Biodegradation of pyridine in a completely mixed activated sludge process

Novel insights into the co-metabolism of pyridine with different carbon substrates: Performance, metabolism pathway and microbial community

Pyridine is a widely employed nitrogen-containing heterocyclic organic, and the discharge of pyridine wastewater poses substantial environmental challenges due to its recalcitrance and toxicity. Co-metabolic degradation emerged as a promising solution. In this study, readily degradable glucose and the structurally analogous phenol were used as co-metabolic substrates respectively, and the corresponding mechanisms were thoroughly explored. To treat 400 mg/L pyridine, all reactors achieved remarkably high removal efficiencies, surpassing 98.5%. And the co-metabolism reactors had much better pyridine-N removal performance. Batch experiments revealed that glucose supplementation bolstered nitrogen assimilation, thereby promoting the breakdown of pyridine, and resulting in the highest pyridine removal rate and pyridine-N removal efficiency. The high abundance of Saccharibacteria (15.54%) and the enrichment of GLU and glnA substantiated this finding. On the contrary, phenol delayed pyridine oxidation, potentially due to its higher affinity for phenol hydroxylase. Nevertheless, phenol proved valuable as a carbon source for denitrification, augmenting the elimination of pyridine-N. This was underscored by the abundant Thauera (30.77%) and Parcubacteria (7.21%) and the enriched denitrification enzymes (narH, narG, norB, norC, and nosZ, etc.). This study demonstrated that co-metabolic degradation can bolster the simultaneous conversion of pyridine and pyridine-N, and shed light on the underling mechanism.

Removal of organic pollutants in shale gas fracturing flowback and produced water: A review

Shale gas has been developed as an alternative to conventional energy worldwide, resulting in a large amount of shale gas fracturing flowback and produced water (FPW). Previous studies focus on total dissolved solids reduction using membrane desalination. However, there is a lack of efficient and stable techniques to remove organic pollutants, resulting in severe membrane fouling in downstream processes. This review focuses on the concentration and chemical composition of organic matter in shale gas FPW in China, as well as the hazards of organic pollutants. Organic removal techniques, including advanced oxidation processes, coagulation, sorption, microbial degradation, and membrane treatment are systematically reviewed. In particular, the influences of high salt on each technique are highlighted. Finally, different treatment techniques are evaluated in terms of energy consumption, cost, and organic removal efficiency. It is concluded that integrated coagulation-sorption-Fenton-membrane filtration represents a promising treatment process for FPW. This review provides valuable information for the feasible design, practical operation, and optimization of FPW treatment.

Structural characteristics and microbial function of biofilm in membrane-aerated biofilm reactor for the biodegradation of volatile pyridine

In order to avoid the serious air pollution caused by the volatilization of high recalcitrant pyridine, membrane-aerated biofilm reactor (MABR) with bubble-free aeration was used in this study, with the structural characteristics and microbial function of biofilm emphasized. The results showed that as high as 0.6 kg·m^-3·d^-1 pyridine could be completely removed in MABR. High pyridine loading thickened the biofilm, but without obvious detachment observed. The distinct stratification of microbes and extracellular polymeric substances were shaped by elevated pyridine load, enhancing the structural heterogeneity of biofilm. The increased tryptophan-like substances as well as α-helix and β-sheet proportion in proteins stabilized the biofilm structure against high influent loading. Based on the identified intermediates, possible pyridine biodegradation pathways were proposed. Multi-omics analyses revealed that the metabolic pathways with initial hydroxylation and reduction reaction was enhanced at high pyridine loading. The functional genes were mainly associated with Pseudomonas and Delftia, might responsible for pyridine biodegradation. The results shed light on the effective treatment of wastewater containing recalcitrant pollutants such as pyridine via MABR.

Synergy between pyridine anaerobic mineralization and vanadium (V) oxyanion bio-reduction for aquifer remediation

The co-occurrence of toxic pyridine (Pyr) and vanadium (V) oxyanion [V(V)] in aquifer has been of emerging concern. However, interactions between their biogeochemical fates remain poorly characterized, with absence of efficient route to decontamination of this combined pollution. In this work, microbial-driven Pyr degradation coupled to V(V) reduction was demonstrated for the first time. Removal efficiencies of Pyr and V(V) reached 94.8 ± 1.55% and 51.2 ± 0.20% in 72 h operation. The supplementation of co-substrate (glucose) deteriorated Pyr degradation slightly, but significantly promoted V(V) reduction efficiency to 84.5 ± 0.635%. Pyr was mineralized with NH₄⁺-N accumulation, while insoluble vanadium (IV) was the major product from V(V) bio-reduction. It was observed that Bacillus and Pseudomonas realized synchronous Pyr and V(V) removals independently. Interspecific synergy between Pyr degraders and V(V) reducers also functioned with addition of co-substrate. V(V) was bio-reduced through alternative electron acceptor pathway conducted by gene nirS encoded nitrite reductase, which was evidenced by gene abundance and enzyme activity. Cytochrome c, nicotinamide adenine dinucleotide and extracellular polymeric substances also contributed to the coupled bioprocess. This work provides new insights into biogeochemical activities of Pyr and V(V), and proposes novel strategy for remediation of their co-contaminated aquifer.

Evaluating the effect of fenton pretreated pyridine wastewater under different biological conditions: Microbial diversity and biotransformation pathways

Pyridine contamination poses a significant threat to human and environmental health. Due to the presence of nitrogen atom in the pyridine ring, the pi bond electrons are attracted toward it and make difficult for pyridine treatment with biological and chemical methods. In this study, coupling Fenton treatment with different biological process was designed to enhance pyridine biotransformation and further mineralization. After Fenton oxidation process optimized, pretreated pyridine was evaluated under three biological (anaerobic, aerobic and microaerobic) operating conditions. Under optimum Fenton oxidation, pyridine (30-75%) and TOC (5-25%) removal efficiencies were poor. Biological process alone also showed insignificant removal efficiency, particularly anaerobic (pyridine = 8.2%; TOC = 5.3%) culturing condition. However, combining Fenton pretreatment with biological process increased pyridine (93-99%) and TOC (87-93%) removals, suggesting that hydroxyl radical generated during Fenton oxidation enhanced pyridine hydroxylation and further mineralization in the biological (aerobic > microaerobic > anaerobic) process. Intermediates were analyzed with UPLC-MS and showed presence of maleic acid, pyruvic acid, glutaric dialdehyde, succinic semialdehyde and 4-formylamino-butyric acid. High-throughput sequencing analysis also indicated that Proteobacteria (35-43%) followed by Chloroflexi (10.6-24.3%) and Acidobacteria (8.0-29%) were the dominant phyla detected in the three biological treatment conditions. Co-existence of dominant genera under aerobic/microaerobic (Nitrospira > Dokdonella > Caldilinea) and anaerobic (Nitrospira > Caldilinea > Longilinea) systems most probably play significant role in biotransformation of pyridine and its intermediate products. Overall, integrating Fenton pretreatment with different biological process is a promising technology for pyridine treatment, especially the combined system enhanced anaerobic (>10 times) microbial pyridine biotransformation activity.

Pre-electrochemical treatment combined with fixed bed biofilm reactor for pyridine wastewater treatment: From performance to microbial community analysis

To overcome the high biotoxicity and poor biodegradability of pyridine and its derivatives, a pre-electrochemical treatment combined with fixed bed biofilm reactor (EC-FBBR) was designed for multi-component stream including pyridine (Pyr), 3-cyanopyridine (3-CNPyr), and 3-chloropyridine (3-ClPyr). The EC-FBBR system could simultaneously degrade these pollutants with a mineralization efficiency of 90%, especially for the persistent 3-ClPyr. Specifically, the EC could partially degrade all pollutants, and allow them to be completely destructed in FBBR. With EC off, Rhodococcus (35.5%) became the most abundant genus in biofilm, probably due to its high tolerance to 3-ClPyr. With EC on, 3-ClPyr was reduced to an acceptable level, thus Paracoccus (21.1%) outcompeted among interspecies competition with Rhodococcus and became the dominant genus. Paracoccus was considered to participate in the subsequent degradation for the residual 3-ClPyr, and led to the complete destruction for all pollutants. This study proposed promising combination for effective treatment of multi-component pyridine wastewater.

BiVO4/FeOOH semiconductor-microbe interface for enhanced visible-light-driven biodegradation of pyridine

Pyridine, a highly toxic nitrogen-containing heterocyclic compound, is recalcitrant in the conventional biodegradation process. In this study, BiVO₄/FeOOH semiconductor-microbe interface was developed for enhanced visible-light-driven biodegradation of pyridine, where the efficiencies of pyridine removal (100%), total organic carbon (TOC) removal (88.06±3.76%) and NH₄⁺-N formation (84.51±8.95%) were remarkably improved, compared to the biodegradation system and photodegradation system. The electron transport system activity and photoelectrochemical analysis implied the significant improvement of photogenerated carriers transfer between microbes and semiconductors. High-throughput sequencing analysis suggested functional species related to pyridine biodegradation (Shewanella, Bacillus and Lysinibacillus) and electron transfer (Shewanella and Tissierella) were enriched at the semiconductor-microbe interface. The light-excited holes played a crucial role in promoting pyridine mineralization. This study demonstrated that this bio-photodegradation system would be a potential alternative for the efficient treatment of wastewater containing recalcitrant pollutant such as pyridine.

UV activation of the pi bond in pyridine for efficient pyridine degradation and mineralization by UV/H2O2 treatment

Pyridine and organics containing pyridine rings are widely used but persist in the environment and cause toxic pollution. Due to the attraction of the nitrogen atoms to the electrons in the pi bond, the pyridine ring is difficult to oxidize by oxidant. Here, we propose that ultraviolet (UV) irradiation activates the electrons in the pi bond and enables combination with the hydroxyl radical (OH) originating from hydrogen peroxide (H₂O₂) to eliminate pyridine quickly and mineralize the byproducts. The removal rates of pyridine and total organic carbon (TOC) were compared in different treatments: UV irradiation, UV/H₂O₂ treatment and Fenton oxidation with different initial pyridine concentrations, pH values and H₂O₂ concentrations. The UV/H₂O₂ treatment yielded a higher pyridine removal rate and greater mineralization than the other treatments. The removal rate of pyridine was highest in neutral aqueous solution and H₂O₂ concentration of 10 mM. At an initial H₂O₂ concentration of 10 mM, more than 90% of the pyridine was degraded in 10 min, and approximately 70% of the TOC was removed in 60 min. The absorption of UV light at 254 nm by the pi bond of pyridine can accelerate the damage to the stable pyridine structure, especially in the presence of OH. This study provides a promising alternative for the removal and mineralization of pyridine ring-containing materials.

Development of an LC-MS method for determination of nitrogen-containing heterocycles using mixed-mode liquid chromatography

N-containing heterocycles (NCHs) are largely used as precursors for pharmaceuticals and can enter the environment. Some NCHs have been shown to be toxic, persistent, and very mobile in the environment. Thus, they have received increasing attention in the past years. However, the analysis of these polar compounds in environmental samples is still a challenge for liquid chromatography. This paper investigates the use of mixed-mode liquid chromatography (MMLC), which has reversed-phase and ion exchange characteristics for measurements of NCHs in water. NCHs with low pK_a (i.e., < 2.5) display mainly reversed-phase interactions (neutral species) with the stationary phase and those with higher pK_a (i.e., > 5) interact by a mixture of reversed-phase/ion exchange/HILIC mechanism. It was also shown that the presented method performs well in the quantification of the majority of the selected NCHs in surface water with MDLs between 3 and 6 μg/L, a low matrix effect and recoveries in the range of 77–96% except for pyridazine exhibiting 32% were achieved. The method was successfully employed to follow the degradation of NCHs in ozonation.

Merits of photocatalytic and antimicrobial applications of gamma-irradiated Co x Ni1-x Fe2O4/SiO2/TiO2; x = 0.9 nanocomposite for pyridine removal and pathogenic bacteria/fungi disinfection: implication for wastewater treatment

In this paper, we report a layer-by-layer approach for the preparation of a concentric recyclable composite (Co x Ni1-x Fe2O4/SiO2/TiO2; x = 0.9) designed for wastewater treatment. The prepared composite was investigated by X-ray diffraction spectroscopy, high-resolution transmission electron microscopy and scanning electron microscopy (SEM) supported with energy dispersive X-ray (EDX) spectroscopy to analyze crystallinity, average particle size, morphology and elemental composition, respectively. The antimicrobial activities of the prepared composite have been investigated against multi-drug-resistant bacteria and pathogenic fungi using a variety of experiments, such as zone of inhibition, minimum inhibitory concentration, biofilm formation and SEM with EDX analysis of the treated bacterial cells. In addition, the effects of gamma irradiation (with different doses) and UV irradiation on the antibacterial abilities of the prepared composite have been evaluated. Moreover, the effect of gamma irradiation on the crystallite size of the prepared composite has been studied under varying doses of radiation (25 kGy, 50 kGy and 100 kGy). Finally, the photocatalytic efficiency of the prepared composite was tested for halogen-lamp-assisted removal of pyridine (artificial wastewater). Various parameters affecting the efficiency of the photocatalytic degradation, such as photocatalyst dose, pyridine concentration, pH, point of zero charge and the presence of hydrogen peroxide, have been studied. Our results show that the synthesized composite has a well-crystallized semi-spherical morphology with an average particle size of 125.84 nm. In addition, it possesses a high degree of purity, as revealed by EDX elemental analysis. Interestingly, the prepared composite showed promising antibacterial abilities against almost all the tested pathogenic bacteria and unicellular fungi, and this was further improved after gamma and UV irradiation. Finally, the prepared composite was very efficient in the light-assisted degradation of pyridine and its degradation efficiency can be tuned based on various experimental parameters. This work provides a revolutionary nanomaterial-based solution for the global water shortage and water contamination by offering a new wastewater treatment technique that is recyclable, cost effective and has an acceptable time and quality of water.

Improvement of antimalarial activity of a 3-alkylpiridine alkaloid analog by replacing the pyridine ring to a thiazole-containing heterocycle: Mode of action, mutagenicity profile, and Caco-2 cell-based permeability

The development of new antimalarial drugs is urgent to overcome the spread of resistance to the current treatment. Herein we synthesized the compound 3, a hit-to‑lead optimization of a thiazole based on the most promising 3-alkylpyridine marine alkaloid analog. Compound 3 was tested against Plasmodium falciparum and has shown to be more potent than its precursor (IC₅₀ values of 1.55 and 14.7 μM, respectively), with higher selectivity index (74.7) for noncancerous human cell line. This compound was not mutagenic and showed genotoxicity only at concentrations four-fold higher than its IC₅₀. Compound 3 was tested in vivo against Plasmodium berghei NK65 strain and inhibited the development of parasite at 50 mg/kg. In silico and UV-vis approaches determined that compound 3 acts impairing hemozoin crystallization and confocal microscopy experiments corroborate these findings as the compound was capable of diminishing food vacuole acidity. The assay of uptake using human intestinal Caco-2 cell line showed that compound 3 is absorbed similarly to chloroquine, a standard antimalarial agent. Therefore, we present here compound 3 as a potent new lead antimalarial compound.

Enhanced anoxic biodegradation of pyridine coupled to nitrification in an inner loop anoxic/oxic-dynamic membrane bioreactor (A/O-DMBR)

Enhanced biodegradation of high-strength pyridine was successfully achieved in the inner loop anoxic/oxic-dynamic membrane bioreactor (A/O-DMBR) in this study. Due to the key role of dynamic membrane in biomass retention, NH₄⁺ released from pyridine biodegradation could be effectively nitrified to NO₃^- in oxic zone, which was then recirculated into the anoxic zone to serve as electron acceptor for pyridine biodegradation. Acetate dosage adversely affected pyridine biodegradation, due to the competitive effect of acetate towards NO₃^-. Increase of recirculation ratio positively affected pyridine biodegradation, due to high availability of NO₃^- at high recirculation ratio. At influent pyridine concentration as high as 1500 mg L^-1, effluent turbidity was well maintained below 10 NTU, indicating excellent biomass retention performance of the dynamic membrane. Microbial community analysis confirmed the enrichment of specific functional species in both anoxic and oxic zones. Stable performance during 260 days' operation confirmed the potential of A/O-DMBR for full-scale application.

Diffusional effects on anaerobic biodegradation of pyridine in a stationary basket bioreactor with immobilized Bacillus spp. cells

The effects of external and internal diffusions of pyridine on its biodegradation rate in a bioreactor with a stationary basket bed of immobilized Bacillus spp. cells have been investigated for various biocatalyst diameters and thicknesses of the basket bed, considering the adapted Haldane kinetic model for substrate inhibition. Due to the very low values of pyridine mass flow inside the biocatalyst particles, the 'biological inactive region' appeared mainly near the particles' centre. This region is extended up to 38.5% from the overall volume of each studied size of the biocatalysts, increasing at higher biocatalyst size and basket bed width. Compared to the system containing free Bacillus spp. cells, the basket configuration of packed bed led to the reduction of biodegradation rate up to 82 times, similar to the mobile bed or column packed bed. The cumulated analysis of the influences of the studied factors allowed concluding that the optimum diameter of biocatalysts is 3 mm.

Competition for electrons between pyridine and quinoline during their simultaneous biodegradation

Biodegradation of pyridine and quinoline is initiated with mono-oxygenation reactions that require an intracellular electron donor. Simultaneous biodegradation of both substrates should set up competition for the intracellular electron donor that may inhibit one or more of the mono-oxygenation steps. An internal circulation baffled biofilm reactor (ICBBR) was used to evaluate the impacts of competition during pyridine and quinoline biodegradation. Compared with independent biodegradation, pyridine and quinoline removal rates were slowed when biodegraded simultaneously, although the pyridine removal rate decreased more than for quinoline. The first mono-oxygenation of quinoline (to 2-hydroxyquinoline) always was faster than the first mono-oxygenation of pyridine (to 2-hydroxypyridine), and the difference was accentuated with pyridine and quinoline which were biodegraded simultaneously due to the competition for intracellular electron donor. Competition also existed between the second mono-oxygenations, and the removal rate of 2-hydroxypyridine was faster than the rate for 2-hydroxyquinoline, even though the rate was faster for quinoline than pyridine. Adding an exogenous electron donor accelerated all mono-oxygenations in proportion to the amount of donor added, but the increments were greater for quinoline due to its higher affinity for intracellular electron donors than pyridine. When actual coking wastewater was used as the background matrix, removals of pyridine and quinoline exhibited the same competitive trends.

Synergic Adsorption-Biodegradation by an Advanced Carrier for Enhanced Removal of High-Strength Nitrogen and Refractory Organics

Coking wastewater contains not only high-strength nitrogen but also toxic biorefractory organics. This study presents simultaneous removal of high-strength quinoline, carbon, and ammonium in coking wastewater by immobilized bacterial communities composed of a heterotrophic strain Pseudomonas sp. QG6 (hereafter referred as QG6), ammonia-oxidizing bacteria (AOB), and anaerobic ammonium oxidation bacteria (anammox). The bacterial immobilization was implemented with the help of a self-designed porous cubic carrier that created structured microenvironments including an inner layer adapted for anaerobic bacteria, a middle layer suitable for coaggregation of certain aerobic and anaerobic bacteria, and an outer layer for heterotrophic bacteria. By coating functional polyurethane foam (FPUF) with iron oxide nanoparticles (IONPs), the biocarrier (IONPs-FPUF) could provide a good outer-layer barrier for absorption and selective treatment of aromatic compounds by QG6, offer a conducive environment for anammox in the inner layer, and provide a mutualistic environment for AOB in the middle layer. Consequently, simultaneous nitrification and denitrification were reached with the significant removal of up to 322 mg L^-1 (98%) NH₄, 311 mg L^-1 (99%) NO₂, and 633 mg L^-1 (97%) total nitrogen (8 mg L^-1 averaged NO₃ concentration was recorded in the effluent), accompanied by an efficient removal of chemical oxygen demand by 3286 mg L^-1 (98%) and 350 mg L^-1 (100%) quinoline. This study provides an alternative way to promote synergic adsorption and biodegradation with the help of a modified biocarrier that has great potential for treatment of wastewater containing high-strength carbon, toxic organic pollutants, and nitrogen.

Bioaugmentation of a continuous-flow self-forming dynamic membrane bioreactor for the treatment of wastewater containing high-strength pyridine

For the treatment of high-strength pyridine containing wastewater, a bioaugmented continuous-flow self-forming dynamic membrane bioreactor (CSFDMBR), which was consisted of a continuous flow airlift reactor (CFAR) and a dynamic membrane bioreactor (DMBR), was developed in this study. The results indicated that through the bioaugmentation by Rhizobium sp. NJUST18, CSFDMBR could be successfully started, which was confirmed by complete removal of pyridine, efficient nitrification, and significant increase of biomass. Pyridine could be effectively degraded in the CSFDMBR even at influent pyridine loading rate as high as 9.0 kg m^-3 day^-1, probably due to the efficient biomass retention in the CSFDMBR, which could be attributed to the formation of aerobic granules and the key role of dynamic membrane. CSFDMBR presented good polishing performance in treating pyridine wastewater, with effluent total organic carbon (TOC) and turbidity as low as 22.5 ± 6.8 mg L^-1 and 3.8 ± 0.5 NTU, respectively. Membrane fouling could be effectively controlled, as indicated by backwash period as long as 60 days. The observed efficient performance highlights the potential for the full-scale application of the bioaugmented CSFDMBR, particularly for highly recalcitrant pollutant removal.

Aerobic granulation strategy for bioaugmentation of a sequencing batch reactor (SBR) treating high strength pyridine wastewater

Aerobic granules were successfully cultivated in a sequencing batch reactor (SBR), using a single bacterial strain Rhizobium sp. NJUST18 as the inoculum. NJUST18 presented as both a good pyridine degrader and an efficient autoaggregator. Stable granules with diameter of 0.5-1 mm, sludge volume index of 25.6 ± 3.6 mL g(-1) and settling velocity of 37.2 ± 2.7 m h(-1), were formed in SBR following 120-day cultivation. These granules exhibited excellent pyridine degradation performance, with maximum volumetric degradation rate (Vmax) varied between 1164.5 mg L(-1) h(-1) and 1867.4 mg L(-1) h(-1). High-throughput sequencing analysis exhibited a large shift in microbial community structure, since the SBR was operated under open condition. Paracoccus and Comamonas were found to be the most predominant species in the aerobic granule system after the system had stabilized. The initially inoculated Rhizobium sp. lost its dominance during aerobic granulation. However, the inoculation of Rhizobium sp. played a key role in the start-up process of this bioaugmentation system. This study demonstrated that, in addition to the hydraulic selection pressure during settling and effluent discharge, the selection of aggregating bacterial inocula is equally important for the formation of the aerobic granule.

Biotreatment of chlorpyrifos in a bench scale bioreactor using Psychrobacter alimentarius T14

Bacteria tolerant to high pesticide concentration could be used for designing an efficient treatment technology. Bacterial strains T14 was isolated from pesticide-contaminated soil in mineral salt medium (MSM) and identified as Psychrobacter alimentarius T14 using 16S rRNA gene sequence analysis. Bench scale bioreactor was evaluated for biotreatment of high Chlorpyrifos (CP) concentration using P. alimentarius T14. Effect of various parameters on bioreactor performance was examined and optimum removal was observed at optical density (OD600 nm): 0.8; pH: 7.2; CP concentration: 300 mg L(-1) and hydraulic retention time: 48 h. At optimum conditions, 70.3/79% of CP/chemical oxygen demand (COD) removal was achieved in batch bioreactors. In addition, P. alimentarius T14 achieved 95/91, 62.3/75, 69.8/64% CP/COD removal efficiency with addition of CS (co-substrates), CS1 (yeast extract + synthetic wastewater), CS2 (glucose + synthetic wastewater) and CS3 (yeast extract), respectively. Addition of CS1 to bioreactor could accelerate CP removal rate up to many cycles with considerable efficiency. However, accumulation of 3, 5, 6-trichloro-2-pyridinol affects reactor performance in cyclic mode. First-order rate constant k1 0.062 h(-1) and t1/2 11.1 h demonstrates fast degradation. Change in concentration of total chlorine and nitrogen could be the result of complete mineralization. Photodegradation of CP in commercial product was more than its pure form. Commercial formulation accelerated photodegradation process; however no effect on biodegradation process was observed. After bio-photodegradation, negligible toxicity for seeds of Triticum aestivum was observed. Study suggests an efficient treatment of wastewater containing CP and its metabolites in batch bioreactors could be achieved using P. alimentarius.

Kinetics study of pyridine biodegradation by a novel bacterial strain, Rhizobium sp. NJUST18

Biodegradation of pyridine by a novel bacterial strain, Rhizobium sp. NJUST18, was studied in batch experiments over a wide concentration range (from 100 to 1,000 mg l(-1)). Pyridine inhibited both growth of Rhizobium sp. NJUST18 and biodegradation of pyridine. The Haldane model could be fitted to the growth kinetics data well with the kinetic constants μ* = 0.1473 h(-1), K s = 793.97 mg l(-1), K i = 268.60 mg l(-1) and S m = 461.80 mg l(-1). The true μ max, calculated from μ*, was found to be 0.0332 h(-1). Yield coefficient Y X/S depended on S i and reached a maximum of 0.51 g g(-1) at S i of 600 mg l(-1). V max was calculated by fitting the pyridine consumption data with the Gompertz model. V max increased with initial pyridine concentration up to 14.809 mg l(-1) h(-1). The q S values, calculated from [Formula: see text], were fitted with the Haldane equation, yielding q Smax = 0.1212 g g(-1) h(-1) and q* = 0.3874 g g(-1) h(-1) at S m' = 507.83 mg l(-1), K s' = 558.03 mg l(-1), and K i' = 462.15 mg l(-1). Inhibition constants for growth and degradation rate value were in the same range. Compared with other pyridine degraders, μ max and S m obtained for Rhizobium sp. NJUST18 were relatively high. High K i and K i' values and extremely high K s and K s' values indicated that NJUST18 was able to grow on pyridine within a wide concentration range, especially at relatively high concentrations.

UV photolysis for accelerating pyridine biodegradation

Pyridine, a nitrogen-containing heterocyclic compound, is slowly biodegradable, and coupling biodegradation with UV photolysis is a potential means to accelerate its biotransformation and mineralization. The initial steps of pyridine biodegradation involve mono-oxygenation reactions that have molecular oxygen and an intracellular electron carrier as cosubstrates. We employed an internal circulation baffled biofilm reactor for pyridine biodegradation following three protocols: direct biodegradation (B), biodegradation after photolysis (P+B), and biodegradation with succinic acid added (B+S). Succinic acid was the main UV-photolysis product from pyridine, and its catabolic oxidation generates internal electron carriers that may accelerate the initial steps of pyridine biodegradation. Compared with direct biodegradation of pyridine (B), the removal rate for the same concentration of photolyzed pyridine (P+B) was higher by 15 to 43%, depending on the initial pyridine concentrations (increasing through the range of 130 to 310 mg/L). Adding succinic acid alone (B+S) gave results similar to P+B, which supports that succinic acid was the main agent for accelerating the pyridine biodegradation rate. In addition, protocols P+B and B+S were similar in terms of increasing pyridine mineralization over 10 h: 84% and 87%, respectively, which were higher than with protocol B (72%). The positive impact of succinic acid-whether added directly or produced via UV photolysis-confirms that its catabolism, which produced intracellular electron carriers, accelerated the initial steps of pyridine biotransformation.

Bioaugmentation with a pyridine-degrading bacterium in a membrane bioreactor treating pharmaceutical wastewater

The bacterial strain Paracoccus denitrificans W12, which could utilize pyridine as its sole source of carbon and nitrogen, was added into a membrane bioreactor (MBR) to enhance the treatment of a pharmaceutical wastewater. The treatment efficiencies investigated showed that the removal of chemical oxygen demand, total nitrogen, and total phosphorus were similar between bioaugmented and non-bioaugmented MBRs, however, significant removal of pyridine was obtained in the bioaugmented reactor. When the hydraulic retention time was 60 hr and the influent concentration of pyridine was 250-500 mg/L, the mean effluent concentration of pyridine without adding W12 was 57.2 mg/L, while the pyridine was degraded to an average of 10.2 mg/L with addition of W12. The bacterial community structure of activated sludge during the bioaugmented treatment was analyzed using polymerase chain reaction -denaturing gradient gel electrophoresis (PCR-DGGE). The results showed that the W12 inoculum reversed the decline of microbial community diversity, however, the similarity between bacterial community structure of the original sludge and that of the sludge after bioaugmentation decreased steadily during the wastewater treatment. Sequencing of the DNA recovered from DGGE gel indicated that Flavobacteriaceae sp., Sphingobium sp., Comamonas sp., and Hyphomicrobium sp. were the dominant organisms in time sequence in the bacterial community in the bioaugmented MBR. This implied that the bioaugmentation was affected by the adjustment of whole bacterial community structure in the inhospitable environment, rather than being due solely to the degradation performance of the bacterium added.

Catalytic wet peroxidation of pyridine bearing wastewater by cerium supported SBA-15

Cerium supported SBA-15 (Ce/SBA-15) was synthesized by two-step synthesis method in acidic medium. It was further characterized by various characterization techniques such as X-ray diffraction, field-emission scanning electron microscopy, Fourier transform infrared spectroscopy and N2 adsorption-desorption pore size distribution analysis. The Ce/SBA-15 showed highly ordered meso-structure with pore diameter≈70-100Ǻ and pore volume≈0.025cm(3)/g. Ce/SBA-15 was further evaluated as a catalyst for the oxidation of highly toxic and non-biodegradable material, pyridine, by catalytic wet-peroxidation method. The effects of various operating parameters such as catalyst dose (0.5-6g/l), stoichiometric ratio of H2O2/pyridine (1-6), initial pyridine concentration (50-800mg/l) and temperature (313-358K) have been evaluated and optimized. Ce/SBA-15 showed stable performance during reuse for six cycles with negligible cerium leaching. Kinetic and thermodynamic parameters and operation cost have also been determined.

Comparison of denitrifier communities in the biofilms of bioaugmented and non-augmented zeolite-biological aerated filters

The denitrifier communities of a bioaugmented and non-augmented zeolite-biological aerated filter (Z-BAFs) were investigated and compared because the bioaugmented Z-BAF provided better and more stable treatment efficiency for nitrate and nitrite removal. Terminal restriction fragment length polymorphism (T-RFLP) and reverse transcription T-RFLP (RT-T-RFLP) were applied to analyse the denitrifier community diversity in the biofilm collected from each Z-BAF. The results showed that the bioaugmentation technology favourably changed the indigenous denitrifier community and enhanced denitrification under nitrogen loading shocks. The cDNA clone libraries were developed to explore the active denitrifier community structures of both filters. The results showed that the active denitrifiers in both the bioaugmented and non-bioaugmented Z-BAF belonged to alpha-, beta- and gamma-proteobacteria. However, the sequence of the introduced denitrifier (Paracoccus sp. BW001) was not found in the clone library of the bioaugmented filter, which implied that the removal of nitrate and nitrite was attributed mainly to the indigenous denitrifiers in the adjusted bacterial community in the bioaugmented Z-BAF.

Removal of pyridine from liquid and gas phase by copper forms of natural and synthetic zeolites

Zeoadsorbents on the basis of copper forms of synthetic zeolite ZSM5 and natural zeolite of the clinoptilolite type (CT) have been studied taking into account their environmental application in removing harmful pyridine (py) from liquid and gas phase. Sorption of pyridine by copper forms of zeolites (Cu-ZSM5 and Cu-CT) has been studied by CHN, X-ray photoelectron spectroscopy, X-ray powder diffractometry, FTIR spectroscopy, thermal analysis (TG, DTA and DTG) and analysis of the surface areas and the pore volumes by low-temperature adsorption of nitrogen. The results of thermal analyses of Cu-ZSM5, Cu-(py)(x)ZSM5, Cu-CT and Cu-(py)(x)CT zeolitic products with different composition (x depends on the experimental conditions of sorption of pyridine) clearly confirmed their different thermal properties as well as the sorption of pyridine. In the zeolitic pyridine containing samples the main part of the pyridine release process occurs at considerably higher temperatures than is the boiling point of pyridine, which proves strong bond and irreversibility of py-zeolite interaction. FTIR spectra of Cu-(py)(x)zeolite samples showed well resolved bands of pyridine. The results of thermal analysis and FTIR spectroscopy are in a good agreement with the results of other used methods.

Removal of pyridine and quinoline by bio-zeolite composed of mixed degrading bacteria and modified zeolite

In the process of the biodegradation of pyridine and quinoline, ammonium is often generated because of the transformation of N from pyridine and quinoline. Zeolite has been proven to be an effective sorbent for the removal of the ammonium. The natural zeolite can be modified to be the macroporous carrier in the biological wastewater treatment process. In this study, a specific bio-zeolite composed of mixed bacteria (a pyridine-degrading bacterium and a quinoline-degrading bacterium) and modified zeolite was used for biodegradation and adsorption in two types of wastewater: sterile synthetic and coking wastewater. The experimental results indicated that pyridine and quinoline could be degraded simultaneously by the mixed bacteria. Furthermore, NH(4)(+)-N transformed from pyridine and quinoline could be removed by the modified zeolite. In addition, the bacterial community structures of the coking wastewater and the bio-zeolite were monitored by the amplicon length heterogeneity polymerase-chain reaction (LH-PCR) technique. Both LH-PCR results and scanning electron microscope (SEM) observations indicated that the microorganisms, including BW001 and BW003, could be easily attached on the surface of the modified zeolite and that the bio-zeolite could be used in the treatment of wastewater containing pyridine and/or quinoline.

Alkaline cyanide degradation by Pseudomonas pseudoalcaligenes CECT5344 in a batch reactor. Influence of pH

Water containing cyanide was biologically detoxified with the bacterial strain Pseudomonas pseudoalcaligenes CECT5344 in a batch reactor. Volatilization of toxic hydrogen cyanide (HCN) was avoided by using an alkaline medium for the treatment. The operational procedure was optimized to assess cyanide biodegradation at variable pH values and dissolved oxygen concentrations. Using an initial pH of 10 without subsequent adjustment allowed total cyanide to be consumed at a mean rate of approximately 2.81 mg CN(-) L(-1) O.D.(-1) h(-1); however, these conditions posed a high risk of HCN formation. Cyanide consumption was found to be pH-dependent. Thus, no bacterial growth was observed with a controlled pH of 10; on the other hand, pH 9.5 allowed up to 2.31 mg CN(-) L(-1) O.D.(-1) h(-1) to be converted. The combination of a high pH and a low dissolved oxygen saturation (10%) minimized the release of HCN. This study contributes new basic knowledge about this biological treatment, which constitutes an effective alternative to available physico-chemical methods for the purification of wastewater containing cyanide or cyano-metal complexes.

Bioaugmentation treatment for coking wastewater containing pyridine and quinoline in a sequencing batch reactor

Two pyridine-degrading bacteria and two quinoline-degrading bacteria were introduced for bioaugmentation to treat the coking wastewater. Sequencing batch reactors (SBRs) were used for a comparative study on the treatment efficiency of pyridine, quinoline, and chemical oxygen demand. Results showed that the treatment efficiency with coking-activated sludge plus a mixture of the four degrading bacteria was much better than that ones with coking-activated sludge only or mixed degrading bacteria only. Moreover, a 52-day continuous operation of the bioaugmented and general SBRs was investigated. The bioaugmented SBR showed better treatment efficiency and stronger capacity to treat high pyridine and quinoline shock loading. The general SBR failed to cope with the shock loading, and the biomass of the activated sludge decreased significantly. In order to monitor the microbial ecological variation during the long-term treatment, the bacterial community in both reactors was monitored by the amplicon length heterogeneity polymerase chain reaction technique. The diversity of the bacterial community decreased in both reactors, but the introduced highly efficient bacteria were dominant in the bioaugmented SBR. Our experiment showed clearly that the use of highly efficient bacteria in SBR process could be a feasible method to treat wastewater containing pyridine or/and quinoline.

Pyridine degradation in the microbial fuel cells

The objective of this study was to investigate the feasibility of pyridine biodegradation in the microbial fuel cell (MFC), from which electricity was generated. Experiments were initially conducted in a graphite-packed MFC (G-MFC) using a pyridine concentration of 500 mg/L combined with different glucose concentrations. Pyridine of 500 mg/L only used as the G-MFC fuel resulted in a maximal voltage of 116 mV and a maximal power density of 1.7 W/m(3). The maximal voltage reached within 12 h when pyridine was totally depleted. The glucose supplement with concentrations of 500, 250, and 100 mg/L resulted in the maximum voltages of 623, 538, and 349 mV, respectively, correspondingly the maximal volumetric power densities were 48.5, 36.2, and 15.2 W/m(3). Pyridine biodegradation rates reached 95% within 24h using the G-MFC. Interestingly, after 90 d of acclimation, the biodegradation rates of pyridine in the G-MFC using pyridine only as the fuel were higher than those using the glucose-pyridine mixtures. Further experiments were conducted using a graphite fiber brush MFC (B-MFC). Compared to the G-MFC, the B-MFC enhanced the electrical charges by 89, 186, and 586% for the mixtures with ratios of glucose-to-pyridine of 1:1, 1:2, and 1:5, respectively. GC/MS analyses of the anode solution indicated that the metabolism of pyridine in the MFC was initiated by ring reduction and NH3-N production. The results suggest that pyridine may be used as the MFC fuel in practical applications of wastewater treatment.

Effects of the COD/NO3(-)-N ratio and pH on the accumulation of denitrification intermediates with available pyridine as a sole electron donor and carbon source

Batch experiments were conducted to investigate the effects of COD/NO3(-)-N ratio and pH on the accumulation of the denitrification intermediates - nitrite and nitrous oxide - with pyridine as the sole electron donor and carbon source. Significant transient accumulation of nitrite was observed at COD/NO3(-)-N ratios in the range of 2-13 and pH in the range of 6.5-9.5. The optimal pH was 7.5 and the minimum COD/NO3(-)-N ratio was 4 for complete denitrification. The pH had a significant effect on denitrification. At a lower pH of 6.5, the reaction was severely inhibited whereas at a higher pH of 8.5 and 9.5, nitrate was completely reduced, but a high concentration of nitrite remained in the reactors while pyridine was almost completely degraded after one hour, even at the COD/NO3(-)-N ratio of 4. While the specific nitrate reduction rate and nitrite reduction rate in the absence of nitrate remained constant at different COD/NO3(-)-N ratios, they increased with the increase in pH. The nitrite reduction was inhibited in the presence of nitrate because of the faster rate of nitrate reduction over nitrite reduction. Nitrous oxide accumulation was also observed with a COD/NO3(-)-N ratio below 3 in the pH range of 7.5-8.5. At a COD/NO3(-)-N ratio of 4 and pH of 6, the production of nitrous oxide was much higher than that at pH 7 and 8.

Biodegradation of pyridine by the new bacterial isolates S. putrefaciens and B. sphaericus

In this study, two bacterial strains capable of utilizing pyridine as a sole carbon source were isolated from biofilters. Based on the biochemical test, the organisms were identified as Shewanella putrefaciens and Bacillus sphaericus. In liquid cultures, S. putrefaciens and B. sphaericus degraded pyridine quite effectively up to 500 mg L(-1). S. putrefaciens degrades 500 mg L(-1) of pyridine completely within 140 h, whereas the B. sphaericus degrades 500 mg L(-1) of pyridine only nearly 75% and takes a longer duration of 150 h. S. putrefaciens used pyridine as sole carbon and energy source better than B. sphaericus. Monod's and Haldane's inhibitory growth models were used to obtain maximum specific growth rate (micro(max)), half saturation (K(s)) and substrate inhibition (K(i)) constant for pyridine by using S. putrefaciens and B. sphaericus. The high value of K(i) for S. putrefaciens than B. sphaericus indicates that the inhibition effect can be observed only in a high concentration range. The S. putrefaciens degrades pyridine with a faster rate than B. sphaericus. S. putrefaciens can be used effectively for the treatment of pyridine bearing wastewater and as an inoculum in a biofilter treating pyridine-laden gas.

Microbial degradation and metabolic pathway of pyridine by a Paracoccus sp. strain BW001

A bacterial strain using pyridine as sole carbon, nitrogen and energy source was isolated from the activated sludge of a coking wastewater treatment plant. By means of morphologic observation, physiological characteristics study and 16S rRNA gene sequence analysis, the strain was identified as the species of Paracoccus. The strain could degrade 2,614 mg l(-1) of pyridine completely within 49.5 h. Experiment designed to track the metabolic pathway showed that pyridine ring was cleaved between the C2 and N, then the mineralization of the carbonous intermediate products may comply with the early proposed pathway and the transformation of the nitrogen may proceed on a new pathway of simultaneous heterotrophic nitrification and aerobic denitrification. During the degradation, NH3-N occurred and increased along with the decrease of pyridine in the solution; but the total nitrogen decreased steadily and equaled to the quantity of NH3-N when pyridine was degraded completely. Adding glucose into the medium as the extra carbon source would expedite the biodegradation of pyridine and the transformation of the nitrogen. The fragments of nirS gene and nosZ gene were amplified which implied that the BW001 had the potential abilities to reduce NO2- to NO and/or N2O, and then to N2.

Pyridine biodegradation in a novel rotating rope bioreactor

A novel immobilised bioreactor has been developed especially for the treatment of pollutants characterized by high volatility along with high water solubility and low microbial yields. The new bioreactor referred to as the rotating rope bioreactor (RRB) provides higher interfacial area (per unit reactor liquid volume) along with high oxygen mass transfer rate, greater microbial culture stability; and consequently higher substrate loadings and removal rates in comparison to other conventional rectors for the treatment of volatile compounds. Pyridine was used as a model compound to demonstrate the enhanced performance with RRB, when compared to that reported with other conventional bioreactors. The experimental results indicate that the novel RRB system is able to degrade pyridine with removal efficiency of more than 85% at higher pyridine concentration (up to 1000 mg/l) and loading [up to 400 mg/m(2)/h (66.86 g/m(3)/h)], with a shorter hydraulic retention time (9-18 h). The reactor has been in operation for the past 15 months and no loss of activity has been observed.

Monitoring thiocyanate-degrading microbial community in relation to changes in process performance in mixed culture systems near washout

Changes in microbial community structure, associated with changes in process performance, were investigated with respect to the sludge retention time (SRT) in bioreactors treating thiocyanate. Among the seven reactors operated at 0.8-3.0 d SRTs, respectively, the reactor at 2.0 d SRT displayed the maximal thiocyanate removal rate of 240.2mg/L/d. However, the thiocyanate removal efficiency suddenly decreased from 96.1% to 43.1% when the SRT was reduced from 2.0 to 1.8d, corresponding to a 50.1% drop in the removal rate. Microbial communities in the reactors operated at short SRTs, near washout, were analyzed by denaturing gradient gel electrophoresis (DGGE) based on bacterial 16S rRNA genes. All band sequences recovered were assigned to two phyla, Proteobacteria and Bacteriodetes. A Thiobacillus-like microorganism was commonly detected in all the reactors and is suggested to be the main organism responsible for thiocyanate decomposition. Several DGGE band sequences were closely related to the environmental clones detected in environments rich in sulfur and/or nitrogen compounds. Statistical analysis of the DGGE profiles demonstrated that the structure of thiocyanate-degrading communities, as well as the process performance, changed with change in SRT. The microbial community profiles were not always more closely related to those at similar SRT than those at less similar SRT on the non-metric multidimensional scaling (NMDS) map. This was also supported by clustering analysis. These results were contrary to the general notion that the community structures in continuous systems will be controlled by the washout of microbial populations. Our experimental results suggest that the structure of a microbial thiocyanate-degrading community at a given SRT would not be determined only by the washout effect.

Biotreatment of waste gas containing pyridine in a biofilter

Industrial waste gas emissions containing pyridine are generated from pyridine manufacturing industries, and in industrial operations where pyridine is used as a solvent, as an intermediate for synthesis and as a catalyst for a variety of applications. Pyridine has unpleasant fishy odor with an odor index of 2390 and waste gaseous emissions containing pyridine require proper treatment prior to discharge. A biofilter, packed with compost and wood chips and inoculated with Pseudomonas pseudoalcaligenes-KPN for enrichment of pyridine-degrading microorganisms, was operated on a continuous feed basis for a period of more than 2 years. The results indicate that the biofilter medium with optimal moisture content of 68% and an effective bed retention time (EBRT) of 28.50s could degrade pyridine effectively (>99%) at a loading of 434 g pyridine m(-3)h(-1). The treated waste gas was also found to be free from pyridine odor.