Evaluation of Ceraflow-70 as a Filtration Media for High Rate Surface Water Filtration - Case Study
The existing water filtration facility in Clinton MA is a high rate, direct filtration process that has been on-line since 2006. The water filtration plant draws it raw water from the Wachusett Reservoir. Chemical feed systems are provided for chemically assisted filtration, pre-oxidation (potassium permanganate), coagulation, pH and alkalinity adjustment (sodium bicarbonate and sodium hydroxide), and disinfection (sodium hypochlorite).
There are six pressure filters, each 102 inches in diameter and each filter has a maximum flow capacity of 560 gpm and hydraulic loading of 9.87 gpm/square foot. The filter beds are comprised of 24 inch deep beds of granular ceramic media. Standard operation has 5 of the 6 tanks on-line, with one in standby, giving a normal service flow capacity of 2,800 gpm, and a peak capacity of 3,360 gpm.
Pilot testing was conducted to evaluate the performance of Ceraflow-70 filter media, as a direct replacement for the existing fine grain ceramic originally installed. Some of the existing ceramic material had been lost through backwashing over more than 10 years of operations. The Ceraflow-70 is a 0.15 – 0.25 mm, textured, spherical ceramic media with a uniformity coefficient < 1.3.
Pilot Test Results
Ceraflow-70 was installed in one of the 102 inch filtration vessel at a 24 inch depth on the existing garnet under bedding. The plant had existing on-line turbidimeters on the effluent of each filter vessel. Plant operations installed on-line particle counters (HACH 2200 PCX), one on the Ceraflow-70 vessel and one on an adjacent tank with the existing ceramic filter media. These on-line measurements were required to both evaluate the filter performance overall but also to facilitate State Approval.
Typical raw water influent turbidities during the pilot test ranged between 0.28 NTU to 0.44 NTU. The requirements of the Enhanced Surface Water Treatment Rule required the turbidity to be equal to or less than 0.3 NTU in combined filter effluent at 95%.
The Ceraflow-70 effluent turbidity ranged from 0.025 NTU to 0.030 NTU. As seen in Figure # 1 the Ceraflow-70 media achieved turbidity consistent with the existing filter media and was consistently below the 0.3 NTU requirements.