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City's flushes have sweet smell of savings

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By Lou Elliott Jones, Editor

The staff at the Chiefland Water Reclamation Plant, the place where every toilet flush meets it end, have turned off two 40-horsepower fans that keep the smell down on the sludge digester.

It sounds like a pretty noxious idea.

But a change in the way sludge is separated from 168,000 to 170,000 gallons of wastewater daily means the smell emanating from the plant is that of money saved on the electric bill, blowers that no longer need maintenance, and less use of a petroleum-based chemical whose cost has been rising with crude oil prices.

"Those blowers run 24/7," Chiefland City Manager Grady Hartzog said. "They can cut the blowers off and using this chemical oxidizer can save the city $17,000 to $18,000 a year. That's tremendous savings."

Randy Wilkerson, sewer superintendent, is much more humble, saying he does not know the exact savings, but he thinks Hartzog's figures are close.

Wilkerson said to get the savings it will take a little upfront money. He must spend $2,000 for a new pump and buy freeze-dried bacteria for the digester tank. "We'll have the money back for the pump in a few months," he said. The savings on the bacteria will also pile up.

Every Tuesday the staff at the plant mixes the bacteria into a 5-gallon bucket of non-chlorinated water, lets it sit for 4 hours, and pours it into the digester tank holding solids that have been separated from the wastewater.

The new pump, attached to the sludge digester, keeps the stuff whirling around, so the bacteria stay happy.

Sludge, says Wilkerson, is basically a lot of bacteria. It's the product left after all those flushes from the city collect in two huge blue tanks at the plant. Those tanks are aerated by a separate set of blowers then allowed to settle. Water goes to the top to be skimmed off to the chlorinator tank, and the remaining 2,000 to 3,000 gallons of solids - sludge - settles to the bottom to be whisked off to the digester.

The digester is a smaller brown tank that was once the city?s original sewer plant.

At this point the freeze-dried bacteria changes the whole process."Basically, its bacteria eating bacteria," he said. "And it reduces the amount of sludge. We expect to cut it by 50 percent.

"We used to aerate the tanks to keep the odor down. It's like an aquarium. You have to pump air into it to keep the odor down."

Instead the new bacteria release gases, including any oxygen to keep noxious odors down. Every week, more bacteria are fed into the brown mess to gorge themselves.

After being thoroughly "digested," a polymer is added and the sludge moves into three sludge beds to wring out more water. The petroleum-based polymer ties up the solids making it easier for the water to drain through the strainer-like tile beds.

Because there's less sludge to be wrung from the water, that means less of the polymer, which has been steadily rising in price, must be used. Wilkerson says. The sludge also dries quicker.

Even at the tile beds it's the smell of money being saved.

Once the sludge dries, it's broken up and moved into stalls to get a final airing. After 90 to 120 days at the plant, the sludge is trucked out to be spread on city property.

Consider that Chiefland produced 88.9 dry tons of sludge last year.

Wilkerson says he's getting 20-30 percent more solid material wrung out of the wet material that reaches the drain beds. As a result he has less dirty water to recirculate through the digester. "We're able to get more water out," he said.

And what happens to that water? After the sludge is removed, the water flows into the plant's chlorinator tank and then six sand filter ponds so nature can take its course.