Clarifier renovations had been challenging for City Water, Light and Power (CWLP) in Springfield, Illinois.

The conversion of two existing clarifiers to a new design involved installing new steel components to which coatings were applied to resist corrosion. The initial epoxy coatings began to fail within a few years after application.

In 2013, the utility faced converting a third clarifier. This time, utility leaders wanted a longer-lasting coating. They found it in an edge-retentive ultra-high-solids epoxy engineered for immersion service. The clarifier with the new coating was commissioned in April 2014.

Proud history

In 1930, Springfield voters passed a $2.5 million bond issue to construct Lake Springfield, a dam, a power plant and a water purification plant, all completed under the Depression-era Works Progress Administration.

In 1936, the water purification plant began operations with four filters and three clarifying basins called Spaulding Precipitators, invented by Charles Spaulding, at the time CWLP water superintendent and chief chemist. The plant soon became the model upon which other water treatment plants nationwide based their designs.

In 1999, the clarifiers needed renovation. The first project, a $1.2 million conversion from the original clarifier to a ClariCone helical upflow solids contact clarifier, aimed to increase the unit’s capacity from 6 mgd to 10 mgd. The converted unit would produce softer, lower-turbidity water at less cost, use significantly less electricity, and treat more water with the same chemical dosage. Dave Wyness, former CWLP superintendent, invented the ClariCone, now a product of CB&I.

“Typically, ClariCone units are above-ground steel structures with only a few steel internals,” says William Peffley, senior project manager at Crawford, Murphy and Tilly (CMT), engineer and consultant for the project. “The Springfield ClariCone units were the first to be below-grade concrete tank structures.

“The steel internals are there to remove sludge, support the bridge and direct the hydraulic, helical upflow pattern of the water through the mixing, flocculation and sedimentation zones. Finally, the water flows into the radial collection troughs and on to the next step in the treatment process.”

Second conversion

In the treatment process, water is pumped from Lake Springfield to the lime-softening water treatment plant into a dosing well, where most of the chemicals are added. Then, it flows into the clarifiers to remove suspended solids and precipitate hardness, calcium and magnesium, making the water softer. The water then flows to recarbonation and filtration to a clearwell and into the distribution system.  

In 2002, CWLP commissioned a second converted unit at a cost of $2.1 million. To install the new ClariCone unit, the old precipitators were gutted of their steel parts. The original clarifier footprint remained the same, while the depth increased about 30 feet to match the ClariCone design. Then new internal steel parts were installed.

The first two ClariCone units’ steel surfaces were protected with a traditional epoxy system. Each of these coating systems failed within a decade of service. “Each unit has steel internals, and any time you have steel and water, you need a protective coating,” says Peffley. “In the first two conversions, we specified a traditional epoxy three-coat, 4 mil system for a total of 12 mils. Over time, we observed premature rust along edges and in corner areas.”

A better solution

In 2013, CWLP decided to renovate the third precipitator into a ClariCone, bringing total treatment capacity to 30 mgd. Leaders considered it imperative to choose a coatings system that would last more than 10 years.  

“During the first two conversions, we used standard epoxy coatings systems from a couple different manufacturers, which began failing within the first three years of operation,” says Todd LaFountain, CWLP general superintendent of water treatment. “This time we chose different specialty coatings. We needed a coating to last more than 20 years.”

CWLP and CMT specified edge-retentive high-performance coatings and in a competitive process selected Sherwin-Williams’ Dura-Plate UHS epoxy, valuing its edge-retentive qualities. “The edge-retentive aspect meant the failure point was less likely to occur, because there is more paint there to protect the edges before failure,” says Peffley. The coating chemistry ensures that a single coat retains nearly the same degree of coverage on an edge or corner as on flat steel.

Naval origins

This characteristic of Dura-Plate UHS results from its ability to overcome surface tension, which causes other coatings to shrink from edges. The capability of such coatings was first demanded by the U.S. Navy and is now a key requirement of the Navy’s MIL-PRF-23236 standard. The use of Dura-Plate UHS has expanded from the marine market to public works. It contains about 98 percent paint and 2 percent solvent.

“The U.S. Navy has been using this product since the 1990s,” says Tony Ippoliti, project development manager of Sherwin-Williams Protective & Marine Coatings. “It provides protection on the edges of steel — corrosion begins there and then moves elsewhere, compromising the remainder of the asset. The Navy had been using it on ballast tanks and chemical holding tanks. In about 2000, it became NSF approved for use in the water and wastewater industry.”

The product’s one-coat protection, edge-retentive qualities and NSF approval to Standard 61 for potable water tanks of 1,000 gallons or greater made it a good fit for Springfield’s project.

“In coatings, all paint that comes in contact with drinking water must be NSF certified,” says Peffley. “All of the steel inside the ClariCone unit was for immersion service and received the Dura-Plate UHS epoxy coat, prepared at a steel fabrication shop.”

Extended life

At the fabrication shop, the steel was first primed using Sherwin-Williams Copoxy Shop Prime to keep it from rusting after sandblasting. Then the Dura-Plate UHS was spray-applied. The rest of the ClariCone components not immersed in water were painted with a traditional epoxy system: Sherwin-Williams Zinc Clad IV, Macropoxy 646-100 PW, and a topcoat of Acrolon 218 HS Acrylic Polyurethane, a high-solids urethane that provides strong color and gloss retention against UV exposure.

“High-build qualities more than justified using this premium coatings system,” says Peffley. “The original two conversions have a total of 12 mils of protective coatings on the submerged and wetted surfaces, whereas this edge-retentive system was applied at 28 to 34 mils. It is thicker and anticipated to last nearly twice as long, and therefore is an excellent value.”

The third clarifier conversion began in September 2013 and was complete in time for the start of the city’s high-flow season, running from May through mid-September.

About the author

Kevin Morris is water and wastewater market segment director for Sherwin-Williams, a major coating manufacturer. He can be reached at kevin.l.morris@sherwin.com.