The Everfilt® M-Series: How It Works (Stormwater Treatment Emphasis)

Everfilt® M-Series Multi-Media Filter

When stormwater needs to be cleaned up before it is discharged, infiltrated, or reused, the Everfilt® M-Series Multi-Media Filtration System (MMF) takes a straightforward approach: move water through a carefully designed bed of filtration media that captures suspended solids throughout its depth.

A typical stormwater treatment flow looks like this:

Storm Runoff → Collection/Detention → Pretreatment → M-Series Filter → Treated Discharge or Reuse

What Happens Inside the M-Series?

Inside each M-Series pressure vessel is a layered bed of granular filtration media. Depending on the application and configuration, this typically includes:

• Anthracite: a relatively coarse, lightweight media at the top of the bed

• Silica Sand: provides finer filtration below the anthracite

• Garnet: a denser, finer media that captures smaller particles

• Graded Gravel: supports the media layers and helps distribute water through the underdrain

Together, these layers create what we call progressive depth filtration. Instead of forcing all the solids to collect on one surface, the M-Series uses the full depth of the media bed to capture particles. Larger suspended particles are captured near the top of the bed, while smaller particles travel farther into the media before being trapped.

Depending on the vessel and media configuration, the M-Series can be designed for approximately 5–40 micron filtration.

What Happens During a Storm?

Imagine a storm moving through an industrial site, commercial property, or other developed area. Runoff may carry sediment, fine silt, and other suspended solids into the stormwater system.

Here's what happens when that water reaches the M-Series:

1. Runoff Enters Under Pressure

Stormwater enters the M-Series pressure vessel and is directed into the multi-media filtration bed.

2. Water Moves Downward Through the Media

The water travels downward through the layered media bed, passing through progressively finer filtration layers.

3. Larger Particles Are Captured First

Larger suspended solids are trapped relatively high in the media bed.

4. Smaller Particles Move Deeper

Finer suspended solids continue farther into the bed, where they are captured by the finer media.

5. Filtered Water Reaches the Underdrain

After passing through the media, the treated water reaches our 304 stainless-steel wedge-wire underdrain.

6. Treated Water Exits the Vessel

The filtered water then leaves the M-Series and can be directed toward its intended destination, whether that's discharge, infiltration, reuse, or another downstream treatment process.

Why does this matter?

The M-Series isn't simply putting a screen in the path of stormwater and hoping it catches everything.

We're using the depth of the media bed to capture solids throughout the filter.

That gives the M-Series a fundamentally different filtration mechanism than a simple screen or surface-loading cartridge filter.

What Happens as the Storm Continues?

Every filter eventually collects what it was designed to remove. As the M-Series captures more suspended solids, those solids accumulate within the media bed. As the bed loads with solids, resistance to flow increases. The result is an increase in differential pressure, or head loss, across the vessel.

That's an important part of how the M-Series operates. When the filter reaches its backwash condition, we reverse the flow and clean the media.

The Backwash Cycle

During normal filtration, water flows approximately like this:

Influent ↓ → Multi-Media Bed → Underdrain → Effluent

During backwash, the direction is reversed:

Backwash Water ↑ → Underdrain → Media Bed → Waste/Drain

The upward flow expands and agitates the media bed. This loosens the accumulated solids and carries them out of the filter with the backwash water. The result?

The media is cleaned, and the filter is ready to return to service.

The M-Series uses an automatic backwash system, including automatic valves and controls for backwash and rinse cycles.

A Smarter Use of Water

Depending on the M-Series configuration, we can also use filtered water from other vessels in the system to backwash an individual vessel. This multi-vessel approach can reduce the need for a completely separate backwash-water source and allows the system to make efficient use of treated water already available within the process.

More Than Just Suspended Solids, With the Right Media

Stormwater can contain a wide range of pollutants. Depending on the site, that may include:

• Suspended solids

• Sediment

• Hydrocarbons

• Heavy metals

• And other pollutants

The M-Series can be configured to address different treatment objectives, but there's an important distinction:

The standard multi-media bed isn't automatically a heavy-metal or hydrocarbon treatment system simply because those contaminants are found in the stormwater.

The media package needs to be selected based on what you're trying to remove and what level of treatment you need.

A conventional anthracite, sand, and garnet configuration is primarily designed for particulate and depth filtration. If the treatment objective includes dissolved metals, hydrocarbons, nutrients, or other dissolved constituents, the system may require specialty media and/or additional upstream or downstream treatment.

That's why we don't take a one-size-fits-all approach. At Everfilt®, we can customize the media package around the application and its specific treatment objectives.

The M-Series is built around a simple principle: give stormwater a deep, engineered filtration path instead of relying on a single surface to catch everything. Water moves through multiple media layers. Larger particles are captured higher in the bed, finer particles are captured deeper down, and the filtered water exits through a durable stainless-steel underdrain.

As solids accumulate, the system recognizes the increasing pressure loss and initiates a backwash cycle to clean the media and restore filtration capacity. It's depth filtration, automated cleaning, and application-specific media selection, all working together to turn challenging stormwater into a more manageable treatment process.