The Racine (WI) Water Utility looked to USFilter Zimpro Products to increase the capacity of its clarification facilities.
The utility wanted to improve turbidity control, especially during spring runoff from melting ice and snow. Its concrete sedimentation basins were underground, with city streets on three sides and the water treatment plant filtration and control building on the fourth, further complicating the expansion.
The utilitys engineering consultant, Camp, Dresser & McKee Inc. of Chicago, recommended a plan to increase clarification capacity by retrofitting the existing sedimentation basins with inclined plate separators. Each of the sedimentation basins contained about 4,850 square feet of area. In the CDM design, each basin was retrofitted with inclined separator plate "packs," increasing the effective basin area more than seven times
Plate separator packs were furnished to Racine during two phases of construction. Zimpro Products supplied the inclined plate separators completely pre-assembled, with a series of parallel plates spaced by stiffeners, installed in a welded stainless steel frame.
In the Racine flow scheme, water passes first through a rapid mix chemical addition step, then fine particle flocculation. There are four flocculation stages, with a total flow of 20 mgd.
The water then flows to the sedimentation basin, where it enters through the lower side. The design of the feed piping prevents the shear of solids, and influent velocity is further dissipated in the bottom section so that heavier particles will settle out immediately.
The flow then enters the plate area through inlet slots near the bottom and along one or both sides of the plates. The liquid is distributed across the width of the plates and flows upward under ideal laminar conditions, to the effluent launders.
V-notch weirs balance flow equally among the plates. The notches are designed so that the head at the weir (head loss) is several times greater than the total head loss through other components of the unit.
Solids settle out on the inclined plates and slide down into a quiescent solids compartment mounted directly beneath the plates, to be collected by vacuum type sludge collection mechanisms mounted on the basin floor. Sand filtration and disinfection follow the sedimentation process.
Racine called for the retrofit to be accomplished in two phases. In Phase I, one existing settling basin was shut down and retrofitted, while the others continued to serve the communitys needs. In Phase II, the new settling basin was brought on line to allow an additional basin to be retrofitted.
Phase I performance tests were conducted using Lake Michigan water. The inclined plate separators exceeded the required turbidity removal, using far fewer chemicals than allowed by specifications. Flow-weighted turbidity during testing averaged 1.57 NTU in the effluent, with influent turbidity of up to 36 NTU. Influent turbidities in excess of 100 NTU were experienced immediately after testing. During this period, effluent turbidity remained essentially unchanged.
The plate packs were manufactured at Zimpro Products Rothschild, WI, facility, and were designed according to required National Sanitation Foundation (NSF) Section 61 standards. Zimpro Products has supplied similar plate packs at other locations, including Fulton County, GA; the Lenain Water Treatment Facility serving Anaheim, CA; as well as hundreds of package plate separators-flocculator modules for industries and municipalities.
