Delivering an Economical Treatment Solution

June 29, 2015

When the Town of Marana, Ariz. experienced rapid growth in 2000, quick but effective system solutions to their existing wastewater treatment lagoons were sought.

The upgraded facility required meeting three basic criteria: expand capacity in the short term to 150,000 gpd; enhance biological treatment capability in order that some (or all) effluent could be re-used; be cost-effective because long-term growth would eventually require a replacement system ten times larger (or 1.5 mgd).

Thus, a proposed interim treatment system solution would bridge the gap between the original lagoons and a future large-capacity wastewater treatment facility (WWTF).

To meet these criteria, the governing Pima (Ariz.) County Wastewater Management Department procured and installed three Smith & Loveless Addigest package wastewater treatment plants with identical 50,000 gpd capacities. Multiple units were selected to meet gradual flow increases in the interim period.

Additionally, Smith & Loveless provided the county with a process guarantee and single-source responsibility and service.

Each Addigest system integrates aeration, clarification, nitrification, denitrification and sludge storage into one complete factory-built system. This means all tank sections and components were assembled in a quality-controlled facility with the designer's oversight and inspection to ensure quality.

Ready for operation

The complete outer tank structure incorporates exclusive V-Crimp design, which provides additional rigidity and economy in manufacturing while minimizing weight. The entire shell is finished with patented Versapox coating to strongly protect against abrasion and corrosion. The systems arrived to the job site ready for simple installation and connection.

Nearly four years later, the county sought ways to quickly add limited capacity for water reclamation from an expanding subdivision. Because of the high effluent nutrient performance achieved within the three existing systems, they determined that the Addigest plants could each handle up to 15,000 gpd additional capacity. This brought the combined maximum capacity of the Marana WWTF to nearly 200,000 gpd, but another 50,000 gpd capacity was still desired to meet near-term growth.

The county evaluated several options, including retrofitting hybrid fixed-film/suspended growth process, installing an integral membrane process similar to one employed elsewhere in the county and new equipment and retrofit options provided by Smith & Loveless. The hybrid retrofit option was rejected because it was not permitted by the Arizona Dept. of Environmental Quality (ADEQ) BADCT program, and the membrane option was too costly.

Ultimately, a fourth Addigest system was selected because it met the budget, county approval and would meet the time requirements for installation.

Because of the established Smith & Loveless designs, the county did not have to retain outside consulting engineering services. All contract documents, designs, specifications, drawings, permitting and construction management was handled internally by county staff. The on-site installation work only required 12 working days, and the project incurred no change orders or overruns. In fact, the system was delivered ahead of schedule and was operational well before the contractual date in July 2005. It was a successful, no-hassles project that satisfied all of the needs of the county.

About the Author

Mike Microbi

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