Leakage from water and wastewater treatment vessels due to mechanical or chemical influences can pose a serious threat to workers, the public and the environment. In addition, leaking containment systems can lead to unplanned downtime and diminished capacities, accompanied by time-consuming, expensive and recurring repairs.
As safe as they may be initially, the ongoing integrity of many water and wastewater containment structures depends on the ability of the containment system linings — often consisting of coatings — to provide thorough protection against leakage over time.
A range of products is used to protect against leaking or spilling of the aqueous materials held by primary and secondary containment structures. Yet many of the most popular products — polyurea, polyurethane, polysulfide, silicone and epoxy — offer only limited protection and will fail due to a variety of chemical and mechanical challenges.
A Host of Challenges
A number of chemical challenges to primary containment vessels are not sufficiently addressed by the above products. Those challenges follow from the wide array of chemicals found in industrial water and wastewater treatment operations.
These include hydrogen sulfide, sodium hydroxide, sulfuric acid, sodium hypochlorite and chlorine, as well as numerous other industry-specific and harsh chemicals such as nitric or hydrofluoric acids. Such chemicals attack both steel and concrete in process or storage tanks, clarifiers, thickeners, cooling towers with concrete bottoms, concrete tanks and the concrete bottoms in steel-walled clarifiers and thickeners.
Mechanical issues include abrasion or erosion of primary containment linings via solid contaminants, and cracking of concrete substrates used for primary containment vessels — e.g. the bottoms of clarifiers. On steel substrates, linings often lack high permeation resistance, which will cause the linings topcoat to display blisters. These blisters are symptoms that linings are failing due to molecular vapor transmission through the lining on a steel or concrete substrate.
While secondary containment dikes are required that can enclose leaks and spills for a minimum of three days or 72 hours, lining damage usually accompanies the spill of most chemicals, compromising the dike’s integrity, resulting in costly and time-consuming maintenance and downtime. Ultraviolet rays and weather also cause concrete to move and crack and just plain degrade most polymers, causing the same problems.
So, the choice of material to line primary and secondary containment vessels and dikes can make a major difference, particularly in the many water and wastewater treatment facilities that are in demand 24/7.
The Elastomeric Bridge
There is a solution to the combined threats of the various chemical challenges to water and wastewater containment facilities, an engineered elastomeric lining system that can be applied to primary and secondary containment structures. The engineered elastomeric lining is noteworthy for its long service life, ability to “bridge” joints and cracks in concrete, imperviousness to UV light and harsh chemicals, and ease of installation.
The Elasti-Liner system from KCC, Houston, Texas, is a leading line of engineered elastomeric lining products applied by brush or roller to concrete substrates and directly over expansion and control joints.
A polymer lining that cracks in containment dikes is no containment at all, and it is misleading to even call it a containment lining if that so-called containment lining cracks when the concrete cracks.
“In the past, we used 100% epoxy coatings on our secondary containment structures,” says Brian Peroni, corrosion control specialist at Florida Power & Light (FP&L). “Epoxy might work well enough for some primary containment applications, but for concrete structures, it’s inadequate. In concrete structures live cracks will occur, and because epoxies are a rigid coating, they tend to crack right along with the concrete. As a result, you have continual maintenance to seal those cracks as they occur.”
Peroni describes FP&L’s typical secondary containment as basically a concrete dike consisting of a wall and base around the facility’s primary tanks. Those tanks contain a variety of liquids, ranging from very harsh, low pH chemicals, such as 98% sulfuric acid, to very caustic solutions with a pH as high as 10-12. Tanks located in Florida are subjected to a lot of sunlight, which contributes to the cracking of concrete dikes.
Clarifiers at power plants are another example of containment structures where cracking can be a serious problem. These primary containment vessels are often designed with metal sidewalls resting on a concrete base. In an attempt to prevent leaks when the concrete base cracks, the concrete is often reinforced with grout. However, the grout seal can fracture when the concrete moves or cracks.
To overcome the problems of leaks resulting from cracked concrete in primary and secondary containment structures, Peroni uses and recommends an elastomeric liner. “The product has great crack bridging properties,” he explains. “That’s why it is so effective for us. We don’t have to worry about cracks in the concrete and we don’t have a lot of maintenance. We simply put it on and forget about it.”
The Inside Story
“I would say that this Elasti-Liner product line is the only truly monolithic containment liner available,” says Art Rak, president of Ultimate Corrosion Control, Clarkston, Mich. One of the main benefits in using this elastomeric lining on containment and other concrete structures is that concrete joints are simply taken care of by the lining overlaying the joint, so joint problems are eliminated.
Rak cites the 1994 installation of the elastomeric formula as a lining of a large, 4-foot containment dike for an 18,000 square-foot tank farm holding highly-corrosive phosphoric acid in Chicago Heights, Ill. “The lining still looks and works great after 17 years,” he says.
Although chemical storage poses different requirements than many water treatment plants, the ability of the elastomeric coating system in this environment dramatizes the material’s imperviousness to harsh chemicals that may be found in water and wastewater facilities.
Rak says this elastomeric product line is great at bridging cracks up to 1/8-inch because of the way it is engineered. The polymers are cross-linked and act like coiled springs that expand and also contract as concrete moves.
“The elastomeric liner exceeds the tensile strength of concrete,” he says. “If you deliberately tried to pull the liner off the concrete, you would have to exceed 500 PSI in pulling strength. This elastomeric-based lining stays well-bonded to concrete no matter what the concrete does.”
Because you can apply the solution over expansion and control joints in concrete structures, considerable installation time and costs are saved. “One customer told us that using the system, including the joint sealer, cost him less than it would have just to have an installer take care of sealing the joints using a standard method,” Rak explains.
As an end user customer put it, “You know that concrete cracks. And you know that hazardous materials, if spilled, will leak into the ground and contaminate ground water. Therefore you know you cannot use a coating or lining that cracks.”