Figure 3. Hydrocyclone

ERDC TN-DOER-T7

October 2004

Materials loading to the presses and equipment abrasion are reduced.

Polymer costs may be reduced. Dosage of polymers added for the purpose of coagulating

fine materials is determined by the solids concentration in the slurry, and is expressed in

terms of grams polymer per gram solids. Chemical demand can be reduced by removing the

sand, which competes with the fine materials for the polymer.

Long-term storage capacity requirements may be reduced if alternative uses are available for

the sand. Sand removal as a volume reduction measure and beneficial use of dredged

materials are topics extensively discussed in a number of other publications (Olin-Estes et al.

2002; Olin-Estes and Palermo 2000a, b; Olin-Estes 2000; Great Lakes Commission 2004a, b).

Figure 3. Hydrocyclone

Figure 4. Wet screen

Wet Screen. A wet screen may be used to achieve preliminary size separation of material.

Material may be fed onto the screen dry, and washed through the screen by water jets mounted

on the top of the screen (Figure 4). The screens are usually mechanically vibrated to facilitate

separation. Vibrating wet screens can be useful in breaking up agglomerated clay containing

material. Decks are wire or polymer with square or rectangular openings. The openings may

blind when presented with grasses or similar debris, thus necessitating the scalping screen.

Surge Tanks/Mixers. One of the principal challenges in incorporating a dewatering circuit as

part of a dredging process is the interface between the dredge and the dewatering circuit.

Typical dredge sizes used in large-scale maintenance dredging projects are too large to interface

well with a dewatering circuit unless significant buffering capacity and system redundancy are

incorporated in the dewatering circuit. Because of this, smaller dredges (6- or 8-in. dredges) are

typically used. The comparative cost compromise between reduced production at the dredge

versus increased capacity of the dewatering circuit, must be balanced in the cost/benefit

evaluation.