Challenge

Atlanta-Fulton County, Ga., needed effective technology to remove suspended solids from raw water drawn from the Chattahoochie River. The utility constructed a new 45 million gallon per day water treatment plant in 1991, and then increased design flow to 90 mgd in 1995, to keep up with growing population.

Raw water enters the plant at 15-20 NTUs (turbidity), and the plant must meet state and federal standards of 0.5 NTUs. 

Space was also a consideration in the design of the water treatment clarification systems.

Solution

For both the 1991 plant, and the 1995 expansion, the utility and its engineers (Jordan, Jones and Goulding, Inc., and Williams, Russell & Johnson) selected USFilter, Zimpro's inclined plate separators. USFilter provided the plates in “plate packs” set in concrete basins.

The  packs are designed and manufactured at the USFilter Zimpro Products site in Rothschild, Wis. Water is first flocculated, then flows upward at a constant velocity between the inclined plates. Solids settle out on the plate surfaces and slide into the settling and collection zone below. Effluent flows over v-notch weirs and exits the plate packs through a top-mounted effluent trough.

The 1991 project called for four basins, each with 900 plates, providing over 103,000 square feet of settling area. The 1995 expansion also consisted of 900 plates in four basins—providing a total of more than 206,000 square feet of clarification area.

Results

The primary goal of the settling process is to reduce solids content and meet turbidity standards. This has been accomplished. The produced water at Atlanta-Fulton County averages about 0.3 NTUs—surpassing the requirements of 0.5 NTU.

In addition, the plate packs have conserved space, and reduced construction and operating costs when compared with conventional
water clarifiers.

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