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Gravity filters
  Four gravity filters are used as the last treatment stage before the treated water is post-chlorinated and pumped to the distribution system or to the reservoirs for storage. The sedimentation, flocculation, and clarification stages that are completed at the front end of the treatment plant to settle the suspended solids or turbidity from the raw water, prepare the water for filtration. The gravity filters remove small particles from the Clarifier effluent water that are too light to settle in the Clarifier. Typically the top of filter turbidity averages 1.0 ntu. The filter effluent turbidity annual average is 0.09 ntu. The Filter backwash water waste pipe outfall is located downstream of the raw water intakes.
Pressure filters
Pressure Filters, with the exception of the Rotary Drum Pressure Filter, are semi-continuous type machines that enter a wash and cake discharge mode at the end of the filtration cycle. The filtration cycle may extend from 5-10 minutes on cake filtration applications and up to 8 or even more hours for the polishing of liquids. Since the operation is in batches, that are usually fed from and discharged to a continuous process, a surge tank is required upstream the filter and batch collection of cake downstream the filter. The collection of filtrate depends on the operating mode of the filter which can be constant flow rate, constant pressure or both with pressure rising and flow rate reducing as for a centrifugal pump.