PWPF Settled Solids Dewatering Facility

The City of Cumming operated an 18.0 MGD potable water production facility that used a series of shallow ponds to remove solids generated by the water treatment process. The settled solids removal process in the shallow pond system was inefficient and significantly undersized for the 18.0 MGD capacity of the water treatment plant. CEC recommended a plate and frame filter press process to improve the capture and dewatering of the settled solids, which can be characterized as alum sludge.

The overall process included two 80-foot circular gravity thickeners, two thickened sludge transfer pumps (air diaphragm pumps, 100 gpm @ 40-feet), sludge conditioning with polymer, positive displacement and a sludge press feed pump (211 gpm at 150 psi). The filter press metal plates are 1,500 mm with a 113 cf capacity in 74 chambers. The filter press is equipped with a 22 psi membrane squeeze system and automatic 50 gpm, 1,500 psi cloth wash system. The filter press also has a compressed air 240 SCFM at 100 psi core blow system.

Settled solids dewatered to about 35% solids are automatically removed from the filter press and drop into a 16 cy dump truck for disposal. The solids are transported and disposed of in the old shallow ponds previously used for the settled solids removal. The settled solids dewatering facility has been operating successfully since 2001. The press system is housed in a two-floor, 90-ft by 53-ft by 35-ft high brick veneer and block building. The building includes an office and small process lab.

1.0 Million Gallon Hendrix Road Elevated Water Tank

The Hendrix Road 1.0 Million Gallon Elevated Water Tank provides water to the City of Cumming’s customers in the northern portion of the City’s service area. This tank is the most recent tank project CEC has designed and managed for Cumming. The fluted-style column tank stands approximately 148-feet from the ground to the overflow elevation and includes 40-feet of operating depth. Soil conditions allowed the tank to be constructed on a shallow foundation consisting of approximately 380 cubic yards of concrete and 30,000 pounds of steel reinforcement.

Continuous Sludge Collection System

The City of Cumming 6.0 MGD Potable Water Production Facility (PWPF) (shown in the photo near the ball fields) represents an upgrade to the City’s existing 18.0 MGD PWPF. Construction was completed in June of 2009.

The expansion includes three 2.0 MGD Microfloc Trident HS units manufactured by Siemens. The treatment plant includes enhanced coagulation with tube settlers, high rate settling and adsorption clarification, and filtration. The Trident HS process provides tube settlers prior to the adsorption clarifiers and filters while the existing plant only includes sedimentation and filtration.

Continuous Sludge Collection System

Quarles WTP Reservoir Rehabilitation

Cobb County-Marietta Water Authority’s Quarles Water Treatment Plant Raw Water Storage Reservoir has a volume of approximately 27.8 million gallons. Approximately 14 million gallons (69,000 CY or 50.4% of the reservoir) had filled with water treatment plant residuals from years of settling river sand from influent pumping and alum precipitant returned from recycle backwash operations.

This project included rehabilitating the reservoir by removing 69,000 CY of accumulated material and rehabilitating existing intake and outlet structures. Due to water plant operating constraints, the project schedule required that all material be removed in approximately five months. Two subcontractors teamed up to meet this schedule. The solids removal equipment included two dredges, four plate and frame presses and four belt presses.

In-place solids content in the reservoir ranged between 12-20%.  The plate and frame presses were able to increase the cake solids to 65% with no polymer addition while the belt presses were able to achieve 45% with the addition of polymer. The dewatering equipment was able to reduce the in-place volume by a factor of almost four, proportionally reducing trucking costs and tipping fees.

CEC arranged the project to place the burden on the contractor to determine the most advantageous combination of dewatering and trucking. CEC did not specify solids content requirements; the only requirement was that material pass a paint filter test.  CEC structured the method of payment for material removal based on restored capacity to the reservoir. CEC believed that it was in the Owner’s best interest to define the scope of the project in terms of restored capacity instead of dry tonnage removed or some other arrangement.

Cumming 2.0 MG Water Storage Tank