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Recycled Water Supplies Nuclear Plant Wetlands Park

In the more than half a century since the 91st Avenue Wastewater Treatment Plant was constructed near the Salt River outside of Phoenix, it has grown and evolved to meet the changing needs of the burgeoning communities it serves - a far cry from the original plant built in the 1950s and handling 5 million gallons of sewage a day. Today, after its latest expansion, the plant can treat over 230 mgd, providing environmentally sound wastewater disposal and protecting the public health for more than two million customers.

Perhaps as significant, this "showcase" plant transforms wastewater from a liability into a valuable water resource for recycle and reuse - a critical element for water resource planning in the arid Southwest. Highly treated wastewater effluent is reused as cooling water for a nuclear power plant, as agricultural irrigation water, and to sustain an innovative constructed wetlands project, with possible future application to recharge the area's declining groundwater aquifer.

Growing and Changing

The 91st Avenue WWTP consists of six activated sludge sub-plants operating in parallel to treat municipal and industrial wastewaters from five cities - Glendale, Mesa, Phoenix, Scottsdale and Tempe - all members of the Sub-Regional Operating Group (SROG) formed in 1979 to co-own and operate the plant.

Numerous improvements to the plant were completed over the years. Five projects - plants 1A, 1B, 2A, 2B and 3A - were constructed from 1962 to 2001. Malcolm Pirnie, the Water Division of Arcadis, was the design engineer for the Plant 3B expansion, as well for the Nitrification-Denitrification (NdeN) project (1995 through 1997) that converted the plant's activated sludge system from a high-rate process to the NdeN process.

With this unique NdeN biological nutrient removal (BNR) process - its first known application in a large wastewater treatment plant - air is added in the first zone through fine-bubble diffusers to achieve mixing and jump-start oxygen-demanding reactions. Other modifications and operating changes improved efficiency, saving millions of dollars in capital costs, and an additional expansion added 8 mgd of new treatment capacity at one of the five plants at a cost of about a dollar per added gallon - only a fraction of the typical cost.

The Plant 3B Upgrade and Expansion Project also expanded the plant's process air capabilities and provided odor control for the plant's preliminary treatment facilities. It was constructed concurrent with a Disinfection Improvements Project that significantly renovated and expanded the chlorine disinfection system.

Also around this time, SROG conducted two significant solids treatment projects: construction of a new solids thickening facility for centrifuge thickening of primary and waste activated sludge and the multi-phase digestion project, which converted the plant's digestion process from high-rate mesophilic digestion to a multiple-step mesophilic and thermal process to achieve Class A sludge.

For the full articlke please use link below

Water World

http://www.waterworld.com/articles/print/volume-29/issue-4/editorial-features/sustainable-synergy-recycled-water-supplies-nuclear-plant-wetlan.html