Removal of tetracycline by denitrifying Mn(II)-oxidizing bacterium Pseudomonas sp. H117 and biomaterials (BMO and MBMO): Efficiency and mechanisms

Simultaneous removal of groundwater manganese and ammonia nitrogen based on high-flux gravity driven ceramic membrane (HF-GDCM) coupled with aerated fluidized birnessite

High concentrations of manganese ion (Mn2+) and ammonia nitrogen (NH3-N) in groundwater are indicative of a critical environmental issue that necessitates immediate attention. The gravity-driven ceramic membrane (GDCM) technology has shown great potential for groundwater treatment in rural communities, owing to its low energy demand and user-friendly operation. Active manganese oxide (MnOx) is extensively used for the concurrent removal of Mn2+ and NH3-N, leveraging its large specific surface area and abundant adsorption sites. Our research group has developed a GDCM-MnOx coupled system to address this challenge. However, membrane fouling, manifested as a reduction in flux or an increase in transmembrane pressure, has been a significant barrier to its widespread adoption. To address this challenge, we have implemented a continuous aeration system in conjunction with GDCM to fluidize birnessite to achieve the higher membrane flux, which has also proven effective in mitigating fouling while maintaining high water purification performance. Over a period of 100 days or more, the high membrane flux in the high-flux GDCM system (HF-GDCM) enhanced with aerated fluidized birnessite has been consistently maintained at approximately 34 L/(m2·h) at a water head of 1 m. Moreover, the HF-GDCM system efficiently removed manganese and NH3-N from groundwater under a hydraulic retention time (HRT) of less than 2.5 h, while also improving membrane permeability. The involvement of manganese oxidizing bacteria (MnOB) and ammonium-oxidizing bacteria (AOB) of Hypomicrobium and Nocardioides in the removal processes within the HF-GDCM system was confirmed. Additionally, XPS analysis confirmed the predominant oxidation state of MnOx to be Mn(III). The MnOx, deposited on powdered activated carbon (PAC) particles in a flower-like configuration, progressively formed a birnessite-like functional layer as the manganese ion content increased over time. Consequently, the HF-GDCM coupled with aerated fluidized birnessite is deemed suitable for water purification in small-scale rural or reservoir settings.

A critical review of Mnammox coupled with the NDMO for innovative nitrogen removal

In the context of increasing global nitrogen pollution, traditional biological nitrogen removal technologies like nitrification and denitrification are hindered by high energy consumption. Additionally, the deployment of anaerobic ammonium oxidation (Anammox) technology is constrained due to the slow growth rate of Anammox bacteria and there is a bottleneck in nitrogen removal efficiency. To overcome these technical bottlenecks, researchers have discovered a revolutionary nitrogen removal technology that cleverly combines the redox cycling of manganese with nitrification and denitrification reactions. In this new process, manganese dependent anaerobic ammonium oxidation (Mnammox) bacteria can convert NH4+ to N2 under anaerobic conditions, while nitrate/nitrite dependent manganese oxidation (NDMO) bacteria use NO3-/NO2- as electron acceptors to oxidize Mn2+ to Mn4+. Mn4+ acts as an electron acceptor in Mnammox reaction, thereby realizing the autotrophic nitrogen removal process. This innovative method not only simplifies the steps of biological denitrification, but also significantly reduces the consumption of oxygen and organic carbon, providing a more efficient and environmentally friendly solution to the problem of nitrogen pollution. The article initially provides a concise overview of prevalent nitrogen removal technologies and the application of manganese in these processes, and discusses the role of manganese in biogeochemical cycles, including its discovery, mechanism of action, microbial communities involved, and its impact on these key factors in the process. Subsequently, metabolic principles, benefits, advantages, and environmental considerations of Mnammox coupled with the NDMO process are analyzed in detail. Finally, this article summarizes the shortcomings of current research and looks forward to future research directions. The goal of this article is to provide a valuable reference for researchers to fully understand the application of manganese in nitrogen removal processes.

Prospects of Pseudomonas in Microbial Fuel, Bioremediation, and Sustainability

Microbial applications in agriculture and industry have gained significant attention due to their potential to address environmental challenges and promote sustainable development. Among these, the genus Pseudomonas stands out as a promising candidate for various biotechnological uses, thanks to its metabolic flexibility, resilience, and adaptability to diverse environments. This review provides a comprehensive overview of the current state and future prospects of microbial fuel production, bioremediation, and sustainable development, focusing on the pivotal role of Pseudomonas species. We emphasize the importance of microbial fuel as a renewable energy source and discuss recent advancements in enhancing biofuel generation using Pseudomonas strains. Additionally, we explore the critical role of Pseudomonas in bioremediation processes, highlighting its ability to degrade a wide spectrum of pollutants, including hydrocarbons, pesticides, and heavy metals, thereby reducing environmental contamination. Despite significant progress, several challenges remain. These include refining microbial strains for optimal process efficiency and addressing ecological considerations. Nonetheless, the diverse capabilities of Pseudomonas offer promising avenues for innovative solutions to pressing environmental issues, supporting the transition to a more sustainable future.

Characteristic and mechanism of biological nitrogen and phosphorus removal facilitated by biogenic manganese oxides (BioMnOx) at various concentrations of Mn(II)

Biogenic manganese oxides (BioMnOx) have attracted considerable attention as active oxidants, adsorbents, and catalysts. However, characteristics and mechanisms of nitrification-denitrification in biological redox reactions mediated by different concentrations of BioMnOx are still unclear. Fate of nutrients (e.g., NH4+-N, TP, NO3--N) and COD were investigated through different concentrations of BioMnOx produced by Mn(II) in the moving bed biofilm reactor (MBBR). 34% and 89.2%, 37.8% and 89.8%, 57.3% and 88.9%, and 62.1% and 90.4% of TN and COD by MBBR were synchronously removed in four phases, respectively. The result suggested that Mn(II) significantly improved the performance of simultaneous nitrification and denitrification (SND) and TP removal based on manganese (Mn) redox cycling. Characteristics of glutathione peroxidase (GSH-Px), reactive oxygen species (ROS), and electron transfer system activity (ETSA) were discussed, demonstrating that ROS accumulation reduced the ETSA and GSH-Px activities when Mn(II) concentration increased. Extracellular polymeric substance (EPS) function and metabolic pathway of Mn(II) were explored. Furthermore, effect of cellular components on denitrification was evaluated including BioMnOx performances, indicating that Mn(II) promoted the non-enzymatic action of cell fragments. Finally, mechanism of nitrification and denitrification, denitrifying phosphorus and Mn removal was further elucidated through X-ray photoelectron spectroscopy (XPS), high throughput sequencing, and fourier transform infrared reflection (FTIR). This results can bringing new vision for controlling nutrient pollution in redox process of Mn(II).

Biodegradation of ciprofloxacin using machine learning tools: Kinetics and modelling

Recently, the rampant administration of antibiotics and their synthetic organic constitutes have exacerbated adverse effects on ecosystems, affecting the health of animals, plants, and humans by promoting the emergence of extreme multidrug-resistant bacteria (XDR), antibiotic resistance bacterial variants (ARB), and genes (ARGs). The constraints, such as high costs, by-product formation, etc., associated with the physico-chemical treatment process limit their efficacy in achieving efficient wastewater remediation. Biodegradation is a cost-effective, energy-saving, sustainable alternative for removing emerging organic pollutants from environmental matrices. In view of the same, the current study aims to explore the biodegradation of ciprofloxacin using microbial consortia via metabolic pathways. The optimal parameters for biodegradation were assessed by employing machine learning tools, viz. Artificial Neural Network (ANN) and statistical optimization tool (Response Surface Methodology, RSM) using the Box-Behnken design (BBD). Under optimal culture conditions, the designed bacterial consortia degraded ciprofloxacin with 95.5% efficiency, aligning with model prediction results, i.e., 95.20% (RSM) and 94.53% (ANN), respectively. Thus, befitting amendments to the biodegradation process can augment efficiency and lead to a greener solution for antibiotic degradation from aqueous media.

Can xenobiotics support the growth of Mn(II)-oxidizing bacteria (MnOB)? A case of phenol-utilizing bacteria Pseudomonas sp. AN-1

Biogenic manganese oxides (BioMnOx) produced by Mn(II)-oxidizing bacteria (MnOB) have garnered considerable attention for their exceptional adsorption and oxidation capabilities. However, previous studies have predominantly focused on the role of BioMnOx, neglecting substantial investigation into MnOB themselves. Meanwhile, whether the xenobiotics could support the growth of MnOB as the sole carbon source remains uncertain. In this study, we isolated a strain termed Pseudomonas sp. AN-1, capable of utilizing phenol as the sole carbon source. The degradation of phenol took precedence over the accumulation of BioMnOx. In the presence of 100 mg L-1 phenol and 100 µM Mn(II), phenol was entirely degraded within 20 h, while Mn(II) was completely oxidized within 30 h. However, at the higher phenol concentration (500 mg L-1), phenol degradation reduced to 32% and Mn(II) oxidation did not appear to occur. TOC determination confirmed the ability of strain AN-1 to mineralize phenol. Based on the genomic and proteomics studies, the Mn(II) oxidation and phenol mineralization mechanism of strain AN-1 was further confirmed. Proteome analysis revealed down-regulation of proteins associated with Mn(II) oxidation, including MnxG and McoA, with increasing phenol concentration. Notably, this study observed for the first time that the expression of Mn(II) oxidation proteins is modulated by the concentration of carbon sources. This work provides new insight into the interaction between xenobiotics and MnOB, thus revealing the complexity of biogeochemical cycles of Mn and C.

Denitrification driven by additional ferrous (Fe2+) and manganous (Mn2+) and removal mechanism of tetracycline and cadmium (Cd2+) by biogenic Fe-Mn oxides

Zoogloea sp. MFQ7 achieved excellent denitrification of 91.71% at ferrous to manganous ratio (Fe/Mn) of 3:7, pH of 6.5, nitrate concentration of 25 mg L-1 and carbon to nitrogen ratio of 1.5. As the Fe/Mn ratio increasd, the efficiency of nitrate removal gradually decreased, indicating that strain MFQ7 had a higher affinity for Mn2+ than Fe2+. In situ generated biogenic Fe-Mn oxides (BFMO) contained many iron-manganese oxides (MnO2, Mn3O4, FeO(OH), Fe2O3, and Fe3O4) as well as reactive functional groups, which play an significant part in tetracycline (TC) and cadmium (Cd2+) adsorption. The adsorption of TC and Cd2+ by BFMO can better fit the pseudo-second-order and Langmuir models. In addition, multiple characterization results of before and after adsorption indicated that the removal mechanism of BFMO on TC and Cd2+ was probably surface complexation adsorption and redox reactions.

New insights for simultaneous nutrient removal enhancement and greenhouse gas emissions reduction of constructed wetland by optimizing its redox environment through manganese oxide addition

Manganese oxide (MnOx) is receiving increased interest in the nutrient removal of constructed wetlands (CWs); however, its service effectiveness for simultaneous greenhouse gas (GHG) emissions reduction is still vague. In this study, three vertical flow CWs, i.e., volcanics (CCW), manganese sand uniformly mixing with volcanics (Mn-CW) and MnOx doped volcanics (MnV-CW), were constructed to investigate the underlying mechanisms of MnOx on nutrient removal enhancement and greenhouse gas (GHG) emissions reduction. The results showed that the MnOx doped volcanics optimized the oxidation-reduction potential surrounding the substrate (-164.0 ∼ +141.1 mv), and resulted in the lowest GHG emissions (CO2-equivalent) from MnV-CW, 16.8-36.5 % lower than that of Mn-CW and CCW. This was mainly ascribed to mitigation of N2O produced during the NO3--N reduction process, according to results of 15N stable isotope labeling. Analysis of the microbial community structure revealed that due to the optimized redox conditions through chemical doping of MnOx on volcanics, the abundance of microbe involved in denitrification and Mn-oxidizing process in the MnV-CW was significantly increased at genus level, which led to a higher Mn cycling efficiency between biogenic MnOx and Mn2+, and enhanced denitrification efficiency and N2O emission reduction. This study would help to understand and provide a preferable reference for future applications for manganese-based CW.

Tetracyclines contamination in European aquatic environments: A comprehensive review of occurrence, fate, and removal techniques

Tetracyclines are among the most commonly used antibiotics for the treatment of bacterial infections and the improvement of agricultural growth and feed efficiency. All compounds in the group of tetracyclines (tetracycline, chlorotetracycline, doxycycline, and oxytetracycline) are excreted in an unchanged form in urine at a rate of more than 70%. They enter the aquatic environment in altered and unaltered forms which affect aquatic micro- and macroorganisms. This study reviews the occurrence, fate, and removal techniques of tetracycline contamination in Europe. The average level of tetracycline contamination in water ranged from 0 to 20 ng/L. However, data regarding environmental contamination by tetracyclines are still insufficient. Despite the constant presence and impact of tetracyclines in the environment, there are no legal restrictions regarding the discharge of tetracyclines into the aquatic environment. To address these challenges, various removal techniques, including advanced oxidation, adsorption, and UV treatment, are being critically evaluated and compared. The summarized data contributes to a better understanding of the current state of Europe's waters and provides insight into potential strategies for future environmental management and policy development. Further research on the pollution and effects of tetracyclines in aquatic environments is therefore required.

Simultaneous removal of phosphorus, zinc, and lead from oligotrophic ecosystem by iron-driven denitrification: Performance and mechanisms

Based on the current situation of complex pollution caused in surface water by oligotrophic condition and heavy metal release from river and lake bottom sediments. This study aimed to achieve the simultaneous removal of nitrate, phosphorus, Zn2+ and Pb2+ through microbial approach. At nitrate concentration of 4.82 mg L-1, carbon to nitrogen ratio of 1.5, pH of 6.0, and Fe2+ concentration of 5.0 mg L-1, the nitrate removal efficiency of Zoogloea sp. FY-6 reached 95.17%. The addition of pollutants under these conditions resulted in 88.76% removal of total phosphorus at 18 h, and 85.46 and 78.59% removal of Zn2+ and Pb2+ respectively, and there was competition for adsorption between Zn2+ and Pb2+. Extracellular polymers and fluorescence excitation-emission substrates confirmed that Fe2+ reduced heavy metal toxicity through promoting bacterial production of secretions and promotes denitrification as a carbon source. Meanwhile, contaminant removal curves and Fourier transform infrared spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy demonstrated the synchronous removal of Zn2+ and Pb2+ mainly through biological action and the formation of nanoscale iron oxides. Biological-iron precipitation also provided adsorption sites for phosphorus. This research provides the theoretical foundation for applying microorganisms to restore oligotrophic source water (rivers and lakes) containing complex pollutants.

Novel Ag-bridged dual Z-scheme g-C3N4/BiOI/AgI plasmonic heterojunction: Exceptional photocatalytic activity towards tetracycline and the mechanism insight

Rational design and synthesis of highly efficient and robust photocatalysts with positive exciton splitting and interfacial charge transfer for environmental applications is critical. Herein, aiming at overcoming the common shortcomings of traditional photocatalysts such as weak photoresponsivity, rapid combination of photo-generated carriers and unstable structure, a novel Ag-bridged dual Z-scheme g-C₃N₄/BiOI/AgI plasmonic heterojunction was successfully synthesized using a facile method. Results showed that Ag-AgI nanoparticles and three-dimensional (3D) BiOI microspheres were decorated highly uniformly on the 3D porous g-C₃N₄ nanosheet, resulting in a higher specific surface area and abundant active sites. The optimized 3D porous dual Z-scheme g-C₃N₄/BiOI/Ag-AgI manifested exceptional photocatalytic degradation efficiency of tetracycline (TC) in water with approximately 91.8% degradation efficiency within 165 min, outperforming majority of the reported g-C₃N₄-based photocatalysts. Moreover, g-C₃N₄/BiOI/Ag-AgI exhibited good stability in terms of activity and structure. In-depth radical scavenging and electron paramagnetic resonance (EPR) analyses confirmed the relative contributions of various scavengers. Mechanism analysis indicated that the improved photocatalytic performance and stability were ascribed to the highly ordered 3D porous framework, fast electron transfer of dual Z-scheme heterojunction, desirable photocatalytic performance of BiOI/AgI and synergistic effect of Ag plasmas. Therefore, the 3D porous Z-scheme g-C₃N₄/BiOI/Ag-AgI heterojunction had a good prospect for applications in water remediation. The current work provides new insight and useful guidance for designing novel structural photocatalysts for environment-related applications.

Efficient utilization of biogenic manganese oxides in bioaugmentation columns for remediation of thallium(I) contaminated groundwater

Little attention has been paid to the in situ-generated biogenic manganese oxides (BMnOx) for practical implementation in continuous groundwater remediation systems. The enrichment effects of manganese oxidizing bacteria (MOB) in bioaugmentation columns and the in situ-generated BMnOx for continuous thallium(I) (Tl(I)) removal from groundwater were investigated. Results indicated that Pseudomonas Putida MnB1 (strain MnB1) attached on the groundwater sediments (GS) can achieve a maximum of 97.37 % Mn(II) oxidation and generate 29.6 mg/L BMnOx, which was superior than that of traditional quartz sand (QS). The in situ-generated BMnOx in MOB_GS column effectively removed 10-100 μg/L Tl(I) under the interference of high concentrations of Fe(II) and Mn(II) in groundwater. Distinctive microbial enrichment effects occurred in the bioaugmentation columns under the competition of indigenous microbes in groundwater. The release of Mn(II) from the BMnOx inhibited with the decrease in Tl(I) removal efficiency. XAFS analysis revealed Tl(I) was effectively adsorbed by BMnOx and Mn-O octahedra with Tl-O tetrahedral coordination existed in BMnOx. This study provides an in-depth understanding of the in situ-generated BMnOx for the Tl(I) removal and contributes to the application of BMnOx in groundwater remediation.

Application of manganese oxides in wastewater treatment: Biogeochemical Mn cycling driven by bacteria

Manganese oxides (MnOx) are recognized as a strongest oxidant and adsorbent, of which composites have been proved to be effective in the removal of contaminants from wastewater. This review provides a comprehensive analysis of Mn biochemistry in water environment including Mn oxidation and Mn reduction. The recent research on the application of MnOx in the wastewater treatment was summarized, including the involvement of organic micropollutant degradation, the transformation of nitrogen and phosphorus, the fate of sulfur and the methane mitigation. In addition to the adsorption capacity, the Mn cycling mediated by Mn(II) oxidizing bacteria and Mn(IV) reducing bacteria is the driving force for the MnOx utilization. The common category, characteristics and functions of Mn microorganisms in recent studies were also reviewed. Finally, the discussion on the influence factors, microbial response, reaction mechanism and potential risk of MnOx application in pollutants' transformation were proposed, which might be the promising opportunities for the future investigation of MnOx application in wastewater treatment.

Treatment of micro-polluted water with low C/N ratio by immobilized bioreactor using PVA/sintered ores@sponge cube: Performance effects and potential removal pathways

The widespread use of industrial products containing lead (Pb²⁺) and tetracycline (TC) medications led to the combined pollution of nitrate, Pb²⁺, and TC in water. A novel biomaterial containing polyvinyl alcohol (PVA) and sponge cube with sintered ores (PVA/sintered ores@sponge cube) was prepared to ensure the maximum NO₃^--N removal efficiency (96.21 %) of the bioreactor under the hydraulic retention time (HRT) of 7.0 h, pH of 6.0, and the carbon to nitrogen (C/N) of 1.5 that had the ability to remove TC and Pb²⁺ synergistically. Composite pollutants slightly decreased denitrification performance in the combined pollution system on account of the addition of sintered ores. Results of scanning electron microscopy (SEM) showed that the sintered ores in the biocarrier induced denitrification and the adsorption of bio‑iron oxides were involved in the removal of TC and Pb²⁺. The simultaneous removal of composite pollutants during denitrification was facilitated by extracellular polymeric substances (EPS) as revealed by Fourier transform infrared spectroscopy (FTIR) and fluorescence excitation-emission matrix (EEM). In addition, high-throughput sequencing results showed that Zoogloea had the highest proportion in the bioreactor.

Detoxification and metabolism of glyphosate by a Pseudomonas sp. via biogenic manganese oxidation

Biogenic manganese oxides (BMO) are widely distributed in groundwater and provides promise for adsorbing and oxidizing a wide range of micropollutants, however, the continuous biodegradation and bioavailability of micropollutants via cycle biogenic Mn(II) oxidation remains to be elucidated. In this study, glyphosate was degraded and to serve as the nutrient source by a Pseudomonas sp. QJX-1. The addition of glyphosate will not affect the Mn(II) oxidation function of the strain but will affect its Mn(II) oxidation process and effect. The glyphosate degradation products could further be used as the C, N and P sources for bacterium growth. Analysis of the RNA-seq data suggested that Mn(II) oxidation driven by oxidoreductases for glyphosate degradation. The long-term column experiments using biological Mn(II) cycling to realize continuous detoxification and metabolism of glyphosate, and thus revealed the synergism effects of biological and chemical conversion on toxic micropollutants and continuous metabolism in an aquatic ecosystem.

Coupled mixotrophic denitrification and utilization of refractory organics driven by Mn redox circulation for significantly enhanced nitrogen removal

Coupled mixotrophic denitrification and degradation of organics driven by redox transition of Mn for nitrogen removal has attracted much attention. Herein, this study explored the removal performance and mechanisms for nitrogen and refractory organics from secondary effluent in up-flow MnOx biofilter. Results showed that the removal of organics and nitrate was significantly enhanced by the synergistic process of heterotrophic denitrification and Mn(II)-driven autotrophic denitrification (MnAD), which were originated from the facilitation of Mn circulation. But nitrate removal was closely related to the types of carbon source and Mn(II) concentration. Single small molecular carbon source (glucose) performed better than mixed carbon source (humic acid and glucose) in nitrate removal process (74.8% in stage 1-2 vs. 54.1% in stage 3-5). And raising external Mn(II) concentration increased the contribution of MnAD (60.2% in stage 5 vs. 46.5% in stage 3) to nitrate removal. Furthermore, the relationship between Mn/N transformation and microbial community structure shifts revealed that the redox transition between Mn(II) and Mn(IV) promoted the enrichment of denitrogenation bacteria and functional genes, thus contributing to pollutants removal. Our studies expand the knowledge of MnOx-mediated pollutants removal processes and support the potential application of MnOx for removal of residual refractory organics and nitrogen.

Aerobic denitrification of oligotrophic source water driven by reduced metal manganese

The lack of organic electron donors limits the potential utility of aerobic denitrification in treatment of oligotrophic source water. Here, reduced manganese (Mn) was used as an inorganic electron donor to improve the denitrification of oligotrophic source water under the high dissolved oxygen condition (7-9 mg L^-1). Over 30 days, the total nitrogen removed by the treatment with reduced Mn was 76.21 ± 2.11% (maximum), substantially higher than that of the control treatment, which was 41.48 ± 2.33%. Furthermore, the addition of Mn resulted in the directional evolution of the microbial community. Water samples with Mn added showed a higher abundance of Limnohabitans, the dominant denitrifying genus, reaching 51.02%, 36.79%, and 20.19% (with 30, 50, and 70 g Mn, respectively), versus only 5.54% in the control. In biofilm, Mn promoted Hydrogenophaga and Brevundimonas growth while Pseudarthrobacter growth was promoted by 30 and 50 g Mn, but inhibited by 70 g Mn. This study demonstrates an improved performance in aerobic denitrification of water sources through the use of inorganic electron donors.

A review: Manganese-driven bioprocess for simultaneous removal of nitrogen and organic contaminants from polluted waters

Water pollutants, such as nitrate and organics have received much attention for their harms to ecological environment and human health. The redox transformation between Mn(Ⅱ) and Mn(Ⅳ) for nitrogen and organics removal have been recognized for a long time. Mn(Ⅱ) can act as inorganic electron donor to drive autotrophic denitrification so as to realize simultaneous removal of Mn(Ⅱ), nitrate and organic pollutants. Mn oxides (MnOx) also play an important role in the adsorption and degradation of some organic contaminants and they can change or create new oxidation pathways in the nitrogen cycle. Herein, this paper provides a comprehensive review of nitrogen and organic contaminants removal pathways through applying Mn(Ⅱ) or MnOx as forerunners. The main current knowledge, developments and applications, pollutants removal efficiency, as well as microbiology and biochemistry mechanisms are summarized. Also reviewed the effects of factors such as the carbon source, the environmental factors and operation conditions have on the process. Research gaps and application potential are further proposed and discussed. Overall, Mn-based biotechnology towards advanced wastewater treatment has a promising prospect, which can achieve simultaneous removal of nitrogen and organic contaminants, and minimize sludge production.

Efficient Mn(II) removal mechanism by Serratia marcescens QZB-1 at high manganese concentration

Manganese (Mn(II)) pollution has recently increased and requires efficient remediation. In this study, Serratia marcescens QZB-1, isolated from acidic red soil, exhibited high tolerance against Mn(II) (up to 364 mM). Strain QZB-1 removed a total of 98.4% of 18 mM Mn(II), with an adsorption rate of 71.4% and oxidation rate of 28.6% after incubation for 48 h. The strain synthesized more protein (PN) to absorb Mn(II) when stimulated with Mn(II). The pH value of the cultural medium continuously increased during the Mn(II) removal process. The product crystal composition (mainly MnO₂ and MnCO₃), Mn-O functional group, and element-level fluctuations confirmed Mn oxidation. Overall, strain QZB-1 efficiently removed high concentration of Mn(II) mainly via adsorption and showed great potential for manganese wastewater removal.

Simultaneous removal of nitrate and heavy metals in a biofilm reactor filled with modified biochar

A biofilm reactor filled with chia seeds gum modified biochar was set up for the simultaneous removal of nitrate, cadmium and zinc from calcium-containing wastewater via denitrification and microbially-induced (calcium) carbonate precipitation. The reactor performance was studied under different conditions of pH, Cd concentration, and hydraulic retention time. The optimal removal efficiency of the reactor for NO₃^--N, Ca²⁺, Cd²⁺, and Zn²⁺ were 99.98, 79.89, 100, and 99.84 %, respectively. 3D-EEM indicated the aromatic compounds confirming the stability of the reactor. FTIR illustrated the presence of -OH, CaCO₃, C-O-C, and C-O-H indicating the precipitation and role of gum in MICP. SEM confirmed that the seed crystal induced the repeated crystallization of free metal ions. XRD showed that heavy metals were removed in the form of CaCO₃, CdCO₃, ZnCO₃, Ca₃(PO₃)₂, Cd₃(PO₃)₂, and Zn₃(PO₃)₂ co-crystallization. SEM-EDS showed the composition and distribution of elements. High-throughput sequencing showed that Curpriavidus sp. GMF1 and Ochrobactrum sp. GMC12 were the dominant bacterial species, with powerful denitrification and MICP mineralization capabilities.

Effect of live and inactivated Chlamydomonas reinhardtii on the removal of tetracycline in aquatic environments

With the development of medical drugs, the widely used tetracycline has brought many adverse effects on the ecosystem and human health. Tetracycline pollution of water environment is becoming more and more serious, and has become an emerging environmental problem. As single celled organisms, microalgae are not only model organisms for risk assessment of aquatic ecosystems, but also can efficiently purify sewage. Microalgae-mediated pollutant remediation has attracted more and more attention from researchers. In this paper, Chlamydomonas reinhardtii (C. reinhardtii) was used to remove tetracycline in aqueous solution, and the removal efficiency and mechanism of microalgae on tetracycline were studied. The results showed that the removal rates of tetracycline by active and inactivated microalgae at a density of 5 × 10⁶ cells·mL^-1 were 81.9% and 89.8%, respectively. C. reinhardtii removed tetracycline through biosorption and nonmetabolic processes. Microalgal cell supernatant and hydroxyl radicals could significantly promote the removal of tetracycline. The positively charged tetracycline was electrostatically adsorbed on the microalgae surface and extracellular polymeric substances. Microalgae biomass can promote the production of ROS and enhance the ability of microalgae to remove tetracycline.

Simultaneous removal of nitrate, tetracycline, and Pb(II) by iron oxidizing strain Zoogloea sp. FY6: Performance and mechanism

Based on the prevalence of combined antibiotics and heavy metals contamination in the aquatic environment, this study utilized a microbial approach to achieve simultaneous removal of nitrate (NO₃^--N), tetracycline (TTC), and Pb(II). Zoogloea sp. FY6 could achieve an optimal NO₃^--N removal efficiency of 91.5% under C/N ratio of 2.0, at a pH of 6.3, and Fe(II) concentration of 20.23 mg L^-1 based on response surface methodology. Additionally, strain FY6 was further found to achieve 89.9 and 81.7% removal of TTC and Pb(II) at 6 h under the optimal conditions. Finally, the results of Fluorescence excitation-emission matrix, X-ray diffraction, Fourier transform infrared spectrometer, and X-ray photoelectron spectroscopy further proved that the biologically formed nanoscale iron oxides and biological action jointly led to the removal of TTC and Pb(II). This study provided a theoretical basis for the application of microbially driven process to remove multi-pollutants in micro-polluted water bodies.

Performance and mechanism of tetracycline removal by the aerobic nitrate-reducing strain Pseudomonas sp. XS-18 with auto-aggregation

The coexistence of multiple pollutants has become a distinctive feature of water pollution. However, there are a few strains that can remove nitrate and tetracycline (TC). Here, the efficiency of strain XS-18 in removing nitrate and TC was analyzed, and the mechanism of tolerance and removal of TC was investigated by infrared spectroscopy, three-dimensional fluorescence spectroscopy, and genome analysis. XS-18 could efficiently remove TC (0.40 mg·L^-1·h^-1) at pH 7.0-11.0 with auto-aggregation. TC was removed via extracellular polymeric substance (EPS) (55.90%) and cell surface (44.10%) adsorption. TC (10 mg/L) could stimulate XS-18 to secrete more polysaccharides and hydrophobic proteins to improve its auto-aggregation ability. The findings also confirmed that TC resistance genes were present. Furthermore, the bacterial flagellum, signal transduction of the chemotactic system and regulatory genes were shown to be related to the auto-aggregation of the strain. XS-18 has potential applications in the treatment of wastewater containing nitrate and TC.

Efficient remediation of Mn2+ and NH4+-N in co-contaminated water and soil by Acinetobacter sp. AL-6 synergized with grapefruit peel biochar: Performance and mechanism

Electrolysis manganese slag produced in industrial manganese production causes massive leachate containing heavy metal Mn²⁺ and inorganic NH₄⁺-N, which causes serious hazard to the water body and soil. A cost-effective alternative to address the multiple pollution is urgently needed. This study investigated the synergy of grapefruit peel biochar (BC) and strain AL-6 to remediate Mn²⁺ and NH₄⁺-N in sequencing batch bioreactor (SBR) and soil column. The results showed that, in SBR, under the condition of C/N 5, temperature 30°C, BC and strain AL-6 showed fabulous performance to remove Mn²⁺ (99.3%) and NH₄⁺-N (97.7%). The coexisting ions Mg²⁺ and Ca²⁺ had no effects on the removal of Mn²⁺ and COD, however, 23.3% removal efficiency of NH₄⁺-N was curtailed. Characterization found that the presence of MnCO₃ confirmed the adsorption of Mn²⁺ by functional groups action, and gas chromatography indicated that BC and strain AL-6 promoted the reduction of N₂O and organic carbon. In addition, BC and strain AL-6 helped to immobilize 799.41 mg L^-1 of Mn²⁺ and 320 mg L^-1 of NH₄⁺-N after 45 d in the soil column. And the determination of TOC, CEC, pH, Eh, soil enzymatic activity (catalase and urease), and microbial diversity and abundance confirmed that BC and strain AL-6 increased the soil fertility and bioavailability of pollutants. Totally, BC and strain AL-6 possess great potential to remediate Mn²⁺ and NH₄⁺-N pollution in water and soil.

Insights into the synergistic removal mechanisms of thallium(I) by biogenic manganese oxides in a wide pH range

The behavior and mechanism of thallium (Tl) adsorption by biogenic manganese oxides (BMnOx) are poorly understood. In this study, BMnOx was applied for Tl(I) removal from aqueous solution, and the adsorption interactions were systematically revealed for the first time. BMnOx was successfully prepared with high productivity by effectively oxidizing Mn(II) with a manganese oxide bacterium in an optimal Mn(II) concentration range of 4.0-28 mg/L. Compared with other adsorbents, the prepared BMnOx achieved high Tl(I) adsorption capacity over a wide pH range from 3.0 to 9.0 and high humic acid (HA) concentration (40 mg/L) interference. The experimental results were well depicted by pseudo-second-order kinetics and the Langmuir isotherm model, indicating that chemisorption played the dominant role during the adsorption process. The adsorption mechanisms were verified as synergetic interactions of oxidation-precipitation, electrostatic attraction, ion exchange and surface complexation. X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) results suggested that 19.46% of the highly toxic Tl(I) was transformed into the much less toxic product Tl₂O₃ after adsorption onto BMnOx. This study provides theoretical guidance for high-concentration Tl(I) decontamination from groundwater by biogenic manganese oxides.

Phenol and 17β-estradiol removal by Zoogloea sp. MFQ7 and in-situ generated biogenic manganese oxides: Performance, kinetics and mechanism

The pollution of multifarious pollutants such as heavy metal, organic compounds, and nitrate are a hot research topic at present. In this study, the functions of Zoogloea sp. MFQ7 and its biological precipitation formed during bacterial manganese oxidation on the removal of phenol and 17β-estradiol (E2) were investigated. Strain MFQ7, a manganese-oxidizing bacteria, can remove 98.34% of phenol under pH of 7.1, a temperature of 30 ℃ and Mn²⁺ concentration of 24.34 mg L^-1, additionally, the optimum E2 removal by strain MFQ7 was 100.00% at pH of 7.1, temperature of 28 ℃ and Mn²⁺ concentration of 28.45 mg L^-1 by using response surface methodology (RSM) based on Box-Behnken design (BBD) model. The maximum adsorption capacity of bio-precipitation for phenol and E2 was 201.15 mg g^-1 and 65.90 mg g^-1, respectively. Furthermore, adsorption kinetics and isotherms analysis, XPS, FTIR spectra, Mn(III) trapping experiments elucidated chemical adsorption and Mn(III) oxidation contribute to the removal of phenol and E2 by biogenic manganese oxides. These findings indicated that the adsorption and oxidation of manganese are expected to be one of the effective means to remove these typical organic pollutants containing phenol and E2.

Effect of Mn2+ on the phosphorus removal and bioflocculation under anoxic condition

Manganese ion (Mn²⁺) generated from metallurgical, steel making and chemical industries enters sewage treatment plants and affects the sludge activity and flocculation. The effect of Mn²⁺ on the removal of chemical oxygen demand (COD) and total phosphorus (TP) and sludge activity were investigated in anoxic zone of an anaerobic/anoxic/oxic (A²O) process. The compositions and structures of extracellular polymeric substances (EPS) were characterized using three-dimensional excitation emission matrix fluorescence spectroscopy (3D-EEM), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) to reveal the relationship among Mn²⁺, EPS and sludge flocculation. The results showed that low concentration of Mn²⁺ (<5 mg/L) improved removal efficiencies of COD and TP and increased the activity of alkaline phosphatase, acid phosphatase and dehydrogenase. Meanwhile, the addition of Mn²⁺ increased total EPS, sludge contact angle, Zeta potential and sludge particle size, and thus enhanced sludge flocculation. However, high concentration of Mn²⁺ (>10 mg/L) hindered microbial flocculation and reduced removal efficiencies of the pollutants. When Mn²⁺was 5 mg/L, removal efficiencies of COD and TP reached 65% and 90%, respectively. Sludge flocculation was the best and SVI was 70.56 mL/g. The changes of Mn²⁺ concentration caused deviation of groups' compositions in LB-EPS and TB-EPS, where the main components were always protein (PN) and polysaccharide (PS). The addition of Mn²⁺ resulted in the degradation of humic acids. However, it did not give rise to significant morphology changes of EPS.

Bioaugmented removal of 17β-estradiol, nitrate and Mn(II) by polypyrrole@corn cob immobilized bioreactor: Performance optimization, mechanism, and microbial community response

The coexistence of nitrate and endocrine substances (EDCs) in groundwater is of global concern. Herein, an efficient and stable polypyrrole@corn cob (PPy@Corn cob) bioreactor immobilized with Zoogloea sp. was designed for the simultaneous removal of 17β-estradiol (E2), nitrate and Mn(II). After 225 days of continuous operation, the optimal operating parameters and enhanced removal mechanism were explored, also the long-term toxicity and microbial communities response mechanisms under E2 stress were comprehensively evaluated. The results showed that the removal efficiencies of E2, nitrate, and Mn(II) were 84.21, 82.96, and 47.91%, respectively, at the optimal operating conditions with hydraulic retention time (HRT) of 8 h, pH of 6.5 and Mn(II) concentration of 20 mg L^-1. Further increased of initial E2 (2 and 3 mg L^-1) resulted in the inhibiting effect of denitrification and manganese oxidation, but excellent E2 removal efficiencies maintained, which were associated with the formation and continuous accumulation of biomanganese oxides (BMO). Characterization analysis of biological precipitation demonstrated that adsorption and redox conversion on the BMO surface played key roles in the removal of E2. In addition, different levels of E2 exposure are decisive factors in community evolution, and bioaugmented bacterial communities with Zoogloea as the core group can dynamically adapt to E2 stress. This study offers the possibility to better utilize microbial metabolism and to advance opportunities that depend on microbial physiology and material characterization applications.

Denitrification performance of nitrate-dependent ferrous (Fe2+) oxidizing Aquabacterium sp. XL4: Adsorption mechanisms of bio-precipitation of phenol and estradiol

In this study, a nitrate-dependent ferrous (Fe²⁺) oxidizing strain under anaerobic conditions was selected and identified as XL4, which belongs to Aquabacterium. The Box-Behnken design (BBD) was used to optimize the growth conditions of strain XL4, and the nitrate removal efficiency of strain XL4 (with 10% inoculation dosage, v/v) could reach 91.41% under the conditions of 30.34 ℃, pH of 6.91, and Fe²⁺ concentration of 19.69 mg L^-1. The results of Fluorescence excitation-emission matrix spectra (EEM) revealed that the intensity of soluble microbial products (SMP), aromatic proteins and the fulvic-like materials were obvious difference under different Fe²⁺ concentration, pH, and temperature. X-ray diffraction (XRD) data confirmed that the main components of bio-precipitation were Fe₃O₄ and FeO(OH), which were believed to be responsible for the adsorption of phenol and estradiol. Furthermore, the maximum adsorption capacity of bio-precipitation for phenol and estradiol under the optimal conditions were 192.6 and 65.4 mg g^-1, respectively. On the other hand, the adsorption process of phenol and estradiol by bio-precipitation confirmed to the pseudo-second-order and Langmuir model, which shows that the adsorption process is chemical adsorption and occurs on the uniform surface.

Enhanced nitrate, manganese, and phenol removal by polyvinyl alcohol/sodium alginate with biochar gel beads immobilized bioreactor: Performance, mechanism, and bacterial diversity

Water pollutants, such as nitrate, heavy metals, and organics have attracted attention due to their harms to environmental and biological health. A novel polyvinyl alcohol/sodium alginate with biochar (PVA/SA@biochar) gel beads immobilized bioreactor was established to remove nitrate, manganese, and phenol. The optimum conditions for preparing gel beads were studied by response surface methodology (RSM). Notably, the removal efficiencies of nitrate, Mn(II), and phenol were 94.64, 72.74, and 93.97% at C/N of 2.0; the concentrations of Mn(II) and phenol were 20 and 1 mg L^-1, respectively. Moreover, addition of different concentrations of phenol significantly affected the components of dissolved organic matter, bacterial activity, and bioreactor performance. The biological manganese oxide (BMO) with three-dimensional petal-type structure produced during Mn(II) oxidation showed excellent adsorption capacity. The removal of phenol relied on a combination of biological action and adsorption processes. High-throughput analysis showed that Zoogloea sp. was the predominant bacterial group.

A feasibility study of metal sulfide (FeS and MnS) on simultaneous denitrification and chromate reduction

Metal sulfide-based biological process is considered as a promising biotechnology for next-generation wastewater treatment. However, it is not clear if simultaneous bio-reduction of nitrate and chromate was achievable in this process. This study aimed to evaluate the feasibility of metal sulfides (FeS and MnS) on simultaneous denitrification and chromate reduction in autotrophic denitrifying column bioreactors. Results showed that simultaneous reduction of nitrate and chromate was achieved using metal sulfides (FeS and MnS) as electron donors, in which sulfate was the sole soluble end-product. Apart from the sulfur element in the metal sulfides, Fe(II) and Mn(II) were also involved in nitrate and chromate reduction as indicative by the formation of their oxidative states compounds. In microbial communities, SHD-231 and Thiobacillus were the most predominant bacteria, which might have played important roles in simultaneous denitrification and chromate reduction. Compared to FeS, MnS showed a higher performance on nitrate and chromate removal, which could also reduce the toxic inhibition of chromate on nitrate reduction. According to results of XRD and XPS, as well as a lower sulfate production in the FeS system, FeS might have been covered easily to hydroxides due to its bio-oxidation, which limited mass transfer efficiency and bio-availability of FeS. The findings in this study offered insights in the development of promising approaches for the treatment of toxic and hazardous compounds using metal sulfide.

Insights into the mechanism of enhanced peroxymonosulfate degraded tetracycline using metal organic framework derived carbonyl modified carbon-coated Fe0

Tetracycline (TC) is a commonly used antibiotic that has gained wide spread notoriety owing to its high environmental risks. In this study, rich carbonyl-modified carbon-coated Fe⁰ was obtained by pyrolysis of MIL-100(Fe) in an Ar atmosphere, and used to activate peroxymonosulfate (PMS) for the degradation of tetracycline in water. The roles of Fe⁰, carbon and surface carbonyl on PMS activation were investigated. Fe⁰ continuously activated PMS, acted as a sustained-release source of Fe²⁺, and could effectively activate PMS to produce SO₄^•-, O₂^•- and •OH. Carbon was found to do responsible for electron transportation during the activation of PMS and slow down the oxidation of Fe⁰. The carbonyl group on the carbon surface layer was the active site of ¹O₂, which explains the enhanced performance for TC degradation. When Ca = 0.1 g/L and C₀ = 0.4 mM, TC degradation rate reached 96%, which was attributed to the synergistic effect of radicals (i.e., SO₄^•-, O₂^•-, •OH) and non-radical (i.e., ¹O₂). Finally, the degradation pathway was proposed by combining density functional theory (DFT) calculations with liquid chromatography-mass spectrometry (LC-MS), toxicities of the intermediate products were also evaluated. All results show that carbonyl-modified carbon-coated Fe⁰ possesses promising capacity for the removal of antibiotics from water.

Carbon source type can affect tetracycline removal by Pseudomonas sp. TC952 through regulation of extracellular polymeric substances composition and production

The objective of this work is to elucidate the mechanism of tetracycline (TC) removal by Pseudomonas sp. TC952. The TC removal characteristics of strain TC952 under various environmental conditions were studied. Results showed that the bio-removal efficiency was significantly affected by initial TC and peptone concentration, pH values, divalent metal ion (Zn²⁺) and carbon source, and the strain TC952 efficiently removed approximately 72.8% of TC within 6 days with 10 g/L peptone. The best conditions for strain TC952 to remove TC are as follows: initial TC concentration is 50 mg/L, solution initial pH is 7, Zn²⁺ concentration is 0.1 μg/L, carbon source is peptone. And through intra- and extracellular fractions assay and extracellular polymeric substances (EPS) component analysis, TC removal by strain TC952 was mainly attributed to the adsorption by bacterial EPS and bacterial cell. Furthermore, different carbon source affected the EPS production content and component of strain TC952, so EPS produced under peptone and serine conditions could bio-adsorb TC and formed a buffer area outside the cells, thus reducing or preventing TC from entering the bacteria cells. All the results obtained showed that secretion of EPS and adsorption of TC by EPS and bacterial cell wall may be a common way for bacteria to reduce TC in the environment, which brought novel insights for better management of TC contamination by functional bacteria and for understanding the natural removal process of antibiotics by microorganisms in the environment.

ZnO@Bi5O7I Heterojunction Derived from ZIF-8@BiOI for Enhanced Photocatalytic Activity under Visible Light

In the study, ZIF-8@BIOI composites were synthesized by the hydrothermal method and then calcined to acquire the ZnO@Bi₅O₇I composite as a novel composite for the photocatalytic deterioration of the antibiotic tetracycline (TC). The prepared ZnO@Bi₅O₇I composites were physically and chemically characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer-Emmet-Teller (BET) surface area, UV-Vis diffuse reflectance spectroscopy (DRS), emission fluorescence spectra, transient photocurrent response, electrochemical impedance spectra and Mott-Schottky. Among the composites formed an n-n heterojunction, which increased the separation efficiency of electrons and holes and the efficiency of charge transfer. After the photocatalytic degradation test of TC, it showed that ZnO@Bi₅O₇I (2:1) had the best photodegradation effect with an 86.2% removal rate, which provides a new approach to the treatment of antibiotics such as TC in wastewater.

Efficient removal of nitrate, manganese, and tetracycline in a novel loofah immobilized bioreactor: Performance, microbial diversity, and functional genes

The remediation of multiple pollutants in water, for instance, nitrate, heavy metals, and antibiotics is urgent and necessary for the global water resources protection. Herein, a modified loofah bioreactor was designed for simultaneous denitrification, manganese (Mn) oxidation, and tetracycline (TC) removal. The maximum removal efficiencies of NO₃^--N (91.97%), Mn(II) (71.25%), and TC (57.39%) were achieved at a hydraulic retention time (HRT) of 9 h, Mn(II) concentration of 20 mg L^-1, and TC concentration of 1 mg L^-1. SEM and XRD were carried out to characterize the bioprecipitation in the operation of bioreactor. TC addition affected the gaseous denitrification products, dissolved organic matter, as well as reduced the OTU in the bioreactor. The Zoogloea were regarded as the dominant species in the microbial community and played an essential role in the operation of bioreactor. Metagenomic analysis proved the great potential for denitrification, manganese oxidation, and antibiotic removal of loofah bioreactor.

Simultaneous removal of nitrate, manganese, and tetracycline by Zoogloea sp. MFQ7: Adsorption mechanism of tetracycline by biological precipitation

A Mn(II) oxidizing-denitrifying and tetracycline (TC) removal bacterium Zoogloea sp. MFQ7 was isolated in this study. Nitrogen removal was 83.49% by nitrogen balance experiment. The maximum removal efficiencies of nitrate, Mn(II), and TC by strain MFQ7 within 96 h was 100.00, 74.56, and 63.59% at C/N of 2.0, pH of 7.0, Mn(II) of 20 mg L^-1, temperature of 30.0 °C, and TC of 0.2 mg L^-1. SEM illustrated that biogenic manganese oxides (BMO) was petal-like, XRD and XPS analyses confirmed that MnO₂ was the main component of BMO. Besides, the maximum adsorption capacity of BMO for TC was 52.21 mg g^-1. FTIR detected the changes in TC adsorption by BMO. Pseudo-second-order model (R² = 0.994) explained the adsorption kinetics of TC on BMO and Langmuir isotherm model (R² = 0.983) suggested that it was homogeneous adsorption, thermodynamics data (ΔG < 0, ΔH = 18.31 kJ mol^-1, ΔS = 72.8 J (mol*K)^-1) confirmed that adsorption was endothermic and spontaneous.

Denitrification potential of sodium alginate gel beads immobilized iron-carbon, Zoogloea sp. L2, and riboflavin: Performance optimization and mechanism

A kind of gel beads loaded with iron-carbon powder (Fe-C), Zoogloea sp. L2, and riboflavin (VB2) were prepared through cross-linking of sodium alginate (SA) to establish an immobilized bioreactor. The optimal ratio of SA beads was adjusted by orthogonal experiment. The change of oxidation-reduction potential (ORP) and the concentration of Fe²⁺ and Fe³⁺ showed that the addition of VB2 as a redox mediator can promote denitrification. Under the optimal conditions (carbon to nitrogen (C/N) ratio = 2.0, pH = 7.0, and hydraulic retention time (HRT) = 8 h), the nitrate removal efficiency (NRE) of bioreactor reached 98.48% (1.99 mg L^-1h^-1). Furthermore, Fourier transform infrared spectrometer (FTIR), Fluorescence excitation-emission matrix (EEM), X-ray diffraction (XRD), and gas chromatography (GC) analysis revealed that the immobilization and denitrification of the immobilized bioreactor were excellent. High throughput sequencing also showed that Zoogloea played a vital role in nitrate removal.

Enhanced performance of sulfamethoxazole degradation using Achromobacter sp. JL9 with in-situ generated biogenic manganese oxides

Little information is known about the relationships of in-situ generated BioMnOx and sulfamethoxazole (SMX) degradation. In this study, a novel efficient bioremediation technology was presented for simultaneous remove the nitrogen-N, SMX, and Mn(II) from water. Mn(II) can be completely oxidized with a oxidized rate of 0.071 mg/(L·h), the SMX and nitrogen-N removal ratios were 97.43% and 85.61%, respectively. The Ratkowsky kinetic models were established for described the SMX degradation influence by temperature. Furthermore, the microbial degradation, Mn(III) trapping, and intermediates identified experiments were used to explore the mechanisms of SMX and nitrogen-N removal. These results indicated that microbial activity play a decisive role in SMX and nitrogen-N removal, and the catalytic character of sediment could enhanced the SMX degradation. Furthermore, proposed the possible SMX degradation pathway based on the intermediates and microbial metabolism theory, the environmental toxicity of SMX and each intermediates were calculated via ECOSAR program.

Effects of two ecological earthworm species on tetracycline degradation performance, pathway and bacterial community structure in laterite soil

This study explored the change of tetracycline degradation efficiency, metabolic pathway, soil physiochemical properties and degraders in vermiremediation by two earthworm species of epigeic Eisenia fetida and endogeic Amynthas robustus. We found a significant acceleration of tetracycline degradation in both earthworm treatments, and 4-epitetracycline dehydration pathway was remarkably enhanced only by vermiremediation. Tetracycline degraders from soils, earthworm intestines and casts were different. Ralstonia and Sphingomonas were potential tetracycline degraders in soils and metabolized tetracycline through direct dehydration pathway. Degraders in earthworm casts (Comamonas, Acinetobacter and Stenotrophomonas) and intestines (Pseudomonas and Arthrobacter) dehydrated 4-epitetracycline into 4-epianhydrotetracycline. More bacterial lineages resisting tetracycline were found in earthworm treatments, indicating the adaptation of soil and intestinal flora under tetracycline pressure. Earthworm amendment primarily enhanced tetracycline degradation by neutralizing soil pH and consuming organic matters, stimulating both direct dehydration and epimerization-dehydration pathways. Our findings proved that vermicomposting with earthworms is effective to alter soil microenvironment and accelerate tetracycline degradation, behaving as a potential approach in soil remediation at tetracycline contaminated sites.

Removal of Mn(II) by a nitrifying bacterium Acinetobacter sp. AL-6: efficiency and mechanisms

A nitrifying bacterium Acinetobacter sp. AL-6 showed a high efficiency of 99.05% for Mn(II) removal within 144 h when the Mn(II) concentration was 200 mg L^-1; meanwhile, 64.23% of NH₄⁺-N was removed. With the Mn(II) concentration increased from 25 to 300 mg L^-1, bacterial growth and Mn(II) removal were stimulated. However, due to the electron acceptor competition between Mn(II) oxidation and nitrification reactions, the increase in NH₄⁺-N concentration would inhibit Mn(II) removal. By measuring Mn metabolic form and locating oxidative active factors, it was proved that extracellular oxidation effect played a dominant role in the removal process of Mn(II). The self-regulation of pH during strain metabolism further promoted the occurrence of biological Mn oxidation. Characterization results showed that the Mn oxidation products were tightly attached to the surface of the bacteria in the form of flakes. The product crystal composition (mainly MnO₂ and Mn₂O₃), Mn-O functional group, and element level fluctuations confirmed the biological oxidation information. The changes of -OH, N-H, and -CH₂ groups and the appearance of new functional groups (such as C-H and C-O) provided more possibilities for Mn ion adsorption and bonding.

Characterization and mechanism of Mn(II)-based mixotrophic denitrifying bacterium (Cupriavidus sp. HY129) in remediation of nitrate (NO3--N) and manganese (Mn(II)) contaminated groundwater

The co-contamination of groundwater with nitrate (NO₃^--N) and manganese (Mn(II)) is a global issue that needs to be efficiently remediated. In this research, a novel denitrifying and manganese-oxidizing strain HY129 was isolated from the sediments sample of a drinking water and identified as Cupriavidus sp. HY129. The remediation ability of strain HY129 regarding the nitrate and Mn(II) pollution were investigated. The removal efficiency of nitrate and Mn(II) were 99.81% (0.229 mgL^-1 h^-1) and 87.24% (0.233 mgL^-1 h^-1) in bacterial culture after 72 h, respectively. Moreover, the addition of Mn(II) significantly enhanced the denitrification process, while excessive concentration of Mn(II) caused more NO₂^--N accumulation. The impacts of adsorption and oxidation activity on Mn(II) removal were investigated. Protein in extracellular polymeric substance (EPS) which produced in the Mn-oxidizing process was speculated to be the main cause of extracellular adsorption of Mn(II). Characterization of biogenic manganese oxides (BMO) confirmed the formation of high-valent manganese and the trapping experiment with sodium pyrophosphate (NaPP) demonstrated the existence of Mn(III)-intermediates. Furthermore, multicopper oxidase gene amplification provided evidence for the molecular biology of Mn(II) oxidation by strain HY129.

Heterotrophic nitrification and biomineralization potential of Pseudomonas sp. HXF1 for the simultaneous removal of ammonia nitrogen and fluoride from groundwater

Pseudomonas sp. HXF1, a strain capable of heterotrophic nitrification, aerobic denitrification (HNAD), and biomineralization was identified and employed for the simultaneous removal of ammonia nitrogen (NH₄⁺-N) and fluoride (F^-). It removed 99.2% of NH₄⁺-N without accumulation of nitrous nitrogen (NO₂^--N) and nitrate nitrogen (NO₃^--N), while removed 87.3% of F^-. Response surface methodology (RSM) was used to study the best removal conditions for NH₄⁺-N and F^-. The results of nitrogen balance experiments with NH₄Cl, NaNO₂, and NaNO₃ as single nitrogen sources and amplification experiments of denitrification genes proved that the bacterial strains may remove NH₄⁺-N through HNAD. The experimental results of Scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffractometer (XRD) indicated that the way of F^- removal may be adsorption and co-precipitation. The results demonstrated that the strain HXF1 has great potential in the biological denitrification and F^- removal of groundwater.

Interrelationships between tetracyclines and nitrogen cycling processes mediated by microorganisms: A review

Due to their broad-spectrum antibacterial activity and low cost, tetracyclines (TCs) are a class of antibiotics widely used for human and veterinary medical purposes and as a growth-promoting agent for aquaculture. Interrelationships between TCs and nitrogen cycling have attracted scientific attention due to the complicated processes mediated by microorganisms. TCs negatively impact the nitrogen cycling; however, simultaneous degradation of TCs during nitrogen cycling mediated by microorganisms can be achieved. This review encapsulates the background and distribution of TCs in the environment. Additionally, the main nitrogen cycling process mediated by microorganisms were retrospectively examined. Furthermore, effects of TCs on the nitrogen cycling processes, namely nitrification, denitrification, and anammox, have been summarized. Finally, the pathway and microbial mechanism of degradation of TCs accompanied by nitrogen cycling processes were reviewed, along with the scope for prospective studies.