Phosphorus removal in a catch basin takes a media built for the dissolved fraction. See how Smart Sponge® HM sits in an Ultra Urban® Filter and where the approach stops.
Phosphorus removal in a catch basin works by placing a phosphorus-targeting media, such as Smart Sponge® HM, inside the existing inlet so dissolved phosphorus binds to it as runoff passes through. A trash screen or sediment insert cannot do this, because it only holds the particulate share. The media is the part that treats; the insert is only the format that holds it.
Why Does a Standard Insert Miss Dissolved Phosphorus?
Phosphorus in runoff travels in two forms. Particulate phosphorus rides on sediment and is captured when solids settle or are screened out. Dissolved phosphorus, mostly orthophosphate, is already in the water, so it slides past a sump or screen with the rest of the flow. That is why a basin can look clean at inspection, with sediment removed on schedule, and an outfall can still report a phosphorus benchmark exceedance under an NPDES or MSGP permit, or miss a nutrient TMDL allocation for an MS4.
Sediment control is still worth doing. It simply answers a different question. Our guide to choosing a catch basin insert filter covers the format side; this page covers what has to go inside it when the target is the dissolved fraction.
What Does Smart Sponge® HM Treat Besides Phosphorus?
Smart Sponge® HM is formulated to target dissolved metals, including lead, zinc, copper, arsenic and selenium, along with phosphorus. That pairing suits sites where both show up in the same runoff, such as metal recycling yards, fabrication shops and junkyard facilities, where water crosses scrap and exposed metal stock. One media can address both benchmarks without a second treatment train. Our page on metal recycling facility stormwater treatment covers the metals side in more depth.
If the same runoff carries bacteria, Smart Sponge® Plus, an antimicrobial media for E. coli and coliform, can be combined with HM in one system. Standard Smart Sponge® is a different media: it is built for hydrocarbons and oil sheen, not nutrients. Abtech's principle is that the media follows the contaminant and the format follows the site, so the contaminant mix is settled first.
Which Component Handles Which Part of the Runoff?
| Runoff component | What captures it | Where it sits |
|---|---|---|
| Trash and debris | Screen or basket in the insert | Format |
| Particulate phosphorus on sediment | Settling and high-porosity solids capture | Format and sump |
| Dissolved phosphorus (orthophosphate) | Smart Sponge® HM media | Media inside the insert |
| Dissolved metals such as zinc and copper | Smart Sponge® HM media | Media inside the insert |
| Bacteria | Smart Sponge® Plus media | Media combined in the same system |
| Hydrocarbons and oil sheen | Standard Smart Sponge® media | Media combined in the same system |
How Does the Ultra Urban® Filter Fit an Existing Basin?
The Ultra Urban® Filter is Abtech's catch basin insert, custom-fabricated to fit the shape, size and design of the basin it goes into. Municipal drainage networks and industrial yards rarely have uniform inlets, so a fitted insert matters for retrofits. It is a passive, high-flow format, so it retrofits existing infrastructure without excavation, pumps or power. Stainless steel Ultra Urban® Filter inserts carry a 20-year warranty; that warranty applies to the stainless steel inserts only and does not describe media performance.
Treat that as a product characteristic, not a promise about your basin: the actual result depends on your flow, your concentrations and the basin geometry. Our related posts on how the Ultra Urban® Filter and Smart Sponge® media work together and on when a catch basin retrofit makes sense go further.
When Is the Catch Basin the Wrong Place?
An insert intercepts runoff where it enters the storm drain, which is useful, but it is not always the right spot. Larger or more variable catchments may suit bulk Smart Sponge® media loaded into existing vessels, tanks or vaults, or Abtech's Smart Skid. Do not read Smart Skid as passive: it is installed with pumps, pressure and flow controls. Wastewater operators working toward a phosphorus discharge limit are also usually looking at vessels or skids rather than an inlet insert.
Media capacity is also finite. The LID SWM Planning and Design Guide on filter media additives for phosphorus removal notes that the two main mechanisms, chemical precipitation and adsorption, are ultimately finite. Plan for media replacement as part of maintenance, and see what sets catch basin insert cleaning schedules for how that interval gets decided.
What Should You Confirm Before Specifying Phosphorus Media?
Abtech starts every project with a site assessment covering contaminant concentrations, typical and peak flows, space, effluent targets and access for maintenance, and some projects add lab column or pilot testing on the customer's own water. For the pre-installation checks specific to the inlet itself, read what to check before adding a filter insert. For permit and regulatory background, the US EPA's NSCEP document library record is an authority source to consult alongside your own regulator.
FAQ
Does a catch basin insert remove all the phosphorus in stormwater?
No insert can promise that. Smart Sponge® HM is designed to bind dissolved phosphorus passing through it, but Abtech does not publish a guaranteed removal rate or compliance outcome for a given site. Results depend on flow, concentration and basin configuration.
Can one system treat phosphorus, metals and bacteria together?
Yes, in principle. Smart Sponge® media types can be combined in one system, so HM for phosphorus and dissolved metals can be paired with Smart Sponge® Plus for bacteria when the runoff carries both.
Does trash capture also treat dissolved phosphorus?
No. Trash and TSS capture address particulate material. Dissolved phosphorus needs a media formulated for it, such as Smart Sponge® HM, in the same or a paired device.
Is every Abtech format passive?
No. The Ultra Urban® Filter runs without pumps or power, but Smart Skid systems use pumps, pressure and flow controls. Match the format to the flow and space at the site.
How do I know sediment control alone is not enough?
A phosphorus exceedance that persists after sediment and trash capture are working points to the dissolved fraction. Comparing your sample data to the permit target, as in a site assessment, shows whether a phosphorus-targeting media is the next step, and our guide to sorptive media compared with sand filters and bioretention helps weigh the alternatives.
Related resources
- What Is a Catch Basin Insert Filter, and How Do You Choose the Right One?
- Metal Recycling Facility Stormwater Treatment: Zinc, Copper, and Lead Reduction at the Catch Basin
- Catch Basin Insert Filter for Stormwater: How Ultra Urban® Filter and Smart Sponge® Media Work Together
- Catch Basin Retrofit Stormwater Treatment: When Does It Make Sense, and How Do You Choose a Retrofit?
- What Sets Catch Basin Insert Cleaning Schedules — and How to Get Yours Right
- Stormwater Pit and Catch Basin: What to Check Before Adding a Filter Insert
- Phosphorus Removal Compared: Sorptive Media vs Sand Filters and Bioretention
- Catch Basin Filter Inserts — Ultra-Urban® Smart Sponge® | — Abtech Industries
- Catch Basin Insert Filter for Stormwater — Abtech Industries
- Catch Basin Inserts That Stop Hydrocarbons Before They Reach the Outfall