Water Works to turn toxic sludge into green money

Published 12:00 am Tuesday, August 17, 2010

NATCHEZ — The Natchez Water Works Wastewater Treatment Plant is receiving a green makeover that Superintendent David Gardner said will save $400,000 annually.

The upgrade, which will convert toxic sludge into a class-A biosolid that can be sold for agricultural purposes, is estimated to be online by Sept. 26.

“Ultimately, we are turning a liability into an asset,” Gardner said. “It will be a really sophisticated process utilizing German technology when it is all said and done.”

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Currently, the treatment plant has 17,000 tons of sludge in two lagoons. The Department of Environmental Quality classifies the sludge as a toxic hazard and only permits the sludge to remain in the lagoons for 10 years.

During the last two years, Natchez Water Works has hauled 3,300 tons of the sludge to a special DEQ-permitted dump site on Airport Road. Transporting the sludge to the dump site costs approximately $400,000 a year.

The upgrades are partially being built using $4.3 million in American Recovery and Reinvestment Act funds, and Natchez Water Works will take out a 20-year loan at 1.57 percent interest to make up the difference.

The original estimate for the work was $5.8 million, but Gardner said he expects the project to cost less, hopefully only spending $450,000 of city dollars.

“Instead of $400,000 a year, we will only be spending $2,500 a month on the loan, and I believe that will be mostly offset by the sale of the class-A biosolid, which is essentially manure,” Gardner said. “This will be a good use of taxpayer money and will keep our rates competitive.”

The Natchez Wastewater Treatment Plant produces 576 dry tons of the sludge every year. Gardner said it would take 25 years to empty the lagoon, converting the yearly waste along with gradually emptying the 17,000 dry tons already in the lagoon.

The class-A biosolid currently sells for $15 a ton.

To remove the 17,000 dry tons of sludge currently in the lagoon over 25 years and keep up with what Natchez produces yearly, the plant would have to treat 1,256 dry tons a year.

The biosolid would create $1,570 a month at the current market price.

The process to create the class-A biosolid will start with a newly installed fine mechanical screen filter system. The filter system is used to sort rags, jugs and other large debris that will be automatically pumped into a Dumpster.

“With our old, wider system, our staff would have to go in and dig out that debris,” Gardner said. “It was a dirty job.”

From there, it goes into a contaminating chamber where the waste is introduced to naturally occurring bacteria that feed on the waste. Gardner said it becomes a feeding frenzy once oxygen is introduced to the mix.

“The motors introduce oxygen into the sewage, and the bugs, which are purposely kept hungry, start chomping at the sewage and get fat and happy,” Gardner said.

Once the bacteria are full, they go into clarifier that separates the sludge from the liquids. The water, which will be chlorinated and de-chlorinated, ultimately ends up in the Mississippi River.

Two 40 horsepower pumps used to extract the bacteria, but now three computer controlled 8 horsepower pumps extract them.

“These RAS pumps alone will save us $10,000 a year,” Gardner said.

The bacteria will now start consuming each other and will ultimately end up in the lagoons. At this point, the sludge is 8 percent solid.

Once the new system comes online, a dredge boat will be employed to help filter the sludge into a new tank. The tank will funnel it into a three belt filter press that will squeeze the sludge like a sponge, until it is 70 percent solid.

“At this point, the sludge looks like a brownie,” Gardner said.

The brownies will go onto a conveyer belt that will dump them into a trailer that will take the sludge to one of two greenhouses, where the goal is to make the brownies 100 percent dry.

“What (the greenhouse) will do is kill any bacteria that could even think about existing in the brownie,” Gardner said. “It kills their environment.”

The greenhouse, a solar drying unit, will harness the energy of the sun to reduce the brownies volume by an additional 97 percent over a six-week period.

“This system is high tech,” Gardner said. “All we have to do is enter in a starting moisture point into the computer, and the computer will take care of the rest.”

The computer will monitor and optimize the environment. It even controls a plow that is called a mole.

“The mole looks like a Volkswagen Beetle,” Gardner said. “It will turn and plow up the solid.”

Once the period is over, a DEQ representative will come down to confirm the final product’s classification as a class-A biosolid.

“I have the fullest confidence that we can do it,” Gardner said.

Gardner said that if, for some reason, the solid is not up to the DEQ’s standard, it will still be much cheaper to haul. In this worse case scenario, Gardner said it would still save approximately $400,000 a year, because Natchez Water Works could use one truck to carry it to the dump site versus 100 truckloads, as it takes now.

“Other water treatment plants have done this across the country and have had no trouble with the process,” Gardner said. “I don’t see why we would have any trouble.”