Removal and degradation characteristics of quinolone antibiotics in laboratory-scale activated sludge reactors under aerobic, nitrifying and anoxic conditions

Deciphering the natural and anthropogenic drivers on the fate and risk of antibiotics and antibiotic resistance genes (ARGs) in a typical river-estuary system, China

This study conducts an in-depth assessment of the spatial distribution, ecological risks, and correlations among 12 antibiotics, antibiotic resistance genes (ARGs), and dominant microorganisms in a representative river-estuary system, classified by land use and hydrodynamic conditions. Sulfonamides and quinolones were identified as the major contaminants in surface waters, with aquaculture and healthcare wastewater responsible for over 80 % of the antibiotic load. Contrasting seasonal patterns were observed between freshwater (wet season: 215 ng/L, dry season: 99.9 ng/L) and tidal estuaries (wet season: 45.9 ng/L, dry season: 121 ng/L), attributed to antibiotic transport from terrestrial sources or coastal aquaculture areas. The estimated annual antibiotic influx into Jiaozhou Bay was 70.4 kg/year, posing a considerable threat to aquatic algae and disrupting the stability of aquatic food chain. BugBase predictions suggested that antibiotics in the environment suppressed bacteria characterized by biofilm formation (FB) and the presence of mobile elements (CME). However, ARG transmission was likely to drive the spread of CME, FB, and stress-tolerant (OST) bacteria within microbial communities. The significant positive correlations observed between sulfamethoxazole and 63 microbial genera indicate a broad distribution of microbial resistance, which exacerbates the potential for ARG accumulation and dissemination across both the bay and the Yellow Sea.

Fate of emerging antibiotics in soil-plant systems: A case on fluoroquinolones

Fluoroquinolones (FQs), a class of broad-spectrum antibiotics widely used to treat human and animal diseases globally, have limited adsorption and are often excreted unchanged or as metabolites. These compounds enter the soil environment through feces, urban wastewater, or discharge of biological solids. The fluorine atoms in FQs impart high electronegativity, chemical stability, and resistance to microbial degradation, allowing them to potentially enter food chains. The persistence of FQs in soils raises questions about their impacts on plant growth, an aspect not yet conclusively determined. We reviewed whether, like other organic compounds, FQs are actively absorbed by plants, resulting in bioaccumulation and posing threats to human health. The influx of FQs has led to antibiotic resistance in soil microbes by exerting selective pressure and contributing to multidrug-resistant bacteria. Therefore, the environmental risks of FQs warrant further attention. This work provides a comprehensive review of the fate and behavior of FQs at the plant-environment interface, their migration and transport from the environment into plants, and associated toxicity. Current limitations in research are discussed and prospects for future investigations outlined. Thus, understanding antibiotic behavior in plants and translocation within tissues is not only crucial for ecosystem health (plant health), but also assessing potential human health risks. In addition, it can offer insights into the fate of emerging soil pollutants in plant-soil systems.

Advances and solutions in biological treatment for antibiotic wastewater with resistance genes: A review

Biological treatment represents a fundamental component of wastewater treatment plants (WWTPs). The transmission of antibiotic resistance bacteria (ARB) and resistance genes (ARGs) occurred through the continuous migration and transformation, attributed to the residual presence of antibiotics in WWTPs effluent, posing a significant threat to the entire ecosystem. It is necessary to propose novel biological strategies to address the challenge of refractory contaminants, such as antibiotics, ARGs and ARB. This review summarizes the occurrence of antibiotics in wastewater, categorized by high and low concentrations. Additionally, current biological treatments used in WWTPs, such as aerobic activated sludge, anaerobic digestion, sequencing batch reactor (SBR), constructed wetland, membrane-related bioreactors and biological aerated filter (BAF) are introduced. In particular, because microorganisms are the key to those biological treatments, the effect of high and low concentration of antibiotics on microorganisms are thoroughly discussed. Finally, solutions involving functional bacteria, partial nitrification (PN)-Anammox and lysozyme embedding are suggested from the perspective of the entire biological treatment process. Overall, this review provides valuable insights for the simultaneous removal of antibiotics and ARGs in antibiotics wastewater.

Physiological adaptation and population dynamics of a nitrifying sludge exposed to ampicillin

Antibiotics in wastewater treatment plants can alter the physiological activity and the structure of microbial communities through toxic and inhibitory effects. Physiological adaptation, kinetic, and population dynamics behavior of a nitrifying sludge was evaluated in a sequential batch reactor (SBR) fed with 14.4 mg/L of ampicillin (AMP). The addition of AMP did not affect ammonium consumption (100 mg NH4+-N/L) but provoked nitrite accumulation (0.90 mg NO2--N formed/mg NH4+-N consumed) and an inhibition of up to 67% on the nitrite oxidizing process. After 30 cycles under AMP feeding, the sludge recovered its nitrite oxidizing activity with a high nitrate yield (YNO3-) of 0.87 ± 0.10 mg NO3--N formed/mg NH4+-N consumed, carrying out again a stable and complete nitrifying process. Increases in specific rate of nitrate production (qNO3-) showed the physiological adaptation of the nitrite oxidizing bacteria to AMP inhibition. Ampicillin was totally removed since the first cycle of addition. Exposure to AMP had effects on the abundance of bacterial populations, promoting adaptation of the nitrifying sludge to the presence of the antibiotic and its consumption. Nitrosomonas and Nitrosospira always remained within the dominant genera, keeping the ammonium oxidizing process stable while an increase in Nitrospira abundance was observed, recovering the stability of the nitrite oxidizing process. Burkholderia, Pseudomonas, and Thauera might be some of the heterotrophic bacteria involved in AMP consumption.

Review on antibiotic pollution dynamics: insights to occurrence, environmental behaviour, ecotoxicity, and management strategies

Antibiotic contamination poses a significant global concern due to its far-reaching impact on public health and the environment. This comprehensive review delves into the prevalence of various antibiotic classes in environmental pollution and their interactions with natural ecosystems. Fluoroquinolones, macrolides, tetracyclines, and sulphonamides have emerged as prevalent contaminants in environmental matrices worldwide. The concentrations of these antibiotics vary across diverse environments, influenced by production practices, consumer behaviours, and socio-economic factors. Low- and low-middle-income countries face unique challenges in managing antibiotic contamination, with dominant mechanisms like hydrolysis, sorption, and biodegradation leading to the formation of toxic byproducts. Ecotoxicity reports reveal the detrimental effects of these byproducts on aquatic and terrestrial ecosystems, further emphasizing the gravity of the issue. Notably, monitoring the antibiotic parent compound alone may be inadequate for framing effective control and management strategies for antibiotic pollution. This review underscores the imperative of a comprehensive, multi-sectoral approach to address environmental antibiotic contamination and combat antimicrobial resistance. It also advocates for the development and implementation of tailored national action plans that consider specific environmental conditions and factors. Thus, an approach is crucial for safeguarding both public health and the delicate balance of our natural ecosystems.

Effect of streptomycin sulphate on the nitrification system in activated sludge: insight into nitrification characteristic, antibiotic resistance gene and microbial community

Wastewater with residual streptomycin sulphate usually contains high content of ammonia-nitrogen. However, the biological removal process of ammonia-nitrogen under streptomycin sulphate circumstance was unclear. In this study, short-term and long-term effects of streptomycin sulphate on biological nitrification systems, including AOB, NOB, SAOR, SNOR and SNPR, were evaluated comprehensively. The results indicated IC50 for AOB and NOB were 7.5 and 6.6 mg/L. SAOR and SNPR could be decreased to 3.43 ± 0.52 mg N/(g MLSS·h) and 0.24 ± 0.03 mg N/(g MLSS·h) while the addition of streptomycin sulphate was 10 mg/L. When streptomycin sulphate addition was stopped, nitrification ability recovered slightly, SAOR and SNPR increased to 9.37 ± 0.36 mg N/(g MLSS·h) and 1.66 ± 0.49 mg N/(g MLSS·h), respectively. The protein of EPS increased gradually during the acclimatization process, and the maximal protein value was 68.24 mg/g MLSS on the 100th day, however, no significant change of polysaccharose was observed during the acclimatization process. High abundance of ARGs and intI1 was detected in effluent and sludge of the biological treatment system. The maximal relative abundance of aadA1 in the sludge appeared on the 140th day, and increased by 0.99 orders of magnitude. Biological diversity decreased significantly during the acclimatization process, relative abundance of nitrosomonas was changed from 9.07% to 38.68% on the 61st day, while relative abundance of nitrobacter was changed from 1.30% to 0.64%. It should be noted that relative abundances of nitrosomonas and nitrobacter were reduced to 16.17% and 0.25% on the 140th day. This study would be helpful for nitrogen removal in wastewater with antibiotic.

Degradation of COD in antibiotic wastewater by a combination process of electrochemistry, hydroxyl-functionalized ball-milled zero-valent iron/Fe3O4 and Oxone

In this study, the significant iron-based material, hydroxyl-functionalized ball-milled zero-valent iron/Fe3O4 (HFB-ZVI/Fe3O4) was employed for the experiments. The performance of the Electro + HFB-ZVI/Fe3O4 + Oxone system for the degradation of chemical oxygen demand (COD) in antibiotic wastewater was investigated. A direct current was applied between a graphite plate anode and two iron plate cathodes, and a series of operational parameters, such as applied electric current, the dosage of HFB-ZVI/Fe3O4 composite, the dosage of Oxone, and initial solution pH, were explored to evaluate the oxidation process. The application of electric current enhanced the gradual degradation of COD and the increase of current intensity accelerated COD degradation. The neutral condition was favourable for the rapid degradation of COD in a short reaction time by the Electro + HFB-ZVI/Fe3O4 + Oxone process and promoted the degradation efficiency of COD. An increase of electric current gradually decreased the reaction solution pH, the larger the electric current applied in the reaction process, the lower the final pH of the reaction solution. Under the optimal experimental conditions (1 g/L HFB-ZVI/Fe3O4 composite, 0.3 g/L Oxone, current intensity = 500 mA, initial solution pH = 7.85), Electro + HFB-ZVI/Fe3O4 + Oxone achieved 99% COD degradation in antibiotic wastewater. Radicals quenching experiments indicated the contribution to COD degradation by hydroxyl radicals (HO•), sulphate radicals (SO4•-) and other oxidants were 66.03%, 24.014% and 9.756%, respectively. The possible mechanism of COD degradation in the Electro + HFB-ZVI/Fe3O4 + Oxone system was also discussed in this study. The findings in this work provided useful information for the treatment of wastewater.

Do contaminants compromise the use of recycled nutrients in organic agriculture? A review and synthesis of current knowledge on contaminant concentrations, fate in the environment and risk assessment

Use of nutrients recycled from societal waste streams in agriculture is part of the circular economy, and in line with organic farming principles. Nevertheless, diverse contaminants in waste streams create doubts among organic farmers about potential risks for soil health. Here, we gather the current knowledge on contaminant levels in waste streams and recycled nutrient sources, and discuss associated risks. For potentially toxic elements (PTEs), the input of zinc (Zn) and copper (Cu) from mineral feed supplements remains of concern, while concentrations of PTEs in many waste streams have decreased substantially in Europe. The same applies to organic contaminants, although new chemical groups such as flame retardants are of emerging concern and globally contamination levels differ strongly. Compared to inorganic fertilizers, application of organic fertilizers derived from human or animal feces is associated with an increased risk for environmental dissemination of antibiotic resistance. The risk depends on the quality of the organic fertilizers, which varies between geographical regions, but farmland application of sewage sludge appears to be a safe practice as shown by some studies (e.g. from Sweden). Microplastic concentrations in agricultural soils show a wide spread and our understanding of its toxicity is limited, hampering a sound risk assessment. Methods for assessing public health risks for organic contaminants must include emerging contaminants and potential interactions of multiple compounds. Evidence from long-term field experiments suggests that soils may be more resilient and capable to degrade or stabilize pollutants than often assumed. In view of the need to source nutrients for expanding areas under organic farming, we discuss inputs originating from conventional farms vs. non-agricultural (i.e. societal) inputs. Closing nutrient cycles between agriculture and society is feasible in many cases, without being compromised by contaminants, and should be enhanced, aided by improved source control, waste treatment and sound risk assessments.

Optimizing ciprofloxacin removal through regulations of trophic modes and FNA levels in a moving bed biofilm reactor performing sidestream partial nitritation

The performance of partial nitritation (PN)-moving bed biofilm reactor (MBBR) in removal of antibiotics in the sidestream wastewater has not been investigated so far. In this work, the removal of ciprofloxacin was assessed under varying free nitrous acid (FNA) levels and different trophic modes. For the first time, a positive correlation was observed between ciprofloxacin removal and FNA levels, either in the autotrophic PN-MBBR or in the mixotrophic PN-MBBR, mainly ascribed to the FNA-stimulating effect on heterotrophic bacteria (HB)-induced biodegradation. The maximum ciprofloxacin removal efficiency (∼98 %) and removal rate constant (0.021 L g-1 SS h-1) were obtained in the mixotrophic PN-MBBR at an average FNA level of 0.056 mg-N L-1, which were 5.8 and 51.2 times higher than the corresponding values in the autotrophic PN-MBBR at 0 mg FNA-N L-1. Increasing FNA from 0.006 to 0.056 mg-N L-1 would inhibit ammonia oxidizing bacteria (AOB)-induced cometabolism and metabolism from 10.2 % and 6.9 % to 6.2 % and 6.4 %, respectively, while HB-induced cometabolism and metabolism increased from 31.2 % and 22.7 % to 41.9 % and 34.5 %, respectively. HB-induced cometabolism became the predominant biodegradation pathway (75.9 %-85.8 %) in the mixotrophic mode. Less antimicrobial biotransformation products without the piperazine or fluorine were newly identified to propose potential degradation pathways, corresponding to microbial-induced metabolic types and FNA levels. This work shed light on enhancing antibiotic removal via regulating both FNA accumulation and organic carbon addition in the PN-MBBR process treating sidestream wastewater.

How efficiently does a metabolically enhanced system with denitrifying anaerobic methane oxidizing microorganisms remove antibiotics?

In this work, the novel N-damo (Nitrite dependent anaerobic methane oxidation) process was investigated at high biomass activities for its potential to remove simultaneously nitrite and methane, as well as selected antibiotics commonly found in sewage in trace amounts. For this purpose, two MBRs were operated at three high nitrite loading rates (NLRs), namely 76 ± 9.9, 161.5 ± 11.4 and 215.2 ± 24.2 mg N-NO⁻2 L-1 d-1, at long-term operation. The MBRs performance achieved a significantly high nitrite removal activity for an N-damo process (specific denitrifying activity of up to 540 mg N-NO⁻2 g-1 VSS d-1), even comparable to heterotrophic denitrification values. In this study, we have implemented a novel operational strategy that sets our work apart from previous studies with similar bioreactors. Specifically, we have introduced Cerium as a trace element in the feeding medium, which serves as a key differentiating factor. It allowed maintaining a stable reactor operation at high NLRs. Microbial community composition evidenced that both MBRs were dominated with N-damo bacteria (67-87% relative abundance in period III and I, respectively). However, a decrease in functional N-damo bacteria (Candidatus Methylomirabilis) abundance was observed during the increase in biomass activity and concentration, concomitantly with an increase of the other minor families (Hypomicrobiaceae and Xanthobacteraceae). Most of the selected antibiotics showed high biotransformation such as sulfamethoxazole, trimethoprim, cefalexin and azithromycin, whereas others such as roxithromycin and clarithromycin were only partially degraded (20-35%). On the contrary, ciprofloxacin showed almost no removal. Despite the metabolic enhancement, no apparent increase on the antibiotic removal was observed throughout the operation, suggesting that microbiological composition was of greater influence than its primary metabolic activity on the removal of antibiotics.

Recent perspective of antibiotics remediation: A review of the principles, mechanisms, and chemistry controlling remediation from aqueous media

Antibiotic pollution is an ever-growing concern that affects the growth of plants and the well-being of animals and humans. Research on antibiotics remediation from aqueous media has grown over the years and previous reviews have highlighted recent advances in antibiotics remediation technologies, perspectives on antibiotics ecotoxicity, and the development of antibiotic-resistant genes. Nevertheless, the relationship between antibiotics solution chemistry, remediation technology, and the interactions between antibiotics and adsorbents at the molecular level is still elusive. Thus, this review summarizes recent literature on antibiotics remediation from aqueous media and the adsorption perspective. The review discusses the principles, mechanisms, and solution chemistry of antibiotics and how they affect remediation and the type of adsorbents used for antibiotic adsorption processes. The literature analysis revealed that: (i) Although antibiotics extraction and detection techniques have evolved from single-substrate-oriented to multi-substrates-oriented detection technologies, antibiotics pollution remains a great danger to the environment due to its trace level; (ii) Some of the most effective antibiotic remediation technologies are still at the laboratory scale. Thus, upscaling these technologies to field level will require funding, which brings in more constraints and doubts patterning to whether the technology will achieve the same performance as in the laboratory; and (iii) Adsorption technologies remain the most affordable for antibiotic remediation. However, the recent trends show more focus on developing high-end adsorbents which are expensive and sometimes less efficient compared to existing adsorbents. Thus, more research needs to focus on developing cheaper and less complex adsorbents from readily available raw materials. This review will be beneficial to stakeholders, researchers, and public health professionals for the efficient management of antibiotics for a refined decision.

Risk control of antibiotics, antibiotic resistance genes (ARGs) and antibiotic resistant bacteria (ARB) during sewage sludge treatment and disposal: A review

Sewage sludge is an important reservoir of antibiotics, antibiotic resistance genes (ARGs), and antibiotic resistant bacteria (ARB) in wastewater treatment plants (WWTPs), and the reclamation of sewage sludge potentially threats human health and environmental safety. Sludge treatment and disposal are expected to control these risks, and this review summarizes the fate and controlling efficiency of antibiotics, ARGs, and ARB in sludge involved in different processes, i.e., disintegration, anaerobic digestion, aerobic composting, drying, pyrolysis, constructed wetland, and land application. Additionally, the analysis and characterization methods of antibiotics, ARGs, and ARB in complicate sludge are reviewed, and the quantitative risk assessment approaches involved in land application are comprehensively discussed. This review benefits process optimization of sludge treatment and disposal, with regard to environmental risks control of antibiotics, ARGs, and ARB in sludge. Furthermore, current research limitations and gaps, e.g., the antibiotic resistance risk assessment in sludge-amended soil, are proposed to advance the future studies.

Investigating the biodegradability of iodinated X-ray contrast media in simultaneous nitrification and denitrification system

The present study investigated the biodegradation of three iodinated X-ray contrast media (ICM), namely, iopamidol, iohexol, and iopromide, in simultaneous nitrification-denitrification (SND) system maintained in a sequencing batch reactor (SBR). The results showed that variable aeration patterns (anoxic-aerobic-anoxic) and micro-aerobic condition were most effective in the biotransformation of ICM while achieving organic carbon and nitrogen removal. The highest removal efficiencies of iopamidol, iohexol, and iopromide were 48.24%, 47.75%, and 57.46%, respectively, in micro-aerobic condition. Iopamidol was highly resistant to biodegradation and possessed the lowest K_bio value, followed by iohexol and iopromide, regardless of operating conditions. The removal of iopamidol and iopromide was affected by the inhibition of nitrifiers. The transformation products after hydroxylation, dehydrogenation, and deiodination of ICM were detected in the treated effluent. Due to the addition of ICM, the abundance of denitrifier genera Rhodobacter and Unclassified Comamonadaceae increased, and the abundance of class TM7-3 decreased. The presence of ICM affected the microbial dynamics, and the diversity of microbes in SND resulted in improving the biodegradability of the compounds.

Recent advances in simultaneous nitrification and denitrification for nitrogen and micropollutant removal: a review

Simultaneous Nitrification and Denitrification (SND) is a promising process for biological nitrogen removal. Compared to conventional nitrogen removal processes, SND is cost-effective due to the decreased structural footprint and low oxygen and energy requirements. This critical review summarizes the current knowledge on SND related to fundamentals, mechanisms, and influence factors. The creation of stable aerobic and anoxic conditions within the flocs, as well as the optimization of dissolved oxygen (DO), are the most significant challenges in SND. Innovative reactor configurations coupled with diversified microbial communities have achieved significant carbon and nitrogen reduction from wastewater. In addition, the review also presents the recent advances in SND for removing micropollutants. The micropollutants are exposed to various enzymes due to the microaerobic and diverse redox conditions present in the SND system, which would eventually enhance biotransformation. This review presents SND as a potential biological treatment process for carbon, nitrogen, and micropollutant removal from wastewater.

Unravelling ciprofloxacin removal in a nitrifying moving bed biofilm reactor: Biodegradation mechanisms and pathways

Although moving bed biofilm reactors (MBBRs) have shown excellent antibiotic removal potentials, the information on underlying mechanisms is yet limited. This work assessed the removal of ciprofloxacin in an enriched nitrifying MBBR by clarifying the contribution of adsorption and microbial-induced biodegradation. Results demonstrated the considerable biomass adsorption (55%) in first 30 min. Limiting nitrite oxidizing bacteria growth or inhibiting nitrification would lead to lower adsorption capacities. The highest ciprofloxacin biodegradation rate constant was 0.082 L g SS^-1 h^-1 in the presence of ammonium, owing to ammonia oxidizing bacteria (AOB)-induced cometabolism, while heterotrophs played an insignificant role (∼9%) in ciprofloxacin biodegradation. The developed model also suggested the importance of AOB-induced cometabolism and metabolism over heterotrophs-induced biodegradation by analyzing the respective biodegradation coefficients. Cometabolic biodegradation pathways of ciprofloxacin mainly involved the piperazine ring cleavage, probably alleviating antimicrobial activities. It implies the feasibility of nitrifying biofilm systems towards efficient antibiotic removal from wastewater.

Chitosan beads coated with almond and walnut shells for the adsorption of gatifloxacin antibiotic compound from aqueous solutions

In the present study, chitosan (C), walnut (W), and almond shell (A) powder adsorbent (in different combinations as almond shells:walnut:chitosan 2:1:1 (AWC), chitosan:almond shell:walnut 2:1:1 (CAW), and walnut:almond shells:chitosan 2:1:1 (WAC)) powder were combined in different ratios to produce low-cost composite adsorbent beads for the removal of antibiotics gatifloxacin (GAT) from synthetic wastewater. The beads were characterized by a scanning electron microscope, Fourier transform infrared spectrum spectrophotometer, and energy-dispersive X-ray spectroscopy. The batch adsorption approach was employed to remove the antibiotic from the water. Moreover, isotherm and kinetics were conducted to illustrate the adsorption mechanism. Parameters like the effect of the adsorbent's dosage, pH, initial concentration, and contact time on antibiotic adsorption were evaluated. Adsorption percentage increased slightly with the increase in adsorbent dosage. The optimum pH for GAT adsorption on beads was 5-7. In addition, adsorption increased with initial antibiotic concentration and time rise. The adsorption isotherm data were successfully fitted to Langmuir isotherm for AWC and CAW beads, while WAC beads followed the Freundlich isotherm. The highest adsorption was attained at pH 5 on CAW beads and pH 7 on AWC and WAC beads. The optimal contact time for equilibrium studies was 120 min for all types of beads. The adsorption isotherm data in AWC beads fit well with the Langmuir model and Freundlich adsorption for CAW and WAC beads. The rate of adsorption on beads follows Lagergren pseudo-second-order kinetics. The results indicate that prepared combination beads can be used to remove antibiotics from wastewater.

Degradation and solid-liquid distribution of antibiotics in microbial electrolysis cells treating sewage sludge: Effects of temperature and applied voltage

The microbial electrolysis cell (MEC) is a promising technology for antibiotic removal in sewage sludge. Temperature and voltage are key operating factors, but information about their effects on antibiotic degradation in MECs is still limited. Therefore, the effects of the temperature and applied voltage on the degradation and solid-liquid distribution of antibiotics in MECs treating sewage sludge were investigated. The results showed that the thermophilic (55 °C) MEC (T-MEC) at 0.8 V achieved the highest total antibiotic removal efficiency of 58.7 % due to the increase in bioelectrochemical activity for anodes and microbial activity in suspended sludge. The solid-liquid migration of antibiotics was facilitated, which had a significant positive correlation with antibiotic removal. Biodegradation was the rate-limiting step for the removal of fluoroquinolones, which had the highest levels in sludge. Geobacter and Thermincola were dominant bacteria in the anode biofilms of mesophilic (37 °C) MECs (M-MECs) and T-MECs, respectively.

Insights into antibiotic stewardship of lake-rivers-basin complex systems for resistance risk control

Antibiotic stewardship is hindered by a lack of consideration for complicated environmental fate of antibiotics and their role in resistance development, while the current methodology of eco-toxicological risk assessment has not been fully protective against their potential to select for antibiotic resistance. To address this problem, we established a novel methodologic framework to perform comprehensive environmental risk assessment of antibiotics in terms of resistance development, which was based on selection effect, phenotype resistance level, heteroresistance frequency, as well as prevalence and stability of antibiotic resistance genes. We tracked the contribution of antibiotic load reduction to the mitigation of environmental risk of resistance development by fate and transport modeling. The method was instantiated in a lake-river network-basin complex system, taking the Taihu Basin as a case study. Overall, antibiotic load posed no eco-toxicological risk but an average medium-level environmental risk for resistance development in Taihu Lake. The effect of antibiotic load on resistance risk was both seasonal-dependent and category-dependent, while quinolones posed the greatest environmental risk for resistance development. Mass-flow analysis indicated that temporal-spatial variation in hydrological regime and antibiotic fate together exerted a significant effect on antibiotic load in the system. By apportioning antibiotic load to riverine influx, we identified the hotspots for load reduction and predicted the beneficial response of resistance risk under load-reduction scenarios. Our study proposed a risk-oriented strategy of basin-scaled antibiotic load reduction for environmental risk control of resistance development.

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.

Multi-Dimensional Elimination of β-Lactams in the Rural Wetland: Molecule Design and Screening for More Antibacterial and Degradable Substitutes

Restricted economic conditions and limited sewage treatment facilities in rural areas lead to the discharge of small-scale breeding wastewater containing higher values of residual beta-lactam antibiotics (β-lactams), which seriously threatens the aquatic environment. In this paper, molecular docking and a comprehensive method were performed to quantify and fit the source modification for the combined biodegradation of β-lactams. Using penicillin (PNC) as the target molecule, combined with contour maps for substitute modification, a three-dimensional quantitative structure-activity relationship (3D-QSAR) model was constructed for the high-performance combined biodegradation of β-lactams. The selected candidate with better environmental friendliness, functionality, and high performance was screened. By using the homology modeling algorithms, the mutant penicillin-binding proteins (PBPs) of Escherichia coli were constructed to have antibacterial resistance against β-lactams. The molecular docking was applied to obtain the target substitute by analyzing the degree of antibacterial resistance of β-lactam substitute. The combined biodegradation of β-lactams and substitute in the constructed wetland (CW) by different wetland plant root secretions was studied using molecular dynamics simulations. The result showed a 49.28% higher biodegradation of the substitutes than PNC when the combined wetland plant species of Eichhornia crassipes, Phragmites australis, and Canna indica L. were employed.

Removal of antibiotics from wastewaters by membrane technology: Limitations, successes, and future improvements

Antibiotics and related pharmaceuticals are applied to enhance public health and life quality. A major environmental concern is wastewaters from pharmaceutical industries, which contain significant amounts of antibiotics. Pharmaceutical industries apply conventional processes (biological, filtration, coagulation, flocculation, and sedimentation) for wastewater treatment, but these approaches cannot remove antibiotics completely. Moreover, unmetabolized antibiotics released by humans and animals are dangerous for municipal and effluent wastewater. Besides, antibiotic resistance is another challenge in treatment of wastewater for superbugs. This comprehensive study summarizes different techniques for antibiotic removal with an emphasis on membrane technology in individual and hybrid systems such as chemical, physical, biological, and conditional-based strategies. A combination of membrane processes with advanced oxidation processes (AOPs), adsorption, and biological treatments can be the right solution for perfect removal. Furthermore, this review briefly compares different procedures for antibiotic removal, which can be helpful for further studies with their advantages and drawbacks.

Current Progress in Natural Degradation and Enhanced Removal Techniques of Antibiotics in the Environment: A Review

Antibiotics are used extensively throughout the world and their presence in the environment has caused serious pollution. This review summarizes natural methods and enhanced technologies that have been developed for antibiotic degradation. In the natural environment, antibiotics can be degraded by photolysis, hydrolysis, and biodegradation, but the rate and extent of degradation are limited. Recently, developed enhanced techniques utilize biological, chemical, or physicochemical principles for antibiotic removal. These techniques include traditional biological methods, adsorption methods, membrane treatment, advanced oxidation processes (AOPs), constructed wetlands (CWs), microalgae treatment, and microbial electrochemical systems (such as microbial fuel cells, MFCs). These techniques have both advantages and disadvantages and, to overcome disadvantages associated with individual techniques, hybrid techniques have been developed and have shown significant potential for antibiotic removal. Hybrids include combinations of the electrochemical method with AOPs, CWs with MFCs, microalgal treatment with activated sludge, and AOPs with MFCs. Considering the complexity of antibiotic pollution and the characteristics of currently used removal technologies, it is apparent that hybrid methods are better choices for dealing with antibiotic contaminants.

Efficient removal of antibiotics from water resources is a public health priority: a critical assessment of the efficacy of some remediation strategies for antibiotics in water

This review discusses the fundamental principles and mechanism of antibiotic removal from water of some commonly applied treatment techniques including chlorination, ozonation, UV-irradiation, Fenton processes, photocatalysis, electrochemical-oxidation, plasma, biochar, anaerobicdigestion, activated carbon and nanomaterials. Some experimental shortfalls identified by researchers such as certain characteristics of degradation agent applied and the strategies explored to override the identified limitations are briefly discussed. Depending on interactions of a range of factors including the type of antibiotic compound, operational parameters applied such as pH, temperature and treatment time, among other factors, all reviewed techniques can eliminate or reduce the levels of antibiotic compounds in water to varying extents. Some of the reviewed techniques such as anaerobic digestion generally require longer treatment times (up to 360, 193 and 170 days, according to some studies), while others such as photocatalysis achieved degradation within short contact time (within a minimum of 30, but up to 60, 240, 300 and 1880 minutes, in some cases). For some treatment techniques such as ozonation and Fenton, it is apparent that subjecting compounds to longer treatment times may improve elimination efficiency, whereas for some other techniques such as nanotechnology, application of longer treatment time generally meant comparatively minimal elimination efficiency. Based on the findings of experimental studies summarized, it is apparent that operational parameters such as pH and treatment time, while critical, do not exert sole or primary influence on the elimination percentage(s) achieved. Elimination efficiency achieved rather seems to be due more to the force of a combination of several factors.

Synthetic organic antibiotics residues as emerging contaminants waste-to-resources processing for a circular economy in China: Challenges and perspective

Synthetic antibiotics have been known for years to combat bacterial antibiotics. But their overuse and resistance have become a concern recently. The antibiotics reach the environment, including soil from the manufacturing process and undigested excretion by cattle and humans. It leads to overburden and contamination of the environment. These organic antibiotics remain in the environment for a very long period. During this period, antibiotics come in contact with various flora and fauna. The ill manufacturing practices and inadequate wastewater treatment cause a severe problem to the water bodies. After pretreatment from pharmaceutical industries, the effluents are released to the water bodies such as rivers. Even after pretreatment, effluents contain a significant number of antibiotic residues, which affect the living organisms living in the water bodies. Ultimately, river contaminated water reaches the ocean, spreading the contamination to a vast environment. This review paper discusses the impact of synthetic organic contamination on the environment and its hazardous effect on health. In addition, it analyzes and suggests the biotechnological strategies to tackle organic antibiotic residue proliferation. Moreover, the degradation of organic antibiotic residues by biocatalyst and biochar is analyzed. The circular economy approach for waste-to-resource technology for organic antibiotic residue in China is analyzed for a sustainable solution. Overall, the significant challenges related to synthetic antibiotic residues and future aspects are analyzed in this review paper.

Continuous antibiotic attenuation in algal membrane photobioreactor: Performance and kinetics

The attenuation of 10 mixed antibiotics along with nutrients in a continuous flow mode by four freshwater microalgae (Haematococcus pluvialis, Selenastrum capricornutum, Scenedesmus quadricauda, and Chlorella vulgaris) was examined in membrane photobioreactors (MPBRs). At lab-scale, consistent removal of both antibiotic and nutrient was shown by H. pluvialis and S. quadricauda, respectively. The system exhibited better performance with enhanced removal at HRT 24 h compared to 12 h and 48 h. The highest removal efficiency of antibiotics was observed in H. pluvialis MPBR, with the mean antibiotic removal values of 53.57%- 96.33%. Biodegradation was the major removal pathway of the antibiotics in the algal-MPBR (AMPBR), while removal by bioadsorption, bioaccumulation, membrane rejection, and abiotic was minor. Then, the bacterial feature was studied and showed significant influence from system hydrodynamics. The kinetics of continuous flow antibiotic removal followed Stover-Kincannon and Grau second-order models, which revealed great potential of AMPBR to withstand antibiotic load. The latter coupled with the computational fluid dynamic simulation was successfully applied for the residual antibiotic prediction and potential system optimization. Overall, these results provide an important reference for continuous flow antibiotic removal using AMPBR.

Impact of Antibiotics as Waste, Physical, Chemical, and Enzymatical Degradation: Use of Laccases

The first traces of Tetracycline (TE) were detected in human skeletons from Sudan and Egypt, finding that it may be related to the diet of the time, the use of some dyes, and the use of soils loaded with microorganisms, such as Streptomyces spp., among other microorganisms capable of producing antibiotics. However, most people only recognise authors dating between 1904 and 1940, such as Ehrlich, Domagk, and Fleming. Antibiotics are the therapeutic option for countless infections treatment; unfortunately, they are the second most common group of drugs in wastewaters worldwide due to failures in industrial waste treatments (pharmaceutics, hospitals, senior residences) and their irrational use in humans and animals. The main antibiotics problem lies in delivered and non-prescribed human use, use in livestock as growth promoters, and crop cultivation as biocides (regulated activities that have not complied in some places). This practice has led to the toxicity of the environment as antibiotics generate eutrophication, water pollution, nutrient imbalance, and press antibiotic resistance. In addition, the removal of antibiotics is not a required process in global wastewater treatment standards. This review aims to raise awareness of the negative impact of antibiotics as residues and physical, chemical, and biological treatments for their degradation. We discuss the high cost of physical and chemical treatments, the risk of using chemicals that worsen the situation, and the fact that each antibiotic class can be transformed differently with each of these treatments and generate new compounds that could be more toxic than the original ones; also, we discuss the use of enzymes for antibiotic degradation, with emphasis on laccases.

The effect of anaerobic pig slurry redox potentials on the degradation of veterinary medicines

Veterinary medicines are frequently used within intensive livestock husbandry and there has been a growing interest regarding their fate in the environment. However, research has seldom assessed the influence of pig slurry properties on the fate of veterinary medicines even though such an understanding is essential for a more robust environmental risk assessment. Changes within manure degradation rates have the potential to alter the concentration of antibiotics applied to land, and the outcome of the risk assessment. The aim of this work was to investigate whether commonly reported redox potentials affect the degradation rates of acetyl-salicylic acid, ceftiofur, florfenicol, oxytetracycline, sulfamethoxazole, and tylosin. The employed redox potentials were -100 mV (reduced), -250 mV (anaerobic) and -400 mV (very anaerobic). A compound specific relationship was observed where the degradation of ceftiofur, florfenicol, oxytetracycline and sulfamethoxazole was inhibited under reduced conditions over that of very anaerobic; the respective DT50 values were 0.7-1.84 h, 1.35-3.61 h, 22.2-49.8 h, 131-211 h and 35.4-94 h. In contrast, tylosin was found to degrade faster at reduced conditions over very anaerobic (DT50 6.88-19.4 h). The presented research demonstrates the importance of redox potential on degradation rates and suggests we need stringent and harmonized redox control to improve the environmental risk assessment of veterinary medicines. Environmental relevance and significance: Given the significant effect of anaerobic redox potentials on veterinary medicine fate tighter regulation is required in manure degradation trials.

Critical review on negative emerging contaminant removal efficiency of wastewater treatment systems: Concept, consistency and consequences

Emerging contaminants (ECs) are not completely removed by wastewater treatment owing to their capabilities of making complexes, toxic derivatives, byproduct formation, and dynamic partitioning. Negative contaminant removal i.e., higher concentrations (up to 5731%) of these ECs in the effluent with respect to the influent sampled on the same occasions, is globally prevalent in almost all types of treatment systems. Conventional WWTPs showed the highest negative removal (NR) for Carbamazepine, and Carbadox. Conjugation-deconjugation, types of WWTPs, transformations, leaching, operational parameters, sampling schemes, and nature of substance governs the NR efficiencies. Among the various categories of micropollutants, pesticides and beta-blockers are reported to exhibit the maximum percentage of NR, posing threat to human and the environment. With > 200% of NR for beta-blockers, low blood-pressure related symptoms may likely to get more prevalent in the near future. Study red-flags this phenomenon of negative removal that needs urgent attention.

Effect of sulfamethoxazole on nitrate removal by simultaneous heterotrophic aerobic denitrification

The increase in mariculture activities worldwide has not only led to a rise of nitrogen compounds in the ecosystem but has also intensified the accumulation of antibiotics in both terrestrial and marine environments. This study focused on the effect of typical antibiotics, specifically sulfamethoxazole (SMX) on nitrate removal from mariculture wastewater by aerobic denitrification process; an aerobic denitrification system feeding with 148.2 mg/L COD, 8.59 mg/L nitrate, 0.72 mg/L nitrite, and 4.75 mg/L ammonium was set up. The hydraulic retention time (HRT) was 8 h. As the aerobic bioreactor started up successfully without SMX dosage, an excellent removal of ammonium, nitrite, and nitrate was achieved at 91.35%, 93.33%, and 88.51%, respectively; the corresponding effluent concentrations were 0.41 mg/L, 0.048 mg/L, and 0.96 mg/L. At the influent SMX doses of 0, 1, 5, and 10 mg/L, the COD removal reached 96.91%, 96.27%, 88.69%, and 85.89%, resulting in effluent concentrations of 4.53, 5.45, 17.38, and 20.6 mg/L, respectively. Nitrification was not inhibited by SMX dosage. However, aerobic denitrification was inhibited by 10 mg/L SMX. Proteobacteria was the most abundant phylum, and surprisingly its abundance increased with the increase in SMX concentration. An excellent SMX degradation was noted at initial SMX dosages of 1, 5, and 10 mg/L; the removal rate was 100%,100%, and 99.8%, respectively. The SMX degrading genera Comamonas sp., Acinetobacter sp., and Thauera sp. are of great validity to wastewater engineers because they have demonstrated efficiency in simultaneous heterotrophic aerobic denitrification and antibiotic degradation as well as COD removal. PRACTITIONER POINTS: Nitrification was not inhibited by increase in SMX dosage. An increase in SMX dosage inhibited aerobic denitrification. COD removal was not affected by increased SMX dosage. Comamonas, Acinetobacter, and Thauera had high efficiency in COD removal and SMX degradation.

Cometabolic biodegradation of antibiotics by ammonia oxidizing microorganisms during wastewater treatment processes

Studies on antibiotic removal during wastewater treatment processes are crucial since their release into the environment could bring potential threats to human health and ecosystem. Cometabolic biodegradation of antibiotics by ammonia oxidizing microorganisms (AOMs) has received special attentions due to the enhanced removal of antibiotics during nitrification processes. However, the interactions between antibiotics and AOMs are less well-elucidated. In this review, the recent research proceedings on cometabolic biodegradation of antibiotics by AOMs were summarized. Ammonia oxidizing bacteria (AOB), ammonia oxidizing archaea (AOA) and complete ammonia oxidizers (comammox) played significant roles in both nitrification and cometabolic biodegradation of antibiotics. Antibiotics at varying concentrations might pose inhibiting or stimulating effect on AOMs, influencing the microbial activity, community abundance and ammonia monooxygenase subunit A gene expression level. AOMs-induced cometabolic biodegradation products were analyzed as well as the corresponding pathways for each type of antibiotics. The effects of ammonium availability, initial antibiotic concentration, sludge retention time and temperature were assessed on the cometabolic biodegradation efficiencies of antibiotics. This work might provide further insights into the fate and removal of antibiotics during nitrification processes.

Enhanced biodegradation of ciprofloxacin by enriched nitrifying sludge: assessment of removal pathways and microbial responses

Antibiotics are mostly collected by sewage systems, but not completely removed within wastewater treatment plants. Their release to aquatic environment poses a great threat to public health. This study evaluated the removal of a widely used fluoroquinolone antibiotic, ciprofloxacin, in enriched nitrifying culture through a series of experiments by controlling ammonium concentrations and inhibiting functional microorganisms. The removal efficiency of ciprofloxacin at an initial concentration of 50 μg L^-1 reached 81.86 ± 3.21% in the presence of ammonium, while only 22.83 ± 8.22% of ciprofloxacin was removed in its absence. A positive linear correlation was found between the ammonia oxidation rate (AOR) and ciprofloxacin biodegradation rate. These jointly confirmed the importance of the AOB-induced cometabolism in ciprofloxacin biodegradation, with adsorption and metabolic degradation pathways playing minor roles. The continuous exposure of AOB to ciprofloxacin led to decreases of ammonia monooxygenase (AMO) activities and AOR. The antibacterial effects of ciprofloxacin and its biodegradation products were further evaluated and the results revealed that biodegradation products of ciprofloxacin exhibited less toxicity compared to the parent compound, implying the potential application of cometabolism in alleviation of antimicrobial activity. The findings provided new insights into the AOB-induced cometabolic biodegradation of fluoroquinolone antibiotics.

Effects of different carbon sources on the removal of ciprofloxacin and pollutants by activated sludge: Mechanism and biodegradation

This research investigated the effects of ciprofloxacin (CIP) (0.5, 5, and 20 mg/L) on SBR systems under different carbon source conditions. Microbial community abundance and structure were determined by quantitative PCR and high-throughput sequencing, respectively. The biodegradation production of CIP and possible degradation mechanism were also studied. Results showed that CIP had adverse effects on the nutrient removal from wastewater. Compared with sodium acetate, glucose could be more effectively used by microorganisms, thus eliminating the negative effects of CIP. Glucose stimulated the microbial abundance and increased the removal rate of CIP by 18%-24%. The mechanism research indicated that Proteobacteria and Acidobacteria had a high tolerance for CIP. With sodium acetate as a carbon source, the abundance of nitrite-oxidizing bacterial communities decreased under CIP, resulting in the accumulation of nitrite and nitrate. Rhodanobacter and Microbacterium played a major role in nitrification and denitrification when using sodium acetate and glucose as carbon sources. Dyella and Microbacterium played positive roles in the degradation process of CIP and eliminated the negative effect of CIP on SBR, which was consistent with the improved removal efficiency of pollutants.

A review of antibiotic removal from domestic wastewater using the activated sludge process: removal routes, kinetics and operational parameters

Many advanced technologies have shown encouraging results in removing antibiotics from domestic wastewater. However, as activated sludge treatment is the most common sewage treatment system employed worldwide, improving its effect on antibiotic removal would be more desirable. Understanding the removal mechanisms, kinetics and factors that affect antibiotic removal in the activated sludge process is important as it would allow us to improve the treatment performance. Although these have been discussed in various literature covering different types of antibiotics and wastewater, a specific review on antibiotics and domestic wastewater is clearly missing. This review paper collates, discusses and analyses the removal of antibiotics from sewage in the activated sludge process along with the removal mechanisms and kinetics. The antibiotics are categorised into six classes: β-lactam, dihydrofolate reductase inhibitor, fluoroquinolone, macrolide, sulfonamides and tetracycline. Furthermore, the factors affecting the system performance with regard to antibiotic removal are examined.

Molecular design of high-efficacy and high drug safety Fluoroquinolones suitable for a variety of aerobic biodegradation bacteria

The present study attempted to improve the biodegradation removal rate of Fluoroquinolones (FQs) in sewage treatment plants. The similarity index analysis (CoMSIA) model for combined biodegradability was constructed, and 33 kinds of molecular derivatives of FQs suitable for a variety of aerobic biodegradation microorganisms were designed. Further, derivative-20 and derivative-28, with high drug efficiency, drug safety, and environmental friendliness were selected through pharmacokinetics (ADMET), toxicokinetics (TOPKAT), FQs functional characteristics, and environmental friendliness evaluations. Compared with the target molecules, the combined biodegradability of the above two FQ-derivative molecules were increased by 193.57 % and 205.07 %, respectively, while their environment-friendly characteristics were improved to a certain degree. Through molecular docking and molecular dynamic simulation analysis, it showed that van der Waals force (decreased by 2.73 %-61.74 %) was the main factor influencing the binding ability of the modified FQ molecules to the receptor proteins. In addition, the relationship among the non-bonding interaction resultant force, the binding effect of the FQ-derivative molecules, and the receptor protein-related amino acid residues were studied for the first time. It was observed that the higher the value of the non-bonding interaction resultant force, the better was the binding effect, which demonstrating the significantly improved biodegradability of the designed FQ-derivative molecules.

Pharmaceuticals and personal care products' (PPCPs) impact on enriched nitrifying cultures

The impact of pharmaceutical and personal care products (PPCPs) on the performance of biological wastewater treatment plants (WWTPs) has been widely studied using whole-community approaches. These contaminants affect the capacity of microbial communities to transform nutrients; however, most have neither honed their examination on the nitrifying communities directly nor considered the impact on individual populations. In this study, six PPCPs commonly found in WWTPs, including a stimulant (caffeine), an antimicrobial agent (triclosan), an insect repellent ingredient (N,N-diethyl-m-toluamide (DEET)) and antibiotics (ampicillin, colistin and ofloxacin), were selected to assess their short-term toxic effect on enriched nitrifying cultures: Nitrosomonas sp. and Nitrobacter sp. The results showed that triclosan exhibited the greatest inhibition on nitrification with EC₅₀ of 89.1 μg L^-1. From the selected antibiotics, colistin significantly affected the overall nitrification with the lowest EC₅₀ of 1 mg L^-1, and a more pronounced inhibitory effect on ammonia-oxidizing bacteria (AOB) compared to nitrite-oxidizing bacteria (NOB). The EC₅₀ of ampicillin and ofloxacin was 23.7 and 12.7 mg L^-1, respectively. Additionally, experimental data suggested that nitrifying bacteria were insensitive to the presence of caffeine. In the case of DEET, moderate inhibition of nitrification (<40%) was observed at 10 mg L^-1. These findings contribute to the understanding of the response of nitrifying communities in presence of PPCPs, which play an essential role in biological nitrification in WWTPs. Knowing specific community responses helps develop mitigation measures to improve system resilience.

Occurrence and removal of PPCPs from on-site wastewater using nitrogen removing biofilters

The presence of pharmaceuticals and personal care products (PPCPs) in the environment is primarily the result of discharge of waste, including from onsite wastewater treatment systems (OWTSs) which are employed by 25% of homes in the United States. However, the occurrence and removal of PPCPs in OWTSs is not well understood, particularly given the large diversity in PPCP compounds as well as in OWTS designs. In this study, we monitored 26 different PPCPs in 13 full-scale nitrogen removing biofilters (NRBs), an innovative/alternative type of OWTS that utilizes an overlying sand layer and an underlying woodchip/sand layer to simultaneously remove nitrogen and other wastewater-derived contaminants. The specific objectives of this study were (i) to measure the occurrence of PPCPs in septic tank effluent (STE) that served as an influent to NRBs, (ii) to quantify PPCP removal in three types of NRB configurations (n = 13), and (iii) to evaluate PPCP removal with depth and environmental conditions in NRBs. Aqueous samples were taken during 42 separate sampling events during 2016 - 2019 and analyzed by liquid chromatography tandem mass spectrometry. Analysis of the STE samples yielded detection of 23 of the 26 PPCPs, with caffeine being the most abundant and frequently detected compound at 52,000 ng/L (range: 190 - 181,000 ng/L), followed by acetaminophen and paraxanthine at 47,500 ng/L (190 - 160,000 ng/L), and 34,300 ng/L (430 - 210,000 ng/L), respectively. Cimetidine, fenofibrate, and warfarin were the only compounds not detected. The average removal of PPCPs by NRBs ranged from 58% to >99% for the various compounds. PPCP removal as a function of depth in the systems showed that 50 to >99% of the observed removal was achieved within the top oxic layer (0 - 46 cm) of the NRBs for 19 analytes. Seven of the compounds had >85% removal by the same depth. These results indicate that NRBs are effective at removing PPCPs and that a large portion of the removal is achieved within the oxic nitrifying layer of the NRBs. Overall, the removal of PPCPs in NRBs was comparable (n = 8) or better (n = 15) than that observed for conventional wastewater treatment plants.

Evaluating the application of antibiotic treatment using algae-algae/activated sludge system

Biological methods are promising treatment methods to remove pollutants from wastewater. Recently, microalgae have been proved to be of strong application potential in wastewater treatment. In this study, a microalga - antibiotic treatment system was built to evaluate the treatment capacity of microalgae in antibiotic wastewater. In the group with Chlorella pyrenoidosa, the removal rate of cefradine was 41.47 ± 0.62% after 24 h of treatment, which was 3.4 times higher than that without microalgae (12.37 ± 2.30%). Algal decomposition was the main removal mechanism. Meanwhile, the effect of multiple microalgae species on antibiotic treatment was studied. The removal rates of cefradine by C. pyrenoidosa cultivated in the filtered fluid of Microcystis aeruginosa were 75.48 ± 0.29%, which was significantly higher than those by C. pyrenoidosa only. Those indicated that multiple microalgae species strategy was a potential enhancement strategy for algae-based antibiotic treatment. Finally, amoxicillin and norfloxacin were used to study the treatment potential of this technology for more different kinds antibiotics and the integration of microalgae with activated sludge was also investigated. Amoxicillin can be quickly removed by microalgae, but the removal effect of norfloxacin by microalgae is poor. The refractory antibiotic norfloxacin can be treated by co-culturing microalgae and activated sludge. Those showed the good expansibility of microalgae-based technology. The findings indicated that with microalgae-based antibiotic removal method has good application potential, and combined with other technologies, it can effectively remove the refractory antibiotics.

Strategies to Control Human Health Risks Arising from Antibiotics in the Environment: Molecular Modification of QNs for Enhanced Plant-Microbial Synergistic Degradation

In the present work, a comprehensive screening and evaluation system was established to improve the plant-microbial synergistic degradation effects of QNs. The study included the construction of a 3D-QSAR model, the molecular modification, environmental friendliness and functional evaluation of drugs, degradation pathway simulation, and human health risk assessment. Molecular dynamics was applied to quantify the binding capacity of QNs toward the plant degradation enzyme (peroxidase) and microbial degradation enzymes (manganese peroxidase, lignin peroxidase, and laccase). The fuzzy comprehensive evaluation method was used in combination with the weighted average method for normalization and assigning equal weights to the plant and microbial degradation effect values of the QNs. Considering the synergistic degradation effect value as the dependent variable and the molecular information of the QNs as the independent variable, a 3D-QSAR model was constructed for the plant-microbial synergistic degradation effect of QNs. The constructed model was then employed to conduct the molecular modification, environmental friendliness and functional evaluation, degradation pathway simulation, and human health risk assessment of transformation products using pharmacokinetics and toxicokinetics. The results revealed that the synergistic degradation effect 3D-QSAR (CoMSIA) model exhibited good internal and external prediction ability, fitting ability, stability, and no overfitting phenomenon. Norfloxacin (NOR) was used as the target molecule in the molecular modification. A total of 35 NOR derivatives with enhanced plant-microbial synergistic degradation effect (1.32-21.51%) were designed by introducing small-volume, strongly electronegative, and hydrophobic hydrogen bond receptor groups into the active group of the norfloxacin structure. The environment-friendliness and the functionality of NOR were evaluated prior to and after the modification, which revealed seven environment-friendly FQs derivatives exhibiting moderate improvement in stability and bactericidal efficacy. The simulation of the NOR plant and microbial degradation pathways prior to and after the modification and the calculation of the reaction energy barrier revealed Pathway A (D-17 to D-17-2) and Pathway B (D-17 to D-17-4) as the most prone degradation pathways in plants and Pathway A (D-17 to D-17-1) and Pathway B (D-17 to D-17-4) as the most prone degradation pathways in microorganisms. This demonstrated that the degradation of the modified NOR derivatives was significantly enhanced, with the hydroxylation and piperazine ring substitution reaction playing an important role in the degradation process. Finally, the parameters, including hepatotoxicity, mutagenicity, and rodent carcinogenicity, among others, predicted using the pharmacokinetics and toxicokinetics analyses revealed a significant reduction in the human health risk associated with the modified NOR, along with a considerable reduction in the toxicity of its transformation products, implying that the human health risk associated with the transformation products was reduced remarkably. The present study provides a theoretical basis for novel ideas and evaluation programs for improving the plant-microbial synergistic degradation of the QNs antibiotics for source control and drug design, thereby reducing the residues of these antibiotics and the associated hazard in the complex plant-soil environment, ultimately decreasing the potential risks to human health.

Profiles of antibiotic resistance genes in an inland salt-lake Ebinur Lake, Xinjiang, China: The relationship with antibiotics, environmental factors, and microbial communities

Lakes in arid northwestern China, as the main pollutant-holding water bodies in the typical ecologically fragile areas, are facing the unknown risk of exposure to antibiotics and antibiotic resistance genes (ARGs). In this study, five ARGs and one mobile genetic element (intI1) and their relation with antibiotics, microbial communities and water quality were investigated in Ebinur Lake Basin, a typical salt-lake of China. Quantitative PCR analysis indicated that ARGs decreasing order in both surface water and sediment was sul1 >sul2 >tetW>ermB>qnrS, which means sulfonamide resistance genes were the main pollution ARGs. Macrolide antibiotics were the predominant antibiotics in the surface water and sediment in winter, while sulfonamides and quinolones accounted for a high proportion in summer. There was a non-corresponding relationship between ARGs and antibiotics. Moreover, the relationship between ARGs and microbial communities were defined. Sulfonamide resistance genes were carried by a greater diversity of potential host bacteria (76 genera) than other ARGs (9 genera). And their positive correlation with intI1 (p < 0.05) which promotes their migration and provides possibility of their co-occurrence in bacterial populations (e.g., Nitrospira). Bacterial genera were the main driver of ARGs distribution pattern in highly saline lake sediment. Environmental factors like salinity, total nitrogen and organic matter could have a certain influence on the occurrence of ARGs by affecting microorganisms. The results systematically show the distribution and propagation characteristics of ARGs in typical inland salt-lakes in China, and preliminarily explored the relationship between ARGs and antibiotics, resistance genes and microorganisms in lakes in ecologically fragile areas.

Potential biotransformation pathways and efficiencies of ciprofloxacin and norfloxacin by an activated sludge consortium

Fluoroquinolones (FQs), such as ciprofloxacin (CIP) and norfloxacin (NOR), are types of emerging trace pollutants that have attracted great attention. In this study, an activated sludge (AS) consortium with high bio-removal capability to CIP and NOR was obtained by acclimating with CIP and NOR for 10 d. Meanwhile, a CIP- and NOR- transforming bacterial strain (S5), which is highly homologous to the 16S rRNA gene sequence of Enterobacter sp., was isolated from the acclimated AS. The bio-removal efficiency of CIP under the acclimated AS consortium was better than that under the pure culture of Enterobacter sp. S5 (93.1% vs. 89.3%), while the bio-removal efficiency of NOR under the acclimated AS consortium was lower than that under the pure culture of Enterobacter sp. S5 (83.9% vs. 89.8%). The biotransformation and bio-adsorption were two main ways to bio-remove CIP and NOR. However, the CIP and NOR biotransformation efficiencies of the acclimated AS were higher than under the pure culture of Enterobacter sp. S5, while the CIP and NOR adsorption of acclimated AS were lower than that under the pure culture of Enterobacter sp. S5. The N-acetylciprofloxacin and N-acetylnorfloxacin were the main biotransformation products of CIP and NOR. It is possible that acetyltransferase may be involved in the biotransformation process. Whether under the pure culture or AS consortium, the cytotoxicity of CIP and NOR transformation products to gram-negative bacteria was alleviated. Therefore, the acclimated AS and Enterobacter sp. S5 might provide a new strategy for removing contaminants and alleviating of FQs resistance.

Fate of antibiotics and antibiotic resistance genes during aerobic co-composting of food waste with sewage sludge

Aerobic composting is widely used on transforming organic solid waste into proliferating products. However, the removal of antibiotics and antibiotic resistance genes (ARGs) in the process of co-composting of food waste with sewage sludge has been rarely reported to date. Therefore, we investigated a laboratory-scale composting using food waste and sewage sludge as substrates to study changes in antibiotics and ARGs during composting. Varying dose of antibiotics were added to allow the evaluation of changes in antibiotics, the microbial community and ARGs. The results revealed that composting effectively removed fluoroquinolones and macrolides, while showed poor efficiency in removing sulfonamides. Results from the 16S rRNA sequencing revealed that Firmicutes dominated on D0, while Proteobacteria and Actinomycetes dominated on D28, and a high concentration of antibiotics affected the microbial succession. The quantitative PCR demonstrated that the abundance of sul3, sulA, qnrB, qnrS, and ermB was reduced after 28 days composting, while an increase in the abundance of sul1, sul2, qnrD, ermC, and ermF was induced by high concentrations of antibiotics. Redundancy analysis revealed that total organic matter was the most important factor for the variation in the ARGs abundance. Overall, our findings indicated that the aerobic co-composting of food waste with sewage sludge can effectively remove antibiotics and ARGs. Our study sheds a new idea light on the strategy for the removal of antibiotics and ARGs from organic solid waste.

Responses of aerobic granular sludge to fluoroquinolones: Microbial community variations, and antibiotic resistance genes

In this study, aerobic granular sludge (AGS) was operated under high levels of ammonium for removing three fluoroquinolones (FQs), i.e., ciprofloxacin (CFX), ofloxacin (OFX), and norfloxacin (NFX) at 3, 300, and 900 µg/L, respectively. Two key objectives were to investigate the differential distribution of antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) in sludge fractions and to evaluate correlations between ARGs and MGEs to nitrifying and denitrifying bacteria. AGS showed excellent stability under the exposure of FQs, with nitrite-oxidizing bacteria (NOB) more sensitive to FQs than ammonium-oxidizing bacteria (AOB). Specific oxygen utilization rates (SOUR) showed a reduction of 26.9% for NOB but only 4.0% of the reduced activity of AOB by 3 μg/L FQs. AGS performed better removal efficiencies for CFX and NFX than OFX, and the efficiencies increased with their elevated concentrations, except at 900 μg/L FQs. The elevated FQ concentrations led to a significant enrichment of intI1 and genus Thauera, while qnrD and qnrS showed no accumulation. Compared to nitrifiers, FQs relevant ARGs and the intI1 gene preferred to exist in denitrifiers, and the abundance of denitrifiers behaved a decreasing trend with the sludge size. Two quinoline-degrading bacteria were found in the AGS system, i.e., Alicycliphilus and Brevundimonas, possibly carrying qnrS and qnrD, respectively. Their relative abundance increased with the sludge size, which was 2.18% in sludge <0.5 mm and increased to 3.70% in sludge >2.0 mm, suggesting that the AGS may be a good choice in treating FQs-containing wastewater.

Carbon-based adsorbents for fluoroquinolone removal from water and wastewater: A critical review

This review summarizes the adsorptive removal of Fluoroquinolones (FQ) from water and wastewater. The influence of different physicochemical parameters on the adsorptive removal of FQ-based compounds is detailed. Further, the mechanisms involved in the adsorption of FQ-based antibiotics on various adsorbents are succinctly described. As the first of its kind, this paper emphasizes the performance of each adsorbent for FQ-type antibiotic removal based on partition coefficients of the adsorbents that is a more sensitive parameter than adsorption capacity for comparing the performances of adsorbents under various adsorbate concentrations and heterogeneous environmental conditions. It was found that π-π electron donor-acceptor interactions, electrostatic interactions, and pore-filling were the most prominent mechanisms for FQ adsorption by carbon and clay-based adsorbents. Among all the categories of adsorbents reviewed, graphene showed the highest performance for the removal of FQ antibiotics from water and wastewater. Based on the current state of knowledge, this review fills the gap through methodolically understanding the mechanism for further improvement of FQ antibiotics adsorption performance from water and wastewater.

Spatial variation of pharmaceuticals in the unit processes of full-scale municipal wastewater treatment plants in Korea

Several reports have elucidated the removal of pharmaceutical residues in municipal wastewater treatment plants (WWTPs). However, there remains a need to determine the spatial distribution of pharmaceuticals in the unit processes of full-scale municipal WWTPs. Herein, spatial variations of fifteen pharmaceuticals in the unit processes of four full-scale municipal WWTPs were assessed by analyzing both solid and liquid samples. Furthermore, different pathways of each pharmaceutical such as biodegradation, adsorption, deconjugation, and electrostatic interaction were investigated. Pharmaceutical mass loading were measured at various points for the different unit process and evaluated using liquid chromatography-tandem mass spectrometry. The average mass loading of acetaminophen and caffeine decreased tremendously in the first biological treatment process regardless of the process configuration. In contrast, a temporary increase was observed in the mass loading of ibuprofen in the anaerobic and/or anoxic processes, which was presumably caused by deconjugation. Additionally, the adverse effect of coagulation on ibuprofen removal was validated. The major removal mechanism for the selected antibiotics, except for sulfamethoxazole, was the adsorption by biosolids due to electrostatic interaction. Subsequently, a drastic decrease was observed in their mass loadings in the solid-liquid separation process of the WWTPs. The membrane bioreactor (MBR) shows excellent capability for mitigation of pharmaceuticals in municipal wastewater because it comprises a high concentration of biosolids that act as adsorbents. The evaluation of the spatial variations of the selected pharmaceuticals in different unit processes provides valuable information on their behavior and removal mechanisms.

Investigation of the Prevalence of Antibiotic Resistance Genes According to the Wastewater Treatment Scale Using Metagenomic Analysis

Although extensive efforts have been made to investigate the dynamics of the occurrence and abundance of antibiotic resistance genes (ARGs) in wastewater treatment plants (WWTPs), understanding the acquisition of antibiotic resistance based on the WWTP scale and the potential effects on WWTPs is of relatively less interest. In this study, metagenomic analysis was carried out to investigate whether the WWTP scale could be affected by the prevalence and persistence of ARGs and mobile genetic elements (MGEs). As a result, 152 ARG subtypes were identified in small-scale WWTP samples, while 234 ARG subtypes were identified in large-scale WWTP samples. Among the detectable ARGs, multidrug, MLS (macrolide–lincosamide–streptogramin), sulfonamide, and tetracycline resistance genes had the highest abundance, and large and small WWTPs had similar composition characteristics of ARGs. In MGE analysis, plasmids and integrons were 1.5–2.0-fold more abundant in large-scale WWTPs than in small-scale WWTPs. The profile of bacteria at the phylum level showed that Proteobacteria and Actinobacteria were the most dominant bacteria, representing approximately 70% across large- and small-scale WWTPs. Overall, the results of this study elucidate the different abundances and dissemination of ARGs between large- and small-scale WWTPs, which facilitates the development of next-generation engineered wastewater treatment systems.

Treatment technologies for emerging contaminants in wastewater treatment plants: A review

The "emerging contaminants" (ECs) are predominantly unregulated anthropogenic chemicals that occur in air, soil, water, food, and human/animal tissues in trace concentrations. The ECs are persistent in the environment, capable of perturbing the physiology of target receptors and, therefore, are regarded as contaminants of emerging environmental concerns in recent years. The prominent classes of ECs include pharmaceuticals and personal care products (PCPs), surfactants, plasticizers, pesticides, fire retardants, and nanomaterials. Some of the ECs with harmful effects on endocrine systems have been recognized as endocrine disrupting chemicals (EDCs). Since the 1990s intensive research has been done covering environmental occurrence, fate, ecological effects, and treatment technologies of ECs. However, a comprehensive summary of the EC removal techniques, particularly in wastewater treatment plants (WWTPs) are limited. Though the WWTPs are inefficient when it comes to ECs removal, they act as primary barriers against the spread of ECs. Therefore, this paper reviews the treatment technologies currently engaged for ECs removal in WWTPs for further possible upgrades of the existing designs. Results of this review indicate that the fate and distribution of ECs can be approximately estimated based on physicochemical properties like octanol-water partitioning coefficient (e.g., log K_OW > 4, maximum sorption potential) and solid-water distribution coefficient [e.g., K_d < 300-500 L/kg MLSS (mixed liquor suspended solids), insignificant sorption into sludge]. Biodegradation potential of ECs can be predicted from biodegradation constant values (e.g., K_bio < 0.01 = low biodegradation and >10 = high biodegradation). In WWTPs, the EC removal efficiency varies in the range of 20-50%, 30-70%, and >90% during the primary, secondary, and tertiary treatment steps, respectively. Tertiary treatment technologies are considered as the most suitable alternatives for ECs treatment, but complete ECs removal is yet to be achieved. Further advancements in the treatment technologies will unquestionably be necessary in the future.

Removal of pharmaceuticals by ammonia oxidizers during nitrification

The adverse effect of pharmaceuticals on ecosystem and human health raises great interest for the removal of pharmaceuticals in wastewater treatment plants (WWTPs). Enhanced removal of pharmaceuticals by ammonia oxidizers (AOs) has been observed during nitrification. This review provides a comprehensive summary on the removal of pharmaceuticals by AOs-ammonia oxidizing bacteria (AOB), ammonia oxidizing archaea (AOA), and complete ammonia oxidizer (comammox) during nitrification in pure ammonia oxidizing culture and mixed microbes systems. The superior removal of pharmaceuticals by AOs in conditions with nitrifying activity compared with the conditions without nitrifying activity was proposed. The contribution of AOs on pharmaceuticals removal in pure and mixed microbe systems was discussed and activated sludge modeling was suggested as the proper measure on assessing the contribution of AOs on the removal of pharmaceuticals in mixed microbe culture. Three transformation processes and the involved reaction types of pharmaceuticals transformation during nitrification were reviewed. The present paper provides a systematical summary on pharmaceuticals removal by different AOs across pure and mixed microbes culture during nitrification, which opens up the opportunity to optimize the wastewater biological treatment systems for enhanced removal of pharmaceuticals. KEY POINTS: • The superior removal of pharmaceuticals by ammonia oxidizers (AOs) was summarized. • The removal contribution of pharmaceuticals attributed by AOs was elucidated. • The transformation processes and reaction types of pharmaceuticals were discussed.