M-Series vs. C1-Series: Understanding Particulate Filtration & Dissolved Contaminant Removal in Stormwater

3 days ago
3 min read

The M-Series Multi-Media Filter (MMF) is primarily a particulate/depth filter, with multiple filtration medias while the C1-Series Carbon Media Vessel utilizes granular activated carbon (GAC) and is primarily an adsorption/polishing system for dissolved contaminants.

How the C1-Series Carbon Media Vessels works

A C1-Series vessel is a pressure vessel filled with a bed of granular activated carbon. Stormwater flows through the carbon bed, and contaminants are captured primarily by adsorption onto the enormous internal surface area of the carbon.

Conceptually:

Stormwater → Pretreatment → C1-Series Carbon Media Vessel → Treated Water

Inside the vessel:

Influent

↓

GAC bed

↓

304 SS Wedge-Wire Underdrain

↓

Effluent (Outlet)

The C1-Series is designed to accept GAC as well as other media such as ion-exchange resin, zeolite, and organoclay. C1-Series vessels come in 24–84 inches in diameter and configurations from roughly 10 to 3,000+ GPM, with multiple vessels able to be linked for higher flows.

What Does the GAC Actually Remove?

This is the important distinction for stormwater. GAC is particularly useful for dissolved organic contaminants, rather than simply removing suspended sediment.

Depending on the carbon selected and the contaminant, it can adsorb things such as:

Petroleum hydrocarbons
VOCs
Synthetic organic compounds
Certain PFAS
Solvents & other organic chemicals
Odor-producing organic compounds
Some pesticides & similar organic pollutants

Everfilt's GAC systems are used for VOCs, petroleum-based pollutants and organic contaminants.

So if your stormwater contains something like dissolved hydrocarbons, an M-Series filter alone may not be enough. The M-Series can remove the particulate fraction, while the C1-Series can provide a subsequent adsorptive polishing step.

Why Pretreatment is Particularly Important

This is probably the biggest design consideration if you're looking at using a C1-Series for stormwater. GAC is expensive relative to ordinary sand/media, and you don't want the carbon bed being used as a sediment filter.

For example:

Stormwater Containing:

Leaves/debris
Sand
Silt
Suspended solids
Oil droplets
Dissolved hydrocarbons

Could be Treated Approximately as:

1. Trash/debris removal

↓

2. Sedimentation / hydrodynamic separation

↓

3. M-Series multi-media filter

↓

4. C1-Series carbon media filter

↓

5. Discharge

The M-Series removes much of the suspended particulate load before the water reaches the GAC. The C1-Series then focuses on the dissolved organic fraction.

What Happens as the Carbon Becomes Exhausted?

This is another major difference from the M-Series. With the M-Series, you monitor differential pressure because solids accumulate in the media and cause headloss. You can backwash the media to remove those solids.

With GAC, the major concern is carbon exhaustion. The carbon has a finite adsorption capacity. As contaminants occupy the available adsorption sites, the carbon eventually becomes saturated.

You can think of it like:

Fresh Carbon → Contaminant Adsorption → Increasing Loading → Breakthrough → Carbon Changeout/Regeneration

Eventually contaminants begin appearing in the effluent. This is called breakthrough.

Therefore, GAC systems are often operated with monitoring and/or a predetermined carbon replacement schedule.

The C1-Series can be configured in lead/lag arrangements, where one carbon vessel is upstream of another. This is particularly useful when breakthrough control is important: the lead vessel takes most of the contaminant loading while the lag vessel provides additional protection.