Getting a Recharge
By K. Robert Wendel

The city of Glendale, Ariz. is planning for a thirsty future with the construction of an expanded wastewater treatment plant near the Glendale Airport.

Crews from Sundt Construction started the $31.5 million, construction manager at-risk project in January 2003. Contractors plan to finish the 6 million gallon-a-day expansion in November. When complete, this second phase features a peak processing capacity of 16 MGD, with a constant flow of 10 MGD. The project's first phase processes 4.3 MGD and depending on population growth, a third phase may be constructed.

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"Based on population projects, this should be enough, but it's going to be close to the edge," said Thomas Bolyn, senior plant operator at Glendale's West Area Water Reclamation Facility. "This second phase pretty much doubles everything."

The treatment plant takes wastewater from a 91st Avenue plant main line, treats the water and then injects the finished product into recharge basins for future use. The plant sends the remaining solids back into the mainline, taking the sludge to the 91st Avenue plant, where it is processed.

"This is sort of a weird plant," said Ben Herman, a project engineer with Phoenix-based Nabar Stanley Brown. "Regular wastewater treatment plants have a high point and low point, but this one scalps a certain amount off the line that is pretty much constant, so you don't have peaks and valleys."

To treat the water, it first goes through a series of filters to screen solid waste out. The water then passes through a grit pump and basin that removes any remaining sediment. Water then flows to aeration basins where its mixed with oxygen and then through another filtration process using anthracite filters. It's on to ultraviolet disinfection after that, and then finally, it is injected into the ground.

"If you take a look at the water going into the plant, it's gray and greenish," said Ed Martin, an engineer with Malcolm Pirnie. "When it gets through the ultraviolet disinfection system, you can actually see through the water to the bottom of the basin.
That's how clean it gets."

The finished water is not potable, but it can be used for irrigation, fountains and recharging the acquifer.

The expansion project entails a doubling or tripling of the plant's components and equipment. Four, 35-horsepower generators are getting replaced with seven, 250-horsepower generators. New concrete aeration basins, screens and filters are also planned.

One of the most challenging aspects of the project involved the shut down, connection phase and start up of the expanded plant. Crews worked 24 hours a day, seven days a week to accomplish the work.

"The plant has to have a week of preparation for the shut down and it takes two weeks to bring it back on line, so you are talking about month where you aren't processing anything," Martin said. "We actually finished 12 days ahead of schedule, which was a big achievement."