“New plant has Fresno on its way to becoming one of the few drought-resilient cities in the Western U.S.“

– Fresno Mayor Ashley Swearengin

Orthos Liquid Systems, Inc. (Orthos), the leading manufacturer of nozzle-based filter underdrain systems in water/wastewater treatment, is helping the City of Fresno CA to turn from its reliance on groundwater pumping through the commissioning of the new $159 million Southeast Surface Water Treatment Facility (SWTF). The biggest public works project in Fresno’s history, the Southeast SWTF will enable the city to use many 10,000s of acre-feet of surface water yearly and take stress off rapidly-depleting underground water supplies.

The Southeast SWTF will initially treat 54 million gallons of water daily (MGD) from Millerton Lake and Pine Flat Reservoir when fully operational in late 2018. Within a few years, facility capacity will be increased to 80 MGD. The Southeast SWTF is a cornerstone of “Recharge Fresno,” a more than $400 million project to revamp the city’s water system, that utilizes the San Joaquin and Kings Rivers to ease dependence on underground water supplies, which have plunged more than 100 feet in recent years.

The Process

The Southeast SWTF treatment process includes pre-treatment flocculation and plate settling, ozonation, biologically active filtration, and chlorine disinfection.
Biologically active filtration uses granular activated carbon to remove organics, filterable solids, and micropollutants. Ozonation prior to filtration converts total organic carbon to biodegradable dissolved organic carbon, which microbes growing on the media may consume. Final disinfection using chlorine results in significantly less harmful byproducts due to the reduction of organics by the biologically active filters.

Eight downflow filters utilizing Orthos’ nozzle-based Centurion™ monolithic underdrains each measure 60′ x 15′ (7200 ft2 total). Filtration media of 12″ of ±0.6 mm sand and 48″ of ±1.1 mm anthracite is placed directly on the Centurion media-retaining nozzles, eliminating the need for a gravel packing layer. Combined air-water media backwash methods effectively clean the media with lower flowrates and wash water volume, reducing capital expense and energy consumption.

Why Orthos

Carollo Engineers was responsible for planning, design, and construction management of the Southeast SWTF and worked closely with Orthos Liquid Systems, Inc., regarding the biologically active filters. Nozzle-based monolithic filter underdrains were chosen for design by Carollo over block and triangular lateral types because of the following compelling benefits:

⇒ Structurally-superior concrete construction
⇒ Construction is less dependent on hard-to-control installation practices
⇒ Excellent filter and backwash distribution characteristics

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Remember Orthos’ HUGE life cycle cost benefits – At the end of the filter’s life cycle (~25 years), in contrast to a complete plastic block or folded sheet metal underdrain overhaul, nozzles are simply replaced potentially saving $Millions.

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