Underdrain System Improves Plants Filter Performance

The Dallas East Side Water Treatment Plant wanted to upgrade its filtration system to meet growing demand as well as regulatory standards but was limited by the space available and budget constraints.

The Dallas East Side Water Treatment Plant wanted to upgrade its filtration system to meet growing demand as well as regulatory standards but was limited by the space available and budget constraints.

Water utilities manager Ted Kilpatrick recalls, "Our system relied on three banks of older clay-tile filters placed into operation at different times in the 60s, 70s and 80s. As our system began to exceed its useful life, we needed to upgrade for several reasons. First and foremost, we wanted to deliver the best water quality possible to our customers. Containing operational costs and improving efficiency was another priority. We also needed to reduce turbidity to comply with regulatory requirements."

Dallas Water Utilities wanted to go to dual media but the existing filters were shallow and raising the troughs was not a possibility. Moreover, the plant needed to remain operational throughout the implementation and installation of any additional filters or other construction.

Dallas Water Utilities retained consulting engineer Edward Motley from Chiang, Patel & Yerby. After evaluating the current systems limitations and determining the solution would involve modifying or replacing filters, Motley recommended obtaining the input of the F.B. Leopold Company, a filter design and rehabilitation company. Leopolds Mike Wild, Ron Port and Dean Berkebile met with Dallas water officials and Motley to discuss the issues involved: source and type of incoming water; current operational conditions; anticipated customer demand; budget constraints; future environmental/ regulatory concerns and treatment goals.

As various goals were expressed by city officials, a list of criteria emerged. The system would need to accommodate additional media to improve filter performance. L/D ratios would also need to improve. Generally, the greater the L/D ratio, which is the ratio of media depth to media particle size, the better the water quality produced.

The team settled on the Leopold Type SLTM Underdrain system. It would provide the necessary depth to accommodate additional media and ultimately improve the filter performance. In addition, it would improve the L/D ratios to the desired levels for increased water quality.

The SL block also was attractive because it was designed to be used with air scour. With surface water treatment rules changing and backwash recycling taking effect in 2000, the ability to add air scouring became an important consideration. Only minor modifications to the flume will be necessary to provide air scouring to the filter in the future. Adding air will reduce the production of backwash water and help Dallas comply with the new standards.

A mock-up of the existing flume was tested in Leopolds Product Development Center. During this phase, adjustments were made to enhance the distribution of the existing filter backwash, further improving filter performance and, at the same time, confirming optimal performance of the future air scour backwash. Eagle Contracting was chosen to install the new system. Both Paul Graham and Jim Brassart from Eagle Contracting had extensive experience installing Leopold products.

During the installation, a few unforeseen complications arose including discrepancies in old dimensions. As they were already on-site to inspect the installation, Leopolds Wild and John Geibel were able to recommend immediate solutions. For example, after observing the installation and the assembly of the laterals, they determined a better, more effective position for the baffle system. They also modified the backwash procedures to use older control systems.

This kind of "active partnering" throughout the project impressed Kilpatrick. "Leopold was very cooperative with everyone involved and demonstrated a can do attitude no matter what kind of challenges were presented, either by the design engineer or during installation."

About the Author:

Thomas Getting is a registered Professional Engineer in five states, including Pennsylvania, and is a member of the American Academy of Environmental Engineers. He has over 25 years of experience in the water and wastewater industry, having been previously associated with several consulting engineering firms as well as equipment manufacturers. Currently, Mr. Getting is the Filtration Product Manager for the F.B. Leopold Co.

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