Five years ago, Sikorsky Aircraft Corp. of Stratford, Connecticut, generated eight to ten 55-gallon drums of wastewater a day, all of which had to be hauled away at a hefty cost to the company. In 1996, however, the aircraft manufacturer began discharging that wastewater directly into the municipal sewer system, saving the company thousands of dollars a year. Key to this accomplishment was the installation of an ultrafiltration (UF) system custom-designed for the unique properties of the wastewater. 

When Walter Joseph, a foreman with Sikorsky, began evaluating wastewater treatment systems and technologies, he was aware that the diester-based synthetic air compressor lubricant used in their manufacturing process was toxic enough to destroy many plastics used in filtration systems. Therefore, all components in the system -- down to the membrane housing -- needed to be constructed from corrosion-resistant material. The company accepted the design presented by Arbortech Corporation of McHenry, Illinois, which called for an all-stainless steel system that could stand up to caustic wastewater.

"We build aircraft -- we aren't experts in running pollution control equipment," said Joseph. "We wanted to reduce our disposal costs, but we also wanted a system that was easy to maintain and operate."

From the UF element to the two tanks used, low maintenance and ease of operation were priorities in the design of the 60-psi system, notes Ray Graffia, president of Arbortech. "The 1-inch-diameter tubular ultrafiltration elements are virtually impossible to plug, and they can be cleaned hydraulically or mechanically. That alone can make the difference between the ability to clean or the necessity to replace a membrane," he says. 

Membrane preservation also was the reason for providing a "soft start" on the system's circulation pump. Instead of an immediate circulation of 60 psi from startup, the system ramps up and shuts down slowly to prevent membrane shock.

Because the UF system was installed in a remote area of the plant, Arbortech used two operator interface terminals -- one at the system's location and one in the plant's main control room. The setup allows the system to be monitored and controlled from either location. The alarm/shutoff feature of the system also is very flexible, offering alarm and/or shutdown for various conditions, including a drop in processing speed or a reduction in circulation pressure. Alarm conditions can be addressed at either terminal.

Finally, the two tanks used in the system allow cleaning procedures to run separately from processing operations. According to Graffia, this feature is a real timesaver.

"Many smaller UF systems run from one tank, which means it [the tank] has to be completely evacuated before cleaning," notes Graffia. "With two tanks, you can begin cleaning from the second tank as soon as treatment is shut down."

Bells and whistles aside, the UF system allows Sikorsky to achieve compliance while saving money. According to Joseph, Arbortech's UF system paid for itself in less than a year.

"I looked everywhere for a system like this," Joseph says. "It has a clean, professional appearance, and it definitely does the job it is supposed to do."