Dorr-Oliver Eimco USA Inc.
The conventional thickener (clarifier) is a rotary raked vessel designed to accept dilute slurry and provide a pre-thickening step in the dewatering process. Thickened sludge typically ranges 12 – 15 % solids and may be pumped to a disposal area for final settling and drying. Thickener capacities range from small to tens of thousands of gallons per minute.
Literature Review & Summary Report Design Basis Memorandum St. Johns River Water Management District Contract # SK940AA
Table 1 Dewatering Technologies
BCI Project No. 19-15089 September 2007 Page 6
Mitchell Dryers Ltd Denton Holme, Carlisle, Cumbria CA2 5DU England
Thermal drying removes water from sludge to a significantly higher degree than all other dewatering processes. Solids reaching 90% are attainable, but the sludge is typically dewatered to a minimum of 18-20% solids before it is directed to the drying facility. Sludge is pumped into the filter press 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. Flocculated sludge is pumped onto the gravity drain section of the belt press where it is slowly rolled and spread across the belt by a series of “rakes” & “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.