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The average clump of biochar is practically indistinguishable from something you might find in a bag of Kingsford charcoal briquettes. And the truth is, their ingredients aren’t all that different. Most biochar is composed of forest or agricultural waste, or biomass, that has been thermally decomposed via pyrolysis, the process of cooking the material in a low-oxygen environment and binding its embodied carbon to the charred yield.
While the use of biochar to improve soil properties is nothing new (ancient Amazonians were fertilizing agricultural lands using charred biomass some 2,000 years ago), the material’s carbon sequestration benefits have recently come into focus. As Martin Holladay wrote on the topic in 2020, biochar represents “a relatively stable form of carbon … [and one] that is not readily released into the atmosphere.” Biochar production has also been heralded as a carbon-negative process, effectively storing carbon that would otherwise be released through burning or natural decay.
Nowadays, biochar is finding new and unexpected feedstocks, and its applications now go well beyond soil remediation.
It’s in the concrete
California-based OurCarbon (an offshoot of Bioforcetech) manufactures a biochar product using what the company calls “impact feedstocks.” Those feedstocks are biosolids, which come from residual solids that are made from the treatment of municipal wastewater. Once procured, those biosolids then undergo pyrolysis to become a new form of biochar, which is now a viable admixture in low-carbon concrete.
Breaking all that down, yes, the company is making biochar from sewage sludge, and yes, that biochar is used to make structural grade concrete. OurCarbon’s biochar is not a substitute for cement but rather an additive that replaces a sizable percentage of the sand required in typical concrete mixes. “We don’t decrease the amount of cement, but we can store hundreds of pounds per cubic yard because we’re…
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4 Comments
I love reading about these new technological developments that will save the planet but there is always a ¨but¨. In this case I wonder where the PFAS and other contaminants are removed to.
Nilst stated my concerns. This sounds like an effective solution to an important problem, but "pyrolysis machines, which use high heat (650°C for 15 minutes) in a low-oxygen environment to remove all contaminants, including microplastics, pharmaceuticals, and forever chemicals" makes it sound like those compounds are sent into our atmosphere. Concrete seems like a perfect place to store PFAS and microplastics.
Agreeing with nilst & Michael, presumably most of the microplastics, pharmaceuticals, and PFAS are ripped apart during the heating process, turned into char, gasses, and 'other', seems like a good question where the fluorine ends up.
A little bit of clicking around located this "Review of PFAS Destruction Technologies" article: https://pmc.ncbi.nlm.nih.gov/articles/PMC9778349/
It seems there are questions. I guess inside concrete isn't the worst place for long-lasting toxic waste, standard concrete often has heavy metals etc. and you could do worse, still a bit of a head-scratcher as to how OK it is to introduce persistent/elemental poisons into the built environment. (We are still struggling with lead-based paint every month on our sites and it was banned nearly 50 years ago, not something we should repeat if avoidable.)
I got interested in this question (where do they go?) and so went down the rabbit hole reading the EPA paper describing the testing. https://www.tandfonline.com/doi/full/10.1080/10962247.2021.2009935 It seems like most of the PFAS is getting transformed by pyrolysis into other, smaller fluorinated compounds such as fluoromethane that are then released from the system. The article does not comment on whether those other molecules are better or worse for people or the environment than PFAS. They are gases and will stay in the atmosphere until broken down. My hunch is that they are better (less bad) for people, worse for climate.
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