Researchers explore the application of Biochar and Iron-Enhanced Sands in septic systems

Of the 600,000 subsurface sewage treatment systems (SSTS) processing over 40 billion gallons of wastewater per year in Minnesota, estimates put 25% of these SSTS on or near shoreland. Final treatment of sewage occurs in the soil within the septic  system drain field. Researchers are exploring the benefits of Biochar and iron-enhanced sand (IES) in boosting the effectiveness of soil filtration. Clean water relies on natural soil treatment of septic system effluent for nutrient and bacteria removal. PI Sara Heger (Water Resources Center, Onsite Sewage Treatment Program) is hopeful that this project will show that conventional soil-based septic system performance can be enhanced with the addition of biochar and/or IES. “Successful incorporation of Biochar and IES into soil treatment systems could be a game-changer for septic systems in fragile ecosystems like lakeshore properties,” said Heger.


Lakeshore mound septic system installation. Photo credit: John Bilotta

Biochar is produced by the thermal decomposition of biomass through a process called pyrolysis, resulting in a highly porous material with ample surface area making it highly absorbent. IES is sand with added iron fillings. Biochar and IES could enhance the treatment in septic systems of organic matter, bacteria and viruses, nitrogen and phosphorus.

Heger and the research team will test several types of Biochar and IES’s effectiveness at removing contaminants from wastewater in a laboratory setting with absorption testing, and in enhanced soil columns to evaluate its potential to improve SSTS treatment. Biochar selection for pilot tests will be facilitated through collaboration with researchers at the Natural Resources Research Institute.


Septic system drainfield with perennial plantings. Cover plantings limit erosion as well as disguising the drainfield. Photo credit: John Bilotta

A research by-product could include future Minnesota-based Biochar and IES market development opportunities.

Co-researchers and other partners:

Bo Hu, Department of Biosystems and Agricultural Engineering U of M
Bridget Ulrich, NRRI
Stantec Engineering 
MPCA Subsurface Sewage Treatment System