Photodegradation and photocatalysis of per- and polyfluoroalkyl substances (PFAS): A review of recent progress.

Per- and polyfluoroalkyl substances (PFAS) are oxidatively recalcitrant organic synthetic compounds. PFAS are an exceptional group of chemicals that have significant physical characteristics due to the presence of the most electronegative element (i.e., fluorine). PFAS persist in the environment, bioaccumulate, and have been linked to toxicological impacts. Epidemiological and toxicity studies have shown that PFAS pose environmental and health risks, requiring their complete elimination from the environment. Various separation technologies, including adsorption with activated carbon or ion exchange resin; nanofiltration; reverse osmosis; and destruction methods (e.g., sonolysis, thermally induced reduction, and photocatalytic dissociation) have been evaluated to remove PFAS from drinking water supplies. In this review, we will comprehensively summarize previous reports on the photodegradation of PFAS with a special focus on photocatalysis. Additionally, challenges associated with these approaches along with perspectives on the state-of-the-art approaches will be discussed. Finally, the photocatalytic defluorination mechanism of perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) following complete mineralization will also be examined in detail.

Photooxidative decomposition and defluorination of perfluorooctanoic acid (PFOA) using an innovative technology of UV-vis/ZnxCu1-xFe2O4/oxalic acid.

Per- and polyfluoroalkyl substances (PFAS) are a large group of perfluorinated organic molecules that have been in use since the 1940s for industrial, commercial, and consumer applications. PFAS are a growing concern because some of them have shown persistent, bioaccumulative and toxic effects. Herein, we demonstrate an innovative technology of UV-vis/ZnxCu1-xFe2O4/oxalic acid for the degradation of perfluorooctanoic acid (PFOA) in water. The magnetically retrievable nanocrystalline heterogeneous ferrite catalysts, ZnxCu1-xFe2O4 were synthesized using a sol-gel auto-combustion process followed by calcination at 400 °C. The combination of ZnxCu1-xFe2O4 and oxalic acid generate reactive species under UV light irradiation. These reactive species are then shown to be capable of the photodegradation of PFOA. The degree of degradation is tracked by identifying transformation products using liquid chromatography coupled with quadrupole time-of-flight mass spectroscopy (LC-QTOF-MS).

Material recovery from electronic waste using pyrolysis: Emissions measurements and risk assessment.

Electronic waste (e-waste) generation has been growing in volume worldwide, and the diversity of its material composition is increasing. Sustainable management of this material is critical to achieving a circular-economy and minimizing environmental and public health risks. This study's objective was to investigate the use of pyrolysis as a possible technique to recover valuable materials and energy from different components of e-waste as an alternative approach for limiting their disposal to landfills. The study includes investigating the potential environmental impact of thermal processing of e-waste. The mass loss and change in e-waste chemicals during pyrolysis were also considered. The energy recovery from pyrolysis was made in a horizontal tube furnace under anoxic and isothermal conditions of selected temperatures of 300 °C, 400 °C, and 500 °C. Critical metals that include the rare earth elements and other metals (such as In, Co, Li) and valuable metals (Au, Ag, Pt group) were recovered from electronic components. Pyrolysis produced liquid and gas mixtures of organic compounds that can be used as fuels. Still, the process also emitted particulate matter and semi-volatile organic products, and the remaining ash contained leachable pollutants. Furthermore, toxicity characteristics leaching procedure (TCLP) of e-waste and partly oxidized products were conducted to measure the levels of pollutants leached before and after pyrolysis at selected temperatures. TCLP result revealed the presence of heavy metals like As, Cr, Cd, and Pd. Lead was found at 160 mg/L in PCBs leachate, which exceeded the toxicity characteristics (TC) limit of 5 mg/L. Liquid sample analysis from TCLP also showed the presence of C10-C19 components, including benzene. This study's results contribute to the development of practical recycling alternative approaches that could help reduce health risks and environmental problems and recover materials from e-waste. These results will also help assess the hazard risks that workers are exposed to semi-formal recycling centers.

Effectiveness of biosurfactant for the removal of trihalomethanes by biotrickling filter.

In this study, the biodegradation of a mixture of two trihalomethane (THM) compounds, chloroform (CF) and dichlorobromomethane (DCBM), was evaluated using two laboratory-scale biotrickling filters (BTFs). The two BTFs, hereby designated as "BTF-A" and "BTF-B," were run parallel and used ethanol as co-metabolite at different loading rates (LRs), and a lipopeptide-type biosurfactant that was generated by the gram-positive bacteria, Surfactin, respectively. The results using BTF-A showed that adding ethanol at a higher rate of 4.59 g/(m3 h) resulted in removal efficiencies of 85% and 87% for CF and DCBM, respectively. Conversely, for the same LR, the use of Surfactin without ethanol (BTF-B) showed comparable removal efficiencies of 85% and 80% for CF and DCBM, respectively. The maximum rate constant for CF and DCBM for the BTF-A was 0.00203 s-1 and 0.0022 s-1, respectively. For the same THMs LR, similar reaction rate constants resulted for the BTF-B. Further studies were conducted to investigate and understand the microbial diversity within both BTFs. The result indicated that for BTF with co-metabolite, Fusarium sp. was the most dominant fungi over 98% followed by F. Solani with less than 2%. F. oxysporum and Fusarium sp. were instead the dominant fungi for the BTF with Surfactin. Before introducing the Surfactin into the BTF, the batch experiment was conducted to evaluate the effectiveness of synthetic surfactant as compared to a biosurfactant (Surfactin). In this regard, vials with Surfactin showed better performance than vials with Tomadol 25-7 (synthetic surfactant).

Comparative Study on the Performance of Anaerobic and Aerobic Biotrickling Filter for Removal of Chloroform.

Use of biotrickling filter (BTF) for gas phase treatment of volatile trihalomethanes (THMs) stripped from water treatment plants could be an attractive treatment option. The aim of this study is to use laboratory-scale anaerobic BTF to treat gaseous chloroform (recalcitrant to biological transformation) as a model THM and compare results with aerobic BTF. Additional investigations were conducted to determine the microbial diversity present within the BTFs. Chloroform is a hydrophobic volatile THM known to be difficult to biodegrade. To improve the degradation process, ethanol was used as a cometabolite at a different ratio to chloroform. The experimental plan was designed to operate one BTF under anaerobic condition and the other one under aerobic acidic condition. Higher elimination capacity (EC) of 0.23 ± 0.01 g/[m3·h] was observed with a removal efficiency of 80.9% ± 4% for the aerobic BTF operating at pH 4 for the concentration ratio of 1:40 chloroform to ethanol. For similar ratio, the anaerobic BTF supported lower removal efficiency of 59% ± 10% with corresponding lower EC of 0.16 ± 0.01 g/[m3·h]. Carbon recovery acquired for anaerobic and aerobic BTFs was 59% and 63%, respectively. The loading rate for chloroform on both BTFs was 0.27 g/[m3·h] (per m3 of filter bed volume). Variations of the microbial community were attributed to degradation of chloroform in each BTF. Azospira oryzae and Azospira restrica were the dominant bacteria and potential candidates for chloroform degradation for the anaerobic BTF, whereas Fusarium sp. and Fusarium solani were the dominant fungi and potential candidates for chloroform degradation in the aerobic BTF.

Performance of Anaerobic Biotrickling Filter and its Microbial Diversity for the Removal of Stripped Disinfection Byproducts.

The objective of this research was to evaluate the biodegradation of chloroform by using biotrickling filter (BTF) and determining the dominant bacteria responsible for the degradation. The research was conducted in three phases under anaerobic condition, namely, in the presence of co-metabolite (Phase I), in the presence of co-metabolite and surfactant (Phase II) and in the presence of surfactant but no co-metabolite (Phase III). The results showed that the presence of ethanol as a co-metabolite provided 49% removal efficiency. The equivalent elimination capacity (EC) was 0.13 g/(m3.hr). The addition of Tomadol 25 - 7 as a surfactant in the nutrient solution increased the removal efficiency of chloroform to 64% with corresponding EC of 0.17 g/(m3.hr). This research also investigated the overall microbial ecology of the BTF utilizing culture-independent gene sequencing alignment of the 16S rRNA allowing identification of isolated species. Taxonomical composition revealed the abundance of deltaproteobacteria and deltaproteobacteria with species level of 97%. A. oryzae (formally dechlorosoma suillum), A. restrica and Geobacter spp. together with other similar groups were the most valuable bacteria for the degradation of chloroform.

Biofiltration of Chloroform in a Trickle Bed Air Biofilter Under Acidic Conditions.

In this paper, the application of biofiltration is investigated for controlled removal of gas phase chloroform through cometabolic degradation with ethanol. A trickle bed air biofilter (TBAB) operated under acidic pH 4 is subjected to aerobic biodegradation of chloroform and ethanol. The TBAB is composed of pelleted diatomaceous earth filter media inoculated with filamentous fungi species, which served as the principle biodegrading microorganism. The removal efficiencies of 5 ppmv of chloroform mixed with different ratios of ethanol as cometabolite (25, 50, 100, 150, and 200 ppmv) ranged between 69.9 and 80.9%. The removal efficiency, reaction rate kinetics, and the elimination capacity increased proportionately with an increase in the cometabolite concentration. The carbon recovery from the TBAB amounted to 69.6% of the total carbon input. It is postulated that the remaining carbon contributed to excess biomass yield within the system. Biomass control strategies such as starvation and stagnation were employed at different phases of the experiment. The chloroform removal kinetics provided a maximum reaction rate constant of 0.0018 s-1. The highest ratio of chemical oxygen demand (COD)removal/nitrogenutilization was observed at 14.5. This study provides significant evidence that the biodegradation of a highly chlorinated methane can be favored by cometabolism in a fungi-based TBAB.

Experimental and modeling studies of sorption of ceria nanoparticle on microbial biofilms.

This study focuses on the interaction of ceria nanoparticles (CeO2-NPs) with Pseudomonas fluorescens and Mycobacterium smegmatis biofilms. Confocal laser microscopy and transmission electron microscopy determined the distribution of NPs in the complex structures of biofilm at molecular levels. Visual data showed that most of the adsorption takes place on the bacterial cell walls and spores. The interaction of nanoparticles (NPs) with biofilms reached equilibrium after the initial high adsorption rate regardless of biofilm heterogeneity and different nanoparticle concentrations in the bulk liquid. Physical processes may dominate this sorption phenomenon. Pseudo first order sorption kinetics was used to estimate adsorption and desorption rate of CeO2-NPs onto biofilms. When biofilms got exposed to CeO2-NPs, a self-protecting mechanism was observed. Cells moved away from the bulk solution in the biofilm matrix, and portions of biofilm outer layer were detached, hence releasing some CeO2-NPs back to the bulk phase.