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An Ohio University professor explains how a source of needed fertilizer has been tainted by “forever chemicals” in our bodies
By: David Forster
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ATHENS, Ohio (WOUB) — When we flush our toilets, the waste goes into the sewer system and ends up at a wastewater treatment plant. What many of us probably don’t know is that the solid waste eventually gets separated from the liquids, and that solid waste would be used as fertilizer. The trend now, however, is to no longer spread that solid waste over the land.
Sarah Davis is a professor of environmental studies in the Voinovich School of Leadership and Public Service at Ohio University and an expert in ecosystem ecology and bioenergy systems.
Davis sat down to speak with WOUB’s David Forster for “Modern Science” about why “forever chemicals” have cut off a source of fertilizer for farmers.
This interview has been edited for brevity and clarity.
On the issue forever chemicals present to wastewater treatment
“Locally, the wastewater treatment plants were starting to run into an issue with contaminants that are present in the sewage sludge.
“Recently, there’s been more discussion about PFAS, which is you may have heard of as forever chemicals.
“A lot of chemicals do degrade over time, even if they have some toxicity level. PFAS chemicals have a tendency to be very recalcitrant and they don’t actually break down. It takes a very deliberate treatment to destroy them. There are not very many known methods of doing that at this point. The important thing I think to know is that our organic waste streams have a lot of nutrients in them that are potentially very valuable.”
What plants are doing with the contaminated sludge
“Most wastewater treatment plants in the area are taking that sewage sludge to landfills. So we have a loss of … those valuable nutrients.”
On the research Davis’ team is conducting to remove forever chemicals from wastewater
“We’re working on testing this hydrothermal treatment process and looking at the degree to which those PFAS chemicals can be destroyed. We have really optimistic results right now that suggests that if we get the conditions right in this hydrothermal treatment, that we can eliminate most or all of those PFAS compounds.
“It stabilizes important nutrients like nitrogen and phosphorus. There’s a substantial amount of those nutrients that are the most important for agricultural crops that could still be useful as a fertilizer in that way.”
“We have enough information now that we’ve actually started to test the the product of this hydrothermal treatment called hydrotar. We’ve started to test it on crops where we’re looking at the plant responses to see how well crops perform when you use this compared to the more standard fertilizers that people would buy on the market.
“We have some results and we have some ongoing experiments. It seems that a lot of the crops do have positive responses, although there are definitely some differences between leafy greens and crops like corn and grass-like crops. We have more work to do to figure out the perfect recipe of what that fertilizer would look like.
“I have some students who are doing projects right now that are mixing hydrotar with different soils and mixing hydrotar with different composts to figure out which ones would be the best soil amendments in different kinds of cropping systems.
The first draft of the transcript used for this story was created in Adobe Podcast, which includes an AI transcription tool. A WOUB news editor then reviewed, corrected and reformatted the transcript before publication.