The Flagstaff Water Group (FWG) is a group of five local scientists and engineers which is deeply concerned about water quality and availability. Over the past two years, we have been studying biochar because of its ability to remove hazardous contaminants from wastewater, especially cancer-causing compounds. We’ve concluded that biochar has a great future for wastewater processing in Flagstaff and elsewhere.
Biochar can be made from wood (forest thinning wastes), other organics and wastewater treatment plant (WWTP) biosolids. Biochar differs from charcoal as it is heated to higher temperatures (750+F) without air. As an agricultural soil-additive, biochar holds water and nutrients until the plants need those elements whereupon the roots take up the stored water and nutrients. If not burned biochar lasts indefinitely and can earn Carbon Sequestration Credits.
Archaeological studies show that biochar/charcoal was used to improve crop yields by indigenous people for millennia. Nearly a million people were able to grow healthy crops in biochar/charcoal supplemented soils along the Amazon River, where soil nutrients were otherwise leached away by heavy rains in their rain-forest ecosystem. Though most of these human populations died off due to Western diseases, they previously survived with the help of “Terra Preta,� a dark fertile soil made with biochar.
Amending soil is again becoming a primary use of biochar, but there's no large-scale agriculture near Flagstaff. However, the use of biochar for wastewater cleanup is a new use and makes sense for Flagstaff. The City of Flagstaff is interested in biochar and has submitted two grant requests with biochar as central elements, but did not get funded. FWG sought and received a small City Sustainability Grant to test the effectiveness of biochar for wastewater cleanup.
What’s the motivation for using biochar for wastewater cleanup? Our A+ reclaimed wastewater contains contaminants like pharmaceuticals and PFAS. We want this water to be cleaned for safe aquifer recharge and eventually potable use. Arizona recently finished making regulations for making potable water from reclaimed water and biochar has become a candidate process for use in those treatment processes.
PFAS is class of "forever chemical" recently regulated in potable water. Many PFAS compounds are quite toxic (carcinogenic). PFAS compounds bioaccumulate and are significant health hazards. The recent regulation is a maximum of 4ppt (parts per trillion) for some PFAS compounds, a truly tiny level. Other contaminants, such as pharmaceuticals, are not regulated in drinking water; but, we believe they too should be removed. Many researchers have shown the effectiveness of biochar for removing PFAS and other water contaminants.
We found a cost-effective test for PFAS in water and have begun to evaluate biochar's ability to remove PFAS from Flagstaff's reclaimed water. We used wood biochar from Eagar, AZ, as well as biochar made from “primary solids� from our Wildcat Hills WWTP. Testing reclaimed water from our Rio de Flag WWTP shows we can remove up to 50% of PFAS. Literature suggests higher removals are possible by activating the biochar to make “activated carbon� as is used in consumer water filters.
A new method to activate the biochar involves adding nano-Zero-Valent-Iron (nZVI). It has recently been found effective in removing synthetic organic molecules and other water contaminants. When used alone, nZVI particles tend to clump together. However, embedding nZVI in biochar stabilizes the particles and enhances the absorption of heavy metals, potentially toxic synthetic organic chemicals, and even microplastics.
We are in the process of making and testing this new type of activated biochar. By the end of 2025, we plan to make a test unit that will demonstrate how to use the activated biochar to commercially clean up wastewater. The activated biochar can be regenerated in a local biochar plant for repeated use. This becomes a “circular� process, potentially changing the way “activated carbon� is used. Research on the effectiveness of activated biochar is abundant, but implementation information is lacking, hence our planned test unit.
If this sounds interesting to you, please attend the open discussion of our project and see our equipment at the Market of Dreams (2136 N. Fourth St.) on Wednesday, June 25 at 7 p.m.