- 18 October 2006 -

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Space saving with centrifuges
After looking at all of the options Regional Utilities decided that centrifuges would solve its problems - one centrifuge and its building can take up less space than half of one drying bed.

Regional Utilities then looked at several different centrifuges packages. It decided on USFilter's range of centrifuges because it wanted the whole package and a company it knew would take care of them.

As part of the upgrade, Regional Utilities ordered three skid-mounted Centrapac centrifuge dewatering systems. The Centrapac system is completely prefabricated and pre-engineered for operation and offers what USFilter calls a "plug and play" solution to sludge dewatering.

The Centrapac System
The Centrapac system incorporates the Centramax centrifuge, which is skid-mounted with all necessary ancillary equipment, including a positive displacement feed pump controlled via a variable frequency drive (VFD) through the centralised programmable logic controller (PLC). The control panel provides control of all operational parameters for complete system automation. All functions such as sludge feed rate, bowl speed, scroll differential speed, and polymer flow rate are displayed. The system also incorporates a shaftless screw conveyor which takes the dewatered solids from the centrifuge to a bin or truck. The conveyor can also be configured for multiple discharge points, for even distribution of the solids in the dewatered solids container.

Piped and wired, from feed pump to cake transfer, the system is pre-engineered and ready for use, with minimal on-site installation requirements.

The skid mounted Centrapacs appealed to Regional Utilities for another reason. Due to the high water table, the reactor tanks of all three treatment plants are built on the ground. So, the utility was able to easily hook up the centrifuges.

Upgrade issues
During the Point Washington upgrade, the utility was reaching permit limitations at its Sandestin plant and could no longer keep up. To help Regional Utilities respond quickly to that growing problem, Siemens provided a skid that was already in-house and that could be used for a quick delivery. Within six months of placing the Point Washington order, the centrifuge was adapted, installed and functioning at Sandestin. After initial set up, the centrifuge automatically adjusts to achieve maximum cake solids.

After nearly one year of operation, the Centrapac system operates 3-4 days a week for 8-10 hours at a time. The sludge is fed between 65 to 75 gpm and it is possible to achieve 18% dry solids. A second centrifuge has begun operating at the Point Washington plant and a third one is on order for Seacrest.

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