Old Plant, New Technology
The city of New Brunswick, N.J., one of the state’s oldest industrialized cities with roots dating back to 1730, needed to replace the pressure filters at its 18-million-gal-per-day (mgd) surface water treatment plant. The existing treatment plant supplies an average of approximately 12.5 mgd to residents of New Brunswick, Milltown and Franklin. In October 2006, the city broke ground for a $22-million plant upgrade, and in 2008 the plant commissioned a new submerged membrane filtration system, which replaced the pressure filters.
Built in 1916 and originally consisting of two clarifiers followed by eight gravity filters, the plant was upgraded with eight pressure filters in 1935 to expand the capacity to 18 mgd. By 2002, the pressure filters had reached the end of their useful life, and the city performed a feasibility study of potential filter replacement options.
The city considered dual-media gravity filtration and membrane filtration. Gravity media filters remove pathogens via the removal of floc, in which the pathogens are encapsulated. Thus, gravity media filters do not remove pathogens directly, but depend on an important coagulation step. Membrane filtration does not rely on coagulation chemistry to remove particles, and provides up to 4-log removal of Giardia and Cryptosporidium. Membranes also offer guaranteed compliance with the Interim Enhanced Surface Water Treatment Rule.
The submerged membrane system at New Brunswick provides exceptional treated water quality and operational flexibility.
Based on an evaluation performed by the city’s engineering consultant Hatch Mott MacDonald (HMM), New Brunswick ultimately chose membrane filtration based on its superior particle and pathogen removal and ease of integration into the site. The membranes would produce effluent turbidity of less than 0.1 NTU, whereas with dual-media filtration, turbidity breakthrough could occur if there was a problem with coagulation chemistry, especially during cold water temperatures. Membrane filtration also offers ease of operation and the ability to be expanded in the future.
HMM and the city evaluated membrane filtration pilot systems from three manufacturers, and a conceptual design was prepared for each. The conceptual design was used to develop comparative capital, operating and life cycle cost estimates, as well as operational flexibility, maintenance requirements and ease of expansion.
The city ultimately chose the Memcor CS submerged membrane system for its smaller footprint, ability to handle changing feedwater conditions and relatively low maintenance requirements. Although the Memcor CS system had been only recently introduced into the U.S. market at the time of the pilot study, there were several Memcor CS plants in Australia that were treating raw water of similar or worse quality than that of New Brunswick. Since the pilot study, the Memcor CS system has been successfully installed in numerous facilities in the U.S.
Membrane installation at the New Brunswick plant began in July 2008 and the system was started up a month later. Currently the largest surface water membrane plant in New Jersey, it includes four membrane treatment trains, each with a capacity of 2.67 mgd, for a total membrane capacity of 10.7 mgd. Coupled with the existing gravity filtration systems, the submerged membrane system expanded the treatment facility to 20.7 mgd, thus allowing operators to take one of the trains offline without disrupting plant operations. The membrane system is designed for future expansion to 24 mgd, along with the potential to convert the existing gravity filters to granular activated carbon for taste and odor control.
In addition to the submerged membranes, the system as supplied included: clarified feed pumps; filtrate pumps; backwash supply pumps; clean-in-place (CIP) pumps, tank and chemical metering pumps; self-cleaning strainers; air scour blowers; compressed air system; all valves related to the membrane system; service access platform, and CIP waste transfer and neutralization pumps.
Since startup, the submerged membrane system has provided exceptional treated water quality along with operational flexibility, especially during periods of high water turbidity and iron. The open tank design allows the operator to visually inspect the performance of the system, particularly during integrity testing. What’s more, system performance has exceeded the expectations based on the previous pilot testing.
Acknowledgements: John Civardi, PE, vice president, Hatch Mott MacDonald, Millburn, N.J.; Edward O’Rourke, chief operator, City of New Brunswick, N.J.