Removal of nitrate using Paracoccus sp. YF1 immobilized on bamboo carbon

Enhanced nitrate removal efficiency and microbial response of immobilized mixed aerobic denitrifying bacteria through biochar coupled with inorganic electron donors in oligotrophic water

The nitrogen removal characteristics and microbial response of biochar-immobilized mixed aerobic denitrifying bacteria (BIADB) were investigated at 25 °C and 10 °C. BIADB removed 53.51 ± 1.72 % (25 °C) and 39.90 ± 4.28 % (10 °C) nitrate in synthetic oligotrophic water. Even with practical oligotrophic water, BIADB still effectively removed 47.66-53.21 % (25 °C), and 39.26-45.63 % (10 °C) nitrate. The addition of inorganic electron donors increased nitrate removal by approximately 20 % for synthetic and practical water. Bacterial and functional communities exhibited significant temperature and stage differences (P < 0.05), with temperature and total dissolved nitrogen being the main environmental factors. The dominant genera and keystone taxa exhibited significant differences at the two temperatures. Structural equation model analysis showed that dissolved organic matter had the highest direct and indirect effects on diversity and function, respectively. This study provides an innovative pathway for utilizing biochar and inorganic electron donors for nitrate removal from oligotrophic waters.

Electrospun nanofibers electrostatically adsorb heterotrophic nitrifying and aerobic denitrifying bacteria to degrade nitrogen in wastewater

Nanofibers were prepared by electrospinning a mixture of polycaprolactone and silica, and modified to improve the hydrophilicity and stability of the material and to degrade nitrogenous wastewater by adsorbing heterotrophic nitrifying aerobic denitrifying (Ochrobactrum anthropic). The immobilized bacteria showed highly efficient simultaneous nitrification-denitrification ability, which could convert nearly 90 % of the initial nitrogen into gaseous nitrogen under aerobic conditions, and the average TN removal rate reached 5.59 mg/L/h. The average ammonia oxidation rate of bacteria immobilized by modified nanofibers was 7.36 mg/L/h, compared with 6.3 mg/L/h for free bacteria and only 4.23 mg/L/h for unmodified nanofiber-immobilized bacteria. Kinetic studies showed that modified nanofiber-immobilized bacteria complied with first-order degradation kinetics, and the effects of extreme pH, temperature, and salinity on immobilized bacteria were significantly reduced, while the degradation rate of free bacteria produced larger fluctuations. In addition, the immobilized bacterial nanofibers were reused five times, and the degradation rate remained stable at more than 80 %. At the same time, the degradation rate can still reach 50 % after 6 months of storage at 4 °C. It also demonstrated good nitrogen removal in practical wastewater treatment.

Bacillus cereus WL08 immobilized on tobacco stem charcoal eliminates butylated hydroxytoluene in soils and alleviates the continuous cropping obstacle of Pinellia ternata

Butylated hydroxytoluene (BHT), as an emerging contaminant in ecosystems, has potential influences on animals, aquatic organisms, and public health, and has been proven to be a major allelochemical of Pinellia ternata. In this study, Bacillus cereus WL08 was used to rapidly degrade BHT in liquid culture. Strain WL08 immobilized on tobacco stem charcoal (TSC) particles notably accelerated BHT removal in contract to its free cells, and exhibited excellent reutilization and storage capacities. The optimal removal parameters of TSC WL08 were ascertained to be pH 7.0, 30 °C, 50 mg L^-1 BHT and 0.14 mg L^-1 TSC WL08. Moreover, TSC WL08 significantly accelerated the degradation of 50 mg L^-1 BHT in sterile and non-sterile soils compared to that of free WL08 or natural dissipation, and notably shortened their half-lives by 2.47- or 362.14- fold, and 2.20- or 14.99- fold, respectively. Simultaneously, TSC WL08 was introduced into the continuous cropping soils of P. ternata, which accelerated the elimination of allelochemical BHT, and notably enhanced the photosynthesis, growth, yield, and quality of P. ternata. This study provides new insights and strategies for the rapid in situ remediation of BHT-polluted soils and effective alleviation of P. ternata cropping obstacles.

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.

Immobilization of bacterial mixture of Klebsiella variicola FH-1 and Arthrobacter sp. NJ-1 enhances the bioremediation of atrazine-polluted soil environments

In this study, the effects of the immobilized bacterial mixture (IM-FN) of Arthrobacter sp. NJ-1 and Klebsiella variicola strain FH-1 using sodium alginate-CaCl2 on the degradation of atrazine were investigated. The results showed that the optimal ratio of three types of carrier materials (i.e., rice straw powder, rice husk, and wheat bran) was 1:1:1 with the highest adsorption capacity for atrazine (i.e., 3774.47 mg/kg) obtained at 30°C. On day 9, the degradation efficiency of atrazine (50 mg/L) reached 98.23% with cell concentration of 1.6 × 108  cfu/ml at pH 9 and 30°C. The Box-Behnken method was used to further optimize the culture conditions for the degradation of atrazine by the immobilized bacterial mixture. The IM-FN could be reused for 2-3 times with the degradation efficiency of atrazine maintained at 73.0% after being stored for 80 days at 25°C. The population dynamics of IM-FN was explored with the total soil DNA samples specifically analyzed by real-time PCR. In 7 days, the copy numbers of both PydC and estD genes in the IM-FN were significantly higher than those of bacterial suspensions in the soil. Compared with bacterial suspensions, the IM-FN significantly accelerated the degradation of atrazine (20 mg/kg) in soil with the half-life shortened from 19.80 to 7.96 days. The plant heights of two atrazine-sensitive crops (wheat and soybean) were increased by 14.99 and 64.74%, respectively, in the soil restored by immobilized bacterial mixture, indicating that the IM-FN significantly reduced the phytotoxicity of atrazine on the plants. Our study evidently demonstrated that the IM-FN could significantly increase the degradation of atrazine, providing a potentially effective bioremediation technique for the treatment of atrazine-polluted soil environment and providing experimental support for the wide application of immobilized microorganism technology in agriculture.

Bioenhanced degradation of toluene by layer-by-layer self-assembled silica-based bio-microcapsules

In this study, micron-sized monodisperse SiO₂ microspheres were used as sacrificial templates, and chitosan/polylactic acid (CTS/PLA) bio-microcapsules were produced using the layer-by-layer (LBL) assembly method. Microcapsules isolate bacteria from their surroundings, forming a separate microenvironment and greatly improving microorganisms' ability to adapt to adverse environmental conditions. Morphology observation indicated that the pie-shaped bio-microcapsules with a certain thickness could be successfully prepared through LBL assembly method. Surface analysis showed that the LBL bio-microcapsules (LBMs) had large fractions of mesoporous. The biodegradation experiments of toluene and the determination of toluene degrading enzyme activity were also carried out under external adverse environmental conditions (i.e., unsuitable initial concentrations of toluene, pH, temperature, and salinity). The results showed that the removal rate of toluene by LBMs can basically reach more than 90% in 2 days under adverse environmental conditions, which is significantly higher than that of free bacteria. In particular, the removal rate of toluene by LBMs can reach four times that of free bacteria at pH 3, which indicates that LBMs maintain a high level of operational stability for toluene degradation. Flow cytometry analysis showed that LBL microcapsules could effectively reduce the death rate of the bacteria. The results of the enzyme activity assay showed that the enzyme activity was significantly stronger in the LBMs system than in the free bacteria system under the same unfavorable external environmental conditions. In conclusion, the LBMs were more adaptable to the uncertain external environment, which provided a feasible bioremediation strategy for the treatment of organic contaminants in actual groundwater.

Removal of Hydrogen Sulfide from Swine-Waste Biogas on a Pilot Scale Using Immobilized Paracoccus versutus CM1

Hydrogen sulfide (H2S) is a toxic and corrosive component that commonly occurs in biogas. In this study, H2S removal from swine-waste biogas using sulfur-oxidizing Paracoccus versutus CM1 immobilized in porous glass (PG) and polyurethane foam (PUF) biofilters was investigated. Bacterial compositions in the biofilters were also determined using polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE). The biofilters were first tested on a laboratory scale under three space velocities (SV): 20, 30, and 40 h−1. Within 24 h, at an SV of 20 h−1, PG and PUF biofilters immobilized with P. versutus CM1 removed 99.5% and 99.7% of H2S, respectively, corresponding to the elimination capacities (EC) of 83.5 and 86.2 gm−3 h−1. On a pilot scale, with the horizontal PG-P. versutus CM1 biofilter operated at an SV of 30 h−1, a removal efficiency of 99.7% and a maximum EC of 113.7 gm−3 h−1 were achieved. No reduction in methane content in the outlet biogas was observed under these conditions. The PCR-DGGE analysis revealed that Paracoccus, Acidithiobacillus, and Thiomonas were the predominant bacterial genera in the biofilters, which might play important roles in H2S removal. This PG−P. versutus CM1 biofiltration system is highly efficient for H2S removal from swine-waste biogas.

Enhanced biodegradation of oil-contaminated soil oil in shale gas exploitation by biochar immobilization

The enhanced biodegradation of oil-contaminated soil by fixing microorganisms with corn cob biochar was investigated. It was found that the components of oil in the test soil were mainly straight-chain alkanes and branched alkanes. When using corn cob biochar as a carrier to immobilize microorganisms, the best particle size of corn cob biochar as an immobilization carrier was 0.08 mm, and the best immobilization time was 18 h. SEM analysis confirmed that the microorganisms were immobilized on the corn cob biochar. Immobilized microorganisms exhibited high biodegradability under stress to high concentrations of petroleum pollutants, heavy metals, and organic pollutants. Infrared spectroscopy analysis showed that oxygen-containing groups such as hydroxyl, carboxyl, and methoxy on the surface of biochar were involved in the complexation of heavy metals. The mechanism of immobilization promoted microbial degradation of oil contamination was explained by gas chromatography mass. First, alkanes and aromatics were adsorbed by corn cob biochar and passed to immobilized microorganisms to promote their degradation. Their bioavailability increased, especially for aromatics. Second, biochar provided a more suitable environment for microorganisms to degrade. Third, the conversion of ketones to acids was accelerated during the biodegradation of alkanes, and the biodegradation of alkanes was accelerated by immobilization. The biodegradable efficiency of oil by immobilized microorganisms in soil was 70.10% within 60 days, 28.80% higher than that of free microorganisms. The degradation of immobilized microorganisms was highly correlated with the activities of catalase, urease, and polyphenol oxidase.

Genomic evidence for two pathways of formaldehyde oxidation and denitrification capabilities of the species Paracoccus methylovorus sp. nov

Three strains (H4-D09^T, S2-D11 and S9-F39) of a member of the genus Paracoccus attributed to a novel species were isolated from topsoil of temperate grasslands. The genome sequence of the type strain H4-D09^T exhibited a complete set of genes required for denitrification as well as methylotrophy. The genome of H4-D09^T included genes for two alternative pathways of formaldehyde oxidation. Besides the genes for the canonical glutathione (GSH)-dependent formaldehyde oxidation pathway, all genes for the tetrahydrofolate-formaldehyde oxidation pathway were identified. The strain has the potential to utilize methanol and/or methylamine as a single carbon source as evidenced by the presence of methanol dehydrogenase (mxaFI) and methylamine dehydrogenase (mau) genes. Apart from dissimilatory denitrification genes (narA, nirS, norBC and nosZ), genes for assimilatory nitrate (nasA) and nitrite reductases (nirBD) were also identified. The results of phylogenetic analysis based on 16S rRNA genes coupled with riboprinting revealed that all three strains represented the same species of genus Paracoccus. Core genome phylogeny of the type strain H4-D09^T indicated that Paracoccus thiocyanatus and Paracoccus denitrificans are the closest phylogenetic neighbours. The average nucleotide index (ANI) and digital DNA-DNA hybridization (dDDH) with the closest phylogenetic neighbours revealed genetic differences at the species level, which were further substantiated by differences in several physiological characteristics. The major respiratory quinone is Q-10, and the predominant cellular fatty acids are C_18 : 1ω7c, C_19 : 0cyclo ω7c, and C_16 : 0, which correspond to those detected in other members of the genus. The polar lipid profile consists of a diphosphatidylglycerol (DPG), phosphatidylethanolamine (PE), phosphatidylglycerol (PG), phosphatidylcholine (PC), aminolipid (AL), glycolipid (GL) and an unidentified lipid (L).On the basis of our results, we concluded that the investigated isolates represent a novel species of the genus Paracoccus, for which the name Paracoccus methylovorus sp. nov. (type strain H4-D09^T=LMG 31941^T= DSM 111585^T) is proposed.

Simultaneous removal of high concentrations of ammonia nitrogen and calcium by the novel strain Paracoccus denitrificans AC-3 with good environmental adaptability

The novel Paracoccus denitrificans AC-3 strain was isolated and displayed outstanding purification capability for high concentrations of ammonia nitrogen (NH₄⁺-N) and calcium (Ca²⁺). Meanwhile, the strain exhibited excellent environmental adaptability within a wide pH range and high levels of NH₄⁺-N and Ca²⁺. Nitrogen balance analysis demonstrated that the pathways of NH₄⁺-N removal consisted of 80.12% assimilation and 16.60% heterotrophic nitrification aerobic denitrification (HNAD). In addition, Ca²⁺ was removed by forming calcium carbonate (CaCO₃) with carbonate (CO₃^2-) and bicarbonate (HCO₃^-). CO₃^2-and HCO₃^- were obtained from carbon dioxide (CO₂) hydration, which was catalyzed by carbonic anhydrase (CA) secreted by strain AC-3. The alkaline environment for carbonate precipitation was provided by CA and HNAD. The resulting CaCO₃ existed in the form of calcite and exhibited a unique morphology and elemental composition.

Immobilization of microbes on biochar for water and soil remediation: A review

Biochar has caught great attention over the last decade with the loose and porous structure, and carbon stability provides suitable living conditions for the growth and activity of microorganisms. This review provided a comprehensive summary of biochar immobilization microbe (BIM) in water and soil decontamination. Firstly, the bacterial immobilization techniques including adsorption, entrapping, and covalence methods were exhibited. Secondly, the applications of BIM in water and soil environmental remediation were introduced, mainly including the treatment of organic pollutants, heavy metals, and N/P, among which the most frequently immobilized microorganism was Bacillus. Then, the mechanisms of adsorption, redox, and degradation were analyzed. Finally, pertinent questions for future research of BIM technology were proposed. The purpose of this paper is to provide useful background information for the selection of better biochar fixation microorganisms for water and soil remediation.

Biochar immobilized bacteria enhances nitrogen removal capability of tidal flow constructed wetlands

To improve the nitrogen removal (NR) capability of tidal flow constructed wetlands (TFCWs) for treatment of saline wastewater, biochar, produced from Cyperus alternifolius, was used to adsorb and immobilize a salt tolerant aerobic denitrifying bacteria (Zobellella sp. A63), and then was added as a substrate into the systems. Under low (2:1) or high (6:1) C/N ratio, the removal of NO₃^--N and total nitrogen (TN) in the biochar immobilized bacteria (BIB) dosing system (TFCW3) was significantly higher (q < 0.05) than that in the untreated system (TFCW1) and the biochar dosing system (TFCW2). At low C/N ratio, the removal rates of NO₃^--N, TN and chemical oxygen demand (COD) of TFCW3 were 68.2%, 72.6% and 82.5%, respectively, 15-20% higher than TFCW1 and 5-10% higher than TFCW2. When C/N ratio was further increased to 6, the pollutant removal rate of each system was greatly improved, but the removal rate of TFCW3 for NO₃^--N/TN was still nearly 10% and 5% higher than TFCW1 and TFCW2, respectively. Microbial community analysis showed that aerobic denitrifying bacteria, sulfate reducing bacteria and sulfur-driven denitrifiers (DNSOB) played the most important role of NR in TFCWs. Moreover, biochar bacterial agent significantly increased the abundances of genes involved in NR. The total copy numbers of bacterial 16S rRNA, nirS, nirK, drsA and drsB genes in the TFCW3 were 1.1- to 3.76-fold higher than those in the TFCW1; Especially at low C/N ratio, the copy number of drsA and drsB in the upper layer of TFCW3 were 85.5 and 455 times that of TFCW1, respectively. Thus, BIB provide a more feasible and effective amendment for constructed wetlands to improve the N removal of the saline wastewater by enhancing the microbial NR capacity mainly via aerobic and sulfur autotrophic denitrification.

Algicidal Bacteria: A Review of Current Knowledge and Applications to Control Harmful Algal Blooms

Interactions between bacteria and phytoplankton in aqueous ecosystems are both complex and dynamic, with associations that range from mutualism to parasitism. This review focuses on algicidal interactions, in which bacteria are capable of controlling algal growth through physical association or the production of algicidal compounds. While there is some evidence for bacterial control of algal growth in the field, our understanding of these interactions is largely based on laboratory culture experiments. Here, the range of these algicidal interactions is discussed, including specificity of bacterial control, mechanisms for activity, and insights into the chemical and biochemical analysis of these interactions. The development of algicidal bacteria or compounds derived from bacteria for control of harmful algal blooms is reviewed with a focus on environmentally friendly or sustainable methods of application. Potential avenues for future research and further development and application of bacterial algicides for the control of algal blooms are presented.

Ni(II), Cr(VI), Cu(II) and nitrate removal by the co-system of Pseudomonas hibiscicola strain L1 immobilized on peanut shell biochar

At present, the improvement of nitrate and mixed heavy metals removal in wastewater by microorganism are urgently needed. Previous studies have shown that Pseudomonas hibiscicola strain L1 exhibited Ni(II) removal ability under aerobic denitrification. In this study, the characteristics of the free strain L1, peanut shell biochar (PBC) and further the co-system of strain L1 immobilized on PBC were investigated for the removal of Ni(II), Cr(VI), Cu(II) and nitrate in mix-wastewater. The results illustrated that strain L1 could remove 15.51% - 32.55% of Ni(II) (20-100 mg·L^-1), and removal ratios by co-system were ranked as Ni(II) (81.17%) > Cu(II) (45.84%) > Cr(VI) (38.21%). Scanning Electron Microscope (SEM), X-ray Diffractometer (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) images indicated that the strain L1 immobilized well on PBC and had vigorous biological activity; the crystals of Ni(OH)₂, Cu(OH)₂ and CrO(OH) etc. were formed on surface of co-system with various functional groups participated in. In Sequential Batch Reactor (SBR), the pollutant removal ratios by co-system were higher than that by free strain L1. This study illustrated that the co-system of strain L1 immobilized on PBC was qualified to be applied for practical scenarios of effective heavy metal removal of electroplating mix-wastewater.

Harnessing taxonomically diverse and metabolically versatile genus Paracoccus for bioplastic synthesis and xenobiotic biodegradation

The genus Paracoccus represents a taxonomically diverse group comprising more than 80 novel species isolated from various pristine and polluted environments. The species are characterized as coccoid shaped Gram-negative bacteria with versatile metabolic attributes and classified as autotrophs, heterotrophs and/or methylotrophs. Present study highlights the up-to-date global taxonomic diversity and critically discusses the significance of genome analysis for identifying the genomic determinants related to functional attributes mainly bioplastic synthesis and biodegradation potential that makes these isolates commercially viable. The analysis accentuates polyphasic and genomic attributes of Paracoccus spp. which could be harnessed for commercial applications and emphasizes the need of integrating genome based computational analysis for evolutionary species and functional diversification. The work reflects on the underexplored genetic potential for bioplastic synthesis which can be harnessed using advanced genomic methods. It also underlines the degradation potential and possible use of naturally-occurring pollutant-degrading Paracoccus isolates for development of biodegradation system and efficient removal of contaminants. The work contemplates plausible use of such potent isolates to establish the plant-microbe interaction, contributing towards contaminated land reclamation. Overall; the work signifies need and application of genome analysis to identify and explore prospective potential of Paracoccus spp. for environmental application towards achieving sustainability.

Process optimization and modeling of Cd2+ biosorption onto the free and immobilized Turbinaria ornata using Box-Behnken experimental design

The release of effluents containing cadmium ions into aquatic ecosystems is hazardous to humans and marine organisms. In the current investigation, biosorption of Cd2+ ions from aqueous solutions by freely suspended and immobilized Turbinaria ornata biomasses was studied. Compared to free cells (94.34%), the maximum Cd2+ removal efficiency reached 98.65% for immobilized cells obtained via Box-Behnken design under optimized conditions comprising algal doses of 5.04 g L-1 and 4.96 g L-1, pH values of 5.06 and 6.84, and initial cadmium concentrations of 25.2 mg L-1 and 26.19 mg L-1, respectively. Langmuir, Freundlich, and Temkin isotherm models were suitably applied, providing the best suit of data for free and immobilized cells, but the Dubinin-Radushkevich model only matched the immobilized algal biomass. The maximum biosorption capacity of Cd2+ ions increased with the immobilized cells (29.6 mg g-1) compared to free cells (23.9 mg g-1). The Cd2+ biosorption data obtained for both biomasses followed pseudo-second-order and Elovich kinetic models. In addition, the biosorption process is controlled by film diffusion followed by intra-particle diffusion. Cd2+ biosorption onto the free and immobilized biomasses was spontaneous, feasible, and endothermic in nature, according to the determined thermodynamic parameters. The algal biomass was further examined via SEM/EDX and FTIR before and after Cd2+ biosorption. SEM/EDX analysis revealed Cd2+ ion binding onto the algal surface. Additionally, FTIR analysis confirmed the presence of numerous functional groups (hydroxyl, carboxyl, amine, phosphate, etc.) participating in Cd2+ biosorption. This study verified that immobilized algal biomasses constitute a cost-effective and favorable biosorbent material for heavy metal removal from ecosystems.

The immobilized Alcaligenes faecalis strain WT14 for removing high strength nitrate and reducing nitrite accumulation

Microbial immobilization is considered as one of the effective denitrification techniques in the treatment of high load wastewater. In this study, the immobilized cells consisting of polyvinyl alcohol (PVA), sodium alginate (SA), and calcium chloride (CaCl₂) were inoculated with Alcaligenes faecalis strain WT14 to treat wastewater with high nitrate-nitrogen (NO3--N) concentrations. After 48 h of wastewater treatment, 26.2-89.4% of total nitrogen (TN) was removed by the immobilized Alcaligenes faecalis strain WT14. The response surface methodology revealed the highest TN removal efficiency by Alcaligenes faecalis strain WT14 occurred at the immobilized ratio of 9.3% of PVA, 2.2% of SA and 1.9% of CaCl₂. Under the optimal ratio of PVA, SA, and CaCl₂, the conditions for the maximum denitrification efficiency and TN removal were pH of 7, temperature of 40°C, and shaking speed of 60 rpm·min^-1. Compared to the free cells, the immobilization cells had no obvious negative effect on denitrification efficiency, additionally reduced the nitrite accumulation, and thus improved the TN removal. Furthermore, the immobilized cells still maintained 95.4% of NO3--N removal after the eighth cycle reuse. These results demonstrated the immobilized Alcaligenes faecalis strain WT14 can remove TN effectively and additionally reduce nitrite accumulation in treating high strength NO3--N wastewater.

A comprehensive review on preparation, functionalization and recent applications of nanofiber membranes in wastewater treatment

The direct discharge of significant amounts of polluted water into water bodies causes adverse ecological and human health effects. This severe deterioration in water quality creates significant challenges to meet the growing demand for clean water. Therefore, the world urgently needs environmentally friendly advanced technology to overcome this global crisis. In this regard, nanofiber-based membrane filtration is a promising technique in wastewater remediation because of their huge surface area, extremely porous structure, amenable pore size/pore size distribution, variety of material choices, and flexibility to modification with other functional materials. However, despite their unique properties, fouling, poor mechanical properties, shrinkage, and deformation are major drawbacks of nanofiber membranes for treating wastewater. This review presents a comprehensive overview of nanofiber membranes' fabrication and function in water purification applications as well as providing novel approaches to overcoming/alleviating the mentioned disadvantages. The review first presents nanofiber membrane preparation methods, focusing on electrospinning as a versatile and viable technique alongside discussing the parameters controlling nanofiber morphology. Afterward, the functionalization of nanofiber membranes by combining them with other nanomaterials, such as metal and metal-oxide nanoparticles, carbon nanotubes, metal-organic frameworks, and biomolecules, were demonstrated and discussed. In addition, nanofiber membranes functionalized with microorganisms were highlighted. Finally, we introduced and discussed in detail the most relevant and recent advances in nanofiber applications in wastewater treatment in the context of removing different pollutants (e.g., heavy metals, nutrients, radioactive elements, pharmaceuticals, and personal care products, dyes, and pesticides). Moreover, the promising antimicrobial ability of nanofiber membranes in removing microorganisms from wastewater has been fully underscored. We believe this comprehensive review could provide researchers with preliminary data and guide both researchers and producers engaged in the nanofiber membrane industry, letting them focus on the research gaps in wastewater treatment.

Application of microbial immobilization technology for remediation of Cr(VI) contamination: A review

The discharge of chromium (Cr) contaminated wastewater is creating a serious threat to aquatic environment due to the rapid pace in agricultural and industrial activities. Particularly, the long-term exposure of Cr(VI) polluted wastewater to the environment is causing serious harm to human health. Therefore, the treatment of Cr(VI) contaminated wastewater is demanding widespread attention. Regarding this, the bioremediation is being considered as a reliable and feasible option to handle Cr(VI) contaminated wastewater because of having low technical investment and operating costs. However, certain factors such as loss of microorganisms, toxicity to microorganisms and uneven microbial growth cycle in the presence of high concentrations of Cr(VI) are hindering its commercial applications. Regarding this, microbial immobilization technology (MIT) is getting great research interest because it could overcome the shortcomings of bioremediation technology's poor tolerance against Cr. Therefore, this review is the first attempt to emphases recent research developments in the remediation of Cr(VI) contamination via MIT. Starting from the selection of immobilized carrier, the present review is designed to critically discuss the various microbial immobilizing methods i.e., adsorption, embedding, covalent binding and medium interception. Further, the mechanism of Cr(VI) removal by immobilized microorganism has also been explored, precisely. In addition, three kinds of microorganism immobilization devices have been critically examined. Finally, knowledge gaps/key challenges and future perspectives are also discussed that would be helpful for the experts in improving MIT for the remediation of Cr(VI) contamination.

Insight into synergies between Acinetobacter sp. AL-6 and pomelo peel biochar in a hybrid process for highly efficient manganese removal

The manganese contamination of groundwater is a global issue that needs to be solved urgently. In this study, a hybrid process between pomelo peel biochar(BC) and Acinetobacter sp. AL-6 (strain AL-6) was established to remove manganese from water. The results showed that microbe-biochar composite had removed 98.19% of manganese (800 mg L^-1) within 48 h. Compared with two separate systems (biochar, strain AL-6), the co-system (strain AL-6 and BC composite) had an excellent synergy effect on manganese removal. The average removal rate of manganese in the synergistic system was 14.08 mg L^-1 h^-1, which was 6.41 times higher than strain AL-6, 3.45 times higher than biochar, and even at 2.24 times their sum. In addition, the scanning electron microscope (SEM) and the bioassay indicated that many strains were attached to biochar and had vigorous biological activity. The FTIR results showed that the functional groups of OH, CO, CO, CH₂, and CH played a vital role in removing manganese. And the correlation analysis shows that biochar with strains AL-6 has a highly synergistic effect on manganese removal. Meanwhile, the composite material can maintain excellent manganese removal efficiency under different pH conditions. Besides, in the sequence batch reactor (SBR) inoculating with the microbe-biochar composite, more than 96% of manganese was removed, which far exceeded the treatment efficiency of free bacteria in the SBR. Hence, biochar-immobilized AL-6 has great potential and can be applied to degrade manganese polluted wastewater.

Biological removal of deltamethrin in contaminated water, soils and vegetables by Stenotrophomonas maltophilia XQ08

The consideration of ecological and human health risk is an emerging concern with the excessive or inappropriate use of deltamethrin. In this study, the degradation conditions of the newly deltamethrin-degrading strain Stenotrophomonas maltophilia XQ08 were optimized, which were temperature 35 °C, pH 7.5, cell concentration 5.5 × 10⁸ cfu/mL, and substrate concentration 50 mg/L. Strain XQ08 could effectively degrade deltamethrin into three smaller molecular weight and lower toxic compounds. Enriched strain XQ08 was immobilized in a charcoal-alginate matrix and possessed more prominent biodegradability, reusability, storability and thermostability than free XQ08. In a continuous reactor system, immobilized XQ08 could averagely remove 78.81% of deltamethrin at the gradient influent dosages of 50, 75 and 100 mg/L within 30 d. Immobilized XQ08 introduced into the filed brown and yellow soils exhibited a superior degradation potential for deltamethrin with the half-lives of 1.77 and 2.04 d, which were 2.39 and 2.14 folds, or 6.09 and 5.47 folds faster than free XQ08 degradation (4.23 and 4.37 d) or natural dissipation (10.78 and 11.16 d), respectively. Moreover, application of free XQ08 decreased the persistence of deltamethrin in Brassica pekinensis and Brassica chinensis from 5.47 and 6.23 to 2.05 and 2.32 d, or by 62.52% and 62.76%, respectively. This study provides a feasible, effective and rapid biological removal technology for deltamethrin-contaminated environments in situ.

Efficient nitrate removal by Pseudomonas mendocina GL6 immobilized on biochar

The performance of nitrate removal by Pseudomonas mendocina GL6 cells immobilized on bamboo biochar was investigated. The results showed that immobilized bacterial cells performed better nitrate removal than the free bacterial cells, and the nitrate removal rate increased from 6.51 mg/(L·h) of free cells to 8.34 mg/(L·h) of immobilized cells. The nitrate removal of immobilized bacterial cells fitted well to the zero-order kinetics model. Moreover, bath experiments showed that immobilized bacterial cells displayed more nitrate removal capacity under different conditions than free bacterial cells due to the protection of biochar carrier. The subsequent mechanistic study suggested that biochar promoted the expression level of denitrification functional genes (napA and nirK) and electron transfer genes involved in denitrification (napB and napC), which resulted in the increase of nitrate removal efficiency. Thus, biochar-immobilized P. mendocina GL6 has much potential to remove nitrate from wastewater via aerobic denitrification.

Rapid degradation of dimethomorph in polluted water and soil by Bacillus cereus WL08 immobilized on bamboo charcoal-sodium alginate

The presence of hazardous dimethomorph residues in the environment poses a threat to birds, aquatic organisms and mammals. The novel pure strain Bacillus cereus WL08 responsible for detoxifying dimethomorph was isolated from dimethomorph-polluted soils. The immobilized system of WL08 was developed using bamboo charcoal (BC) and sodium alginate (SA). Immobilization significantly improved tolerance and stability of strain WL08. Under optimal conditions of pH 7.0 and 30 ℃, free and immobilized WL08 degraded 66.95% and 96.88% of 50 mg/L dimethomorph within 72 h, respectively. Moreover, strain WL08 effectively degraded dimethomorph to simple products which were lower toxic than dimethomorph. In a continuous reactor system, immobilized WL08 removed 85.61% of dimethomorph for 30 d at an influent concentration of 50-100 mg/L. In the field soil sprayed with 4.20 kg a.i./ha 80% dimethomorph water dispersible granule (WDG) was treated by immobilized WL08, the lower half-life (1.93 d) was observed, as compared with free WL08 (4.28 d) and natural dissipation (23.82 d). Immobilized WL08 can be considered as a tool for the removal of dimethomorph in water-soil systems. This study provides a feasible microbe-based strategy for bioremediation of dimethomorph-polluted environments.

Response Characteristics of Nitrifying Bacteria and Archaea Community Involved in Nitrogen Removal and Bioelectricity Generation in Integrated Tidal Flow Constructed Wetland-Microbial Fuel Cell

This study explores nitrogen removal performance, bioelectricity generation, and the response of microbial community in two novel tidal flow constructed wetland-microbial fuel cells (TFCW-MFCs) when treating synthetic wastewater under two different chemical oxygen demand/total nitrogen (COD/TN, or simplified as C/N) ratios (10:1 and 5:1). The results showed that they achieved high and stable COD, NH₄ ⁺-N, and TN removal efficiencies. Besides, TN removal rate of TFCW-MFC was increased by 5-10% compared with that of traditional CW-MFC. Molecular biological analysis revealed that during the stabilization period, a low C/N ratio remarkably promoted diversities of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) in the cathode layer, whereas a high one enhanced the richness of nitrite-oxidizing bacteria (NOB) in each medium; the dominant genera in AOA, AOB, and NOB were Candidatus Nitrosotenuis, Nitrosomonas, and Nitrobacter. Moreover, a high C/N ratio facilitated the growth of Nitrosomonas, while it inhibited the growth of Candidatus Nitrosotenuis. The distribution of microbial community structures in NOB was separated by space rather than time or C/N ratio, except for Nitrobacter. This is caused by the differences of pH, dissolved oxygen (DO), and nitrogen concentration. The response of microbial community characteristics to nitrogen transformations and bioelectricity generation demonstrated that TN concentration is significantly negatively correlated with AOA-shannon, AOA-chao, 16S rRNA V4-V5-shannon, and 16S rRNA V4-V5-chao, particularly due to the crucial functions of Nitrosopumilus, Planctomyces, and Aquicella. Additionally, voltage output was primarily influenced by microorganisms in the genera of Nitrosopumilus, Nitrosospira, Altererythrobacter, Gemmata, and Aquicella. This study not only presents an applicable tool to treat high nitrogen-containing wastewater, but also provides a theoretical basis for the use of TFCW-MFC and the regulation of microbial community in nitrogen removal and electricity production.

Effects of Hydraulic Retention Time and Influent Nitrate-N Concentration on Nitrogen Removal and the Microbial Community of an Aerobic Denitrification Reactor Treating Recirculating Marine Aquaculture System Effluent

The effects of hydraulic retention time (HRT) and influent nitrate-N concentration on nitrogen removal and the microbial community composition of an aerobic denitrification reactor treating recirculating marine aquaculture system effluent were evaluated. Results showed that over 98% of nitrogen was removed and ammonia-N and nitrite-N levels were below 1 mg/L when influent nitrate-N was below 150 mg/L and HRT over 5 h. The maximum nitrogen removal efficiency and nitrogen removal rate were observed at HRT of 6 or 7 h when influent nitrate-N was 150 mg/L. High-throughput DNA sequencing analysis revealed that the microbial phyla Proteobacteria and Bacteroidetes were predominant in the reactor, with an average relative total abundance above 70%. The relative abundance of denitrifying bacteria of genera Halomonas and Denitratisoma within the reactor decreased with increasing influent nitrate-N concentrations. Our results show the presence of an aerobically denitrifying microbial consortium with both expected and unexpected members, many of them relatively new to science. Our findings provide insights into the biological workings and inform the design and operation of denitrifying reactors for marine aquaculture systems.

Application of glycerol as carbon source for continuous drinking water denitrification using microorganism from natural biomass

The contamination of water resources by nitrate is a global problem. Indeed, traditional treatment technologies are not able to remove this ion from water. Alternatively, biological denitrification is a useful technique for natural water nitrate removal. This study aimed to evaluate the use of glycerol as a carbon source for drinking water nitrate removal via denitrification in a reactor using microorganisms from natural biomass. The experiment was carried out in a continuous fixed bed reactor using immobilised microorganisms from the vegetal Phyllostachys aurea. The tests were started in batch mode to provide cells growth and further immobilisation on the support. Then, the treatment experiments were accomplished in an up-flow continuous reactor. Ethanol was used as the primary carbon source, and it was gradually replaced by glycerol. The C:N (carbon to nitrogen) ratio and the hydraulic residence time (HRT) were evaluated. It was possible to remove 98.14% of nitrate using a C:N ratio and HRT of 3:1 and 1.51 days, respectively. The results have demonstrated that glycerol is a potential carbon source for denitrification in a continuous reactor using immobilised cells from natural biomass.

Enhanced elimination of dimethachlon from soils using a novel strain Brevundimonas naejangsanensis J3

Dimethachlon is a hazardous xenobiotic which poses a potential risk on the ecosystem and human health after foliar spray for mitigating fungal diseases of crops. A novel dimethachlon-degrading strain was isolated and identified as Brevundimonas naejangsanensis J3. Free cells and enzymes of this strain could rapidly eliminate 75 mg/L dimethachlon in liquid medium, especially the latter (>90% of degradation efficiency). Strain J3 completely metabolized dimethachlon by an ideally transformed pathway. Immobilization cells and enzymes exhibited better stability and adaptability for the repeated use, as compared with free cells and enzymes. In laboratory, 68.03 and 65.13%, or 82.67 and 95.41% of dimethachlon were eliminated from non-sterile soils by free or immobilized cells and enzymes within 7 d, respectively. Under the field condition, 95.78 and 98.01% of 20.250 kg a.i./ha dimethachlon wettable powder from soils were degraded by immobilized cells and enzymes in 9 d respectively, which were significant higher than the degradation efficiencies of free cells and enzymes (78.81 and 67.25%). This study highlights immobilized cells and enzymes from strain J3 can be applicable for bioremediating dimethachlon-contaminated soils.

Removal of dimethachlon from soils using immobilized cells and enzymes of a novel potential degrader Providencia stuartii JD

The first potential degrader capable of detoxifying dimethachlon (NDPS) was isolated and identified as Providencia stuartii JD, whose free cells and freely crude enzymes degraded more than 80% and 90% of 50 mg L^-1 NDPS in liquid culture within 7 d and 2 h, respectively. Strain JD metabolized NDPS through the typical pathway, in which NDPS was firstly transformed into succinic acid and 3, 5-dichloroanilin, and the latter was then converted to phenol, which was subsequently degraded to muconic acid further subjected to the mineralization. The immobilization obviously improved the stability and adaptability of cells and enzymes. In laboratory non-sterile soils treated by free or immobilized cells and enzymes, 50 mg kg^-1 NDPS decreased to 15.66 and 13.32 mg kg^-1, or 8.32 and 2.18 mg kg^-1 within 7 d, respectively. In field, immobilized cells and enzymes exhibited significantly higher efficiencies in removing 20.250 kg a.i. ha^-1 NDPS wettable powder from soils after 9 d (96.02% and 98.56%) than free cells and enzymes (79.35% and 66.45%). This study highlights that strain JD promises the great potential to remove hazardous NDPS residues and its immobilized cells and enzymes possess the more promising advantages in the bioremediation of NDPS-contaminated soils in situ.

Mechanism of enhancing pyrene-degradation ability of bacteria by layer-by-layer assembly bio-microcapsules materials

The mechanism of improving pyrene (PYR)-degrading ability of bacteria CP13 in Layer-by-layer (LBL) assembly chitosan/alginate (CHI/ALG) bio-microcapsules was investigated. Flow cytometry analysis showed that LBL microcapsules could effectively slow down the increasing rate of bacterial cell membrane permeability and the decreasing rate of the membrane potential, so as to reduce the death rate and number of the cells, which could protect the degrading bacteria. The results of Fluorescence spectrum, circular dichroism (CD) spectrum and laser light scattering (LLS) analysis revealed that the other possible mechanism for LBL microcapsules to promote bacterial degradation were following: CHI could enter the secondary structure of the protein of the extracellular polymeric substances (EPS) from CP13 and combined with EPS to generate a stable ground material, which had larger molecular weight (3.76×10⁶ g mol^-1) than the original EPS (2.52×10⁶ g mol^-1). The combination of CHI and EPS resulted in the decrease of the density of EPS from 1.18 to 0.72 g L^-1, suggesting that CHI can loosen the EPS configurations, improving the capture ability of bacteria for PYR as well as the mass transfer of PYR from the extracellular to intracellular, thus eventually promoting the bacteria degrade performance.

Adsorption and degradation in the removal of nonylphenol from water by cells immobilized on biochar

To investigate the role of adsorption by biochar and biodegradation by bacteria in the wastewater treatment system of microorganisms immobilized on biochar, Nonylphenol (NP) removal (adsorption + degradation) rates and degradation rates from water by NP degrading bacteria immobilized on bamboo charcoal (BC) and wood charcoal (WC) were examined in a short-term and long-term. Results showed that cells immobilized on different biochar had different NP removal effects, and cells immobilized on bamboo charcoal (I-BC) was better. After eight rounds of long-term reuse, the cumulative removal rate and the degradation rate of NP in water by I-BC were 93.95% and 41.86%, respectively, significantly higher than those of cells immobilized on wood charcoal (69.60%, 22.78%) and free cells (64.79%, 19.49%) (P < 0.01). The rise in the ratio of the degradation rate to the removal rate indicated that the long-term NP removal effect is more dependent on biodegradation. The amount of residual NP in I-BC still accounted for about 50%, indicating that the secondary pollution in the disposal of carrier could not be ignored. In addition, promotion effect of biochar on microorganisms were observed by SEM, quantitative PCR and 16S rRNA. Pseudomonas, Achromobacter, Ochrobactrum and Stenotrophomonas were predominant bacteria for NP degradation. The addition of biochar (especially bamboo charcoal) also effectively delayed the transformation of their community structure.

Denitrification performance and microbial diversity of immobilized bacterial consortium treating nitrate micro-polluted water

A heterotrophic denitrification process using bacterial consortium immobilized by polyurethane foams carriers to treat nitrate micro-polluted water was investigated. Nitrate reduction and nitrite accumulation were studied under several factors including initial COD/NO₃^--N concentration ratio, initial pH, initial NO₂^--N/NO₃^--N concentration ratio and inlet NO₃^--N concentration. Batch denitrification experiments showed that nitrate was completely removed at 5 h without nitrite accumulation under the optimum conditions of COD/NO₃^--N concentration ratio of 5.0-5.5 and initial pH of 7.2 ± 0.1. High initial NO₂^--N/NO₃^--N ratio enhanced denitrification rate mainly by accelerating nitrite reduction. Denitrification processes followed zero-order reaction kinetics at different initial NO₃^--N concentrations and obtained higher denitrification rate at higher inlet nitrate. High-throughput sequencing results showed that microbial community structure differed between the surface and interior space of polyurethane foams carriers while the dominant population in the inner zone of carriers was Pseudoxanthomonas.

Aerobic denitrification by Paracoccus sp. YF1 in the presence of Cu(II)

This study of Cu(II)'s impact on aerobic denitrification of Paracoccus sp. YF1 revealed that the denitrification rate decreased markedly from 99.8%, 98.0%, 68.7% to 16.3% when the concentrations of Cu(II) rose from 0, 0.01 mM, 0.05 mM to 0.1 mM, respectively. This outcome was confirmed by the successful test of OD₆₀₀, total protein and enzyme activities. As the concentration of Cu(II) increased from 0 to 0.1 mM, the total protein contents declined over a period of 48 h, and the activities of nitrate reductase (NR) and nitrite reductase (NIR) decreased remarkably during the first 24 h in a NO₃^- sufficient state. Meanwhile, the reduction of NO₃^- and NO₂^- was positively correlated with the expression level of NR and NIR. The removal rate of nitrate in the control treatment and different concentration of Cu(II) treatment fitted approximately to the zero-order model. Scanning electron microscopy (SEM) confirmed that the cell surfaces of Paracoccus sp. YF1 were disrupted when exposed to 0.1 mM Cu(II). The adsorption of Cu(II) onto the cells' surface was confirmed by Energy dispersive spectrometer (EDS), Fourier transform infrared spectra (FTIR), and X-ray photoelectron spectroscopy analysis (XPS). The insights obtained here regarding the influence of Cu(II) on aerobic denitrification will be of great significance for the treatment of heavy metals and nitrite co-existing sewage.

Comparison of sulphide and nitrate removal from synthetic wastewater by pure and mixed cultures of nitrate-reducing, sulphide-oxidizing bacteria

In this study, the activities of hydrogen sulphide (H₂S) oxidation and nitrate (N-NO₃^-) reduction by three pure and mixed strains of nitrate-reducing, sulphide oxidizing bacteria (NR-SOB) were determined. Batch experiments were performed at 35 °C and pH 7.0-8.0 with initial H₂S concentrations of 650-900 ppm_v and N-NO₃^- concentrations of ∼120 mg/L. The strains MAL 1HM19, TPN 1HM1 and TPN 3HM1 were capable of removing 100% gas-phase H₂S. The co-cultures showed better performance for H₂S and N-NO₃^- removal. The mixed NR-SOB strains showed a higher H₂S oxidation rate (143 ± 18 ppm_v/h), while the highest N-NO₃^- removal rate (5.5 ± 0 and 5.1 ± 0.6 N-NO₃^- mg/L·h) was obtained by a mixture of two NR-SOB strains. The 16S rDNA sequence analysis revealed that all strains belonged to the sub-class Alphaproteobacteria and are closely related to Paracoccus sp. (>99%).

Using natural biomass microorganisms for drinking water denitrification

Among the methods that are studied to eliminate nitrate from drinking water, biological denitrification is an attractive strategy. Although several studies report the use of denitrifying bacteria for nitrate removal, they usually involve the use of sewage sludge as biomass to obtain the microbiota. In the present study, denitrifying bacteria was isolated from bamboo, and variable parameters were controlled focusing on optimal bacterial performance followed by physicochemical analysis of water adequacy. In this way, bamboo was used as a source of denitrifying microorganisms, using either Immobilized Microorganisms (IM) or Suspended Microorganisms (SM) for nitrate removal. Denitrification parameters optimization was carried out by analysis of denitrification at different pH values, temperature, nitrate concentrations, carbon sources as well as different C/N ratios. In addition, operational stability and denitrification kinetics were evaluated. Microorganisms present in the biomass responsible for denitrification were identified as Proteus mirabilis. The denitrified water was submitted to physicochemical treatment such as coagulation and flocculation to adjust to the parameters of color and turbidity to drinking water standards. Denitrification using IM occurred with 73% efficiency in the absence of an external carbon source. The use of SM provided superior denitrification efficiency using ethanol (96.46%), glucose (98.58%) or glycerol (98.5%) as carbon source. The evaluation of the operational stability allowed 12 cycles of biomass reuse using the IM and 9 cycles using the SM. After physical-chemical treatment, only SM denitrified water remained within drinking water standards parameters of color and turbidity.

High nitrate removal by starch-stabilized Fe0 nanoparticles in aqueous solution in a controlled system

This study was conducted to investigate biodenitrification efficiency with starch-stabilized nano zero valent iron (S-nZVI) as the additional electron donor in the presence of S₂O₃ in aqueous solutions, under anaerobic conditions. The main challenge for nZVI application is their tendency to agglomeration, thereby resulting in loss of reactivity that necessitates the use of stabilizers to improve their stability. In this study, S-nZVI was synthesized by chemical reduction method with starch as a stabilizer. The synthesized nanoparticles were characterized by TEM, XRD, and FTIR. Transmission electron microscopy (TEM) image shows S-nZVI has a size in the range of 5-27.5 nanometer. Temperature and S-nZVI concentration were the important factors affecting nitrate removal. Biodenitrification increased at 35°C and 500 mg/L of S-nZVI, in these conditions, biodenitrification efficiency increased from 40.45 to 78.84%. Experimental results suggested that biodenitrification increased by decreasing initial nitrate concentration. In the bioreactor biodenitrification rate was 94.07% in the presence of S-nZVI. This study indicated that, Fe²⁺ could be used as the only electron donor or as the additional electron donor in the presence of S₂O₃ to increase denitrification efficiency.

Pyrene biodegradation with layer-by-layer assembly bio-microcapsules

Biotechnology is considered as a promising technology for the removal of polycyclic aromatic hydrocarbons from the environment. Free bacteria are often sensitive to some biotic and abiotic factors in the environment to the extent that their ability to effect biodegradation of organic pollutants, such as polycyclic aromatic hydrocarbons, is hampered. Consequently, it is imperative to carry out investigations into biological systems that will obviate or aid tolerance of bacteria to harsh environmental conditions. Chitosan/alginate bio-microcapsules produced using layer-by-layer (LBL) assembly method were tested for pyrene (PYR) biodegradation under harsh environmental conditions. Morphology observation indicated that the flake bio-microcapsules could be successfully prepared through LBL assembly method. Surface analysis showed that the bio-microcapsules had large fractions of mesopores. The results of the biodegradation experiments revealed that the 95% of 10mgL^-1 PYR could be removed by the bacteria encapsulated chitosan/alginate bio-microcapsules in 3 days, which was higher than that of the free bacteria (59%). Compared to the free cells, the bacteria encapsulated chitosan/alginate bio-microcapsules produced 1-6 times higher PYR biodegradation rates at a high initial PYR concentration (50mgL^-1) and extremely low pH values (pH =3) or temperatures (10°C or 40°C), as well as high salt stress. The results indicated that bacteria in microcapsules treatment gained a much higher tolerance to environmental stress and LBL bio-microcapsule could be promising candidate for remediating the organic pollutants.

Improvement of biological nitrogen removal with nitrate-dependent Fe(II) oxidation bacterium Aquabacterium parvum B6 in an up-flow bioreactor for wastewater treatment

Aquabacterium parvum strain B6 exhibited efficient nitrate-dependent Fe(II) oxidation ability using nitrate as an electron acceptor. A continuous up-flow bioreactor that included an aerobic and an anoxic section was constructed, and strain B6 was added to the bioreactor as inocula to explore the application of microbial nitrate-dependent Fe(II) oxidizing (NDFO) efficiency in wastewater treatment. The maximum NRE (anoxic section) and TNRE of 46.9% and 79.7%, respectively, could be obtained at a C/N ratio of 5.3:1 in the influent with HRT of 17. Meanwhile, the taxonomy composition of the reactor was assessed, as well. The NDFO metabolism of strain B6 could be expected because of its relatively dominant position in the anoxic section, whereas potential heterotrophic nitrification and aerobic denitrification developed into the prevailing status in the aerobic section after 50days of continuous operation.

Inhibition or promotion of biodegradation of nitrate by Paracoccus sp. in the presence of nanoscale zero-valent iron

To investigate the effect of nanoscale zero-valent iron (nZVI) on the growth of Paracoccus sp. strain and biodenitrification under aerobic conditions, specific factors were studied, pH, concentration of nitrate, Fe (II) and carbon dioxide. Low concentration of nZVI (50mg/L) promoted both cell growth and biodegradation of nitrate which rose from 69.91% to 76.16%, while nitrate removal fell to 67.10% in the presence of high nZVI concentration (1000 mg/L). This may be attributed to the ions produced in nZVI corrosion being used as an electron source for the biodegradation of nitrate. However, the excess uptake of Fe (II) causes oxidative damage to the cells. To confirm this, nitrate was completely removed after 20 h when 100mg/L Fe (II) was added to the solution, which is much faster than the control (86.05%, without adding Fe (II)). However, nitrate removal reached only 45.64% after 20 h, with low cell density (OD 600=0.62) in the presence of 300 mg/L Fe (II). Characterization techniques indicated that nZVI adhered to microorganism cell membranes. These findings confirmed that nZVI could affect the activity of the strain and consequently change the biodenitrification.

Genome-guided insight into the methylotrophy of Paracoccus aminophilus JCM 7686

Paracoccus aminophilus JCM 7686 (Alphaproteobacteria) is a facultative, heterotrophic methylotroph capable of utilizing a wide range of C1 compounds as sole carbon and energy sources. Analysis of the JCM 7686 genome revealed the presence of genes involved in the oxidation of methanol, methylamine, dimethylamine, trimethylamine, N,N-dimethylformamide, and formamide, as well as the serine cycle, which appears to be the only C1 assimilatory pathway in this strain. Many of these genes are located in different extrachromosomal replicons and are not present in the genomes of most members of the genus Paracoccus, which strongly suggests that they have been horizontally acquired. When compared with Paracoccus denitrificans Pd1222 (type strain of the genus Paracoccus), P. aminophilus JCM 7686 has many additional methylotrophic capabilities (oxidation of dimethylamine, trimethylamine, N,N-dimethylformamide, the serine cycle), which are determined by the presence of three separate gene clusters. Interestingly, related clusters form compact methylotrophy islands within the genomes of Paracoccus sp. N5 and many marine bacteria of the Roseobacter clade.

Evaluation of contact time and fiber morphology on bacterial immobilization for development of novel surfactant degrading nanofibrous webs

Novel electrospun fibrous biocomposites were developed by immobilizing two different sodium dodecyl sulfate (SDS) biodegrading bacterial strains on electrospun non-porous cellulose acetate (nCA) and porous cellulose acetate (pCA) webs.

Influence of zero-valent iron nanoparticles on nitrate removal by Paracoccus sp

Nitrate contamination in drinking water is a major threat to public health. This study investigated the efficiency of denitrification of aqueous solutions in the co-presence of synthesized nanoscale zero-valent iron (nZVI; diameter: 20-80 nm) and a previously isolated Paracoccus sp. strain YF1. Various influencing factors were studied, such as oxygen, pH, temperature, and anaerobic corrosion products (Fe(2+), Fe(3+) and Fe3O4). With slight toxicity to the strain, nZVI promoted denitrification efficiency by providing additional electron sources under aerobic conditions. For example, 50 mg L(-1) nZVI increased the nitrate removal efficiency from 66.9% to 85.2%. However, a high concentration of nZVI could lead to increased production of Fe(2+), a toxic ion which could compromise the removal efficiency. Kinetic studies suggest that denitrification by both free cells, and nZVI-amended cells fitted well to the zero-order model. Temperature and pH are the major factors affecting nitrate removal and cell growth, with or without the presence of nZVI. In this study, nitrate removal and cell growth increased in the pH range of 6.5-8.0, and temperature range of 25-35 °C. These conditions favor the growth of the strain, which dominated denitrification in all scenarios involved. As for anaerobic corrosion products, compared with Fe(2+) and Fe(3+), Fe3O4 promoted denitrification by serving as an electron donor. Finally, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) confirmed attachments of nZVI on the surface of the cell, and the formation of iron oxides. This study indicated that, as an electron donor source with minimal cellular toxicity, nZVI could be used to promote denitrification efficiency under biotic conditions.

Nitrate and COD removal in an upflow biofilter under an aerobic atmosphere

A continuous-upflow submerged biofilter packed with ceramsite was constructed for nitrate removal under an aerobic atmosphere. Pseudomonas stutzeri X31, an aerobic denitrifier isolate, was added to the bioreactor as an inoculum. The influent NO3(-)-N concentrations were 63.0-73.8 mg L(-1). The best results were achieved when dissolved oxygen level was 4.6 mg L(-1) and C/N ratio was 4.5. The maximum removal efficiencies of carbon oxygen demand (COD) and NO3(-)-N were 94.04% and 98.48%, respectively at 30°C, when the hydraulic load was 0.75 m h(-1). The top section of the bioreactor possessed less biofilm but higher COD and NO3(-)-N removal rates than the bottom section. Polymerase chain reaction (PCR)-denaturing gradient gel electrophoresis (DGGE) technique combined with electron microscopic examination indicated P. stutzeri X31 and Paracoccus versutus were the most dominant bacteria. Amoeba sp., Vorticella sp., Philodina sp., and Stephanodiscus sp. were also found in the bioreactor.

Impact of iron-based nanoparticles on microbial denitrification by Paracoccus sp. strain YF1

This study investigates the effects of Fe and Fe/Ni nanoparticles on biological denitrification when using Paracoccus sp. strain YF1. Results show that adding Fe and Fe/Ni nanoparticles to the cells decreased their growth and denitrification rate. Compared to that of free cells (control 89.47%), a decrease (64.33%) in the presence of 1000 mg/L Fe/Ni nanoparticles was observed, while a small decline in the denitrification rate (76.36%) was obtained when the concentration of Fe nanoparticles was 1000 mg/L. These were further confirmed by adding Fe(2+), Fe(3+), Fe3O4, Fe(2+)/Ni(2+) and Fe(3+)/Ni(2+) individually to the free cell system. Furthermore, Fe and Fe/Ni nanoparticles influenced the nitrate removal and bacterial growth under different pH and temperature conditions. SEM, XRD and EDS demonstrated that iron oxides formed as a result of nanoparticles corrosion in biological medium. Finally the presence of nanoparticles around some bacteria was observed.