Challenge

With one of the world's largest surface water supply networks, New York City delivers nearly 1.3 billion gallons per day of water to eight million city residents along with nearly a million more consumers in four upstate counties, and hundreds of thousands of commuters and tourists.

Stored in the Catskill/Delaware and Croton watersheds on either side of the Hudson River, these upstate watershed systems include 19 reservoirs and three controlled lakes with a total storage capacity of about 580 billion gallons.

With no immediately viable location for a large central filtration plant about 15 years ago, the city chose to evaluate and upgrade existing wastewater plants to safeguard wastewater discharges into the watersheds and allow for continued evaluation of centralized filtration options.

In implementing its watershed protection program, the New York City Department of Environmental Protection (DEP) needed to upgrade numerous wastewater installations in the upstate region. In the end, it opted for low-pressure membrane filtration due to its performance as a measurable, positive barrier to pathogens such as Cryptosporidium and Giardia.

Solution

Among other technologies in the comprehensive wastewater treatment plant upgrade program, DEP wound up selecting the Memcor® low-pressure membrane system from Siemens Water Technologies as a mechanism for pathogen removal from wastewater effluent. Upgraded wastewater treatment facilities typically treat up to 200,000 gallons per day, using primary sedimentation, followed by secondary clarifiers or sand filtration and then low-pressure membrane treatment.

The upgraded plants are outfitted with the low-pressure membrane systems to prevent discharge of all particles greater than 0.04 microns as well as 99.9% of Giardia lamblia cysts and various enteric viruses, without significant reductions in the plants’ treatment capacities. The final step in the upgraded treatment process is usually addition of ultraviolet disinfection downstream of membrane systems to address any remaining biological contaminants that may be present after the low-pressure filtration.

During design, installation and startup of these upgraded systems, Siemens adds value to the projects, according to Fred Ferguson, project manager at Standard Construction Corp. in Rhinebeck, N.Y., by staying involved to inform stakeholders about the technology and treatment processes. “They are an essential part of the success of the upgrade projects we’ve worked on,” Ferguson said.

Results

With nearly 100 upgrades completed constituting nearly 90% of the total flow being treated, and about two dozen more remaining before conclusion of the upgrade program, it's clear that low-pressure membranes provide a crucial component of the upgrades, protecting water resources that serve one of the largest metropolitan areas in the world.

And as the wastewater treatment plant upgrade program proceeded, it allowed DEP time to evaluate and approve construction of a large, central filtration plant to treat water from the Croton Reservoir in Bronx County, N.Y. One of the largest single construction contracts in New York's history (at nearly $2 billion), the Croton Filtration plant is slated for completion in 2012.