Award-Winning Features
Technical Value

First Immersed Membrane Pilot Study in New York State: For decades, membrane systems were typically pressurized, using pumps to push water through their pores, and furnished with housings containing membrane fibers. However, more recently developed immersed membrane systems operate at about 80% lower pressures and use pumps downstream of the membranes, creating a vacuum to pull water through membrane pores. Due to their lower operating pressures, immersed membrane systems are placed in open tanks and incur lower capital and operational costs for larger-capacity systems.

The Rye Lake Pilot Testing Study, conducted in 2000, represented the first piloting of immersed membranes in New York State. WJWW and its consultant, Hazen and Sawyer, P.C., worked closely with NYSDOH to advance this new technology, and develop a pilot-testing protocol. These pilot tests set a precedent within the regulatory environment, based on NYSDOH’s endorsement of the process design criteria.

Largest Immersed Membrane Water Facility in the Northeast: When constructed, this 20-mgd plant will be the largest immersed membrane system in the Northeast, where surface waters have wide seasonal temperature variations. Since colder water is typically more difficult to treat than warmer waters, this facility will pave the way for other utilities with similar water quality and seasonal temperature differences to consider immersed membrane systems. In implementing this project, concerns have been addressed as to membrane plant capacity limits, affording opportunities for even larger facilities to be implemented in the future.

Innovative Application of Technology

Direct Comparison of Two Full-Scale Immersed Membrane Systems: Since the membrane pilot study was conducted, membrane manufacturers have made significant advances affecting space requirements, effectiveness, and proven performance of their systems in treating drinking water. The manufacturer (Zenon Environmental), has since developed a new system targeted for water supplies that are relatively “clean” (low in suspended solids and dissolved organic materials), such as Rye Lake. The new system’s advantages include more compact construction and lower capital and operating costs.

The latest consent order schedule did not allow WJWW time to pilot test the new membrane system or any other products available through other manufacturers. Obtaining NYSDOH approval of membranes other than those tested posed a challenge. However, the facility conceptual design successfully incorporated one treatment train provided with the new membrane system, resulting in a significant cost savings for the membrane equipment. This innovative approach can benefit other water suppliers considering new or upgraded treatment – it offers full-scale performance data and design criteria for the two membrane systems treating the same source water, enabling state-of-the-art membrane equipment to be used without jeopardizing schedule.

Siphon System Reduces Operating Costs: At the Rye Lake plant, a siphon system will be integrated into the design to eliminate the large suction pumps typically associated with immersed membrane systems. The large suction pumps will be replaced with small vacuum pumps that will be used to initiate the siphon. Once the siphon is created the water will be pulled through the membrane pores. The siphon system reduces operating costs and ultimately saves energy.

Social/Economic Considerations

Protecting Public Health: The most notable social consideration is the benefit to public health associated with implementing membrane filtration. Membrane filtration provides a definitive barrier in which pathogens, including Giardia and Cryptosporidium, are removed from the water supply if present. In addition, disinfection by-products (DBPs) are known or suspected carcinogens that form when naturally occurring organic matter, present in all surface waters, reacts with disinfectants used in water treatment. While disinfected Rye Lake water does not currently exceed DBP regulations, provisions for removal of organic matter have been incorporated since the time of the pilot plant testing, thereby providing further protection of public health.

Waste Stream Recovery to Conserve Water and Reduce Costs: As with all filtration plants, a waste stream is generated when cleaning (“backwashing”) the filter to remove particles that clog the pores. At the Rye Lake Plant, backwash waste will be treated using inclined plate-settler thickeners to remove and concentrate particles for disposal. Treated supernatant, approximately 8% of total plant flow, will be recycled to the head of the plant.

Recycling the waste stream relieves water conservation concerns, since the total system-wide demands of NYC’s Catskill/Delaware customers can exceed the systems’ safe yield. Withdrawing water from Rye Lake for the sole purpose of cleaning membranes would have imposed additional stress on the region’s water supply and inefficiently used water that might have been available for beneficial consumption.

Since WJWW purchases all of its water and pays higher rates as per-capita consumption increases, water conservation also provides economic benefits. On-site waste-stream treatment facilities will pay for themselves in less than five years – with savings ultimately passed on to WJWW customers.