Antidepressants can induce mutation and enhance persistence toward multiple antibiotics.

Antibiotic resistance is an urgent threat to global health. Antidepressants are consumed in large quantities, with a similar pharmaceutical market share (4.8%) to antibiotics (5%). While antibiotics are acknowledged as the major driver of increasing antibiotic resistance, little attention is paid to the contribution of antidepressants in this process. Here, we demonstrate that antidepressants at clinically relevant concentrations induce resistance to multiple antibiotics, even following short periods of exposure. Antibiotic persistence was also enhanced. Phenotypic and genotypic analyses revealed the enhanced production of reactive oxygen species following exposure to antidepressants was directly associated with increased resistance. An enhanced stress signature response and stimulation of efflux pump expression were also associated with increased resistance and persistence. Mathematical modeling also predicted that antidepressants would accelerate the emergence of antibiotic-resistant bacteria, and persister cells would help to maintain the resistance. Overall, our findings highlight the antibiotic resistance risk caused by antidepressants.

DEX Inhibits H/R-induced Cardiomyocyte Ferroptosis by the miR-141-3p/lncRNA TUG1 Axis.

BACKGROUND: Ferroptosis is emerging as a critical pathway in ischemia/reperfusion (I/R) injury, contributing to compromised cardiac function and predisposing individuals to sepsis and myocardial failure. The study investigates the underlying mechanism of dexmedetomidine (DEX) in hypoxia/reoxygenation (H/R)-induced ferroptosis in cardiomyocytes, aiming to identify novel targets for myocardial I/R injury treatment. METHODS: H9C2 cells were subjected to H/R and treated with varying concentrations of DEX. Additionally, H9C2 cells were transfected with miR-141-3p inhibitor followed by H/R treatment. Levels of miR-141-3p, long noncoding RNA (lncRNA) taurine upregulated 1 (TUG1), Fe2+, glutathione (GSH), and malondialdehyde were assessed. Reactive oxygen species (ROS) generation was measured via fluorescent labeling. Expression of ferroptosis-related proteins glutathione peroxidase 4 (GPX4) and acyl-CoA synthetase long-chain family member 4 (ACSL4) was determined using Western blot. The interaction between miR-141-3p and lncRNA TUG1 was evaluated through RNA pull-down assay and dual-luciferase reporter gene assays. The stability of lncRNA TUG1 was assessed using actinomycin D. RESULTS: DEX ameliorated H/R-induced cardiomyocyte injury and elevated miR-141-3p expression in cardiomyocytes. DEX treatment increased cell viability, Fe2+, and ROS levels while decreasing ACSL4 protein expression. Furthermore, DEX upregulated GSH and GPX4 protein levels. miR-141-3p targeted lncRNA TUG1, reducing its stability and overall expression. Inhibition of miR-141-3p or overexpression of lncRNA TUG1 partially reversed the inhibitory effect of DEX on H/R-induced ferroptosis in cardiomyocytes. CONCLUSION: DEX mitigated H/R-induced ferroptosis in cardiomyocytes by upregulating miR-141-3p expression and downregulating lncRNA TUG1 expression, unveiling a potential therapeutic strategy for myocardial I/R injury.

The effect of green infrastructure on resilience performance in combined sewer systems under climate change.

Climate change is currently reshaping precipitation patterns, intensifying extremes, and altering runoff dynamics. Particularly susceptible to these impacts are combined sewer systems (CSS), which convey both stormwater and wastewater and can lead to combined sewer overflow (CSO) discharges during heavy rainfall. Green infrastructure (GI) can help mitigate these discharges and enhance system resilience under historical conditions; however, the quantification of its effect on resilience in a future climate remains unknown in the literature. This study employs a modified Global Resilience Analysis (GRA) framework for continuous simulation to quantify the impact of climate change on CSS resilience, particularly CSOs. The study assesses the efficacy of GI interventions (green roofs, permeable pavements, and bioretention cells) under diverse future rainfall scenarios based on EURO-CORDEX regional climate models (2085-2099) and three Representative Concentration Pathways (2.6, 4.5, 8.5 W/m2). The findings underscore a general decline in resilience indices across the future rainfall scenarios considered. Notably, the total yearly CSO discharge volume increases by a range of 145 % to 256 % in response to different rainfall scenarios. While GI proves effective in increasing resilience, it falls short of offsetting the impacts of climate change. Among the GI options assessed, green roofs routed to pervious areas exhibit the highest adaptive capacity, ranging from 9 % to 22 % at a system level, followed by permeable pavements with an adaptation capacity between 7 and 13 %. By linking the effects of future rainfall scenarios on CSO performance, this study contributes to understanding GI's potential as a strategic tool for enhancing urban resilience.

Characterization of the redox-active extracellular polymeric substances in an anaerobic methanotrophic consortium.

Anaerobic oxidation of methane (AOM) is a microbial process of importance in the global carbon cycle. AOM is predominantly mediated by anaerobic methanotrophic archaea (ANME), the physiology of which is still poorly understood. Here we present a new addition to the current physiological understanding of ANME by examining, for the first time, the biochemical and redox-active properties of the extracellular polymeric substances (EPS) of an ANME enrichment culture. Using a 'Candidatus Methanoperedens nitroreducens'-dominated methanotrophic consortium as the representative, we found it can produce an EPS matrix featuring a high protein-to-polysaccharide ratio of ∼8. Characterization of EPS using FTIR revealed the dominance of protein-associated amide I and amide II bands in the EPS. XPS characterization revealed the functional group of C-(O/N) from proteins accounted for 63.7% of total carbon. Heme-reactive staining and spectroscopic characterization confirmed the distribution of c-type cytochromes in this protein-dominated EPS, which potentially enabled its electroactive characteristic. Redox-active c-type cytochromes in EPS mediated the EET of 'Ca. M. nitroreducens' for the reduction of Ag+ to metallic Ag, which was confirmed by both ex-situ experiments with extracted soluble EPS and in-situ experiments with pristine EPS matrix surrounding cells. The formation of nanoparticles in the EPS matrix during in-situ extracellular Ag + reduction resulted in a relatively lower intracellular Ag distribution fraction, beneficial for alleviating the Ag toxicity to cells. The results of this study provide the first biochemical information on EPS of anaerobic methanotrophic consortia and a new insight into its physiological role in AOM process.

Microbial Stratification Affects Conversions of Nitrogen and Methane in Biofilms Coupling Anammox and n-DAMO Processes.

A methane-based membrane biofilm reactor (MBfR) has a suitable configuration to incorporate anammox and nitrite/nitrate-dependent anaerobic methane oxidation (n-DAMO) processes because of its high gas-transfer efficiency and efficient biomass retention. In this study, the spatial distribution of microorganisms along with the biofilm depth in methane-based MBfRs was experimentally revealed, showing the dominance of anammox bacteria, n-DAMO bacteria, and n-DAMO archaea in the outer layer, middle layer, and inner layer of biofilms, respectively. The long-term and short-term experimental investigations in conjunction with mathematical modeling collectively revealed that microorganisms living in the outer layer of biofilms tend to use substrates from wastewater, while microorganisms inhabiting the inner layer of biofilms tend to use substrates originating from biofilm substratum. Specifically, anammox bacteria dominating the biofilm surface preferentially removed the nitrite provided from wastewater, while n-DAMO bacteria mostly utilized the nitrite generated from n-DAMO archaea as these two methane-related populations spatially clustered together inside the biofilm. Likewise, the methane supplied from the membrane was mostly consumed by n-DAMO archaea, while the dissolved methane in wastewater would be primarily utilized by n-DAMO bacteria. This study offers novel insights into the impacts of microbial stratification in biofilm systems, not only expanding the fundamental understanding of biofilms and microbial interactions therein but also providing a rationale for the potential applications of methane-based MBfRs in sewage treatment.

Novel Use of a Ferric Salt to Enhance Mainstream Nitrogen Removal from Anaerobically Pretreated Wastewater.

This study aims to demonstrate a new technology roadmap to support the ongoing paradigm shift in wastewater management from pollutant removal to resource recovery. This is achieved by developing a novel use of an iron salt (i.e., FeCl3) in an integrated anaerobic wastewater treatment and mainstream anammox process. FeCl3 was chosen to be dosed in a proposed sidestream unit rather than in a primary settler or a mainstream reactor. This causes acidification of returned activated sludge and enables stable suppression of nitrite-oxidizing bacterial activity and excess sludge reduction. A laboratory-scale system, which comprised an anaerobic baffled reactor, a continuous-flow anoxic-aerobic (A/O) reactor, and a secondary settler, was designed to treat real domestic wastewater, with the performance of the system comprehensively monitored under a steady-state condition. The experimental assessments showed that the system had good effluent quality, with total nitrogen and phosphorus concentrations of 12.6 ± 1.3 mg N/L and 0.34 ± 0.05 mg P/L, respectively. It efficiently retained phosphorus in excess sludge (0.18 ± 0.03 g P/g dry sludge), suggesting its potential for further recovery. About half of influent organic carbon was recovered in the form of bioenergy (i.e., methane). This together with low energy consumption revealed that the system could produce a net energy of about 0.11 kWh/m3-wastewater, assessed by an energy balance analysis.

Pyrogenic Carbon Promotes Anaerobic Oxidation of Methane Coupled with Iron Reduction via the Redox-Cycling Mechanism.

Pyrogenic carbon (PC) can mediate electron transfer and thus catalyze biogeochemical processes to impact greenhouse gas (GHG) emissions. Here, we demonstrate that PC can contribute to mitigating GHG emissions by promoting the Fe(III)-dependent anaerobic oxidation of methane (AOM). It was found that the amendment PCs in microcosms dominated by Methanoperedenaceae performing Fe(III)-dependent AOM simultaneously promoted the rate of AOM and Fe(III) reduction with a consistent ratio close to the theoretical stoichiometry of 1:8. Further correlation analysis showed that the AOM rate was linearly correlated with the electron exchange capacity, but not the conductivity, of added PC materials, indicating the redox-cycling electron transfer mechanism to promote the Fe(III)-dependent AOM. The mass content of the C═O moiety from differentially treated PCs was well correlated with the AOM rate, suggesting that surface redox-active quinone groups on PCs contribute to facilitating Fe(III)-dependent AOM. Further microbial analyses indicate that PC likely shuttles direct electron transfer from Methanoperedenaceae to Fe(III) reduction. This study provides new insight into the climate-cooling impact of PCs, and our evaluation indicates that the PC-facilitated Fe(III)-dependent AOM could have a significant contribution to suppressing methane emissions from the world's reservoirs.

Hydrophilic nanofibers with aligned topography modulate macrophage-mediated host responses via the NLRP3 inflammasome.

Successful biomaterial implantation requires appropriate immune responses. Macrophages are key mediators involved in this process. Currently, exploitation of the intrinsic properties of biomaterials to modulate macrophages and immune responses is appealing. In this study, we prepared hydrophilic nanofibers with an aligned topography by incorporating polyethylene glycol and polycaprolactone using axial electrospinning. We investigated the effect of the nanofibers on macrophage behavior and the underlying mechanisms. With the increase of hydrophilicity of aligned nanofibers, the inflammatory gene expression of macrophages adhering to them was downregulated, and M2 polarization was induced. We further presented clear evidence that the inflammasome NOD-like receptor thermal protein domain associated protein 3 (NLRP3) was the cellular sensor by which macrophages sense the biomaterials, and it acted as a regulator of the macrophage-mediated response to foreign bodies and implant integration. In vivo, we showed that the fibers shaped the implant-related immune microenvironment and ameliorated peritendinous adhesions. In conclusion, our study demonstrated that hydrophilic aligned nanofibers exhibited better biocompatibility and immunological properties.

Global resilience analysis of combined sewer systems under continuous hydrologic simulation.

Managing and reducing combined sewer overflow (CSO) discharges is crucial for enhancing the resilience of combined sewer systems (CSS). However, the absence of a standardised resilience analysis approach poses challenges in developing effective discharge reduction strategies. To address this, our study presents a top-down method that expands the existing Global Resilience Analysis to quantify resilience performance in CSS. This approach establishes a link between threats (e.g., rainfall) and impacts (e.g., CSOs) through continuous and long-term simulation, accommodating various rainfall patterns, including extreme events. We assess CSO discharge impacts from a resilience perspective by introducing eight new metrics. We conducted a case study in Fehraltorf, Switzerland, analysing the performance of three green infrastructure (GI) types (bioretention cells, green roofs, and permeable pavements) over 38 years. The results demonstrated that GI enhanced all resilience indices, with variations observed in individual CSO performance metrics and their system locations. Notably, in Fehraltorf, green roofs emerged as the most effective GI type for improving resilience, while the downstream outfall displayed the highest resilience enhancement. Overall, our proposed method enables a shift from event-based to continuous simulation analysis, providing a standardised approach for resilience assessment. This approach informs the development of strategies for CSO discharge reduction and the enhancement of CSS resilience.

A 20-Year Journey of Partial Nitritation and Anammox (PN/A): from Sidestream toward Mainstream.

Anaerobic ammonium oxidation (anammox) was discovered as a new microbial reaction in the late 1990s, which led to the development of an innovative energy- and carbon-efficient technology─partial nitritation and anammox (PN/A)─for nitrogen removal. PN/A was first applied to remove the nitrogen from high-strength wastewaters, e.g., anaerobic digestion liquor (i.e., sidestream), and further expanded to the main line of wastewater treatment plants (i.e., mainstream). While sidestream PN/A has been well-established with extensive full-scale installations worldwide, practical application of PN/A in mainstream treatment has been proven extremely challenging to date. A key challenge is achieving stable suppression of nitrite-oxidizing bacteria (NOB). This study examines the progress of NOB suppression in both sidestream- and mainstream PN/A over the past two decades. The successful NOB suppression in sidestream PN/A was reviewed, and these successes were evaluated in terms of their transferability into mainstream PN/A. Drawing on the learning over the past decades, we anticipate that a hybrid process, comprised of biofilm and floccular sludge, bears great potential to achieve efficient mainstream PN/A, while a combination of strategies is entailed for stable NOB suppression. Furthermore, the recent discovery of novel nitrifiers would trigger new opportunities and new challenges for mainstream PN/A.

Simultaneous Removal of Antibiotic Resistant Bacteria, Antibiotic Resistance Genes, and Micropollutants by FeS2@GO-Based Heterogeneous Photo-Fenton Process.

The co-occurrence of various chemical and biological contaminants of emerging concerns has hindered the application of water recycling. This study aims to develop a heterogeneous photo-Fenton treatment by fabricating nano pyrite (FeS2) on graphene oxide (FeS2@GO) to simultaneously remove antibiotic resistant bacteria (ARB), antibiotic resistance genes (ARGs), and micropollutants (MPs). A facile and solvothermal process was used to synthesize new pyrite-based composites. The GO coated layer forms a strong chemical bond with nano pyrite, which enables to prevent the oxidation and photocorrosion of pyrite and promote the transfer of charge carriers. Low reagent doses of FeS2@GO catalyst (0.25 mg/L) and H2O2 (1.0 mM) were found to be efficient for removing 6-log of ARB and 7-log of extracellular ARG (e-ARG) after 30 and 7.5 min treatment, respectively, in synthetic wastewater. Bacterial regrowth was not observed even after a two-day incubation. Moreover, four recalcitrant MPs (sulfamethoxazole, carbamazepine, diclofenac, and mecoprop at an environmentally relevant concentration of 10 µg/L each) were completely removed after 10 min of treatment. The stable and recyclable composite generated more reactive species, including hydroxyl radicals (HO•), superoxide radicals (O2• -), singlet oxygen (1O2). These findings highlight that the synthesized FeS2@GO catalyst is a promising heterogeneous photo-Fenton catalyst for the removal of emerging contaminants.

Understanding the Effect of Free Nitrous Acid on Biofilms.

Free nitrous acid (FNA, i.e., HNO2) has been recently applied to biofilm control in wastewater management. The mechanism triggering biofilm detachment upon exposure to FNA still remains largely unknown. In this work, we aim to prove that FNA induces biofilm dispersal via extracellular polymeric matrix breakdown and cell lysis. Biofilms formed by a model organism, Pseudomonas aeruginosa PAO1, were treated with FNA at concentrations ranging from 0.2 to 15 mg N/L for 24 h (conditions typically used in applications). The biofilms and suspended biomass were monitored both before and after FNA treatment using a range of methods including optical density measurements, viability assays, confocal laser scanning microscopy, and atomic force microscopy. It was revealed that FNA treatment caused substantial and concentration-dependent biofilm detachment. The addition of a reactive nitrogen species (RNS) scavenger, that is, 2-4-carboxyphenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, substantially reduced biofilm dispersal, suggesting that the nitrosative decomposition species of HNO2 (i.e., RNS, e.g., •NO + •NO2) were mainly responsible for the effects. The study provides insight into and support for the use of FNA for biofilm control in wastewater treatment.

Wastewater Primary Treatment Using Forward Osmosis Introduces Inhibition to Achieve Stable Mainstream Partial Nitrification.

Achieving stable long-term mainstream nitrite oxidizing bacteria (NOB) suppression is the bottleneck for the novel partial nitrification (PN) process toward energy- and carbon-efficient wastewater treatment. However, long-term PN stability remains a challenge due to NOB adaptation. This study proposed and demonstrated a novel strategy for achieving NOB suppression by the primary treatment of mainstream wastewater with a forward osmosis (FO) membrane process, which facilitated two external NOB inhibition factors (salinity and free nitrous acid, FNA). To evaluate the proposed strategy, a lab-scale sequencing batch reactor was operated for 200 days. A stable PN operation was achieved with a nitrite accumulation ratio of 97.7 ± 2.8%. NOB were suppressed under the combined inhibition effect of NaCl (7.9 ± 0.2 g/L, as introduced by the FO direct filtration) and FNA (0.11 ± 0.02 mg of HNO2-N/L, formed as a result of the increased NH4+-N concentration after the FO process). The two inhibition factors worked in synergy to achieve a more stable PN operation. The microbial analysis showed that the elevated salinity and accumulation of FNA reshaped the microbial community and selectively eliminated NOB. Finally, an economic and feasibility analysis was conducted, which suggests that the integration of an FO unit into PN/A is a feasible and economically viable wastewater treatment process.

Selective Enrichment of Comammox Nitrospira in a Moving Bed Biofilm Reactor with Sufficient Oxygen Supply.

The recent discovery of comammox (complete ammonia oxidation) Nitrospira has upended the long-held nitrification paradigm. Although comammox Nitrospira have been identified in wastewater treatment systems, the conditions for their dominance over canonical ammonia oxidizers remain unclear. Here, we report the dominance of comammox Nitrospira in a moving bed biofilm reactor (MBBR) fed with synthetic mainstream wastewater. Integrated 16S rRNA gene amplicon sequencing, fluorescence in situ hybridization (FISH), and metagenomic sequencing methods demonstrated the selective enrichment of comammox bacteria when the MBBR was operated at a dissolved oxygen (DO) concentration above 6 mg O2/L. The dominance of comammox Nitrospira over canonical ammonia oxidizers (i.e., Nitrosomonas) was attributed to the low residual ammonium concentration (0.02-0.52 mg N/L) formed in the high-DO MBBR. Two clade A comammox Nitrospira were identified, which are phylogenetically close to Candidatus Nitrospira nitrosa. Interestingly, cryosectioning-FISH showed these two comammox species spatially distributed on the surface of the biofilm. Moreover, the ammonia-oxidizing activity of comammox Nitrospira-dominated biofilms was susceptible to the oxygen supply, which dropped by half with the DO concentration decrease from 6 to 2 mg O2/L. These features collectively suggest a low apparent oxygen affinity for the comammox Nitrospira-dominated biofilms in the high-DO nitrifying MBBR.

Determining Factors for Nitrite Accumulation in an Acidic Nitrifying System: Influent Ammonium Concentration, Operational pH, and Ammonia-Oxidizing Community.

Acidic nitrification is attracting wide attention because it can enable robust suppression of nitrite-oxidizing bacteria (NOB) in wastewater treatment. This study reports a comprehensive assessment of the novel acidic nitrification process to identify the key factors that govern stable nitrite accumulation. A laboratory-scale moving-bed biofilm reactor receiving low-alkalinity wastewater was continuously operated under acidic conditions (pH < 6) for around two years, including nine stages varying influent and operational conditions. The results revealed that nitrite accumulation was related to three factors, i.e., influent ammonium concentration, operating pH, and ammonia-oxidizing microbial community. These three factors impact nitrite accumulation by altering the in situ concentration of free nitrous acid (FNA), which is a potent inhibitor of NOB. The critical FNA concentration is approximately one part per million (ppm, ∼1 mg HNO2-N/L), above which nitrite accumulation is stably maintained in an acidic nitrifying system. The findings of this study suggest that stable nitrite accumulation via acidic ammonia oxidation can be maintained under a range of influent and operational conditions, as long as a ppm-level of FNA is established. Taking low-strength mainstream wastewater (40-50 mg NH4+-N/L) with limited alkalinity as an example, stable nitrite accumulation was experimentally demonstrated at a pH of 4.35, under which an in situ FNA of 2.3 ± 0.6 mg HNO2-N/L was attained. Under these conditions, Candidatus Nitrosoglobus became the only ammonia oxidizer detectable by 16S rRNA gene sequencing. The results of this study deepen our understanding of acidic nitrifying systems, informing further development of novel wastewater treatment technologies.

An Integrated First Principal and Deep Learning Approach for Modeling Nitrous Oxide Emissions from Wastewater Treatment Plants.

Mathematical modeling plays a critical role toward the mitigation of nitrous oxide (N2O) emissions from wastewater treatment plants (WWTPs). In this work, we proposed a novel hybrid modeling approach by integrating the first principal model with deep learning techniques to predict N2O emissions. The hybrid model was successfully implemented and validated with the N2O emission data from a full-scale WWTP. This hybrid model is demonstrated to have higher accuracy for N2O emission modeling in the WWTP than the mechanistic model or pure deep learning model. Equally important, the hybrid model is more applicable than the pure deep learning model due to the lower requirement of data and the pure mechanistic model due to the less calibration requirement. This superior performance was due to the hybrid nature of the proposed model. It integrated the essential wastewater treatment knowledge as the first principal component and the less understood N2O production processes by the data-driven deep learning approach. The developed hybrid model was also successfully implemented under different circumstances for the prediction of N2O flux, which showed the generalizability of the model. The hybrid model also showed great potential to be applied for the N2O mitigation work. Nevertheless, the capability of the hybrid model in evaluating N2O mitigation strategies still requires validation with experiments. Going beyond N2O modeling in WWTP, the novel hybridization modeling concept can potentially be applied to other environmental systems.

Characterizing and comparing microbial community and biofilm structure in three nitrifying moving bed biofilm reactors.

This study investigated biofilm establishment, biofilm structure, and microbial community composition of biofilms in three laboratory-scale moving bed biofilm reactors. These reactors were filled with three types of plastic carriers with varied depths of living space for microbial growth. The reactors were operated under the same influent and operational conditions. Along with the operation, the results showed that carriers with grids of 50 µm in height delayed the biofilm development and formed the thinnest biofilm and a carpet-like structure with the lowest α-diversity. In comparison, another two carriers with grids of 200 and 400 µm in height formed thick biofilms and large colonies with more voids and channels. Quantified properties of biofilm thickness, biomass, heterogeneity, portion of the biofilm exposed to the nutrient, and maximum diffusion distance were examined, and the results demonstrated that they almost (except for heterogeneity) strongly correlated to the α-diversity of microbial community. These illustrate that depth of living space, as an important parameter for carrier, could drive the formation of biofilm structure and community composition. It improves understanding of influencing factors on biofilm establishment, structure and its microbial community, and would be helpful for the design of biofilm processes.

Microbial Perchlorate Reduction Driven by Ethane and Propane.

Previous studies demonstrated that methane can be used as an electron donor to microbially remove various oxidized contaminants in groundwater. Natural gas, which is more widely available and less expensive than purified methane, is potentially an alternative source of methane. However, natural gas commonly contains a considerable amount of ethane (C2H6) and propane (C3H8), in addition to methane. It is important that these gaseous alkanes are also utilized along with methane to avoid emissions. Here, we demonstrate that perchlorate (ClO4-), a frequently reported contaminant in groundwater, can be microbially reduced to chloride (Cl-) driven by C2H6 or C3H8 under oxygen-limiting conditions. Two independent membrane biofilm reactors (MBfRs) supplied with C2H6 and C3H8, respectively, were operated in parallel to biologically reduce ClO4-. The continuous ClO4- removal during long-term MBfR operation combined with the concurrent C2H6/C3H8 consumption and ClO4- reduction in batch tests confirms that ClO4- reduction was associated with C2H6 or C3H8 oxidation. Polyhydroxyalkanoates (PHAs) were synthesized in the presence of C2H6 or C3H8 and were subsequently utilized for supporting ClO4- bio-reduction in the absence of gaseous alkanes. Analysis by reverse transcription-quantitative polymerase chain reaction (RT-qPCR) showed that transcript abundance of bmoX (encoding alpha hydroxylase subunit of C2H6/C3H8 monooxygenase) was positively correlated to the consumption rates of C2H6/C3H8, while pcrA (encoding a catalytic subunit of perchlorate reductase) was positively correlated to the consumption of ClO4-. High-throughput sequencing targeting 16S rRNA, bmoX, and pcrA indicated that Mycobacterium was the dominant microorganism oxidizing C2H6/C3H8, while Dechloromonas may be the major perchlorate-reducing bacterium in the biofilms. These findings shed light on microbial ClO4- reduction driven by C2H6 and C3H8, facilitating the development of cost-effective strategies for ex situ groundwater remediation.

Insights into Nitrous Oxide Mitigation Strategies in Wastewater Treatment and Challenges for Wider Implementation.

Nitrous oxide (N2O) emissions account for the majority of the carbon footprint of wastewater treatment plants (WWTPs). Many N2O mitigation strategies have since been developed while a holistic view is still missing. This article reviews the state-of-the-art of N2O mitigation studies in wastewater treatment. Through analyzing existing studies, this article presents the essential knowledge to guide N2O mitigations, and the logics behind mitigation strategies. In practice, mitigations are mainly carried out by aeration control, feed scheme optimization, and process optimization. Despite increasingly more studies, real implementation remains rare, which is a combined result of unclear climate change policies/incentives, as well as technical challenges. Five critical technical challenges, as well as opportunities, of N2O mitigations were identified. It is proposed that (i) quantification methods for overall N2O emissions and pathway contributions need improvement; (ii) a reliable while straightforward mathematical model is required to quantify benefits and compare mitigation strategies; (iii) tailored risk assessment needs to be conducted for WWTPs, in which more long-term full-scale trials of N2O mitigation are urgently needed to enable robust assessments of the resulting operational costs and impact on nutrient removal performance; (iv) current mitigation strategies focus on centralized WWTPs, more investigations are warranted for decentralised systems, especially decentralized activated sludge WWTPs; and (v) N2O may be mitigated by adopting novel strategies promoting N2O reduction denitrification or microorganisms that emit less N2O. Overall, we conclude N2O mitigation research is reaching a maturity while challenges still exist for a wider implementation, especially in relation to the reliability of N2O mitigation strategies and potential risks to nutrient removal performances of WWTPs.

Effects of pH, Temperature, Suspended Solids, and Biological Activity on Transformation of Illicit Drug and Pharmaceutical Biomarkers in Sewers.

In-sewer stability of biomarkers is a critical factor for wastewater-based epidemiology, as it could affect the accuracy of the estimated prevalence of substances in the community. The spatiotemporal variations of environmental and biological conditions in sewers can influence the transformation of biomarkers. To date, the relationship between environmental variables and biomarker stability in sewers is poorly understood. Therefore, this study evaluated the transformation of common illicit drug and pharmaceutical biomarkers in laboratory sewer reactors with different levels of pH, temperature, and suspended solids. The correlations between degradation rates of 14 biomarkers, 3 controlled environmental variables (pH, temperature, and suspended solids concentration), and 3 biological activity indicators (sulfide production rate, methane production rate, and the removal rate of soluble chemical oxygen demand (SCOD)) were assessed using correlation matrix, stepwise regression method, and principal component analysis. The consistent results affirmed the dominant effects of biological activities and pH on biomarker transformation in sewers, particularly for labile compounds, whereas the impact of temperature or suspended solids was less significant. This study enhances the understanding of factors affecting the fate of micropollutants in sewer systems and facilitates the interpretation of WBE results for assessing drug use and public health in communities.