Complete defluorination of perfluorooctanoic acid (PFOA) by ultrasonic pyrolysis towards zero fluoro-pollution.

Advanced oxidation/reduction of PFAS is challenged and concerned by the formation of toxic, short-chain intermediates during water treatments. In this study, we investigated the complete defluorination of PFOA by ultrasound/persulfate (US/PS) with harmless end-products of CO2, H2O, and F‒ ions. We observed 100% defluorination after 4 h of US treatment alone with a power input of 900 W. PS addition, however, suppressed defluorination. We demonstrated by kinetics-fitted Langmuir-type adsorption modeling, the added PS increased competition with PFOA for adsorption sites on the bubble-water interface where radical oxidation and pyrolysis may occur. Providing sulfate (SO4•-) and hydroxyl (•OH) radicals by means other than US did not defluorinate PFOA, indicating that pyrolysis likely contributes to the high defluorination performance. Bond dissociation energies for CC and CF were independent of pressure but decreased at elevated temperatures within cavitation bubbles (i.e., 5000 K) favoring the pyrolysis reactions. Furthermore, bond length calculations indicated that PFOA cleavage only begins to occur at temperatures in excess of those generated at the bubble interface (i.e., >1500 K) at the femtosecond level. This suggests that PFOA vaporizes or injects by nanodrops upon attachment to the cavitation bubble, enters the bubble, and is then cleaved within the bubble by pyrolysis. Our research in low-frequency ultrasonic horn system challenges the previous founding that defluorination of PFOA initiates and occurs at the bubble-water interface. We describe here that supplementing US-based processes with complementary treatments may have undesired effects on the efficacy of US. The mechanistic insights will further promote the implementation of US technology for PFAS treatment in achieving the zero fluoro-pollution goal.

Enterococcus faecalis thrives in dual-species biofilm models under iron-rich conditions.

Escherichia coli (E. coli) and Enterococcus faecalis (E. faecalis) are pathogenic strains that often coexist in intestinal flora of humans and are prone to cause biofilm-associated infections, such as gastrointestinal tract and urinary tract infections. Earlier studies have demonstrated that E. faecalis biofilm can metabolize ferrous ions in iron-rich environments and promote biofilm growth under in-vivo conditions. However, the influence of iron transporters on dual-species biofilm growth and the nature of molecular-level interactions between iron transporter proteins and Fe2+ remains unknown. Therefore, in this work, co-culture studies were performed and the study indicates that Fe2+ at concentrations of 50-150 µM promotes the colonization of E. coli, and Fe2+ concentrations of 50-200 µM promote the growth of E. faecalis and dual-species colonies. Atomic absorption spectroscopy results reveal that Fe2+ ion augmentation in bacterial cells was increased to 4 folds in the single-species model and 11 folds in the dual-species model under iron-supplemented conditions. Furthermore, Fe2+ augmentation increased the antibiotic resistance of E. faecalis in both single- and dual-species bacterial cultures. In addition, in-silico docking were performed to determine a three-dimensional (3D) structure of ferrous iron-transporter proteins FeoB of E. faecalis and its affinity to extracellular Fe2+. Our model suggests that the FeoB facilitates the Fe2+ uptake in E. faecalis cells in the absence of iron chelator, 2,2-bipyridyl.

Transient Complexity of E. coli Lipidome Is Explained by Fatty Acyl Synthesis and Cyclopropanation.

In the case of many bacteria, such as Escherichia coli, the composition of lipid molecules, termed the lipidome, temporally adapts to different environmental conditions and thus modifies membrane properties to permit growth and survival. Details of the relationship between the environment and lipidome composition are lacking, particularly for growing cultures under either favourable or under stress conditions. Here, we highlight compositional lipidome changes by describing the dynamics of molecular species throughout culture-growth phases. We show a steady cyclopropanation of fatty acyl chains, which acts as a driver for lipid diversity. There is a bias for the cyclopropanation of shorter fatty acyl chains (FA 16:1) over longer ones (FA 18:1), which likely reflects a thermodynamic phenomenon. Additionally, we observe a nearly two-fold increase in saturated fatty acyl chains in response to the presence of ampicillin and chloramphenicol, with consequences for membrane fluidity and elasticity, and ultimately bacterial stress tolerance. Our study provides the detailed quantitative lipidome composition of three E. coli strains across culture-growth phases and at the level of the fatty acyl chains and provides a general reference for phospholipid composition changes in response to perturbations. Thus, lipidome diversity is largely transient and the consequence of lipid synthesis and cyclopropanation.

High Dissolved Oxygen Selection against Nitrospira Sublineage I in Full-Scale Activated Sludge.

A single Nitrospira sublineage I OTU was found to perform nitrite oxidation in full-scale domestic wastewater treatment plants (WWTPs) in the tropics. This taxon had an apparent oxygen affinity constant lower than that of the full-scale domestic activated sludge cohabitating ammonium oxidizing bacteria (AOB) (0.09 ± 0.02 g O2 m-3 versus 0.3 ± 0.03 g O2 m-3). Thus, nitrite oxidizing bacteria (NOB) may in fact thrive under conditions of low oxygen supply. Low dissolved oxygen (DO) conditions selected for and high aeration inhibited the NOB in a long-term lab-scale reactor. The relative abundance of Nitrospira sublineage I gradually decreased with increasing DO until it was washed out. Nitritation was sustained even after the DO was lowered subsequently. The morphologies of AOB and NOB microcolonies responded to DO levels in accordance with their oxygen affinities. NOB formed densely packed spherical clusters with a low surface area-to-volume ratio compared to the Nitrosomonas-like AOB clusters, which maintained a porous and nonspherical morphology. In conclusion, the effect of oxygen on AOB/NOB population dynamics depends on which OTU predominates given that oxygen affinities are species-specific, and this should be elucidated when devising operating strategies to achieve mainstream partial nitritation.

Bucking the current trend in bioelectrochemical systems: a case for bioelectroanalytics.

Turning wastewater directly into electricity is alluring, widespread use of microbial fuel cells (MFCs) to achieve this at industrial scale appears increasingly unlikely despite intense research efforts lasting over a decade. Such endeavors have not been futile, however, and game-changing discoveries have resulted from these well-intentioned, scientifically rigorous but ultimately frustrated attempts to resolve the Waste-Energy dichotomy. The appeal of MFCs is largely of conceptual elegance rather than financial competitiveness, based on the green ideal that bacteria can be turned into cost effective bio-batteries. This notion is founded on the solid principles of extracellular electron transfer (EET), where microbes use electrodes interchangeably with other electron acceptors to generate current as a direct proxy for microbial metabolism. We contend that a nuanced understanding of EET has been restricted by focusing on device performance when in fact this information could be more beneficially channeled into addressing analytical questions pertaining to the presence and activity of microorganisms across systems of environmental and medical import, i.e. bioelectroanalytics. We discuss here relevant literature detailing bioelectrochemical systems and contrast energy-centric conclusions with observations geared towards bioelectroanalytics. We explore the expanding possibilities of bioelectroanalytics enabled by advances in genetic techniques and rooted in the concept that microbial interactions with an electrode extend to more than just cells seeking alternative electron acceptors. Our intention is to highlight alternative directions in the field and encourage researchers to harness bioelectroanalytics to address wider societal problems, in addition to addressing climate change.

Selectively inducing the synthesis of a key structural exopolysaccharide in aerobic granules by enriching for Candidatus "Competibacter phosphatis".

A gel-forming exopolysaccharide was previously shown to play an important structural role in aerobic granules treating nutrient-rich industrial wastewater. To identify whether this exopolysaccharide performs a similar role in other granular biomass and if conditions favouring its production can be more precisely elucidated, extracellular polymeric substances (EPS) were extracted from granules grown under four different operating conditions. (1)H nuclear magnetic resonance (NMR) spectroscopy of their EPS indicated that the gel-forming exopolysaccharide was expressed in two granular sludges both enriched in Candidatus "Competibacter phosphatis". In contrast, it was not expressed in granules performing denitrification with methanol as a carbon source and nitrate as the electron acceptor or granules enriched in Candidatus "Accumulibacter phosphatis" performing enhanced biological phosphorus removal from synthetic wastewater. In one of the first two sludges, the exopolysaccharide contained in the seeding granular sludge continued to be a major component of the granule EPS while Competibacter was being enriched. In the second sludge, a floccular sludge not containing the gel-forming exopolysaccharide initially was also enriched for Competibacter. In this sludge, an increase in particle size was detected coinciding with a yield increase of EPS. NMR spectroscopy confirmed its yield increase to be attributable to the production of this structural gel-forming exopolysaccharide. The results show that (1) the particular gel-forming exopolysaccharide previously identified is not necessarily a key structural exopolysaccharide for all granule types, and (2) synthesis of this exopolysaccharide is induced under conditions favouring the selective enrichment of Competibacter. This indicates that Competibacter may be involved in its production.