Large-Diameter Reverse Osmosis Facility Redefines Water Reuse

by Kevin Alexander, Art Nunez, Binga Talabi, Dave Faber, and Gerry Filteau

A vision for the future was realized when the city of Scottsdale, Ariz., began operating the Scottsdale Water Campus in 1999 to augment the city’s water supply and reclaim water. The facility remains at the forefront of water reuse.

In the early 1990s, Scottsdale, Ariz., managers and planners examined future growth and water needs. They envisioned a water resources management facility that would reclaim the city’s sewage, allow for aquifer storage and recovery, and augment the city’s limited groundwater and surface water sources. The facility—the Water Campus—was strategically designed to allow the city to reclaim water that previously had little chance of being reused as it was discharged to another regional wastewater treatment plant.

The Scottsdale Water Campus Advanced Water Treatment Facility was one of the first water treatment plants to use microfiltration (MF) and reverse osmosis (RO) for treating wastewater to drinking water standards. Since beginning operation in 1999, the facility has reclaimed more than 19 bil gal of wastewater for aquifer recharge and golf course irrigation.

The plant was designed to operate during the winter to treat wastewater for injection into the local groundwater aquifer. The treatment process originally consisted of:
? a conventional nitrification and denitrification activated sludge process.
? tertiary filtration with cloth-media filters.
? chloramination for primary and residual disinfection.
? MF and RO followed by lime stabilization.

Product water from the plant has been recharged to the local aquifer, achieving a higher quality than required by state permitting authorities.

Historically, area golf courses received tertiary treated effluent, but rising salinity in the reclaimed water caused turf management problems and prompted golf course managers to ask the city to improve the irrigation water’s quality. That prompted the city to embark upon the most recent expansion. The city also addressed contaminant removal, including N-nitrosodimethylamine and other unregulated compounds, using a combination of ozonation, chloramination, and ultraviolet (UV) technology.

During the latest expansion (2009–2012), the original primary disinfection system using chlorine gas and aqueous ammonia was replaced with an ozone system. The residual chlorine was converted to a new on-site chlorine-generation system. The MF system was replaced with newer technology that allowed the filtrate production capacity to increase from 16 mgd to 23.6 mgd within the existing process building. The RO system capacity increased from 13.8 mgd to 20 mgd of permeate production using a large-diameter RO system to save space. Additionally, UV treatment was added to the building that housed the expanded RO system.

The Scottsdale Water Campus pioneered the use of the latest RO technology. The facility is a great place to see the history of RO technology and how all of the technology is still successfully operated.

Excerpted from Opflow Online. A PDF of the full article is available here.

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