An ultraviolet solution
Project improves capabilities, links Shreveport plant to remote control center

By Sam Barnes

Shreveport's north wastewater treatment plant is getting a $24.6 million high-tech facelift that will enhance its treatment processes and allow the plant to be remote-controlled.

Critical to the project is the construction of a new ultraviolet treatment system that will reduce the plant's dependence on chlorine.

Max Foote Construction Co. Inc. of Mandeville began construction at the site in September and should finish the project about six months ahead of schedule in early 2005. Camp, Dresser & McKee of Baton Rouge designed the project.

"We knew the winter months would probably be rain-soaked, so we began by performing our biggest excavation and installing a dewatering system," said on-site project manager Billy Lott. The de-watering system consists of wellpoints every 8 to 9 ft. connected to a pump that lifts the water up and over the levee that surrounds the plant.

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The strategy appears to have paid off. By the time a wintertime deluge hit the site in February, most of the plant's new structures were out of the ground.

"We took out a little more than 30,000 cu. yds. during the excavation," Lott said. "Some of it was stockpiled for backfill, but a lot of it we hauled off site." The six-week excavation was necessary to make way for two 110-ft.-diameter clarifiers that will perform end-stage treatment of the wastewater before it is transported by pipeline to the Red River a mile away.

A ductile iron return-sludge line was installed beneath the clarifiers to send solids to a nearby pump station and more than 500 18-in.-diameter auger cast piles were drilled as foundation.

"Berkel & Co. (Austell, Ga.) ran its auger down 20 ft. and pumped grout through the center tube," Lott said. "They continued pumping as the auger was lifted out of the hole." Reinforcing steel was placed into each shaft with hooks at the top to connect to the clarifier slab.

As each shafts will augered, the resulting displaced soil was removed by a trackhoe.

Lott said the concrete clarifier walls - completed in March - are about 22 ft. tall and 18 in. thick. The 1-to-12 sloped clarifier slabs are 2 ft. 4 in. thick.

"Everything is reinforced with a double matting of reinforcing steel," he added.

About 6,000 to 7,000 cu. yds. of 4,000-psi concrete is being supplied for the entire project by Builders Supply Co. of Shreveport.

Justin Haydel, an engineer with Camp, Dresser & McKee, said the plant's new ultraviolet treatment system will enable the plant to meet new treatment requirements mandated by the Environmental Protection Agency.

"Everybody's getting away from chlorine," Haydel added. "With the UV system we should significantly reduce our dependence on the chemical."

The 20-year-old plant is also getting a major electrical upgrade by Feazel Electrical Contracting of Shreveport that will connect the plant to the City of Shreveport's System Control and Data Acquisition system.

The SCADA system will allow city engineers to operate the plant remotely from a control center on the south side of the city. All of the city's plants will eventually be linked to the system.

"This requires a lot of electrical work, including the construction of a couple of electrical buildings and a lot of underground electrical installation," Haydel said. Edison Automation of Nashville, Tenn., will perform necessary SCADA-related instrumentation within a new 1,378-sq.-ft. concrete block control building.

In other work, the contractor is converting an existing oxidation treatment area into an aeration basin by gutting two concrete tanks, erecting 15 12-in.-thick concrete baffle walls and installing aeration equipment.

"The aeration basin will consist of coarse bubble and fine bubble diffusers," Haydel said. "At each diffuser you have a saddle that connects to a PVC pipe." Air for the diffusers will come from four blowers being installed by Max Foote at one end of the basin.

A second oxidation area will remain in operation until the new aeration basin is operational, then will be taken out of service.

"We're also gutting an existing screw pump station and installing six new pumps, and replacing the headworks," jobsite superintendent A. E. "Bubba" Ash said. The pump station is the first step in the treatment process and "lifts" the liquids from the solids as the wastewater enters the plant.

Other work requires the intallation of sludge transfer pumps and associated piping and the conversion of existing final clarifiers into sludge holding tanks.

"The sludge transfer pumps will take the sludge from the holding tanks and pump it to belt presses (which 'presses' the water out)," Ash added. The dry sludge is conveyed to a dumpster and hauled away.

New ductile iron pipe is necessary to connect new structures with existing parts of the plant, while some stainless steel pipe is being installed between the blowers in the blower building.

"We're placing a 48-in.-diameter ductile iron pipeline through the levee to tie into the existing pipeline (that exits the plant)," Lott said. A "T" in the new line will accommodate a second pipeline to be installed during a future contract.

Max Foote expects to finish the project in January, about six months ahead of schedule. Lott attributed the impressive progress to the "generally good weather we experienced through January."

"As of right now, we should hold pretty true to that schedule," he added. At peak this spring, there will be about 60 contractors at the site.

Another project currently in planning will install a new high rate clarifier, new headworks and new pump station at the north plant for about $13.8 million. The project will be completed by 2008.