Integrated Treatment of Per- and Polyfluoroalkyl Substances in Existing Wastewater Treatment Plants-Scoping the Potential of Foam Partitioning.

Foam fractionation is becoming increasingly popular as a treatment technology for water contaminated with per- and polyfluoroalkyl substances (PFAS). At many existing wastewater treatment facilities, particularly in aerated treatment steps, foam formation is frequently observed. This study aimed to investigate if foam fractionation for the removal of PFAS could be integrated with such existing treatment processes. Influent, effluent, water under the foam, and foam were sampled from ten different wastewater treatment facilities where foam formation was observed. These samples were analyzed for the concentration of 29 PFAS, also after the total oxidizable precursor (TOP) assay. Enrichment factors were defined as the PFAS concentration in the foam divided by the PFAS concentration in the influent. Although foam partitioning did not lead to decreased ∑PFAS concentrations from influent to effluent in any of the plants, certain long-chain PFAS were removed with efficiencies up to 76%. Moreover, ∑PFAS enrichment factors in the foam ranged up to 105, and enrichment factors of individual PFAS ranged even up to 106. Moving bed biofilm reactors (MBBRs) were more effective at enriching PFAS in the foam than activated sludge processes. Altogether, these high enrichment factors demonstrate that foam partitioning in existing wastewater treatment plants is a promising option for integrated removal. Promoting foam formation and removing foam from the water surface with skimming devices may improve the removal efficiencies further. These findings have important implications for PFAS removal and sampling strategies at wastewater treatment plants.

Electrochemical Oxidation for Treatment of PFAS in Contaminated Water and Fractionated Foam-A Pilot-Scale Study.

Per- and polyfluoroalkyl substances (PFAS) are persistent synthetic contaminants that are present globally in water and are exceptionally difficult to remove during conventional water treatment processes. Here, we demonstrate a practical treatment train that combines foam fractionation to concentrate PFAS from groundwater and landfill leachate, followed by an electrochemical oxidation (EO) step to degrade the PFAS. The study combined an up-scaled experimental approach with thorough characterization strategies, including target analysis, PFAS sum parameters, and toxicity testing. Additionally, the EO kinetics were successfully reproduced by a newly developed coupled numerical model. The mean total PFAS degradation over the designed treatment train reached 50%, with long- and short-chain PFAS degrading up to 86 and 31%, respectively. The treatment resulted in a decrease in the toxic potency of the water, as assessed by transthyretin binding and bacterial bioluminescence bioassays. Moreover, the extractable organofluorine concentration of the water decreased by up to 44%. Together, these findings provide an improved understanding of a promising and practical approach for on-site remediation of PFAS-contaminated water.

Foam fractionation for removal of per- and polyfluoroalkyl substances: Towards closing the mass balance.

Foam fractionation has recently attracted attention as a low-cost and environmentally benign treatment technology for water contaminated with per- and polyfluoroalkyl substances (PFAS). However, data on the mass balance over the foam fractionation process are scarce and when available, gaps in the mass balance are often identified. This study verified the high treatment efficiency of a pilot-scale foam fractionation system for removal of PFAS from industrial water contaminated with aqueous film-forming foam. ΣPFAS removal reached up to 84 % and the removal of perfluorooctane sulfonic acid (PFOS) up to 97 %, but the short-chain perfluorobutanoic acid (PFBA) was only removed with a mean efficiency of 1.5 %. In general, mobile short-chain PFAS were removed less efficiently when the perfluorocarbon chain length was below six for carboxylic acids and below five for sulfonic acids. Fluctuations in treatment efficiency due to natural variations in the chemistry of the influent water were minor, confirming the robustness of the technology, but significant positive correlations between PFAS removal and influent metal concentration and conductivity were observed. Over all experiments, the mass balance closure did not differ significantly from 100 %. Nonetheless, PFAS sorption to the walls of the reactor was measured, as well as high PFAS emissions by the air exiting the reactor. PFAS emissions in aerosols correlated positively with mass balance closure. The elevated aerial PFAS concentrations measured in the experimental facility have implications for worker safety and prevention of PFAS-emissions to the atmosphere, and demonstrate the importance of installing appropriate filters on the air outlet of foam fractionation systems.

Pilot-Scale Continuous Foam Fractionation for the Removal of Per- and Polyfluoroalkyl Substances (PFAS) from Landfill Leachate.

Per- and polyfluoroalkyl substances (PFAS) are of concern for their ubiquity in the environment combined with their persistent, bioaccumulative, and toxic properties. Landfill leachate is often contaminated with these chemicals, and therefore, the development of cost-efficient water treatment technologies is urgently needed. The present study investigated the applicability of a pilot-scale foam fractionation setup for the removal of PFAS from natural landfill leachate in a novel continuous operating mode. A benchmark batch test was also performed to compare treatment efficiency. The ΣPFAS removal efficiency plateaued around 60% and was shown to decrease for the investigated process variables air flow rate (Q air), collected foam fraction (%foam) and contact time in the column (t c). For individual long-chain PFAS, removal efficiencies above 90% were obtained, whereas the removal for certain short-chain PFAS was low (<30%). Differences in treatment efficiency between enriching mode versus stripping mode as well as between continuous versus batch mode were negligible. Taken together, these findings suggest that continuous foam fractionation is a highly applicable treatment technology for PFAS contaminated water. Coupling the proposed cost- and energy-efficient foam fractionation pretreatment to an energy-intensive degradative technology for the concentrated foam establishes a promising strategy for on-site PFAS remediation.

Poverty and mental health among migrants: When is ingroup exposure more protective than social ties?

•Ingroup exposure in residential areas and social ties are typically positively linked to mental health among migrants.•We argue that whether migrants can reap the benefits of these protective factors depends on their poverty status.•Findings show that migrants below the poverty line do not benefit from ingroup exposure or social ties.•However, compared to natives, migrants above the poverty line do benefit from social ties.•We conclude that migrants might benefit more from protective factors when they are equipped to invest in them.

Photoswitching of DNA Hybridization Using a Molecular Motor.

Reversible control over the functionality of biological systems via external triggers may be used in future medicine to reduce the need for invasive procedures. Additionally, externally regulated biomacromolecules are now considered as particularly attractive tools in nanoscience and the design of smart materials, due to their highly programmable nature and complex functionality. Incorporation of photoswitches into biomolecules, such as peptides, antibiotics, and nucleic acids, has generated exciting results in the past few years. Molecular motors offer the potential for new and more precise methods of photoregulation, due to their multistate switching cycle, unidirectionality of rotation, and helicity inversion during the rotational steps. Aided by computational studies, we designed and synthesized a photoswitchable DNA hairpin, in which a molecular motor serves as the bridgehead unit. After it was determined that motor function was not affected by the rigid arms of the linker, solid-phase synthesis was employed to incorporate the motor into an 8-base-pair self-complementary DNA strand. With the photoswitchable bridgehead in place, hairpin formation was unimpaired, while the motor part of this advanced biohybrid system retains excellent photochemical properties. Rotation of the motor generates large changes in structure, and as a consequence the duplex stability of the oligonucleotide could be regulated by UV light irradiation. Additionally, Molecular Dynamics computations were employed to rationalize the observed behavior of the motor-DNA hybrid. The results presented herein establish molecular motors as powerful multistate switches for application in biological environments.

Ethnic Composition and Friendship Segregation: Differential Effects for Adolescent Natives and Immigrants.

Ethnically diverse settings provide opportunities for interethnic friendship but can also increase the preference for same-ethnic friendship. Therefore, same-ethnic friendship preferences, or ethnic homophily, can work at cross-purposes with policy recommendations to diversify ethnic representation in social settings. In order to effectively overcome ethnic segregation, we need to identify those factors within diverse settings that exacerbate the tendency toward ethnic homophily. Using unique data and multiple network analyses, the authors examine 529 adolescent friendship networks in English, German, Dutch, and Swedish schools and find that the ethnic composition of school classes relates differently to immigrant and native homophily. Immigrant homophily disproportionately increases as immigrants see more same-ethnic peers, and friendship density among natives has no effect on this. By contrast, native homophily remains relatively low until natives see dense groups of immigrants. The authors' results suggest that theories of interethnic competition and contact opportunities apply differently to ethnic majority and minority groups.

Irreconcilable differences? Ethnic intermarriage and divorce in the Netherlands, 1995-2008.

This study uses population data of the Netherlands (municipality registers) between 1995 and 2008 to describe and explain the occurrence of divorce among recently newlywed interethnic and mono-ethnic couples (N=116,745). In line with homogamy theory, divorce risks are higher for interethnic couples, in particular if the spouses were born and raised in countries that are culturally distant from each other. In addition, the effect of cultural distance is smaller for second generation immigrants than for first generation immigrants. There is no evidence for a higher risk of divorce among Black-White marriages. In line with convergence theory, results show that the higher the divorce propensity in the wife's origin country, the higher the divorce risk of a couple is.