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Literature Review & Summary Report Design Basis Memorandum

BCI Project No. 19-15089 September 2007

St. Johns River Water Management District Contract # SK940AA

Page 12

that the novel electrodewatering technique is applicable to a wide range of sludges and indicated that performance might be limited for sludges with high conductivities.

Electrodewatering is considered an ‘emerging’ technology with little full-scale information available.

2.3.4 Equipment Type – Conventional Thickener

Thickeners (Figure 7) accept dilute slurry directly from the dredge, or in the event hydrocyclones are used to remove over-cut sand; sediment laden cyclone overflow may be directed to the thickener. This dilute feed is pre-treated upstream of the clarifier either in-line or in coagulation tanks, and flocculent is added to the feed line prior to the stilling well. Mixing of the flocculent occurs gently in the feed pipe and stilling well which agglomerates the fine particles, quickly forming large sediment flocs that readily settle.

The flow is directed vertically downward towards the base of the clarifier. The solids and flocs continue to settle towards the base of the clarifier forming a sludge blanket. A sludge level detector may be used to monitor the sludge blanket depth. A slowly rotating rake assembly directs the sludge into the center outlet cone. Thickened sludge typically ranges from 12 – 15 % solids and may be pumped to a disposal area for final settling and drying. The clarified water flows over a peripheral weir to a discharge point.

Thickener capacities are specific to the application ranging from small to tens of thousands of gallons per minute. Figure 7 Thickener/Clarifier

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