When a Southern California treatment works wanted to cover the influent of 40 million tons of sewage per day, it specified chemical-resistant isopolyester resin for a structural enclosure. The enclosure measured 48 feet long, 12 feet wide and 22 feet high. It covered five barscreens that screen urban and industrial waste from six cities as it enters San Bernadino County’s Regional Plant Number 1, a wastewater treatment facility in Chino, Calif.
"The barscreen at the headworks of a wastewater treatment plant removes rags, sticks and similar large solid materials from the influent flow," said Tom Rysgaard, president of Fiberglass Structures and Tank Co. (FST), Wyoming, Minn., that made the enclosures. "The screened sewage then continues through the plant process equipment."
More Than Chemical Resistance
"We use isopolyester primarily because the nature of our products mandates high chemical resistance, but that’s not its only advantage," Rysgaard said. "Isopolyester’s good impact resistance and durability also are important attributes." For example, Rysgaard states that during installation of an isopolyester composite cover on a 60¢-high water storage tank, one of the cover panels fell. "It bounced about 15 feet when it hit the ground but sustained very little damage. We repaired it and installed it that same day."
The company manufactured the San Bernadino County enclosure panels by contact molding a sandwich structure over a male form. First down on the mold is an isopolyester gel coat. Next a layer of chopped glass and isopolyester resin is sprayed on, followed by a ply of woven roving, then another spray-up layer. A pre-cut polyurethane foam core is set in, then a mirror-image laminate is fabricated over the core. Finally, another isopolyester gel coat is sprayed on and rolled out so both sides of the structure have a finished surface.
For the San Bernadino County enclosure, each ply was cured before the next was laid down. "We use a special resin formulation that gives us a high reading of 40 to 50 on the Barcol hardness scale, allowing us to lay-up, cure and remove large parts from the mold within three hours," Rysgaard said.
The light tan enclosure consists of four walls, nine doors and a roof constructed over a slab foundation. Eleven-foot-wide panels are field-assembled with bolted connections. "We built panels in sizes that we can ship," Rysgaard said. "We can’t ship anything that’s 22 feet high."
End panels are 11 feet wide by 12 feet long, and side panels are 11 feet wide by 48 feet long. Roof panels are curved to form an arch. The doors are designed to permit easy access for personnel and equipment. Five are standard hinged doors, and four are sliding bypass doors.
The municipal facility enclosed its barscreens when increasing urban development in the area mandated a need to control odors, according to Marshall Locke, the plant’s chief operator. Located near Interstate 10, a major coast-to-coast highway, the open plant was exposing travelers as well as local neighbors to offensive odors. Now odious fumes are drawn off by fans in the enclosure and cleaned by air scrubbers before being released.