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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 26

sand from dredge over-cut. A hydrocyclone contains no moving parts within the unit, and requires no power consumption, other than delivery of feed slurry to the equipment.

Disadvantages:

Feed slurry to a hydrocyclone must first be screened for debris and oversize material prior to introduction. The coarse fraction underflow from a hydrocyclone typically retains a large amount of light organic solids that must be either considered in the return water. Additionally, hydrocyclones are somewhat capacity limited, thus multiple units are typically required.

Sediment laden cyclone overflow must be moved to either a disposal area or to a pre- thickening device. Pre-thickening (thickener or clarifier) will produce a pumpable solids in range of 10 – 15 %, which must then be placed in a confined disposal area. This technology must be considered a step in a more complex process and is not applicable as a stand-alone dewatering system.

4.3.3

Electrodewatering

Advantages:

A cost benefit of electrodewatering is likely greatest for to traditional pressure filtration. Electrodewatering can also

filter

presses.

Studies

have

demonstrated

that

the

novel

sludge that does not be combined with electrodewatering

respond well conventional technique is

applicable to a wide range with high conductivities.

of

sludges

but

indicated

that

performance

might

be

limited

for

sludges

Disadvantages:

Current costs for electrodewatering are higher than costs for standard belt filter presses. With continued improvements, however, costs should be comparable to belt filter presses as the process is a slight modification of the press. Increases in operating cost over conventional belt filter presses due to higher electricity use should be offset by the reduction in tipping fees associated with disposing of a drier and less voluminous product.

It should be noted that electrodewatering is considered an ‘emerging’ technology with little-to-no plant scale use or information available. As an unknown quantity, electrodewatering should be dismissed as a process step in this effort.

4.3.4

Conventional Thickener

Advantages:

Thickeners are used primarily to reduce the volume of sludge to be treated downstream, but provide good process variation mitigation as well (in the case of dredge discharge reporting directly to the thickener). Thickeners can concentrate sludges from a variety of in-plant sources and will produce concentrations ranging from 12 – 15 % solids, depending on the type of sludge.

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