For the test the screened slurry dropped into a truck which delivered it to the mixing station. Photo Courtesy Rutgers CAIT PTM research team. All rights reserved.
In August 2015 Dr. Ali Maher and a team of engineers and soil scientists in the New York City area announced that their field test of the pneumatic flow tube mixing system (PFTM) for combining dredged material with a small amount of Portland cement had been a success.
The system has been used for large scale projects in Japan and Dr. Maher wanted to ascertain whether it would be effective on the fine soft material dredged from the Port of New York and New Jersey and surrounding area.
Accordingly he and his team set up a small demonstration system at the Clean Earth Inc. dredged material processing site in Kearny New Jersey. Clean Earth provided 4500 cubic yards of fine silt dredged from the Arthur Kill and during the test the team ran most of it through the PFTM. Expected contaminants in the material were polycyclic aromatic hydrocarbons metals and pesticides.
After 28 days of curing the mixture had gained sufficient weight for use as geotechnical fill material demonstrating that the PFTM is a viable system for processing the soft material dredged from the port.
Schematic of the plugs of sediment and compressed air moving through the processing tube. Turbulence created by the movement through the pipe thoroughly mixes the sediment with the cement by the time it reaches the placement area. The air plugs reduce friction in the pipe reducing the air pressure necessary to move the material through the pipe. Coastal Development Institute of Technology 2008.
The two-year project was funded by the New Jersey Department of Transportation (NJDOT) Office of Maritime Resources. It started in February 2015 and will continue through January 2017. In the second phase the material is being analyzed to determine the strength of the stabilized material and if contaminants leach over time as the material continues to cure.
Maher is the director of the Center for Advanced Infrastructure and Transportation (CAIT) at Rutgers University and also director of the CAIT Soil and Sediment Management Laboratory. With him for the announcement were his team of researchers from CAIT and representatives of Clean Earth Inc. Masaki Kitazume Ph.D. of the Tokyo Institute of Technology and JAFEC USA Inc. the U.S. subsidiary of Japan Foundation Engineering Company Ltd.
Speaking to the group gathered at the test site in August 2015 Maher said “This is a rapid ‘one-stop’ process for environmentally stabilizing transporting and placing reclaimed contaminated dredged materials soft soils and mud for a wide range of structural and nonstructural applications.”
The dredged material enters the mixing chamber a reinforced tube at the beginning of the delivery tube where the compressed air is introduced into the flow. Photo courtesy Rutgers CAIT PtM research team. All rights reserved.
Dr. Robert Miskewitz associate research professor with Rutgers Department of Environmental Sciences and a CAIT-affiliated researcher described the system which consists of a long steel tube up to one meter in diameter with the larger size giving higher production rates. At the entrance is a reinforced length of tube into which the dredged material is pumped after passing through a grizzly to remove debris. Cement is injected through ports in the entrance tube and a compressor injects short high pressure pulses of air into the material via an automated valve creating a stream of alternating plugs of dredged material and compressed air which move down the tube at a high velocity. Turbulence created by friction with the sides of the tube thoroughly mixes the cement with the dredged material. At the end of the tube a fitting directs the sediment plug downward dissipating the energy behind it.
“Perhaps the greatest benefit is the large reduction in material transport and handling costs” said Miskewitz adding that the PFTM produces environmentally effective stable fill – processed and ready to place.
Though the test was land-based the system can be mobilized as floating plant with a dredge pumping directly into the mixing system.
A baffle at the end of the pipe directs the stabilized material downward. It can be applied directly to the brownfield or other project location and it hardens to a stabilized surface within weeks. Photo Courtesy Rutgers CAIT PTM research team. All rights reserved.
Maher is impressed with the cleanliness and small footprint of the system. From the dredge or scow to the end of the process workers do not come in contact with the material or contaminants. The tube can be arranged around buildings and equipment if necessary and a length of one km is possible with one booster pump. There is no machinery involved except for the pump feeding the PFTM and excavators for loading and stockpiling the material.
Every year 5 million cubic yards of material is dredged from New York Harbor and 1.2 million cubic yards of that is contaminated Maher said. Beginning in the late 1990s processors such as Clean Earth began operating facilities to mix dredged material with Portland cement which was found to immobilize the major contaminants in silty particles and to solidify the material as it cured.
Maher and his team continue to analyze new technologies for treating and handling dredged sediment. Along with other experts in sediment handling and treatment regulatory bodies and others in the environmental and construction industries they analyze high capacity processing technology for annual maintenance dredged material anticipating hundreds of thousands more cubic yards of contaminated material from Superfund cleanup projects expected to start soon including the Gowanus Canal in Brooklyn the Passaic River in New Jersey Newtown Creek in Queens and others as well as new work material from the channel deepening projects.
Eric Stern is Principal of Environmental Adaptive Strategies LLC a strategic consultancy focusing on integrated sediment and waste management who has been involved in sediment challenges since 1986 working for the USACE the U.S. EPA Battelle Memorial Institute and the private and academic sectors. He is working with the CAIT team to further the establishment of a regional sediment management center serving the New York/New Jersey area and nearby states such as Connecticut and Massachusetts.
There are two significant programs that can be integrated Stern said – the need for brownfields remediation and beneficial use of dredged material. Instead of dealing with dredged material on a project by project basis it makes more sense to integrate all the material handling on a regional basis for beneficial use back-end applications.
“We have made inroads into prospective clients’ projects agencies and end users for a fully integrated program. We have the sediment technologies and are actively working on facility locations including brownfield placement sites” he said.
The PFTM could be the key that brings the facility into existence. It was used in offshore reclamation and construction of the Tokyo Haneda International Airport Runway for airport construction in Osaka Nagoya and Hong Kong and for other harbor projects throughout East Asia. Daily capacity of one system can reach 15000 cubic yards depending on the size of the pipe and the system can be engineered to produce fill for a roadway to fill behind bulkheads in a harbor as fill for the many brownfield sites in the Northeast and other construction and remediation projects.
Miskewitz explained that as of 2013 more than 13 million cubic yards of material dredged from the New York Harbor had been processed and reused in brownfields reclamation and development of condominium complexes shopping malls and recreation sites. Some examples in the area include the Susquehanna Bank Center in Camden (220000 cubic yards) mine remediation in Tamaqua Pennsylvania (550000 cubic yards) Jersey Gardens Mall (800000 cubic yards) Philadelphia Airport (1.2 million cubic yards) and the Bayonne Golf Club (5 million cubic yards).
Following the test the dredged material from the Arthur Kill dried to a stable usable product after going through the system. Test pads are still under observation as Phase 2 of the project continues but the question of whether this system would be effective on the NY/NJ dredged material was answered in the affirmative.
A technical paper describing this project entitled Utilization of Pneumatic Tube Mixing Technique for Processing and Stabilization of Contaminated Soft Sediments in the New York/New Jersey Harbor by Ali Maher Masaki Kitazume Masoud Janbaz Robert Miskewitz Scott Douglas David Yang has been submitted to the journal Marine Georesources and Geotechology.