What is the Poseidon Filtration System®?

Orthos nozzle-based monolithic underdrain systems have defined reliability for the past 20 years — we have never had an underdrain system failure. Poseidon extends this repetitious success by using our in-house engineering design expertise to provide complete filter systems for municipal water treatment.

With increasing water quality concerns regarding disinfection byproducts, nitrogen, phosphorus, taste, and odor, Poseidon delivers a systems approach that includes all requisite controls and components.

Municipal Water Treatment Solution


Monolithic Filter Floor

Centurion™ Nozzle-Based Monolithic Underdrains

The Centurion monolithic design is a “cast in-situ” design that becomes part of the surrounding civil structure for municipal water treatment. Unlike other filter underdrain systems that are not a permanent part of the filter structure, there is a negligible risk of degradation or structural failure that may lead to a premature filter failure and overhaul. 

Stainless Steel Underdrain

MAXIMUS™ Free-Flow Filter Underdrain

MAXIMUS™ “free-flow” filter underdrain is constructed of robust, 10-gauge stainless steel (SST).  Chemically-anchored to the filter floor using SST hardware for quick installation, the patent-pending MAXIMUS™ features a low, 6” profile that provides increased filter media depth or operational freeboard in retrofit applications. 

Wash Trough

Ortho-Wash Media Retention Troughs

Poseidon Ortho-Wash™ media-retention troughs prevent media loss using specifically-engineered and integrally-mounted baffles that deflect air and provide an adjacent quiescent volume to settle out lightweight granular activated carbon (GAC) or anthracite.

Ortho-Wash Controls

Controls include all control hardware, programming, and instrumentation to fully automate conventional granular filters used in municipal water and wastewater treatment applications.

Air Header Manifolds & Piping

Orthos’ experienced engineers deliver the proper design and selection of pipework to optimize the functionality of the Poseidon Filtration System.

U-Shaped Troughs

Fabricated from 304 or 316 stainless steel or fiberglass-reinforced plastic (FRP), Poseidon shaped backwash troughs are engineered to uniformly and efficiently remove washwater during backwashing of gravity filters.


A wide array of high-quality filter media, such as sand, GAC, anthracite, and Greensand Plus is offered by Orthos.

Pumps & Blowers

Backwash pumps and air scour blowers are designed for project-specific flow rate requirements. 


Required valve types and sizes are selected by Orthos’ engineers.

Components & Applications

Poseidon Filter Systems Components

How It Works


Potable water

Granular media downflow filters remain the “work horses” of water treatment.  For facilities 2 MGD and above, Poseidon Filtration Systems® in concrete tankage will structurally provide a century of service.  Sand and anthracite dual-media filters are common, with granular activated carbon and greensand also utilized to remove additional contaminants.

Biologically Active

Without pre-chlorination, a granular media (commonly activated carbon over sand) filter may be used to also support natural biological activity in order to remove biodegradable organic matter, ammonium, and perchlorate, and other substances from drinking water.  The underdrain nozzle screens of the Poseidon Filtration Systems® directly retain the filter media, making a gravel packing layer unnecessary, while their slot size is maximized to negate biological fouling.

Wastewater Treatment System

Following wastewater secondary clarification, granular media filters provide excellent supplemental removal of suspended solids, including particulate BOD, chemically-precipitated phosphorous, and other solid-form contaminants above 5-10 microns. For facilities 15 MGD and above, Poseidon Filtration Systems® provide reduced maintenance and enhanced mechanical reliability over other wastewater filtration technology, to include disk filters, upflow filters, and compressed media filters.


In post-filtration applications, granular activated carbon (GAC) or ion exchange (IX) resin is used to adsorb or chemically remove natural organic compounds, synthetic chemicals, unpleasant taste, and odor in order to highly purify water.  Treatment of perfluorinated compounds (PFCs), pharmaceuticals, and personal care products may require multiple treatment technologies, to include adsorption or IX, for acceptable removal efficiencies.  Poseidon Filtration Systems® are the economic choice for flow rates that cannot be properly addressed by GAC or IX pressure vessels.

Wastewater Treatment

Excess nitrogen in wastewater effluent may lead to eutrophication (algae growth) in receiving waters.  The Orthos Denitrifying Deep Bed Filter (DDBF™), a wastewater treatment process of the Poseidon Filtration System®, provides fixed‑film biological denitrification in a downflow filter configuration.  With proper chemical treatment, the DDBF™ is capable of meeting stringent effluent limits of total nitrogen as low as 3 mg/l, total suspended solids to 2 mg/L, and total phosphorus to 0.3 mg/L or less.

Reverse Osmosis

Membrane systems (e.g., ultra- and nano-filtration, reverse osmosis) have highest flux rates when pretreatment provides consistent feedwater with solids of low particle size (e.g., less than 5 micron).  Because granular media filters may reliably produce membrane feedwater with fewer, relatively-large particles per volume than other filtration technology, choose Poseidon Filtration Systems® to optimize treatment efficiency and reduce O&M expense.