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The effluent flows from the 91 st Avenue Wastewater Treatment Plant (WWTP) are a coveted and valuable water resource in the Phoenix area. The current effluent flows of 130-150 mgd are nearly fully allocated, providing cooling water to the Arizona Nuclear Power Project (ANPP) and supplying agricultural users in the Buckeye Irrigation District (BID). The Tres Rios flow regulating and overbank wetlands provide a second tier of reuse. Whilst conveying the effluent to downstream customers, the wetlands provide approximately 300 acres of rare and valuable wetland habitat. In addition, the wetlands will remove total residual chlorine naturally, and achieve advanced ammonia and total nitrogen removal. This paper provides a summary of the wetland design and discusses the challenges of operating a large scale constructed wetland. These include optimizing process control and vegetation maintenance to maintain habitat value and meet treatment objectives, balancing water requirements of the wetlands with downstream customers, controlling mosquitoes and other vectors, overcoming regulatory hurdles, and assessing the cost/benefits of the wetlands over mechanical treatment processes.

In 2007 and the first half of 2008, Glendale, Arizona experienced significant increases in wastewater flows due to population growth and the construction of several sports venues. The flow is treated at the West Area Water Reclamation Facility (WAWRF) which was approaching its capacity. Glendale undertook a master planning project to expand their infrastructure with the goal of an integrated collection, treatment, and reuse system for the near-term and buildout planning horizons. By mid-2010, WAWRF's influent flows decreased 50%, development dropped to a standstill due to the effects of the severe economic downturn, and sewer revenues dropped. The master plan objectives changed and the direction was altered to conform to the new reality. While Glendale remains committed to increasing its beneficial reuse of reclaimed water the final master plan provided the guidance for a short-term compromise due to economic conditions of today while crystallizing the vision for the future system.