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Elimination of microplastics, PFAS, and PPCPs from biosolids via pyrolysis to produce biochar: Feasibility and techno-economic analysis
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Researchers found that heating sewage sludge (biosolids) through a process called pyrolysis at temperatures of 400-700 degrees Celsius removed virtually all harmful contaminants -- over 99.9% of pharmaceuticals and PFAS ("forever chemicals") and 91-97% of microplastics. The process also produces biochar that can be used as a fertilizer, potentially turning a waste disposal problem into a revenue source. This approach could prevent microplastics and other pollutants from spreading to farmland through standard biosolid application.
Biosolids from municipal wastewater treatment contain many contaminants of emerging concern, including microplastics (MPs), per- and polyfluoroalkyl substances (PFAS), pharmaceuticals and chemicals from personal care products (PPCPs). Many of these contaminants have very slow biotic or abiotic degradation rates and have been shown to have human and ecological health impacts. Application of biosolids to agriculture, a common disposal method, can result in extended environmental contamination. An approach for eliminating the contaminants is pyrolysis, which can also generate biochar, enhancing carbon sequestration as a side-benefit. We pyrolyzed biosolid samples from an operating facility at various temperatures from 400 to 700 °C with a 2-hour residence time. We then evaluated contaminant removal, which in many cases was 100 %, with only a few residuals. No trace of PFAS was detectable even at 400 °C. Overall mass removal of PPCPs, including PFAS, was over 99.9 %. MP removal via pyrolysis ranged from 91 to 97 %. The biochar contains significant amounts of Fe and P, which make it a useful fertilizer amendment. The techno-economic analysis indicates that pyrolysis may generate significant cost savings, and revenue from the sale of biochar, sufficient to more than cover the investment and operating costs of the dryer and pyrolysis unit.
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Pyrolysis of Sewage Sludge
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This review paper summarizes existing research on pyrolysis, a heat-based process that breaks down sewage sludge from wastewater plants into biochar, gas and liquids. It notes that pyrolysis can degrade contaminants including pharmaceuticals, PFAS and microplastics, while reducing sludge volume and producing biochar for potential soil use.
Municipal Sludge Resource Recovery: Technologies, Challenges, and Future Directions
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This review paper looks at different ways to treat sewage sludge (the leftover waste from wastewater treatment plants) so it can be reused instead of dumped or burned. It found that one method, called pyrolysis (essentially baking the sludge at high heat without oxygen), is especially promising because it can break down harmful contaminants like microplastics, PFAS ("forever chemicals"), and drug-resistant bacteria genes while turning waste into a useful product called biochar. This matters because sludge is often recycled into fertilizer or soil products, so better treatment methods could reduce the chances of these harmful substances ending up in our
Pyrolysis Solves the Issue of Organic Contaminants in Sewage Sludge while Retaining Carbon—Making the Case for Sewage Sludge Treatment via Pyrolysis
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Pyrolysis of sewage sludge was evaluated as a treatment that destroys organic contaminants including pharmaceuticals, microplastics, and PFAS while retaining carbon and plant nutrients in the resulting biochar, but the authors noted that current EU fertilizer regulations do not yet recognize sewage sludge biochar as an eligible product, creating a policy barrier to its adoption.
Environmental behavior of per- and polyfluoroalkyl substances (PFASs) and the potential role of biochar for its remediation: a review
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This review summarizes how biochar, a carbon-rich material made from organic waste, can be used to clean up PFAS (per- and polyfluoroalkyl substances), the persistent "forever chemicals" found widely in the environment. Since microplastics can carry and transport PFAS through water systems, understanding how to remove PFAS is an important piece of the broader pollution picture.
Land Application of Biosolids-Derived Biochar in Australia: A Review
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This Australian review examined whether converting sewage sludge (biosolids) into biochar through pyrolysis or gasification could safely remove contaminants before the material is spread on agricultural land. Key findings show that thermal processing can effectively destroy persistent organic pollutants, microplastics, and pathogens present in biosolids, and can immobilize over 90% of heavy metals. Biochar from treated biosolids is therefore a safer soil amendment than raw biosolids and could reduce microplastic inputs to farmland from a widely used agricultural practice.
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