Biochar Use In Stormwater Management

Stormwater is the runoff from rain, snow, or ice. Runoff from the built and natural environments alike are often contaminated with pollutants including sediment, heavy metals, petroleum-based hydrocarbons, nutrients, herbicides, insecticides, pesticides, flame retardants, plastic additives and micro-plastics, chlorides, bacteria and oxygen-demanding organic matter.  Over the last decade biochar, a long-lasting form of carbon made from organic materials, has begun to play an ever-expanding role in managing and decontaminating stormwater. This report outlines where and how it can be used effectively, as well as providing an overview of the market potential for biochar producers.

Biochar has been used commercially in stormwater management in the US for more than ten years to bring public and private storm water management systems into compliance with regulatory permits. Use has grown as more trials are being conducted and biochar’s benefits and value proposition are better understood. One of the most publicized projects is from Stockholm, Sweden where biochar is used extensively since initially being piloted in 2009 to reduce runoff and revitalize tree plantings. In the US, Minnesota  has published specifications for biochar use in stormwater management and the City of Minneapolis has begun instituting city wide programs after visiting Stockholm and learning from the project managers there.  Other US municipalities are also exploring biochar in urban stormwater management projects.

Biochar is the product of heating organic feedstocks1  in a low oxygen environment, through a process called pyrolysis creating a stable, carbon-rich form of charcoal. Biochar can be used in many applications where activated carbon is currently used to remove substances from either water or gaseous streams.  Activated carbon is often made from mined carbon sources such as peat and coal, but can also be made from renewable organics including dense coconut shells., Biochar, on the other hand, is made from a wide variety of organic (i.e., renewable) sources. Like conventionally activated carbon, pyrolyzed woody biomass can also be activated to similarly increase its available surface area. 

Biochar can be a cost-effective filtration solution where organic and inorganic substances, as well as some microbial constituents, need to be removed. Research and experience has proven biochar to be useful in a variety of applications which makes it an attractive additive for stormwater treatment as a filtration and water treatment media. It is also used in soil restoration and remediation, constructed wetlands, green roofs, and water treatment.

Stormwater treatment in the US is driven by the 1972 Clean Water Act, a federal law administered by state and local agencies2. For biochar producers, the market potential will be significant once biochar is specified and approved for stormwater projects3.  How big might the market potential be? Using the City of Chicago as an example—with an impervious surface area of about 105,000 acres— in 2020, bids were requested for over $250M of stormwater treatment projects.  A 10% biochar inclusion rate on those projects is estimated to require roughly 100,000 cubic yards of biochar. To put this singular case in perspective, Chicago represents about 4% in area of the 10 largest US cities by population which cover 3900 sq. miles or 2.5 M acres.

The first section of this report provides relevant information for stormwater filtration project managers and designers.  It provides a synopsis of biochar’s potential for stormwater treatment and a short tutorial of biochar’s relevant characteristics for treating stormwater or effluent.  The following two sections provide commercial examples of biochar used in stormwater treatment projects and field trials, as well as a sampling of related research of biochar’s use in stormwater treatment. The last section offers biochar producers insight on how to serve the stormwater treatment sector effectively.