treatment plant, dewatering lime slurry trucked over from the water plant across town, about one mile away.

The press has already driven down the water utility’s lime slurry handling costs by producing cake at greater than 60 percent solids for land application as a soil amendment on two local farms.

Thrown a curveball

Beaver Dam, a city of about 15,000 in south central Wisconsin, operates separate water and wastewater utilities. The activated sludge wastewater treatment plant handles average flows of 4.3 mgd. The 5.8-mgd water treatment plant uses lime softening, the source of the lime slurry, produced at 1.5 million gallons per year.

For years the water utility wasted lime slurry from the water plant clarifiers, held it in storage tanks, and hired a contractor to haul it to farm fields for land application. In early May 2008, the state Department of Natural Resources (DNR) determined that the lime slurry could no longer be land-applied under regulations that applied to wastewater biosolids and instead had to be treated as solid waste and landfilled.

However, the city could not landfill its lime slurry because, in its liquid state, the material could not pass the filter test needed to prove that landfilled material contains no free liquid. That meant the city’s contractor had to haul the material to its own storage facility and mix it with other sludges before landfilling. That more than tripled the handling cost from about 3 cents per gallon for the land application program to more than 9 cents per gallon.