New Approach to Treating the Soft Clay/Silt Fraction of Dreged Material

Abstract

Maintenance and capital dredging is absolutely necessary to keep shipping lanes open and harbors accessible. Since the early 1970s the ecological impact of dredging processes and disposal techniques has been studied carefully. Facing strict environmental regulations, ports worldwide are currently changing their dredged material management plans to stay economically viable. Restrictions and exclusion of traditional disposal techniques require a multifaceted approach to dispose of, recycle, decontaminate and reuse the material. For clean dredged material several strategies of beneficial use have been established successfully throughout the last decades. However, contaminated sediments are more difficult to place. Especially the productive use of the soft clay / silt fraction poses many unsolved problems because it tends to attract the pollutants. Existing technologies are often energyconsuming and expensive, treat only certain fractions of dredged material, raise issues of secondary pollution, or lack community acceptance. At Columbia University, research has been conducted on the beneficiation of dredged material from the Port of New York and New Jersey. Annually about 4.5 million cubic yards have been dredged to maintain and improve its waterways. The bulk of the dredged material is contaminated and not suitable for unrestricted use or disposal. Investigations of physical and chemical properties suggest a beneficial use as filler material in various applications. Prior treatment and detoxification is necessary. A method to prepare dredged material, and especially the fine fraction thereof, for further use was developed. Being able to engineer certain properties according to specific needs, one can obtain dredged material that functions as a valuable semiproduct or end product competing ecologically and economically with existing materials. Herein, the approach, findings and results of the search at Columbia University for beneficial use of dredged material are introduced. Beneficiation is the transformation of a waste material into a valuable resource, which requires the adaptation, modification and engineering of properties according to specific needs. 1) Department of Civil Engineering and Engineering Mechanics Columbia University, 632A S.W. Mudd Building MC 4709, 500 W 120 Street, New York, NY 10027, USA millrath@civil.columbia.edu 2) Department of Civil Engineering and Engineering Mechanics Columbia University, 610 S.W. Mudd Building MC 4709, 500 W 120 Street, New York, NY 10027, USA