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Large-Diameter Reverse Facility Redefines Reuse

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. BY KEVIN ALEXANDER, ART NUNEZ, BINGA TALABI, DAVE FABER, AND GERRY FILTEAU

N THE EARLY 1990s, Scottsdale, Ariz., ■■ tertiary with cloth-media filtrate production capacity to increase from managers and planners examined filters. 16 mgd to 23.6 mgd within the existing future growth and water needs. ■■ for primary and resid- process building. The RO system capacity They envisioned a ual disinfection. increased from 13.8 mgd to 20 mgd of per- Imanagement facility that would reclaim ■■ MF and RO followed by lime meate production using a large-diameter the city’s , allow for aquifer stabilization. RO system to save space. Additionally, UV storage and recovery, and augment the Product water from the plant has been treatment was added to the building that city’s limited and surface recharged to the local aquifer, achieving a housed the expanded RO system. water sources. The facility—the Water higher quality than required by state per- The Scottsdale Water Campus pio- Campus—was strategically designed mitting authorities. neered the use of the latest RO technol- to allow the city to reclaim water that Historically, area golf courses received ogy. The facility is a great place to see previously had little chance of being tertiary treated , but rising salin- the history of RO technology and how reused as it was discharged to another ity in the caused turf all of the technology is still successfully regional plant. management problems and prompted operated. The Scottsdale Water Campus golf course managers to ask the city to A unique aspect of the recent expan- Advanced Facility was improve the water’s quality. sion project is the use of large-diameter one of the first water treatment plants That prompted the city to embark upon RO technology. At the time, the large- to use (MF) and reverse the most recent expansion. The city also diameter RO market had set- osmosis (RO) for treating wastewater to addressed contaminant removal, includ- tled on two membrane sizes—16-in. and standards. Since begin- ing N-nitrosodimethylamine and other 18-in. diameter. Therefore, during design, ning operation in 1999, the facility has unregulated compounds, using a combi- two complete RO train designs were reclaimed more than 19 bil gal of waste- nation of ozonation, chloramination, and developed for competitive bidding. The water for aquifer recharge and golf course (UV) technology. large-diameter RO trains incorporated irrigation. During the latest expansion (2009– additional design features that weren’t The plant was designed to operate 2012), the original primary disinfection used in the original system because of during the winter to treat wastewater for system using gas and aqueous size and system constraints. injection into the local groundwater aqui- ammonia was replaced with an sys- The design represented one of the first fer. The treatment process originally con- tem. The residual chlorine was converted large-diameter RO systems installed in the sisted of to a new on-site chlorine-generation United States as as the first custom ■■ a conventional nitrification and denitri- system. The MF system was replaced RO installation, allowing for competitive fication activated process. with newer technology that allowed the bidding of 16- and 18-in. RO elements.

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Kevin Alexander is with Hazen and Sawyer (www.hazenandsawyer.com), San Diego. Art Nunez and Binga Talabi are with the city of Scottsdale (www.scottsdaleaz.gov), Scottsdale, Ariz. Dave Faber is with H20 Innovation (www.h2oinnovation.com), San Diego. Gerry Filteau is with Separation Processes (www.spi-engineering.com), Carlsbad, Calif.

vessel dimensions, particularly -to- port dimensions for side-ported vessels, reflect marketplace maturity for 8-in. diameter pressure vessels. This wasn’t the case for the large-diameter vessels. The 18-in. vessels use five 61-in. elements, and the 16-in. vessels use seven 40-in. ele- ments. Even among 16-in. diameter ves- sels, there were significant differences in port-to-port dimensions and overall lengths. During design, information from various vessel manufacturers was evalu- The Scottsdale Water Campus ated to allow designers to require port-to- implemented one of the first large- port dimensions to be a fixed value that diameter RO systems installed in could be verified during construction. the United States as well as the Designed piping layouts were flexible to first custom RO installation. allow the contractor to verify final instal- lation dimensions based on port-to-port dimensions. This proved valuable during The system’s design and startup proved crane or forklift to be used and minimiz- installation, as the manufacturer’s dimen- the technology requires focused attention ing floor space requirements around the sions didn’t match their own published on many design aspects that weren’t nec- units. design information. essary for the smaller-diameter RO tech- RO Trains. Existing and new RO train The original RO train pressure vessels nology originally installed. design included goals for were designed to accommodate cellulose low , sodium, and acetate in the 1990s, because DESIGN CONSIDERATIONS chloride, with an overall RO system water new polyamide membrane elements had Membrane Elements. The large-diameter recovery goal of 85 percent. As proven little operating experience. Therefore, RO membrane elements provided 4–5 times by the length of time in operation, water pressure vessels for those RO trains allow the surface area of a standard 8-in. diam- quality and recovery are easy to achieve for 450-psig-rated vessels. After startup of eter element. One significant membrane with standard, brackish RO elements. the original system with polyamide mem- element feature is weight, an important Scottsdale’s actual operating experience branes, it was clear the operating pres- consideration in RO unit maintenance. illustrates that the limiting constituent sure wouldn’t require the 450 psi design. Standard 8-in. diameter, 40-in. long ele- for recovery is calcium phosphate scale, During operation, the maximum pressure ments generally weigh less than 50 lb which is controlled by adding sulfuric has been 125–260 psi. Therefore, a maxi- each, even wet. This means one person acid to a feed pH of 6.5. mum 300-psig rating was adequate for the can safely unload wet elements, and a The existing 8-in. RO trains are con- latest RO system. minimum number of people is needed to figured in a 24:10:5 array of three stages RO Unit Access. The existing 8-in. RO change a complete RO unit. with six-element pressure vessels. The trains use a six-vessel tall-rack design, Large-diameter elements can’t be new 16-in. RO trains were designed in a which allows membranes to be loaded loaded or unloaded by hand because of 13:7 two-stage configuration with seven- and unloaded from floor level without their weight but require special handling element pressure vessels. The size of the platforms or lifting equipment. The 8-in. equipment—scissor lifts, loading tables new RO units was limited to the foot- diameter elements, vessel end caps, and with roller-wheel guides, and ropes and print width of the existing 8-in. RO units. thrust cones are light enough to be han- pulleys—which one would think would Ultimately, this determined the size and dled manually. Membranes are unloaded add considerable time to the loading and capacity of the new large-diameter RO on one end and loaded at the other by unloading process. However, the equip- units. pushing the elements through in one ment actually reduced loading time. The RO Pressure Vessel Design. RO pressure direction. Relatively little clearance space facility’s design ensured membranes vessel design considerations included is required on the feed end where mem- could be loaded and unloaded from one port-to-port dimension coordination and branes are pushed through or into the

PHOTOGRAPH: SEPARATION PROCESSES PHOTOGRAPH: SEPARATION end of the RO trains, allowing a bridge pressure rating. Standardized pressure vessel.

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Scottsdale Process Diagram The facility’s recent expansion addressed contaminant removal using a combination of ozonation, chloramination, and UV technology.

MF system Tertiary water reclamation plant MF clean Compressed Ozone air disinfection RO system To wash-water Reservoir B equalization basin

Automatic Filtrate strainer MF tank Sulfuric Anti- Chloramine acid scalant To water reclamation Advanced water treatment bypass plant

RO Lime UV RO ush addition

To injection Cartridge RO clean lter in place Product water Decarbonator station To RO waste sump Concentrate to sewer

In contrast, the new, longer 16-in. RO However, height was limited by the clear- dealing with a more significant volume of trains (seven elements rather than six- ance of the existing bridge-crane support water wouldn’t be practical. A tee with a element vessels) require more floor space. structure, which was just less than 12 ft. reducing bushing and ¾-in. full-port ball To improve access, the new trains were RO Conductivity Profile Access. The valve was added to each permeate con- designed with traffic-rated grating to existing RO units have a small sample cock nection to facilitate conductivity profiling. allow lifting devices and for the elements at the permeate end of each vessel. The In addition, permeate manifolds must be to be pushed and pulled from one end of units’ low height allows all valves to be removed for membrane replacement. the RO train. This minimized access at the accessible from floor level. U-tube connec- RO Cleaning Considerations. A signif- feed end and allowed designers to match tions have union fittings to accommodate icant difference between existing and the pipe trenches of the 8- and 16-in. RO easy removal and conductivity profiles. new RO trains was the use of automated units. For tall, large-diameter units, how- cleaning valves on the new large-diameter RO Element Lifting. It’s impossible for ever, an operator can’t access the per- trains. Electrically operated valves were one or more persons to safely handle the meate from floor level. Therefore, used to isolate stage-2 vessels from stage-1 larger-diameter RO elements without spe- the permeate sample lines were designed vessels and each row of stage-1 vessels, cial equipment. Therefore, the elements to run back to a sample panel and sink, allowing clean-in-place (CIP) operations were designed so they never had to be each with a valve. Instead of U-tube con- to be performed on smaller groups of ves- lifted by operators. Larger-diameter vessel nections, the permeate ports were mani- sels. By breaking the cleaning sequence end caps are also heavier (145 lb for the folded together. Because permeate tubes into smaller groups of large-diameter ves- 16-in. diameter vessels). Because special on large-diameter elements are 3 in. in sels, the design accommodated continued equipment was necessary, there was lit- diameter, removing the end connection use of the same cleaning pump and piping tle advantage to having a low-profile unit. to perform a conductivity profile without (continued on page 20)

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16-in. RO Performance equipment. Even with height restrictions, the large-diameter trains could provide Operating data for the new RO trains show little reduction in specific flux around 240 percent more capacity than the exist- 0.12 gfd/psi. ing RO trains in a similar footprint, even when considering the need for larger 0.20 feed and piping. This presented 0.18 Train 21 an opportunity to increase capacity to Train 22 20 mgd without requiring the building to 0.16 Train 23 be expanded. However, designers aban- 0.14 doned the idea after considering costs, 0.12 the existing RO equipment’s excellent condition, and the fact that a new elec- lux, gfd/psi 0.10

F trical and UV building would be required 0.08 regardless of RO equipment replacement. 0.06 Specic 0.04 STARTUP SUCCESS Facility expansion was completed in 0.02 the summer of 2012, and the RO trains 0.00 began operating in July 2012. Startup 2 2 2 2 2 12 12 went smoothly, with the city doing the 5/ 15/1 20/1 25/1 30/ 5/12 10/1 20/1 /1 6/ 6/ 6/ 6/ 7/ 7/ 7 7/ programming. Performance test data for the new RO trains show little reduction in spe- (continued from page 18) need for new systems and equipment. cific flux around 0.12 gfd/psi. The data network between the 8- and 16-in. systems. RO Train Layout and Process Area. The represent similar operating specific flux Automated valves were used because some large-diameter RO units provide 25–30 for 8-in. diameter membranes operating of the valves were below the trench grat- percent more treatment capacity per unit at the West Basin Municipal Water Dis- ing and others were high above floor level. of floor area compared with the 8-in. trict, Carson, Calif., and Orange County RO Flushing System. The RO system units. Using seven units similar to the Water District, Fountain Valley, Calif. The was designed with an RO flush system existing 8-in. units would have required large-diameter installation significantly that allows the trains to be flushed with an additional 125 ft × 60 ft of building reduced the expansion’s footprint, pre- permeate on shutdown. The existing flush space. The large-diameter units provided serving space for future unit processes. system consisted of two 15,000-gal tanks the same increase in capacity in a space At the time of its completion, the facil- for permeate storage and pumps. Like about 70 ft x 60 ft. ity was the first installation of 16-in. large- the CIP system, the permeate flush sys- When the Scottsdale Water Campus diameter RO membranes used for water tem was sized so all existing RO trains can was built, the floor plan accommodated 14 reuse in the United States, and the facil- be flushed sequentially within about 3–4 1-mgd RO trains in its existing building. ity continues to be at the forefront of hours after emergency shutdown. Using The original plans called for another 10 advanced water reuse. one flush system to serve existing and new 1-mgd trains in an expanded building, large-diameter RO units was desirable for effectively doubling the building’s area. Authors’ Note: The authors acknowl- operational simplicity and economy. How- The layout using the large-diameter RO edge the contributions of Buddy Boysen ever, flushing the large-diameter units units saved more than 50 percent of the and Robert McCandless for their efforts to requires significantly more permeate, stor- space required for the same capacity as ensure a system with minimal operating age, and possibly two sizes of pumps. To the existing RO trains. challenges; Archer Western Contractors accommodate the limited volume, it was An interesting consideration was that for thoughtful ideas and coordination decided to flush only the second stage of early design concepts for the Advanced assistance; the CSM design team in Korea the large-diameter RO trains on emergency Water Treatment Facility expansion sought that met challenging specifications; and shutdown, allowing use of the same pump, to maximize space savings in the pro- the city of Scottsdale for its contributions pipe network, and tank volume that was cess area (eliminating the need for new during project design, construction, and available for flushing and eliminating the construction) and replacing all existing implementation.

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