A new gasification process designed for the disposal of biosolids is also capable of destroying per- and polyfluoroalkyl substances (PFAS) contaminants, which are typically very resistant to conventional treatment processes. Aries Clean Technologies (Franklin, Tenn.; www.ariescleantech.com) recently validated its fluidized-bed gasification technology’s PFAS-destruction performance at its commercial-scale facility located at a wastewater-treatment plant in Linden, N.J. “The primary goal of Aries’ technology is to provide an alternative, sustainable biosolids disposal solution. As PFAS has become an increasingly prevalent concern in biosolids, we wanted to also test the capabilities of the system to destroy PFAS. The gasification technology works to destroy PFAS across two high-temperature processing steps,” explains Joel Thornton, director of Corporate Development at Aries Clean Technologies.
Following drying, biosolids are fed to the gasifier operating at 1,250o F for preliminary thermal conversion. The two outputs from the gasifier are solid biochar and producer gas (a mixture primarily made up of N2, CO and H2, along with other trace compounds). A closed-loop heat-recovery system captures the energy from the producer gas and uses it to dry the incoming biosolids. “The biochar was found to have PFAS levels below detection limits, so any remaining PFAS is volatilized, and moves into the producer gas stream. The producer gas is then sent to a thermal oxidizer where it is exposed to 1,800oF temperatures for around two seconds, leading to further destruction before moving through the heat recovery system and being discharged. There was PFAS found in the discharge stream, but at levels far lower than what was present in the biosolids, and it was found that the concentrations were over 30 times lower than the current most-stringent PFAS air emissions standards,” explains Thornton.
The findings from the Linden plant are significant because there are no other thermal biosolids-disposal or PFAS-destruction technologies currently operating at commercial scale in the U.S. “The Linden system is designed to process 430 wet tons/d of biosolids and is also designed to process 100% biosolids. The facility can be located close to the biosolids-generation point, eliminating the need for long-distance transportation for disposal. Our gasification system is useful for PFAS elimination from biosolids, but it also has the dual benefit of disposing of biosolids safely,” adds Thornton. Aries Clean Technologies is currently designing another commercial facility in Maine.