Austin, Texas, is a vibrant city with more than 825,600 residents, up 25 percent since 2000. The downtown district buzzes with activity. Retailers, art galleries, restaurants, businesses and condos create excitement – and a lot of wastewater.

Last fall, Austin completed one of its most complex infrastructure projects, a 3.9-mile wastewater tunnel. The tunnel, which moves liquid sewage to treatment plants, will facilitate residential and business growth downtown. An important offshoot of the project was an accompanying odor control system.

ECS Environmental Solutions in Belton, Texas, supplied the odor control equipment, which included more than 1,000 feet of fiberglass ductwork and accessories such as field joint kits, flexible connectors, control and back-draft dampers and bolt gaskets. ECS also provided two fiberglass exhaust fans rated at 40,000 cubic feet per minute (CFM).

“The magnitude of this bio-filter project made it unique,” says Jeff Jones, president of ECS. His company manufactured ductwork in five different sizes, ranging from 72 inches to 12 inches in diameter. Approximately half of it was buried below ground and had to be H-20 wheel loaded so it could withstand thousands of pounds of high-density traffic driving over the site.

The above-ground ductwork is suspended by concrete supports. Fiberglass was an ideal material for this ductwork because of its light weight. “Supports are an expensive piece of the construction puzzle,” says Jones. “With specially-designed FRP ductwork, the contractor could extend the support spacing. That was beneficial to the client because it reduced costs.”

All of the ductwork was manufactured at ECS’ 100,000-square-foot facility. The round ductwork was filament wound using a computerized winder. Direct filament strands were pulled through a resin bath, saturated, then applied on top of a corrosion barrier at a pre-determined angle. The complex fittings and joints were manufactured using hand lay-up. ECS applied alternating layers of 1.5-ounce chopped strand mat and 24-ounce woven roving to the parts until the designated thickness or laminate sequence was achieved. Each separate layer was saturated with resin by hand.

The internal surfaces of every component feature a 100-mil corrosion barrier that was applied by hand lay-up. Because the ductwork is exposed to sunlight, a gelcoat with UV inhibitors was applied to the exterior.

ECS used AOC’s Vipel® K022, a corrosive-resistant vinyl ester resin. “The K022 resin was the best choice for this project,” says Jones. “Some of the gases in the air stream are corrosive – hydrogen sulfide and ammonia. There’s also sulfuric acid. Pipes built with this resin are inert to what goes in them: They will not corrode.”