Ultrasound and Fungi Mediated Degradation of Model Emerging Contaminants: Per- and Polyfluoroalkyl Substances & Nitrotriazolone
Water resources are increasingly being impacted by chemicals of emerging concern like per- and polyfluoroalkyl substances (PFASs) and nitrotriazolone (NTO). PFASs can be found in virtually all consumer and industrial applications that require non-stick or fire-resistant properties. Use of aqueous film-forming foams (AFFF) containing PFASs at the fire training sites and munition constituents like NTO at the munition testing ranges can also introduce these chemicals into the environment. Munition constituents and PFASs are also expected to co-occur on military training sites due to the use of AFFF for extinguishing fires caused by munitions use and firefighting training. Physicochemical treatment strategies may be needed for quick degradation of more recalcitrant chemicals, like PFASs, while biological treatment strategies, being less cost- and energy-intensive, may be more suited for the treatment of large dilute plumes of groundwater and soil at impacted sites. Nevertheless, there is a critical need to develop effective biological as well as abiotic technologies for the degradation of these contaminant classes in various environmental settings. This research investigated the application of ultrasound for the destruction of PFASs as an example of abiotic treatment technology whereas ligninolytic fungi and fungal enzymes were considered representative agents for biodegradation of NTO.Firstly, a comprehensive review of the treatment of per- and polyfluoroalkyl substances (PFASs) by current wastewater treatment plants was conducted by estimating their detection in treated effluents and surface runoffs throughout the world with respect to water recycling and reuse. This work also discussed the advantages of various destructive technologies for the treatment of PFASs as the current treatment plants were found to be ineffective in PFAS removal. The sorption of PFASs was found to be the determining factor of their fate and transport in the natural environment as well as wastewater treatment plants. A review of current analytical methods for the detection of PFAS along with PFAS toxicity studies was also presented. Secondly, the treatment of PFASs by high-frequency ultrasound using a custom-built bench-scale reactor was investigated in various matrices and mixtures, including aqueous film-forming foams (AFFF), Investigation derived waste (IDW), and groundwater. Important parameters for designing and operating an ultrasonic reactor for the degradation of PFASs were discussed. The study revealed that salts and surfactants affect the air-water partitioning coefficients of PFASs and their availability at the ultrasonic cavities, thereby affecting the degradation rates. Near-stoichiometric defluorination of hexafluoropropylene oxide dimer acid (HFPO-DA or GenX) and 6:2 fluorotelomer sulfonamidoalkyl betaine (6:2 FTAB) by ultrasound was demonstrated in laboratory studies. The degradation of PFASs was found to generally follow pseudo-first-order kinetics with degradation rates of sulfonates and short-chain PFASs being lower than those of carboxylates and long-chain PFASs in deionized (DI) water. However, the rates were 30% to 60% higher in groundwater with low total dissolved solids (TDS) than in deionized water, while the rates were generally repressed in the high TDS groundwater. 33 PFASs were degraded by ultrasound in AFFF spiked deionized water and the degradation rates of sulfonates were 40% to 60% higher compared to the 24Mix spiked DI water. The treatment of concentrated, high-TDS IDW resulted in significant mineralization of 41 PFASs, consuming 3 kWh.g-1 - 76 kWh.g-1. Biological-sonolysis and electrochemical-sonolysis treatment trains are also discussed. Thirdly, the learnings of the lab-scale study on the destruction of PFASs by ultrasound were leveraged for designing a field-scale reactor and testing it for the treatment of AFFF impacted groundwater. The ultrasonic treatment of high salinity groundwater demonstrated successful degradation of 15 PFASs (>90%) and 11 PFAS precursors, with 11 PFASs and 7 TOPs degraded to < 70 ng.L-1. No disinfection byproducts or short-chain intermediates were detected during 8 h ultrasonic treatment in all six tested conditions. The energy consumed during 8 h of sonication was 28.01 � 0.47 kWh. The EEO estimated was 599.51 � 52.54 kWh.m-3.order-1 , 797.25 � 42.16 kWh.m-3.order-1, and 699.43 � 3.30 kWh.m-3.order-1 for the treatment of 54 L, 33 L , and 22 L groundwater, respectively. Fourthly, packaging of Trametes versicolor derived laccase enzyme in vault nanoparticles was performed to investigate the applicability of vault-packaged laccase in bioremediation. Three isozymes were expressed by T. versicolor in the Tisma medium out of the five identified isozymes. The activity of the packaged enzyme was retained by using a long Glycine-Serine linker between laccase and INT peptide, along with the addition of 500 �M CuCl2 in the Spodoptera frugiperda (Sf9) insect cell culture expressing the fusion protein. The vault-packaged enzyme (VMLDGI) successfully catalyzed the transformation of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid (ABTS), guaiacol, catechol, 1-naphthol, and 2,6- dichlorohydroquinone. VMLDGI also removed 60% NTO at 5 U.L-1 laccase activity in presence of 1-Hydroxybenzotriazole (HBT). In contrast, the degradation of NTO by unpackaged laccase at the same activity was insignificant. Finally, biotransformation of NTO by ligninolytic fungi, T. versicolor and Phanerochaete chrysosporium, and their extracellularly secreted enzymes, laccase and manganese peroxidase (MnP), was investigated with implications on stormwater biofilter design. Both fungi demonstrated at least 85% removal of NTO within 96 h in batch reactors. About 40% NTO removal by P. chrysosporium was due to biosorption while T. versicolor demonstrated no biosorption of NTO. MnP demonstrated no removal of NTO while the laccase + HBT system was able to degrade 90% NTO in 48 h. This implies that only a subset of environmental fungi and their enzymes are capable of biodegrading munition constituents such as NTO. This research will be important for further developing the ultrasonic treatment technology for industrial applicability in the treatment of various chemicals, including PFASs. This work is also valuable for further developing the technology of ligninolytic fungi-mediated biodegradation of munition constituents and other emerging environmental contaminants.