And There’s Sludge

One of the systems revisited at the plant was the sludge-handling system, which had gone through a number of changes and evaluations.

An air dryer was added in 1991 to the air supply of the double-diaphragm sludge-press feed pump. Despite the fact that it was located inside the building, the pump would occasionally freeze up during cold weather and the smaller air dryer originally installed was solely for the air supply to air-operated valves.

Another change made was that the original sludge-cake chute was replaced with one featuring baffles to better distribute the sludge cake into the roll-off container below the sludge press.

Sludges from the inclined plate settler, American Petroleum Institute (API) units and dissolved-air flotation units are mixed together in a sludge holding tank. It was found that by having the chrome wastewater settled and dewatered separately, the wastewater-treatment plant could be considered a small-quantity generator. Unfortunately, there was not enough floor space available to install a separate sludge press for the chrome sludge.

Additionally, a precoat system that was originally furnished for the sludge press is now used for acid-washing the sludge press because the sludge press has performed well without one. Another surprise is that the filter-press cloths have been changed only once since construction due to a longer than expected cloth life and the benefits of an acid-washing system.

Aisin’s operators are now considering air-drying the sludge cake to reduce the disposal costs that are based on weight rather than volume.

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