Mechanical Dewatering of Navigation Sediments: Equipment, Bench-Scale Testing, and Fact Sheets

ERDC TN-DOER-T7

October 2004

Mechanical Dewatering of Navigation Sediments:

Equipment, Bench-Scale Testing, and Fact Sheets

PURPOSE: This technical note provides an overview and technical guidance for evaluating

mechanical dewatering at dredged material placement sites. This document introduces the basic

pieces of equipment that make up a dewatering circuit or train, some advantages and

disadvantages of different equipment options, the state of the practice in bench-scale testing,

discussions of performance specifications and cost, and several fact sheets on various process

technologies and their applications.

BACKGROUND: The fundamental objective of the Innovative Dredging Technology Focus

Area of the Dredging Operations and Environmental Research (DOER) Program is to identify

and catalog innovative dredging operations, processes, or equipment and techniques developed

by domestic and international dredging entities. A number of technologies developed within the

U.S. Army Corps of Engineers (USACE) are currently undergoing evaluation for potential

demonstration under the DOER Program. Among these is the mechanical dewatering of dredged

material at confined disposal facilities (CDFs).

INTRODUCTION: The solids content of a typical dredge discharge slurry ranges from roughly

100 to 200 g/l, as compared to the in situ solids content, which may range from 250 to 1800 g/l,

depending upon the grain size distribution of the in situ sediment. Conventional upland

placement of dredged material involves discharge of the slurry into a CDF, where clarification

and settling take place. Clarified water is normally returned to the originating water body. Large

areas are required for upland placement of hydraulically dredged sediments, and CDFs must be

in relatively close proximity to the shore in order to economically manage return flows. Over

time, the material placed in the CDF continues to dewater and consolidate, making room for

additional "lifts" from subsequent dredging cycles. Surface trenching and weir management are

typically the only active dewatering efforts that take place.

Mechanical dewatering uses special equipment to reduce the water content of the dredge slurry at

the time of placement. There are a number of possible motivations for considering mechanical

dewatering, including:

Remaining storage capacity in the CDF is insufficient for clarification and water

management.

Sediments are very contaminated and must be transported to a permitted landfill for disposal.

Conditioning of the material is needed to facilitate handling and transport and to reduce

transport costs.

Water content must be reduced to meet disposal or beneficial use specifications.