Catch basin inserts built for trash and sediment don't touch dissolved phosphorus. Here's how Smart Sponge® HM media and the Ultra Urban® Filter target that fraction inside existing inlets.
Phosphorus removal at the catch basin works by loading a phosphorus-targeting media, such as Smart Sponge® HM, into the existing inlet so dissolved phosphorus binds to the media as runoff passes through rather than continuing downstream. This matters because phosphorus that has already dissolved off sediment is the fraction that sediment capture and standard trash screens cannot touch, and it is often the fraction driving a benchmark exceedance or nutrient TMDL.
Why does sediment control leave phosphorus behind?
Phosphorus in runoff shows up in two forms: particulate phosphorus, which is bound to sediment and settles out or gets screened with the solids, and dissolved or soluble phosphorus, most of which is present as orthophosphate — the form that is most readily available to feed algae and oxygen-depleting growth once it reaches a lake, river or estuary. A catch basin insert built to capture total suspended solids (TSS) and trash removes the particulate share. It does nothing for the share that is already in solution. For a municipal stormwater program or an industrial site working against a phosphorus benchmark, that gap is usually the reason a basin that looks clean on inspection still reports exceedances.
Which media targets dissolved phosphorus, and what else does it treat?
Smart Sponge® HM is formulated to target dissolved metals — lead, zinc, copper, arsenic and selenium — alongside phosphorus. That combination matters for sites where metals and nutrients show up together, which is common at metal recycling yards, metal fabrication shops and junkyard facilities where runoff crosses scrap, machining residue and exposed metal stock. A single HM-loaded system can address a facility's metals and phosphorus benchmarks without running two separate treatment trains. Where a site also carries bacteria from illicit discharges, pet waste or sanitary cross-connections, Smart Sponge® Plus — an antimicrobial media — can be combined in the same system to address E. coli, fecal coliform and Enterococcus alongside the HM media's metals and phosphorus work. Abtech's standard Smart Sponge® media, by contrast, is built for hydrocarbons and oil sheen rather than nutrients, which is why matching media to the contaminant mix at the site comes before choosing a format.
What format holds the media in an existing catch basin?
The Ultra Urban® Filter is Abtech's catch basin insert, custom-fabricated to fit the shape, size and design of a given basin rather than forcing a standard basin to accept a standard insert. That matters for retrofits: municipal storm drain networks and industrial yards rarely have uniform basin geometry, and a filter built to the basin's actual dimensions avoids bypass around the edges of a loose-fitting insert. Because the Ultra Urban® Filter is passive, it runs without pumps or power, so it can go into an existing inlet without excavation or electrical work. Stainless steel versions of the insert carry a 20-year warranty. For larger or more variable catchments, the same HM media can also be deployed in vaults, pressure vessels or skid-mounted systems; Abtech's skid-mounted Smart Skid is installed with pumps, pressure and flow controls rather than operating passively, which makes it a better fit for sites with higher or more variable flows than a gravity-fed catch basin sees.
How does a catch basin insert fit into broader stormwater BMPs?
A phosphorus-targeting catch basin insert is one best management practice (BMP) among several a permit holder may need to combine — source control, housekeeping, and structural treatment together make up a functioning stormwater program. Catch basin inserts sit at the structural-treatment layer: they intercept runoff close to where it enters the storm drain, before dissolved pollutants have a chance to travel further into the collection system. For MS4 operators managing phosphorus load under a TMDL, or industrial facilities documenting corrective action after a benchmark exceedance, that proximity to the source is part of why catch basin treatment is specified alongside other BMPs rather than instead of them. California's Full Trash Capture system requirements are a separate but related driver: Abtech's catch basin inserts are built to that standard, which addresses trash and debris capture and TSS removal — a complementary function to the dissolved-phosphorus work the HM media performs in the same device. Stormwater rules change by state and by permit cycle, and the trash-capture and TSS requirements a catch basin insert meets are not the same requirement as a dissolved-phosphorus limit; a permit holder should confirm which standard applies to its basin directly with its regulatory program rather than from a generalized product description.
Frequently asked questions
Does a catch basin insert remove all the phosphorus in stormwater?
A catch basin insert loaded with Smart Sponge® HM is designed to bind the dissolved phosphorus fraction passing through it; Abtech does not publish a guaranteed removal rate or compliance outcome for a given site, because actual performance depends on flow, contaminant concentration and basin configuration — which is why a site assessment, and in some cases lab column testing on the site's own water, precedes specification.
Can one insert handle phosphorus, metals and bacteria together?
Smart Sponge® media types can be combined within a single system, so an Ultra Urban® Filter or vault-mounted system can pair HM media for phosphorus and dissolved metals with Smart Sponge® Plus for bacteria when a site's runoff carries both.
Does a trash-capture-certified insert also treat dissolved phosphorus?
Trash and debris capture and TSS removal address the particulate fraction of runoff pollutants; treating dissolved phosphorus requires a media formulated for it, such as Smart Sponge® HM, loaded into the same or a paired device.
Is a catch basin insert a pump-driven or a passive system?
The Ultra Urban® Filter catch basin insert is passive and runs without pumps or power. Larger-scale systems built around Smart Skid units use pumps, pressure and flow controls, so the right choice depends on the catchment's flow volume and the space available at the site.
How do we know if our basin needs phosphorus-targeting media instead of sediment control?
A benchmark exceedance or TMDL allocation for phosphorus that persists after sediment and trash capture are in place is a signal that the dissolved fraction is driving the result; a site assessment reviewing current contaminant data against the permit's effluent target can confirm whether HM media is the right next step.