Biochar for E. coli Removal From Stormwater

Stormwater filters need to capture bacteria as runoff passes through and retain them when the next storm arrives. Biochar can help with both jobs. Laboratory research has found that adding selected wood biochars to sand improved E. coli capture and reduced the release of bacteria already held in the filter. ¹

That opportunity extends beyond the laboratory. Full-scale projects in Minnesota have used biochar with iron-enhanced sand to treat urban runoff, reporting a modest improvement in E. coli removal over three monitoring seasons. Together, these findings give stormwater designers and treatment-media developers a practical reason to consider biochar as a filter ingredient. ²

Capturing bacteria and keeping them in the filter

Biochar changes the surfaces available for bacteria to attach to as water moves through sand. In the original 2014 study, researchers compared sand alone with sand containing wood biochar, including steam-activated materials. The amended filters captured more E. coli under both steady and interrupted flow. They also released fewer retained bacteria when flow resumed. ¹

That second benefit is especially relevant to stormwater, which arrives in pulses. Holding bacteria through a pause in flow helps a filter retain what it has already removed. Even when added natural organic matter reduced capture, the biochar-amended filters still performed better than sand alone. ¹

Later laboratory work examined different water-loading rates and dry periods between simulated storms. Biochar-amended columns achieved higher E. coli removal and more stable bacterial concentrations in the outgoing water as those conditions changed. This adds evidence for biochar’s value during the changing flows that stormwater filters encounter. ³

Putting biochar to work in urban runoff

At Woodcrest and Pleasure Creek in Minnesota, full-scale installations placed biochar-amended iron-sand media alongside iron-sand media without biochar. These systems treated runoff from urban drainage areas, moving the application into working stormwater infrastructure. ⁴

The results showed an added bacterial-removal benefit at some sites and times. Woodcrest’s biochar cell performed better in the first two monitoring years, with similar performance between the two media in the third. Pleasure Creek showed a larger advantage for biochar in the third year. The project team’s subsequent three-season assessment described the overall increase in E. coli removal as modest. ^{2, 4}

Field results also help define where that benefit can be expected. A separate 2024 trial treating parking-lot runoff found no additional E. coli retention from its red-pine biochar amendment compared with sand. Across these projects, biochar’s contribution varied with the installation and over time. The useful opportunity is to match the material and filter setup to the treatment goal. ^{4, 5}

Choosing biochar for a filtration role

For a filter developer, biochar is an ingredient that works with the surrounding media. The laboratory studies used particular wood biochars, some steam-activated, while the Minnesota installations combined biochar with iron-enhanced sand. Those distinctions make the material’s preparation and its place in the filter part of the selection decision. ^{1, 4}

The benefit discussed here is bacterial capture and retention, rather than disinfection. That gives biochar a defined role within a stormwater treatment system: helping remove bacteria from runoff as it passes through the media.

Wakefield supplies carbon materials for filtration development. Explore our water and air filtration applications to discuss material requirements. For another water-treatment application, our Learning Center article on biochar in municipal wastewater systems explores related uses.