Challenge

Blackhawk Leather, Ltd., one of the most diversified split and grain leather tanners in the world, needed to control wastewater pH and condition sludge at their Milwaukee, Wisconsin, facility.

Solution

They chose a WHM™ bulk chemical handling system from Siemens Water Technologies, which stores, feeds, and slurries lime, and then pumps the slurry to the application points in the pre-treatment system.

The WHM system cleans up sulfide and chromium rinse waters before they are released to the Milwaukee Metropolitan Sewerage District. Between 140,000 and 220,000 gallons a day of rinse water require treatment before sewering.

In the pre-treatment plant, the sulfide stream is first oxidized with manganese sulfide and dosed with a defoamer. Then it is combined with the chromium rinse water for chemical treatment with cationic and anionic polymers, neutralization with lime to a pH of 7-10, and clarification.

Waste solids are conditioned with lime in a sludge holding tank, then filter pressed to a compact cake acceptable for landfilling (>40 percent solids).

Result

On-line since December, 1991, the system was the first of its kind to comply with new federal and state pre-treatment regulations for tanneries in the Milwaukee area.