Architectural Record BE - Building Enclosure

Aluminum Covers

Sustainable Odor Control Covers for Wastewater Treatment
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Sponsored by CST Covers Industries, Inc.
Celeste Allen Novak AIA, LEED AP

Safety, Containment and the Elements

Aluminum covers over wastewater treatment provide safe containment of wastewater treatment processes. Many wastewater systems in communities include ponds or storage containers at grade with only perimeter fencing for the entire facility. Storage ponds can be hundreds of feet wide with internal equipment strategically placed to maximize the process, not minimize maintenance or access for repairs. An aluminum cover is an ideal odor control solution that can be walked on and provides access through hatches or dormers for monitoring and maintenance. With a hard surface aluminum cover, a system is protected from unwanted contamination caused by excessive leaves, refuse and airborne debris.

Protection from the elements is another good reason to cover storage tanks. Covering storage facilities reduces daylight and the accompanying growth of algae in a storage tank. Covering reduces maintenance by reducing the accumulation of pollen, which settles in the bottom of storage tanks. Biological processes in wastewater are most efficient when controlled and covered in a contained system.

Wastewater treatment systems often require the control and monitoring of the temperature of the wastewater. An aluminum cover acts as an insulator providing some protection against freezing. Some biological treatment processes including trickling filters, utilize rotating mechanisms designed to keep the helpful “bugs” and bacteria alive. Sometimes the wastewater freezes when left exposed to the elements, which will not allow the mechanisms in the tanks to rotate as intended. Wastewater is typically warmer than surface temperatures and when covered, this heat is retained helping with the biological treatment process.

The Benefits of Using Aluminum

When calculating the cost of a material, design professionals know that the durability and maintenance contribute to a life-cycle analysis. Aluminum will not rust, rot or spall or require sandblasting and requires little to no maintenance. Aluminum is cost effective as a material choice because its properties of strength and weight are similar to steel but make it lighter to handle, transport and install particularly on projects that require long, self supported spans. “Aluminum covers provide the strength, durability, odor control and protection characteristics unavailable in steel, concrete, fiberglass, fabric or any other materials of construction. They are environmentally benign, structurally robust and operator friendly, and they require little to no maintenance,” says John Delaney, senior vice president of sales with CST Covers.

Corrosion resistant aluminum is a sustainable material to select as a cover for wastewater treatment. Non-corrosive aluminum can be a replacement for polyethylene and in other locations for fiberglass reinforced panels (FRP). The advantage of aluminum over FRP is that it is resistant to ultra-violet light as well as other elements. Aluminum is also the primary choice in all marine applications as well as in water treatment applications, where the metal is exposed to water, humidity, steam and gases. According to the US Army Corps of Engineers, “Aluminum has excellent corrosion resistance in a wide range of water and soil conditions because of the tough oxide film that forms on its surface. Although aluminum is an active metal in the galvanic series, this film affords excellent protection except in several special cases.”ii Aluminum is also resistant to hydrogen sulfide, salt air, chlorine and industrial chemical off-gas. To provide an installation that is durable and easy to maintain, the engineer should:

• Select a marine grade alloy.

• Choose integrated, corrosion resistant fasteners and components.

• Work with the manufacturer to maximize the noncorrosive properties of aluminum and avoid any non-compatible materials during installation.

Aluminum has an estimated fifty to one hundred year service life cycle when engineered and designed properly.

The challenge of wastewater treatment includes the large clear spans over sewage sludge, organic and inorganic wastes. Lightweight, strong aluminum is able to span a great distance without the need for secondary support structures. Some of the largest treatment basins can span over four hundred feet and require rotating mechanisms that preclude the use of columns in the middle of the tank. Large projects such as the one in Beckton, UK, require a cover system that can provide long spans and do not interrupt machine the equipment in the sedimentation tanks.

At Beckton, engineers were faced with the challenge of covering over six hundred thousand square feet of tanks with a variety of equipment. The most challenging problem was to coordinate the aluminum cover supports with scrapers at the sludge trough at the end of each tank. Instead of designing the cover support with multiple vertical columns that would interfere with the track operations, engineers were able to design a structural aluminum beam system with only one mid-span column support. The solution to this problem was developed with input from the owner, the equipment supplier and the engineer for the aluminum covers. Through collaboration, the solution satisfied the need for scraper clearance and provided a safe, removable, odor containing cover system for the sewage treatment process.

Formed flat plate cover in Fitchburg, Massachusetts.

Formed flat plate cover in Fitchburg, Massachusetts.

Photo © CST Covers

Aluminum is 1/3 to 1/5 the weight of steel. When designing a flat, domed or vaulted cover over large spans of sewage sludge, the strength –to-weight ratio is higher for aluminum than it is for steel, wood or concrete. This means that the components can be made of thinner material and in smaller sections. Because it is lightweight, components can be assembled more easily in the field and as in Beckton, components can be lifted by small crane, or by hand into place.


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