NO TIME TO FUDGE ON SLUDGE:
Time to tackle the sludge disposal problem head-on!

THE SYDNEY TAR PONDS
Technology

The Tar Ponds clean up (Sydney, Nova Scotia, Canada) is a massive undertaking. Acres, a leading Canadian engineering and consulting firm, had to supervise selection of subcontractors to develop new technologies both for the incineration plant and for the dredge for excavation. The Acres concept called for dredging without addition of water to the Tar Ponds and then pumping the contaminated sediments through flexible pipelines to an onshore transfer station. At the transfer station the sludge will undergo preliminary conditioning to prepare for the incineration.

The incinerator was completed during the summer of 1991 by Superburn Contractors JV to be capable of generating 10MW of electricity via steam without any release of PAH’s to the atmosphere. The ash will be reburied onsite as part of the restoration program.

The dredging requirements are among the most challenging for any environmental project to date. Not only is the material toxic to humans, but even exposure to fumes can be harmful. The material itself constitutes a significant problem as the in-situ moisture content varies from 85% to as low as 37% of dry weight. This material is actually capable of supporting a man’s weight. Dredging is complicated by an absolute need to minimize the introduction of additional water to the system. While extra water would be helpful to dredge excavation, it would increase incineration costs dramatically.

Selection
Acres issued a worldwide tender to dredge suppliers and selected Mud Cat™ (a division of Ellicott International) in Baltimore, Maryland, USA, based on an innovative dredge design proposal.

Mud Cat™ designed and delivered a special dredge which floats on the top of a shallow water layer and which moves across the pond by winching wires anchored on the sides of the pond. Mud Cat™ developed two special technologies for this application. The first utilizes a vibrating auger cutterhead to handle the thixotropic material effectively. Secondly, the dredge incorporates a positive displacement pump to deal with the high solids content required.

This high-technology dredge is the first of its kind in the world. Mud Cat™ built and assembled the dredge in a local shipyard in Sydney, Nova Scotia.

Environment Canada intends to use this project as a national showpiece for what is possible in environmental remediation. Based on their confidence in the Mud Cat™ design approach, Environmental Canada and Acres International awarded Mud Cat™ a second dredge contract with similar technology for a steel plant clean-up in another Canadian province.

Reprinted from Water & Environment