Challenge

Cumming, Ga., is located almost 40 miles northeast of Atlanta.  With a population of more than 4,000 residents, its small-town charm and proximity to the big city continue to attract new residents and visitors each year.  The city is also the county seat for one of the fastest-growing U.S. counties, Forsyth County, with a population of approximately 98,400 and a 123 percent growth rate.  New commercial and industrial businesses continue to establish themselves in the area.  All which further strains Cumming’s infrastructure.

By 1997, Cumming realized the need to increase capacity at its water and wastewater facilities and decrease traffic congestion.  As the city increased its water treatment plant’s capacity from 3 million gallons per day (mgd) to 8 mgd, it also needed to find an alternative means of disposing of potable water residuals (sludge) that result from the water treatment process.

The city had previously discharged approximately 1.5 tons of sludge per day into a nearby pond where it was allowed to settle.  Water was drawn off of the top of the pond, and the settled sludge was allowed to dry.   

According to Jon Heard, director of utilities for the City of Cumming, the entire process was very time-consuming and expensive.  Moreover, the ponds were quickly reaching their capacity, which raised environmental concerns.

Solution

Siemens Water Technologies provided a complete dewatering system for the facility, with the exception of the sludge conditioning tank and mixer.  This facility reduced sludge volume as well as related transportation and disposal costs.

The $710,000 dewatering system consists of:

• An overhead-style J-Press® filter press with steel-reinforced rubber molded (SRRM) diaphragm filter plates
• A water squeeze system
• A high-pressure cloth wash system and sludge feed pump
• A fully automated programmable logic control (PLC) system with phone modem
• A Willett feed pump with polymer injection system
• A Stranco PolyBlend® system
• An air compressor with air dryer

Sludge from the thickening clarifiers is pumped to a conditioning tank in the dewatering facility.  A mixer in the conditioning tank keeps the sludge suspended until a sufficient amount becomes available for a filter press cycle.  Once the cycle is automatically initiated, the press closes and the fully automatic filter press feed pump starts.

The Stranco Polyblend® system blends the polymer into day tanks.  From here, the Willett feed pump’s polymer injection system injects the polymer into the sludge at precise dosage rates with each pump stroke.  The sludge is then pumped into the press at 100-psi pressure where initial dewatering takes place. 

The amount of polymer and the slurry feed time can be adjusted with the PLC system.  After the press is filled, flexible rubber diaphragms on the filter plates squeeze the filter cakes formed in the press chambers at 225 psi, dewatering them further.  When complete, the press is opened and the cakes are automatically discharged.

Results

• The mechanical squeeze action of the filter press enables the plant operator to compress the cake and obtain a harder, dryer filter cake in a shorter period of time than could normally be achieved through pressure differential alone.
• The extremely strong and corrosion-resistant SRRM plates ensure consistent performance and long life.
• The system is easy to operate and maintain.
• The overhead-style filter press provides easy access to the filter cake for manual or automatic cake removal, inspection and cloth servicing.
• Filter cloths need to be changed only once a year.
• The city’s new sludge disposal has also brought it into compliance with U.S. EPA standards.

“Siemens did a thorough analysis of our situation and provided us with a cost-effective solution that will take care of our dewatering needs well into the future,” says Heard.