New insight into effect of antibiotics concentration and process configuration on the removal of antibiotics and relevant antibiotic resistance genes

Parachlorometaxylenol stress caused multidrug-type antibiotic resistance genes proliferation via simultaneously reshaping microbial community and interfering metabolic traits during wastewater treatment process

Despite biological wastewater treatment processes (e.g., sequencing batch reactors (SBR)) being able to reduce the dissemination of antibiotic resistance genes (ARGs), the variation of ARGs under exogenous pollutant stress is an open question. This work investigated the impacts of para-chloro-meta-xylenol (PCMX, typical antibacterial contaminants) on ARGs spread in long-term SBR operation. Although the SBR process inherently decreased ARGs abundance, the presence of PCMX substantially amplified both the prevalence (mainly multidrug) and abundance of total ARGs (1.17-fold of the control). Further analysis demonstrated that PCMX disintegrated sludge structures as well as increased membrane permeability, facilitating the release of mobile genetic elements and subsequent horizontal transfer of ARGs. In addition, PCMX selectively enriched potential ARG hosts, notably Nitrospira and Candidatus Accumulibacter, which predominantly served as multidrug ARG hosts. Concurrently, the self-adaptive functions of ARGs hosts in the PCMX-exposed SBR system were activated via quorum sensing, two-component regulatory system, ATP-binding cassette transporters, and bacterial secretion system. The upregulation of these metabolic pathways also contributed to the dissemination of ARGs.

Effects of successional sulfadiazine exposure on biofilm in moving bed biofilm reactor: Secretion of extracellular polymeric substances, community activity and functional gene expression

The effects of sulfadiazine (SDZ) on responses of biofilm in a moving bed biofilm reactor were explored with emphasis on the changes in extracellular polymeric substances (EPS) and functional genes. It was found that 3 to 10 mg/L SDZ reduced the protein (PN) and polysaccharide (PS) contents of EPS by 28.7%-55.1% and 33.3%-61.4%, respectively. The EPS maintained high ratio of PN to PS (10.3-15.1), and the major functional groups within EPS remained unaffected to SDZ. Bioinformatics analysis showed that SDZ significantly altered the community activity such as increased expression of s_Alcaligenes faecali. Totally, the biofilm held high SDZ removal rates, which were ascribed to the self-protection by secreted EPS, and genes levels upregulation of antibiotic resistance and transporter protein. Collectively, this study provides more details on the biofilm community exposure to an antibiotic and highlights the role of EPS and functional genes in antibiotic removal.

High-risk antibiotics positively correlated with antibiotic resistance genes in five typical urban wastewater

Antibiotic resistance genes (ARGs) and antibiotic amount increased within close proximity to human dominated ecosystems. However, few studies assessed the distribution of antibiotics and ARGs in multiple ecosystems especially the different urban wastewater. In this study, the spatial distribution of ARGs and antibiotics across the urban wastewater included domestic, livestock, hospital, pharmaceutical wastewater, influent of the wastewater treatment plant (WWTP) in Northeast China. The q-PCR results showed that ARGs were most abundant in community wastewater and followed by WWTP influent, livestock wastewater, pharmaceutical wastewater and hospital wastewater. The ARG composition differed among the five ecotypes with qnrS was the dominant ARG subtypes in WWTP influent and community wastewater, while sul2 dominant in livestock, hospital, pharmaceutical wastewater. The concentration of antibiotics was closely related to the antibiotic usage and consumption data. In addition to the high concentration of azithromycin at all sampling points, more than half of the antibiotics in livestock wastewater were veterinary antibiotics. However, antibiotics that closely related to humankind such as roxithromycin and sulfamethoxazole accounted for a higher proportion in hospital wastewater (13.6%) and domestic sewage (33.6%), respectively. The ambiguous correlation between ARGs and their corresponding antibiotics was detected. However, antibiotics that exhibited high ecotoxic effects were closely and positively correlated with ARGs and the class 1 integrons (intI1), which indicated that high ecotoxic compounds might affect antimicrobial resistance of bacteria by mediating horizontal gene transfer of ARGs. The coupling mechanism between the ecological risk of antibiotics and bacterial resistance needed to be further studied, and thereby provided a new insight to study the impact of environmental pollutants on ARGs in various ecotypes.

Effect of bioaugmentation on tetracyclines influenced chicken manure composting and antibiotics resistance

Antibiotic residue in husbandry waste has become a serious concern. In this study, contaminated chicken manure composting was conducted to reveal the bioaugmentation effect on tetracyclines residue and antibiotics resistance genes (ARGs). The bioaugmented composting removed most of the antibiotics in 7 days. Under bioaugmentation, 96.88 % of tetracycline and 92.31 % of oxytetracycline were removed, 6.32 % and 20.93 % higher than the control (P < 0.05). The high-temperature period was the most effective phase for eliminating antibiotics. The treatment showed a long high-temperature period (7 days), while no high-temperature period was in control. After composting, the treatment showed 13.87 % higher TN (26.51 g/kg) and 13.42 % higher NO₃^--N (2.45 g/kg) than control (23.28 and 2.16 g/kg, respectively) but 12.72 % lower C/N, indicating fast decomposition and less nutrient loss. Exogenous microorganisms from bioaugmentation significantly reshaped the microbial community structure and facilitated the enrichment of genera such as Truepera and Fermentimonas, whose abundance increased by 71.10 % and 75.37 % than the control, respectively. Remarkably, ARGs, including tetC, tetG, and tetW, were enhanced by 198.77 %, 846.77 %, and 62.63 % compared with the control, while the integron gene (intl1) was elevated by 700.26 %, indicating horizontal gene transfer of ARGs. Eventually, bioaugmentation was efficient in regulating microbial metabolism, relieving antibiotic stress, and eliminating antibiotics in composting. However, the ability to remove ARGs should be further investigated. Such an approach should be further considered for treating pollutants-influenced organic waste to eliminate environmental concerns.

A critical review on retaining antibiotics in liquid digestate: Potential risk and removal technologies

Substantial levels of antibiotics remain in liquid digestate, posing a significant threat to human safety and the environment. A comprehensive assessment of residual antibiotics in liquid digestate and related removal technologies is required. To this end, this review first evaluates the potential risks of the residual antibiotics in liquid digestate by describing various anaerobic digestion processes and their half-lives in the environment. Next, emerging technologies for removing antibiotics in liquid digestate are summarized and discussed, including membrane separation, adsorption, and advanced oxidation processes. Finally, this study comprehensively and critically discusses these emerging technologies' prospects and challenges, including techno-economic feasibility and environmental impacts.

Co-impacts of the microplastic polyamide and sertraline on the denitrification function and microbial community structure in SBRs

The co-impacts of microplastics (MPs) and organic pollutants on activated sludge have attracted extensive attention. In this study, microplastic polyamide (PA) and sertraline (SER) were respectively or simultaneously added to sequencing batch reactors (SBRs), and the impacts of these pollutants on activated sludge were investigated. The results showed that NH₄⁺-N and TN removal efficiencies significantly decreased with the simultaneous adding of the two pollutants. The coexistence of PA and SER could observably decrease the settling ability of activated sludge, and more proteins and polysaccharides were generated to reduce the combined toxicity. The microbial diversity, especially the denitrification microorganism, was restrained and the metabolic function and the key enzyme involved in nitrogen metabolism pathways were observably decreased, due to the combined toxicity of this two pollutants. Furthermore, the effective SER interception by PA in SBR could induce the SER enrichment in activated sludge and enhance the biotoxicity toward sludge microorganisms.

Antibiotic resistant bacteria and genes in wastewater treatment plants: From occurrence to treatment strategies

This study aims to discuss the following: (1) occurrence and proliferation of antibiotic resistance in wastewater treatment plants (WWTPs); (2) factors influencing antibiotic resistance bacteria and genes in WWTPs; (3) tools to assess antibiotic resistance in WWTPs; (4) environmental contamination of antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) from WWTPs; (5) effects of ARB and ARGs from WWTPs on human health; and (6) treatment strategies. In general, resistant and multi-resistant bacteria, including Enterobacteriaceae, Pseudomonas aeruginosa, and Escherichia coli, exist in various processes of WWTPs. The existence of ARB and ARGs results from the high concentration of antibiotics in wastewater, which promote selective pressures on the local bacteria present in WWTPs. Thus, improving wastewater treatment technology and avoiding the misuse of antibiotics is critical to overcoming the threat of proliferation of ARBs and ARGs. Numerous factors can affect the development of ARB and ARGs in WWTPs. Abiotic factors can affect the bacterial community dynamics, thereby, affecting the applicability of ARB during the wastewater treatment process. Furthermore, the organic loads and other nutrients influence bacterial survival and growth. Specifically, molecular methods for the rapid characterization and detection of ARBs or their genes comprise DNA sequencing, real-time PCR, simple and multiplex PCR, and hybridization-based technologies, including micro- and macro-arrays. The reuse of effluent from WWTPs for irrigation is an efficient method to overcome water scarcity. However, there are also some potential environmental risks associated with this practice, such as increase in the levels of antibiotic resistance in the soil microbiome. Human mortality rates may significantly increase, as ARB can lead to resistance among several types of antibiotics or longer treatment times. Some treatment technologies, such as anaerobic and aerobic treatment, coagulation, membrane bioreactors, and disinfection processes, are considered potential techniques to restrict antibiotic resistance in the environment.

Antibiotics and antibiotic resistant bacteria/genes in urban wastewater: A comparison of their fate in conventional treatment systems and constructed wetlands

There is a growing concern that the use and misuse of antibiotics can increase the detection of antibiotic resistant genes (ARGs) in wastewater. Conventional wastewater treatment plants provide a pathway for ARGs and antibiotic resistant bacteria (ARB) to be released into natural water bodies. Research has indicated that conventional primary and secondary treatment systems can reduce ARGs/ARB to varying degrees. However, in developing/low-income countries, only 8-28% of wastewater is treated via conventional treatment processes, resulting in the environment being exposed to high levels of ARGs, ARB and pharmaceuticals in raw sewage. The use of constructed wetlands (CWs) has the potential to provide a low-cost solution for wastewater treatment, with respect to removal of nutrients, pathogens, ARB/ARGs either as a standalone treatment process or when integrated with conventional treatment systems. Recently, CWs have also been employed for the reduction of antibiotic residues, pharmaceuticals, and emerging contaminants. Given the benefits of ARG removal, low cost of construction, maintenance, energy requirement, and performance efficiencies, CWs offer a promising solution for developing/low-income countries. This review promotes a better understanding of the performance efficiency of treatment technologies (both conventional systems and CWs) for the reduction of antibiotics and ARGs/ARB from wastewater and explores workable alternatives.

The elimination of cell-associated and non-cell-associated antibiotic resistance genes during membrane filtration processes: A review

With increasing water reuse as a sustainable water management strategy, antibiotic resistance genes (ARGs) which have been identified as emerging contaminants in wastewater are attracting global attentions. Given that wastewater treatment plants are now well-established as a sink and source of ARGs in both cell-associated and non-cell-associated forms, a need is acknowledged to reduce their proliferation and protect public health. Due to their different characteristics, cell-associated and non-cell-associated ARGs may have distinct responses to membrane filtration processes which are widely used as advanced treatment to the secondary effluent. This review improves the understanding of the abundance of cell-associated and non-cell-associated ARGs in wastewaters and the secondary effluents and compares the elimination of ARGs in cell-associated and non-cell-associated forms by low-pressure and high-pressure membrane filtration processes. The former process reduces the concentration of cell-associated ARGs by more than 2-logs on average. An increase of the retention efficiency of non-cell-associated ARGs is observed with decreasing molecular weight cut-offs in ultrafiltration. The high-pressure membrane filtration (i.e., nanofiltration and reverse osmosis) can effectively eliminate both cell-associated and non-cell-associated ARGs, with averagely more than 4.6-log reduction. In general, the two forms of ARGs can be removed from water by the membrane filtration processes via the effects of size exclusion, adsorption, and electrostatic repulsion. The size and conformation of cell-associated and non-cell-associated ARGs, characteristics of membranes, coexisting substances, and biofilm formation influence ARG retention. Accumulation and potential proliferation of cell-associated and non-cell-associated ARGs in foulants and concentrate and corresponding control strategies warrant future research.

Assessment of the occurrence of 455 pharmaceutical compounds in sludge according to their physical and chemical properties: A review

Sludge agronomical reuse is of major interest due to the beneficial contribution of nutrients. However, it implies the introduction of unregulated pharmaceuticals into amended-soils and creates a controversial issue about sludge management. To limit their dissemination, it is essential to identify the compounds of interest and understand their attenuation mechanisms through the sludge processes. This paper summarizes the knowledge on 455 investigated pharmaceuticals among 32 therapeutical categories in amendable sludge matrices. It contributes to enlarging the list of commonly quantified compounds to 305 residues including 84 additional compounds compared to previous reviews. It highlights that sorption appears as the main mechanism controlling the occurrence of pharmaceuticals in sludge matrices and shows the considerable residual levels of pharmaceuticals reaching several mg/kg in dry weight. Antibiotics, stimulants, and antidepressants show the highest concentrations up to 232 mg/kg, while diuretics, anti-anxieties or anticoagulants present the lowest concentrations reaching up to 686 µg/kg. Collected data show the increase in investigated compounds as antifungals or antihistamines, and underline emerging categories like antidiabetics, antivirals, or antiarrhythmics. The in-depth analysis of the substantial database guides onto the pharmaceuticals that are the most likely to occur in these amendable matrices to assist future research.

Straw return promoted the simultaneous elimination of sulfamethoxazole and related antibiotic resistance genes in the paddy soil

Straw return could provide a natural available carbon source for the soil microorganisms, which might affect the environmental behaviours of organic pollutants. In this study, microcosm system was constructed to investigate the effect of rice straw return on the fate of sulfamethoxazole (SMX) and related antibiotic resistance genes (ARGs). The results showed that straw return (1% of soil dry mass) could accelerate the degradation of SMX via co-metabolism. In the treatment group with rice straw, SMX was rapidly decomposed into small molecular compounds (e.g., (Z)-1-amino-3-oxobut-1-en-1-aminium and benzenesulfinic acid) within the first six days, and SMX was undetectable after 60 days; while for the SMX group without rice straw, 1.3 mg kg^-1 of SMX still remained at the 60th day. Straw return could enhance the relative abundances of Proteobacteria involved in SMX degradation, including Microvirga and Ramlibacter, which co-metabolized SMX via the degradation pathways of mineralizable components and aromatic compound. Furthermore, straw return significantly eliminated the ARGs. After 60 days, the int1 and sul1 abundances of the treatment group with rice straw were less than one-tenth of the SMX group without rice straw. The redundancy and network analysis of bacterial community and environmental factors showed that dissolved organic carbon and bacteria belonged to Proteobacteria and Actinobacteria might play positive roles in eliminating ARGs. Our results demonstrate that straw return could promote the simultaneous elimination of SMX and corresponding ARGs, which provides a promising approach to effectively treat antibiotics and ARGs in the farmland.

Performance Efficiency of Conventional Treatment Plants and Constructed Wetlands towards Reduction of Antibiotic Resistance

Domestic and industrial wastewater discharges harbor rich bacterial communities, including both pathogenic and commensal organisms that are antibiotic-resistant (AR). AR pathogens pose a potential threat to human and animal health. In wastewater treatment plants (WWTP), bacteria encounter environments suitable for horizontal gene transfer, providing an opportunity for bacterial cells to acquire new antibiotic-resistant genes. With many entry points to environmental components, especially water and soil, WWTPs are considered a critical control point for antibiotic resistance. The primary and secondary units of conventional WWTPs are not designed for the reduction of resistant microbes. Constructed wetlands (CWs) are viable wastewater treatment options with the potential for mitigating AR bacteria, their genes, pathogens, and general pollutants. Encouraging performance for the removal of AR (2-4 logs) has highlighted the applicability of CW on fields. Their low cost of construction, operation and maintenance makes them well suited for applications across the globe, especially in developing and low-income countries. The present review highlights a better understanding of the performance efficiency of conventional treatment plants and CWs for the elimination/reduction of AR from wastewater. They are viable alternatives that can be used for secondary/tertiary treatment or effluent polishing in combination with WWTP or in a decentralized manner.

Changes of antibiotic resistance genes and bacterial communities in the advanced biological wastewater treatment system under low selective pressure of tetracycline

Effluents of conventional wastewater treatment systems contain antibiotic residues at concentrations below the minimal inhibitory concentrations (MIC), which nevertheless could still select for antibiotic-resistant bacteria. This work focuses on evaluating the changes of antibiotic resistance genes (ARGs) and bacterial communities in a planted advanced biological wastewater treatment system (ABWWTS) under long-term exposure to sub-MIC tetracycline. In the ABWWTS, the removal rates of tetracycline ranged from 97.9% to 99.9%, and a 17.2% decrease in the average removal rates of NH₄⁺-N was observed after the addition of tetracycline. Although the background of ABWWTS contributed to the ARGs in effluents, the concentration of 283 targeted ARGs (ΣARGs) was 83.5% lower in effluents than in influents after sub-MIC tetracycline exposure, and the concentrations of ΣARGs in the ABWWTS were, on average, 30.0% lower than those in an unplanted biological wastewater treatment system (UBWWTS) after a performance of 130 days. The relative abundance of tetracycline resistance genes increased within ABWWTS and UBWWTS under tetracycline exposure. After tetracycline exposure, bacterial diversity in ABWWTS and UBWWTS increased on average by 36.2% and 42.7%, respectively, and the abundances of Nitrosomonas and Nitrospira in the aerobic zone were more than 10-times higher in the ABWWTS than in the UBWWTS. Sub-MIC tetracycline concentrations were linearly correlated with the relative abundance of tetracycline resistance genes in Escherichia coli (E. coli). Long-term exposure to tetracycline at the same concentration increased abundances of the same ARGs (i.e., tetR-02 and tetM-01) in E. coli and the microflora of the ABWWTS, revealing that sub-MIC tetracycline could increase the abundance of ARGs in the ABWWTS by facilitating the vertical transfer of tetracycline resistance genes. These findings demonstrated that planted ABWWTS played a positive role in removing ARGs under low antibiotic selective pressure, which was in accompany with increasing levels of corresponding ARGs within the system.

Degradation of ramipril by residues from the brewing industry: A new carbon-based photocatalyst compound

This study is a pioneer in the use of hydrochar as a support for photocatalytic oxide and its application and evaluation as a catalyst in degradation reactions of ramipril. Novel composites were easily prepared by the support TiO₂ or ZnO nanoparticles on the malt bagasse hydrochar. The preparation of the hydrochar requires low synthesis temperature (250 °C), generating the energy savings of the process. The production of the new composites was well supported by different analytical techniques XRD, FTIR, SSA, SEM, EDS, and reflectance diffuse. The effect of different proportions of TiO₂ or ZnO on the composites was investigated on the degradation efficiency of the pharmaceutical ramipril, without pH adjustment. Composites with a 5:1 hydrochar/TiO₂ or ZnO ratio (MH5T and MH5Z, respectively) showed degradations of 72 and 98% of ramipril at 120 min. This remarkable performance may be associated with the decrease in band gap energy and the electron-hole recombination rate. In addition, the composites were more efficient than metal oxides pristine, and this may be related to the fact that hydrochar have a high concentration of phenolic, hydroxyl, and carboxylic functional groups on their surface. Radical identification tests indicated that h⁺, O₂•^-, and •OH were the reactive species involved in the degradation. The proposed mechanism was studied via LC-MS/MS indicated that the ramipril molecule degrades into low m/z intermediates in the first 60 min of reaction using the MH5Z.

Antibiotics in wastewater: From its occurrence to the biological removal by environmentally conscious technologies

In this critical review, we explored the most recent advances about the fate of antibiotics on biological wastewater treatment plants (WWTP). Although the occurrence of these pollutants in wastewater and natural streams has been investigated previously, some recent publications still expose the need to improve the detection strategies and the lack of information about their transformation products. The role of the antibiotic properties and the process operating conditions were also analyzed. The pieces of evidence in the literature associate several molecular properties to the antibiotic removal pathway, like hydrophobicity, chemical structure, and electrostatic interactions. Nonetheless, the influence of operating conditions is still unclear, and solid retention time stands out as a key factor. Additionally, the efficiencies and pathways of antibiotic removals on conventional (activated sludge, membrane bioreactor, anaerobic digestion, and nitrogen removal) and emerging bioprocesses (bioelectrochemical systems, fungi, and enzymes) were assessed, and our concern about potential research gaps was raised. The combination of different bioprocess can efficiently mitigate the impacts generated by these pollutants. Thus, to plan and design a process to remove and mineralize antibiotics from wastewater, all aspects must be addressed, the pollutant and process characteristics and how it is the best way to operate it to reduce the impact of antibiotics in the environment.

Effects of chlorotetracycline on antibiotic resistance genes and the bacterial community during cattle manure composting

Chlorotetracycline (CTC) is one of the most antibiotics present in cattle manure. In present study, three levels of CTC (0, 20 and 40 mg kg^-1) were added to cattle manure composting systems to investigate its effects on the distribution of antibiotic-resistant genes (ARGs) and succession of bacterial community. Adding CTC hindered the removal of ARGs during composting; the high level of CTC significantly increased the relative abundance (RA) of 9/11 ARGs and four MGEs. The bacterial community could be clustered according to the composting time under various treatments, with the high level of CTC having a more persistent effect on the bacterial community. Based on redundancy analysis, bacterial community explained the most variation in ARGs (50.1%), whereas based on network analysis, Firmicutes and Proteobacteria were the main hosts for ARGs. In conclusion, the presence of CTC increased the risks of spreading ARGs in compost products.

Impacts of carbon-based nanomaterials on nutrient removal in constructed wetlands: Microbial community structure, enzyme activities, and metabolism process

The increasing use of raw carbon-based nanomaterials (CBNs) will inevitably affect wastewater treatment systems. Constructed wetlands (CWs) are ecological wastewater treatment facilities and can intercept the vast particles pollutant, including CBNs. However, the impacts of CBNs on the treatment performance of CWs have no available knowledge. Therefore, we systematically inspected the effects of single-walled and multi-walled carbon nanotubes (SWCNTs and MWCNTs) and fullerene nanoparticles (C₆₀) on CW performance under 180-day exposure to 0, 10 and 1000 μg/L concentrations. The results showed that CBNs had marginally adverse impacts on chemical oxygen demand (COD) and total phosphorus (TP) removal, whereas nitrogen removal declined by 24.1 %-42.7 % following long-term exposure to CBNs. MWCNTs had the greatest inhibition effect on nitrogen removal, followed by SWCNTs and C₆₀. The CBNs also induced reactive oxygen species (ROS) overproduction as the increasing concentration, which confirmed that CBNs have biotoxic effects in CWs. The variation of functional microbial community and the inhibition of enzyme activities were the dominant reasons for the decline in nitrogen removal efficiency. Furthermore, predictive functional profiling showed that CBNs affected functional gene abundance, and caused a decline in the enzymes abundance connected to nitrogen removal by the end of the 180-day exposure period.

Unraveling influence of metal species on norfloxacin removal by mesoporous metallic silicon adsorbent

Metal-modified adsorbent had appreciable adsorption capacity and fast rate toward norfloxacin (NOR), but limited studies focused on the influence of metal species on adsorbents' performance. In this study, Fe and Cu were chosen to be loaded on mesoporous silicon SBA-15 for absorbing NOR and investigating the key function of metal species. An obvious synergy effect was found between active species and supporter. A high adsorption capacity (44.8 mg g^-1 for Fe/SBA-15 and 78.3 mg g^-1 for Cu/SBA-15) and short equilibration time (< 2 h) were obtained. NOR adsorptions on two processes were described well by pseudo-second-order kinetics, particle diffusion equation, and Langmuir isotherm. The adsorption processes were spontaneous, but NOR adsorption on Cu/SBA-15 was endothermic while its adsorption on Fe/SBA-15 was exothermic. HA had dual effect on the adsorption efficiency, with a promotion at low HA concentration but an inhibition at high concentration. NOR removal increased first and then decreased with pH ascension from 3 to 9 for both Fe/SBA-15 and Cu/SBA-15, achieving maximum at pH = 7. Comparative characterizations and experiments suggested that NOR adsorption processes were dominated by electrostatic interactions, n-π EDA interactions, hydrogen bonds, and surface complex. The greater n-π EDA and complex efficiency of Cu with NOR resulted in the superior performance of Cu/SBA-15. Graphical abstract.

Influence of chlortetracycline as an antibiotic residue on nitrous oxide emissions from wastewater treatment

Strengthening the removal of antibiotics in wastewater treatment plants is a research focus, but whether antibiotics affect nitrous oxide (N₂O) emissions from wastewater treatment remains to be determined. In this study, the effect of chlortetracycline (CTC) on N₂O emissions in anaerobic/oxic/anoxic sequential batch reactors was investigated. Experimental results show that CTC promotes N₂O emissions during biological nutrient removal. The addition of 0.1 mg/L CTC increased the N₂O emission factor by 41.4% compared to the control. Mechanism exploration shows that CTC stimulates the release of extracellular polymeric substance (EPS) and binds to it, the generated EPS-CTC conjugates hinder or expand the mass transfer channel, which intensifies the electronic competition between oxidoreductases and the substrate competition between microorganisms, resulting in incomplete denitrification and nitrite accumulation, thereby increasing N₂O emissions.

Changes in gut bacterial communities and the incidence of antibiotic resistance genes during degradation of antibiotics by black soldier fly larvae

As a saprophytic insect, the black soldier fly can digest organic waste efficiently in an environmentally friendly way. However, the ability and efficiency of this insect, and the microbial mechanisms involved, in the degradation of antibiotics are largely uncharacterized. To obtain further details during the degradation of OTC (oxytetracycline) by black soldier fly larvae (larvae), the changes in intestinal bacterial communities were examined. Both ARGs (antibiotic resistance genes) and MGEs (mobile genetic elements) were found within the larval guts. At the end of the degradation period, 82.7%, 77.6% and 69.3% of OTC was degraded by larvae when the initial concentrations were 100, 1000 and 2000 mg kg^-1 (dry weight), respectively, which was much higher than the degradation efficiencies (19.3-22.2%) without larvae. There was no obvious effect of OTC on the development of the larvae. Although the larval gut microorganisms were affected by OTC, they adapted to the altered environment. Enterococcus, Ignatzschineria, Providencia, Morganella, Paenalcaligenes and Actinomyces in the gut responded strongly to antibiotic exposure. Interestingly, numerous ARGs (specifically, 180 ARGs and 10 MGEs) were discovered, and significantly correlated with those of both integron-integrase gene and transposases in the larval gut. Of all the detected ARGs, tetracycline resistance genes expressed at relatively high levels and accounted for up to 67% of the total ARGs. In particular, Enterococcus, Ignatzschineria, Bordetella, Providencia and Proteus were all hosts of enzymatic modification genes of tetracycline in the guts that enabled effective degradation of OTC. These findings demonstrate that OTC can be degraded effectively and prove that the bioremediation of antibiotic contamination is enhanced by larvae. In addition, the abundance of ARGs and MGEs formed should receive attention and be considered in environmental health risk assessment systems.

Bi spheres SPR-coupled Cu2O/Bi2MoO6 with hollow spheres forming Z-scheme Cu2O/Bi/Bi2MoO6 heterostructure for simultaneous photocatalytic decontamination of sulfadiazine and Ni(II)

Environmental problem on the coexistence of organic pollutants and heavy metals in surface waters has become increasingly serious. Few relative researches have focused on their simultaneous decontamination. Herein, a ternary plasmonic Z-scheme Cu₂O/Bi/Bi₂MoO₆ heterojunction was synthesized via two-step route followed by a wet-impregnation, where Bi spheres coupled with Cu₂O particles were anchored on the surface of Bi₂MoO₆ with hollow microflower spheres. The composites were characterized via various measurements. The excellent photocatalytic activity of Cu₂O/Bi/Bi₂MoO₆ displayed in single sulfadiazine (SDZ) oxidation or Ni(II) reduction, and their simultaneous removal. The degradation pathway for SDZ was investigated via LC-MS and Gaussian theory. DFT and FDTD calculations confirmed the electronic structural characteristics in the Cu₂O/Bi/Bi₂MoO₆ heterostructure and the induced electric field enhancement around nearly touching Bi spheres. A possible photodegradation mechanism of the as-prepared photocatalyst was elucidated via combining scavenger experiments with EPR technique. The results suggested h⁺, •O₂^- and •OH all participated in SDZ oxidation, which verified that Z-Scheme electron transfer was major manner in Cu₂O/Bi/Bi₂MoO₆, while •O₂^- and e^-acted on Ni(II) reduction. The improved photocatalytic activity of Cu₂O/Bi/Bi₂MoO₆ could be ascribed to the unique Z-scheme electron transfer among Cu₂O, Bi and Bi₂MoO₆, particularly SPR and local electric field near Bi spheres.

Insight into the nitrification kinetics and microbial response of an enriched nitrifying sludge in the biodegradation of sulfadiazine

The intensive use of antibiotics results in the continuous release of antibiotics into wastewater treatment systems, leading to the spread of antibiotic resistance. Nitrifying system is reported to be capable of degrading antibiotics, yet few studies have systematically investigated the inherent correlation among ammonium oxidation rate, antibiotic degradation and genetic expression of nitrifying bacteria along the process. This study selected a widely used sulfonamide antibiotic, sulfadiazine (SDZ), to investigate its biodegradation potential by an enriched nitrifying culture and the response of nitrifying bacteria against antibiotic exposure. Our results demonstrated that SDZ degradation was mainly contributed by cometabolism of ammonia-oxidizing bacteria (AOB), rather than biomass adsorption. The quantitative reverse transcription PCR (RT-qPCR) analysis revealed that the expression level of amoA gene was down-regulated due to the SDZ exposure. In addition, the degradation products of SDZ did not exhibit inhibitory effect on Escherichia coli K12, indicating the biotoxicity of SDZ could be mitigated after biodegradation. The findings offer insights regarding the biodegradation process of sulfonamide antibiotics via cometabolism by AOB.

Elimination of antibiotic resistance genes and control of horizontal transfer risk by UV-based treatment of drinking water: A mini review

Antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs) have been recognized as one of the biggest public health issues of the 21st century. Both ARB and ARGs have been determined in water after treatment with conventional disinfectants. Ultraviolet (UV) technology has been seen growth in application to disinfect the water. However, UV method alone is not adequate to degrade ARGs in water. Researchers are investigating the combination of UV with other oxidants (chlorine, hydrogen peroxide (H2O2), peroxymonosulfate (PMS), and photocatalysts) to harness the high reactivity of produced reactive species (Cl·, ClO·, Cl2·-, ·OH, and SO4·-) in such processes with constituents of cell (e.g., deoxyribonucleic acid (DNA) and its components) in order to increase the degradation efficiency of ARGs. This paper briefly reviews the current status of different UV-based treatments (UV/chlorination, UV/H2O2, UV/PMS, and UV-photocatalysis) to degrade ARGs and to control horizontal gene transfer (HGT) in water. The review also provides discussion on the mechanism of degradation of ARGs and application of q-PCR and gel electrophoresis to obtain insights of the fate of ARGs during UV-based treatment processes.