Centurion™ Monolithic Filter Underdrain

Monolithic Filter Floor

The Centurion monolithic filter underdrain delivers to utilities their demands of resiliency, reliability, and permanency with a life cycle cost that cannot be beaten.  Our robust, yet flexible, design provides an optimal solution for conventional water treatment, wastewater tertiary filtration, biologically active filtration, GAC adsorption and ion exchange, as well as denitrification.

  • Monolithic Underdrain
  • Monolithic Underdrain
  • Orthos Filter Floor
  • Filter Underdrains
  • Filter Underdrain

Top 5 Reasons to Choose Centurion™ Monolithic Filter Underdrain

Monolithic Underdrain


In 20 years and with 200 filter installations, Orthos has never had an underdrain failure. The Centurion underdrain is straight-forwardly constructed with Orthos’ GRC form panels set on piers with starter rebar floor anchors.  Reinforcing steel, tied on 6” centers and also doweled into the filter wall, is integral to an elevated concrete monolith that becomes part of the civil structure.

Air Scour Test


Nozzles installed on 6” centers provide uniform air/water distribution during backwash and repeatable, effective cleaning with no dead spaces.  Low water and energy usage are imparted by long filter runs and reduced operational costs.catastrophic forces many times that of other types of underdrains.

Water Treatment Facility


Upon construction, our monolithic, reinforced-concrete underdrain becomes part of the filter civil works, likely lasting a century.  Plastic block, folded sheet metal, or concrete block underdrain systems can make no such claim as they will likely have to be completely replaced after approximately 25 years.

Filter Strainers

Life Cycle Cost

The Centurion delivers HUGE life cycle cost benefits: At the end of a filter system’s replacement cycle, (e.g., 25 years), in contrast to ripping out brittle plastic block or corroded folded sheet metal underdrains and starting over, the ORTHOS nozzles are simply replaced, potentially savings millions of dollars.  Monolithic will win every life cycle cost analysis with a term that includes at least one replacement cycle, which it should, because utilities operate treatment plants for many, many decades.

Backwash Testing

Design Flexibility

Our filter underdrains may be any practical size, as they utilize an open plenum that allows for natural, free movement of air and water in all directions, unlike the other systems out there which have length limitations.  High-strength polypropylene nozzles with precision-manufactured cage slots are engineered to the specific filter media design and directly retain media, eliminating problematic gravel.  Specifically-located and -sized air metering hole(s) on the nozzle tailpipe accurately deliver scour air according to the specific air rate(s).  Using the design backwash rate(s), appropriate pressure drop is manufactured into nozzles to properly control backwash distribution by the underdrain, not the media.

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