November 12, 2025
Biochar is a porous solid carbon with unsaturated aromatic carbon species and a myriad of molecular weights and chemical functionality. This porosity and the assortment of chemical functionality allows biochar to act like an adsorbent, or filter, to attract and capture toxins and microbes in its porous structure.
Biochar is emerging as a promising material for filtering PFAS (and other toxins) in landfill leachate due to its porosity, cost-effectiveness, and functional group binding (Holly 2024; Wang 2025). Carba’s application of biochar to landfills as daily cover mixtures is designed to optimize contact area of leachate with biochar in a sequential layered filter design. This design minimizes risks of channeling and improves adsorbent efficiencies. In addition, the biochar is designed to hold onto PFAS and other toxins inside the landfill, thereby eliminating the need for expensive destruction technology.
Based on laboratory and field studies of soil columns, it may be possible to reduce PFAS in leachate by 50% or more (Holly 2024). Carba plans to test the PFAS and toxin removal potential using a combination laboratory leachate testing and landfill burial and sampling over a year's timeframe.
In addition to toxin removal, biochar reduces odors, and when used as a daily cover it can decrease landfill odors for the community. The mechanism for action is similar to carbon air filters, wherein non-specific and specific binding sites bind to volatile organic compounds (VOCs) present in air that are responsible for odor. Because fresh biochar will be added to the landfill cap daily, this process could significantly improve air quality for the communities surrounding landfills and beyond.
The high porosity and surface area of biochar also provide physical niches for colonization and biofilm formation. These microbially favorable habitats allow methane eating microbes, i.e., methanotrophs, to thrive and enhance methane oxidation to carbon dioxide thereby reducing the greenhouse gas potential. Biochar enhancement of methanotrophs has been shown in soils (Lv 2022) and landfills (Green 2022).
Source: Short-Lived Climate Pollutants
Carba’s application approach of biochar into daily covers is a promising method for the improvement of naturally occurring methanotrophy and has the potential to significantly decrease anthropogenic methane emissions when applied to landfills broadly. Landfills are responsible for 17.1% of total US methane emissions (EPA), and this approach could reduce methane emissions by over 50% (Varghese 2018).
Counterfactual biomass fates should also not be ignored. The majority of biomass in the Twin Cities is composted. For every 1000 tonnes of biomass diverted from composting, an estimated 297 tonnes of CO2e in the form of CH4 from composting could be avoided (Scown 2023). This is because anaerobic zones in compost piles lead to the formation of methane from methanogenic microbes.
Taken together, the application of biochar to landfills as daily cover has the potential to drastically improve the environment through:
Filtering of toxins like PFAS
Reduction of odors/VOCs
Oxidation of methane
Prevention of methane produced in counterfactual composting operations.
