THe Sludge Press Experiment

Now that it was understood that the high total suspended solids was a problem the next project was undertaken to accomplish two objectives; reduce TSS so that less aeration was required and to reduce or eliminate the hauling cost of decanted sludge.

A low dollar experiment implemented using the Deming cycle of Plan, Do, Check (study), Act was undertaken to replace the old sludge press that was unable to dewater the sludge sufficiently to pass the paint filter test allowing sludge disposal in the land fill.

The utility supervisor made some calls to the press manufacture and found that some low cost modifications could be made and with the use of the right polymer the press should be able to produce sludge of sufficient quality that land fill disposal would be permissible.
Here’s the SPIN of the project:

Situation

The utility stored the wasted sludge in a 50,000 gallon tank, decanted the mix, and eventually would have it hauled to another facility for disposal.

Problem

The problem was that this was costing the utility $37,000 per year to haul off 94% water and both blowers were running 24 X 7 to maintain DO concentrations at the proper level. In addition the utility was still responsible for the disposal of the sludge, not the hauler.

Implication

$37,000 per year spent to dispose of sludge was a drain on resources and was good money that could be used to create new and additional savings. Unfortunately, this was not the only implication. Due to the cost of hauling, proper wasting (removal of dead bacteria from the process) was delayed significantly. This resulted in a very high total suspended solids (TSS) in the aeration basins and the need for additional aeration (read more energy).

Need Pay Off

With a little work the brushes in the press were replaced, the polymer injection initiated and the press put to work. And work it did to the tune of $37,000 per year plus reduction in energy cost by running a single blower.

Results

The UP side
The resulting press sufficiently dewatered the sludge to the point that land fill disposal was accomplished saving about $37,000 per year. The savings were eventually applied to the purchase of a newer and higher performance rotary fan press. The high TSS require operation of both blowers 24 X 7 or the equivalent of $21,500 per year additional energy cost.

The DOWN side
The press needed almost constant attention to ensure the proper consistency of the sludge. This meant that some of the savings were redirected to the labor to run the press. In addition the utilities backhoe had to be used to catch the dried sludge and then transfer it to a dump truck for disposal. One of the problems with this solution was that any time the backhoe was needed elsewhere then sludge processing had to be postponed.

The Final Analysis

What was proven was that it was possible to reduce the cost of sludge handing by a significant amount and eventually the utility purchased and installed a higher performing press from the savings resulting in the initial experiment.

At this point you might ask, “Why did you choose this project first and why didn’t you just purchase and install the rotary fan press in the beginning?” The answer is slightly occluded because there was a larger opportunity the utility was undertaking and this project was a component of that larger opportunity. But, it was one of the first events in the continuous improvement process and it cost little money. If I may paraphrase Deming, “Start small. The use of prototypes is good.”

The larger picture will be explained a little later in this paper.