Project Type

As-Needed Engineering Services Related to Wastewater Treatment


Vallecitos Water District


San Marcos, CA

Current Status

Ongoing since 2010

Key Features

  • Biological treatment process optimization
  • Filter media design and replacement
  • Nutrient removal assessment
  • Aeration basin equipment preliminary and final design

Project Overview

The Vallecitos Water District (VWD) owns and operates the Meadowlark Water Reclamation Facility (MWRF), which can treat up to 5 MGD of wastewater to produce recycled water for local customers. Since 2010, Trussell has worked with the VWD on an assortment of projects, including operational support/optimization, filter media design and replacement, coliform evaluation, disinfection system design, secondary process optimization, nutrient removal assessment, and aeration basin equipment preliminary and final design.

In 2015, Trussell designed replacement granular media for the MWRF’s filters, developed the technical specifications, and provided construction and operations support during the media replacement. Historically, high doses of coagulant were relied upon to meet Title 22 filter effluent turbidity limits. Trussell identified that the filter media was inadequately sized for effective turbidity removal. A finer media consisting of sand and anthracite was selected that still achieved fluidization and stratification with the existing backwash rates. Upon determining the preferred media design, Trussell provided technical specifications that described the media and requirements for proper testing and installation. Trussell also performed sieve analyses on the replacement media prior to installation to ensure that it met the design specifications. Trussell provided support throughout the installation process by inspecting the underdrains, removing fines, and providing media installation procedures. The new media has reduced coagulant use by 95% and dramatically improved filter performance.

In 2017, Trussell completed an evaluation and preliminary design that assessed the viability, benefits, and cost associated with retrofitting the existing aeration basins at the MWRF with biological selectors. There are anticipated operational and treatment benefits associated with the selectors, including biological phosphorus removal and reductions in sludge bulking and chemical coagulant dosing for tertiary filtration. The anaerobic selector zones at the beginning of each aeration basin were created using non-structural baffles, and a compressed gas system provides mixing with minimal oxygen transfer.

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