As PFAS contamination in biosolids attracts growing regulatory and media attention, stabilisation using RemBind® offers a practical, cost-effective, and scientifically validated approach to managing PFAS in sewage sludge - enabling safe beneficial reuse on agricultural land while protecting groundwater and human health.
Biosolids are nutrient-rich organic materials that result from the treatment of raw sewage sludge during wastewater treatment processes. They are often beneficially reused on agricultural land as they not only add valuable nutrients to the soil but can also improve moisture-holding capacity and other key soil parameters.
However, wastewater treatment processes tend to also concentrate certain heavy metals such as copper and zinc, so the application of biosolids to agricultural land needs to be carefully managed to ensure that environmental regulations are not exceeded.
More recently, per- and polyfluoroalkyl substances (PFAS) — dubbed the ‘forever chemicals’ — have been discovered in various biosolids. This group of synthetic chemicals accumulates in the environment, and there is evidence that some of these compounds can cause toxicity to human health and the environment.
PFAS have been used in a wide range of products including firefighting foams (AFFF) and waterproofing agents used in clothing, shoes, and upholstery sprays, and can make their way from industrial and household wastewater into sewage sludge and ultimately into biosolids.
The discovery of PFAS contaminants in biosolids has received significant media attention because biosolids have been applied to some land and pastures for decades, and although heavy metals have been carefully managed, PFAS levels have remained largely uncontrolled.
Thermal treatment of biosolids (e.g. pyrolysis or incineration) is being touted as a PFAS management solution as it destroys PFAS molecules. However, this approach may not be commercially viable in all situations, as it requires high energy inputs and has relatively limited volume capacity. It is not practical for treating agricultural soils that have already been contaminated with PFAS via broadacre spreading of contaminated biosolids.
Stabilisation (also called ‘immobilisation’) refers to the addition of inert mineral sorbents to biosolids to ‘lock up’ PFAS contaminants and prevent them from leaching into groundwater and causing harm to human health and the environment. The immobilisation process is relatively cost-effective and practical to apply, and the treated biosolids can still be applied to agricultural land for beneficial reuse. The technology can also be applied in-situ to reduce PFAS uptake into plants and biota.
In a study published by State University of New York researchers in the Journal of Hazardous Materials (Zhang et al., 2022), sorbent addition demonstrated positive effects in reducing PFAS leaching from sewage sludge.
In this study, RemBind 100, RemBind 100X, GAC, and biochar were evaluated for their effects on PFAS stabilisation in sewage sludge. At the three tested doses (0.1%, 1%, and 2%), RemBind 100X showed the best stabilisation performance, while biochar showed limited capability for stabilising PFAS in sludge.
Over time, leachable PFAS gradually increased for sludge amended with GAC, but fluctuated in the water leachate of the sludge amended with RemBind 100X during the 115-day study, implying a dynamic adsorption/desorption process and potential degradation of PFAS precursors during the experimental period.
A further study by the same researchers, published in Environmental Pollution (Zhang and Liang, 2022), showed that the application of sorbents significantly reduced PFAS bioavailability to Timothy grass grown in biosolids-amended agricultural soil. When RemBind 100X or GAC were used at a 2% dosage, reductions of over 96% in total PFAS in grass shoots were observed.
This study validates the in-situ application of sorbents to reduce the bioavailability of PFAS to crops and reduce PFAS transport to sensitive biota and water receptors.
Zhang, W. and Liang, Y. (2022) Changing bioavailability of per- and polyfluoroalkyl substances (PFAS) to plant in biosolids amended soil through stabilization or mobilization. Environmental Pollution, 308, 119724. https://doi.org/10.1016/j.envpol.2022.119724
Zhang, W., Jiang, T., Liang, Y. (2022). Stabilization of per-and polyfluoroalkyl substances (PFAS) in sewage sludge using different sorbents. J. Hazard. Mater. Adv. 6, 100089. https://doi.org/10.1016/j.hazadv.2022.100089
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