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SPECIAL PUBLICATION SJ2008-SP11 - page 22 / 48





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Literature Review & Summary Report Design Basis Memorandum St. Johns River Water Management District Contract # SK940AA

BCI Project No. 19-15089 September 2007 Page 14

2.4 Mechanical

2.4.1 Equipment Type- Filter Press

Sludge is pumped into the filter press (Figure 9) via a feed connection. As multiple chambers fill with sludge, liquid passes through a cloth medium, across a drain field, through drain ports and exits through the corner of each plate. As solids build in the press, a pressure differential develops between the feed and the filtrate discharge headers. The pressure differential across the media causes the filtration process to occur. Solids build in each chamber until full and the path for liquid to flow out of the chamber is obstructed. At that point, feed is suspended and the filter plates are shifted to drop the solids from each chamber formed by adjacent plates/cloths. The filter cake (solids) is dropped onto a conveyor beneath the filter plates and is transferred to an appropriate disposal means.

Typical batch filtration rates are 150 to 350 gallons per minute of a pre-thickened sludge (10 – 15 %) with cycle times averaging 1 to 3 hours, with cake solids reaching 30 – 40 % by weight.

Figure 9 Filter Press

2.4.2 Equipment Type- Belt Filter Press

Flocculated sludge is pumped onto the gravity drain section of the belt press (Figure 10) where it is slowly rolled and spread across the belt by a series of “rakes” and “plows”. This causes the flocculated sludge to release most of its liquid, which is then gravity drained through the cloth and into a liquid drain pan. The sludge is then compressed between porous belt cloths as it passes through a series of rollers that steadily decrease in diameter. The net affect is a steady increase in pressure applied to the sludge in order to “squeeze” water out of the

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