An Undercover Job

Visitors to the new David L. Lawrence Convention Center in Pittsburgh are usually struck by the beautiful and environmentally friendly design of the facility. It has 330,000 square feet of exhibition space, of which 250,000 square feet is the column-free main exhibit hall. The facility is the first "green" convention center in the United States, using features such as natural ventilation, natural day lighting, water conservation and energy efficiency and recycled building materials.

Few visitors realize that an important part of that green design lies hidden beneath the building's floor. The architects of the facility opted to install a 50,000-gallon underground wastewater/storage tank designed by Highland Tank.

How the Tank Works
The new tank was designed to intercept the convention center's sanitary wastewater and contain the surging wastewater during peak flows that coincide with large convention events. When the heavy flow abates, the tank is pumped down by a duplex submersible grinder pump system at a controlled pumping rate.

The new tank was also designed to separate and collect large quantities of solids that might interfere with the proper drainage and treatment of municipal wastewater. Compliance with the city's sewer pretreatment regulations was an important design issue. One of the primary causes of sanitary sewer overflows is the clogging of sanitary sewers and pump lift stations by solids or viscous materials. The U.S. Environmental Protection Agency (EPA) now requires that municipal sanitary sewer authorities implement pretreatment programs to control solids or materials that will or may cause an obstruction to the flow in a wastewater collection system or otherwise interfere with the normal operation of the wastewater treatment system.

Green or sustainable building is the practice of creating healthier and more resource-efficient models of construction, renovation, operation and maintenance.

There are more than 1,500 publicly owned treatment works that are required to implement local pretreatment programs. By reducing the level of pollutants discharged by users into municipal sewage systems, the program ensures the protection of America's multi-billion dollar public investment in treatment infrastructure.

In operation, the 50,000-gallon wastewater treatment/storage tank receives wastewater from the convention center's numerous fixtures and facilities, specifically the water fountains, bathrooms, air conditioning, floor drains, etc. Surge flows during large convention events are first collected in the tank. Heavy solids are separated and deposited at the bottom of the tank by means of an advanced switchback baffling system. The switchback baffling system greatly enhances the residence time and produces laminar flow conditions in the tank to aid in the separation process. The switchback baffling also directs the wastewater flow in a serpentine path through the tank to prevent short-circuiting between the inlet and clearwell.

The tank is equipped with duplex submersible grinder wastewater pumps that are mounted in the effluent clearwell on steel rails for easy pump removal. The duplex pump system includes an alarm/control panel with an alternator and effluent level controls to start and stop the pumps at predetermined levels and also alarm at high liquid levels.

The duplex grinder pump's liquid level sensors are actuated at predetermined liquid levels so that the wastewater can be pumped at a controlled rate to the wastewater treatment plant. Since this sewer is always pressurized, the pumps were required in order to pump the sanitary sewage from that site into the pressurized sewer. The pumps were also required to break down sewage waste, sanitary napkins, paper towels, garbage, rubber goods, plastic bags, fabrics, etc., into very small pieces to prevent clogging of the sewer system. The use of the grinder pump system prevents large amounts of pipe-clogging solids from entering the sanitary sewer system.

Conservation Winner: Recycled Steel
According to the Steel Recycling Institute, "many states and cities have instituted 'buy recycled' mandates that require purchasing agents to buy products with recycled content whenever possible. In addition, the Environmental Protection Institute (EPI) has proposed a federal procurement guideline for recycled products." As protected steel tanks are 100 percent recycled steel, the 50,000-gallon wastewater treatment/storage tank forms an integral part of the convention center's overall green design.

The 12-foot diameter by 60-foot long protected steel tank has all the other benefits of steel -- strength, flexibility, durability and compatibility, plus it carries a 30-year warranty against corrosion due to high-tech external and internal corrosion protection systems. Factory-applied rugged polyurethane exterior coatings and NSF-approved interior coatings were applied under modern plant-controlled conditions and thermally cured to assure long lasting performance. Pre-engineered access ways, switchback baffling, grinder pump systems and other components were precision designed, fabricated and fitted, providing an exceptional quality tank delivering rock-solid dependability.

The Greening of U.S. Buildings
Constructing and operating buildings uses enormous amounts of energy, water and materials, and it creates large amounts of wastewater and solid waste. Where and how buildings are built affects our ecosystems in many ways. And the buildings themselves create new indoor environments that present new environmental problems and challenges.

The new tank was also designed to separate and collect large quantities of solids that might interfere with the proper drainage and treatment of municipal wastewater.

As the environmental impact of buildings becomes more apparent, a new field called "green building" is gaining popularity to reduce the impact at the source. Green or sustainable building is the practice of creating healthier and more resource-efficient models of construction, renovation, operation and maintenance. The many elements that must be considered include energy use, water use, types of building materials used in construction, reduction of the generation of wastewater and solid waste and designing healthy indoor environments. The Pittsburgh convention center is an example of a large facility that successfully combines practical design with many of these new green building concepts.


This article originally appeared in the July/August 2003 issue of Environmental Protection, Vol. 14, No. 6.

This article originally appeared in the 07/01/2003 issue of Environmental Protection.

About the Author

Eugen Nisipeanu, PhD, works for Fluent Inc. in Evanston, Ill., as a computational fluid dynamics (CFD) engineer. In his position, he assists assigned customers working primarily in the nuclear power industry and water and wastewater treatment industry in all aspects of their engineering flow analyses such as modeling their application, defining software problems, converging solutions, and interpreting results. Nisipeanu has a PhD in mechanical engineering with the main focus in thermal radiation from Auburn University, Ala.

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