Initial Results from PFAS Destruction Testing in Ultra High Temperature Ionic Gasification for Biosolids Management

Introduction The biosolids treatment industry plays a pivotal role in managing organic waste by converting it into valuable resources. Recent regulatory developments concerning per- and polyfluoroalkyl substances (PFAS) have significantly impacted disposal options, particularly land application, leading to a scarcity of viable methods and a surge in operational costs. The complexity of addressing PFAS contamination in biosolids is compounded by the diverse nature of Public Owned Treatment Works (POTWs) and other multifaceted factors, making it challenging to devise singular, universally applicable solutions for managing and mitigating this issue. In response to the pressing challenges posed by PFAS regulations and the limitations in traditional biosolids disposal methods, a technical solution has emerged, leveraging low temperature conductive drying in tandem with ultra-high-temperature ionic gasification (Image 1.). This innovative approach promises an up to 95% mass reduction with 90% carbon conversion of biosolids depending on waste characterization while concurrently generating two valuable resources: reusable char and clean renewable syngas for energy recovery. Ultra-High Temperature Ionic Gasification The HelioStorm generates electrical arcs across the diameter of the gasifier, arranged in a modular design. Each module generates multiple electric arcs that uniformly fill the internal cross-sectional area of the gasifier. The gasifier is typically arranged with one to three modules depending on the feedstock and solids loading. Resulting temperatures approaching ten thousand degrees Celsius create an ultra-high temperature gasification environment, ionizing compounds in the feedstock into its component atoms. Exiting the plasma modules, hot ionized gases rapidly cool causing the atoms to recombine into simple molecules (H2 and CO) minimizing the production of less desirable molecules such as water, ammonia, and carbon dioxide. This ultra-high temperature ionic zone has been shown through testing data to rapidly and thoroughly destroy impurities in the feed such as microplastics and PFAS. Low Temperature Conductive Heat Drying LTC Dry is a temperature drying process that requires less thermal energy per pound of water evaporated as compared to other drying technologies. Designed to address the challenges faced by wastewater treatment plants and industrial facilities, Heartland's LTC Dry advanced thermodynamic process utilizes recycled dry matter for economic and reliable heat transfer. The thermal efficiency of the LTC dryer is attributed to a conductive heat transfer method which produces Class A EQ biosolids without the use of a carrier gas, thus operating with very high thermal efficiency, while solving some of the historic solids handling issues in thermal drying processes and doing so safely and within a small footprint. Thermal performance measurements and analytical results from the startup and initial running of Heartland's commercial scale LTC Dryer on municipal sludges are expected in Q1 2024 and are planned to be presented at the conference. Depending the project timeline, the plan is to carryout PFAS testing on the incoming solids, the dried product, the condensate and potentially on any off gas from the process, thus provided a complete picture of how the targeted PFAS analytes distribute in this process. Testing for PFAS Destruction The presentation will discuss results from testing done in the pilot gasifier (M1) in Idaho Falls and on the fully operational commercial scale system (M3) at Heartland's Technology Center in Tennessee. Heartland contracted Montrose Air Quality Services (MAQS) to conduct evaluation of destruction and removal efficiency (DRE) of PFAS using the M1 at the Idaho Falls Facility. Biosolid feedstock was spiked with AFFF known to contain PFAS with samples of biosolids, syngas, char, and AFFF collected and analyzed, and mass balances were performed. Based on the testing, the contracted lab presented destruction results for four prominent PFAS compounds (PFOA, PFOS, 6:2 Fluorotelomer sulfonates and 8:2 Fluorotelomer sulfonates). DRE results of the pilot testing indicate a greater than 99% destruction rate in PFOS, 6:2 FTS, and 8:2 FTS, and a 95% destruction rate for PFOA (Table 1). In September, Heartland worked with Pace Analytical Services to analyze char samples using the M3. Lab analyses indicate non detect results for the dozens of PFAS compounds tested. Additionally, Heartland worked with Mostardi Platt to conduct PFAS testing on the M3 HelioStorm gasifier at the Technology Center in late September. Testing was with biosolids and samples of the biosolids, syngas, and char were taken. Results are expected by the end of 2023. During the Mostardi Platt PFAS testing, an FTIR was used to look for fluorine compounds in the syngas and other minor species of interest. The FTIR testing did not detect any fluorine compounds including HF, CF4, C2H6, and SF6. The lack of detection of the short chain perfluorinated compounds is a strong indication the demineralization of the PFAS compounds is complete and that they aren't just being cracked into shorter chains. The lack of HF in the gas, as well as the lack of HCl and H2S, strongly indicates that the F, Cl, and S atoms are being captured in situ by the char in the gasifier, likely as salts with the Ca and Mg in the ash fraction of the char.