Separators Help Protect Disc Centrifuges
To protect its centrifuges from oversize material such as hair, plastic and gritty material, the Ocean County Utilities Authority uses circular screen separators that usually operate 8 to 16 hours per day seven days a week. Located in West Creek, NJ, the 20 mgd activated sludge, secondary wastewater treatment facility uses primary settling tanks, aeration tanks, final clarifiers and chlorine contact tanks to handle a combination of domestic and industrial wastewater from various townships in southern Ocean County. Because of its proximity to beaches along New Jersey's southern shoreline, recreationists boost the amount of wastewater that must be treated during the summer months.
Installed in 1977, the two 48 inch diameter circular screen separators alternate handling approximately 200 GPM of wastewater in the treatment system. In essence, they protect disc centrifuges used to thicken waste sludge from the final clarifiers. The centrifuge nozzle diameters of 0.08 would easily become clogged if oversize material entered the centrifuge. To prevent this from occurring, a Kason VIBROSCREEN® circular screen separator is located upstream from each of the two centrifuges.
The circular screen separators were first installed with 30 mesh stainless steel screens but the plant switched to 10 mesh screens which were found to be optimum. Solids content averages about one-half percent, ranging from .2 to. 9%, according to Bradford R. Hazley, director of the southern division wastewater treatment facility.
Each separator operates with a safety screening system, i.e., each separator is equipped with two screens of the same mesh in series with one another. Under normal operation, the top screen removes the oversize material and the degritted material flows through both the upper and lower screens. In the event that a sharp foreign object enters the system and breaks the upper screen, the lower screen will continue to clarify the flow without requiring a shutdown. The broken screen can be replaced when convenient.
Since each separator has two screens in case the top screen breaks, maintenance personnel need not worry about cleaning out a plugged centrifuge -a nasty half-day job. Screen breakage has not been a problem though, said Hazley.
The hair, plastic and gritty material falls into a basket and is then taken to a landfill while the sludge and water are pumped from a sump to the centrifuge, explained Hazley. The centrate from the centrifuge is routed to the treatment plant headworks and the thickened sludge goes to a primary anaerobic digester for stabilization. After passing through a secondary anaerobic digester and sludge dewatering system consisting of two solid bowl centrifuges, the sludge is disposed of in a landfill.
Final clarifier effluent passes through chlorine contact tanks for disinfection before being pumped to an ocean outfall which extends more than a mile from the shore.
Screen Tips - Volume 5, Number 1 Fall 1990
Two Kason Circular screen separators help protect disc centrifuges from oversize material at the Ocean Count Utilities Authority wastewater treatment facility in West Creek, NJ.