Heterotrophic nitrogen removal by Providencia rettgeri strain YL.

Providencia rettgeri strain YL was found to be efficient in heterotrophic nitrogen removal under aerobic conditions. Maximum removal of NH(4) (+)-N occurred under the conditions of pH 7 and supplemented with glucose as the carbon source. Inorganic ions such as Mg(2+), Mn(2+), and Zn(2+) largely influenced the growth and nitrogen removal efficiency. A quantitative detection of nitrogen gas by gas chromatography was conducted to evaluate the nitrogen removal by strain YL. From the nitrogen balance during heterotrophic growth with 180 mg/l of NH(4) (+)-N, 44.5% of NH(4) (+)-N was in the form of N(2) and 49.7% was found in biomass, with only a trace amount of either nitrite or nitrate. The utilization of nitrite and nitrate during the ammonium removal process demonstrated that the nitrogen removal pathway by strain YL was heterotrophic nitrification-aerobic denitrification. A further enzyme assay of nitrate reductase and nitrite reductase activity under the aerobic condition confirmed this nitrogen removal pathway.

Nitrogen removal capability through simultaneous heterotrophic nitrification and aerobic denitrification by Bacillus sp. LY.

The heterotrophic nitrification and aerobic denitrification capabilities of Bacillus sp. LY were investigated under the aerobic condition. The results indicate that Bacillus sp. LY is not only a heterotrophic nitrifier, but also an aerobic denitrifier. Experiments were carried out in an attempt to determine and quantify the contribution of heterotrophic nitrification and aerobic denitrification to total N removal. By taking the nitrogen balance under the culture condition of 41.1 mg/L of initial NH(4+)-N at a C/N ratio of 15 in 96 h, 8.0% of the initial NH(4)+-N still remained in the medium in the forms of hydroxylamine, nitrite, nitrate and organic N; 40.5% of NH(4+)-N was converted to biomass and 45.9% of NH(4+)-N was estimated to be finally removed in the formation of N2. This conversion of ammonium to N2 with the intermediate formation of N2O under the aerobic condition was confirmed by gas chromatography. Single step nitrogen removal by simultaneous heterotrophic nitrification and aerobic denitrification has great potential in wastewater treatment.

[Antibiotics Induce Horizontal Gene Transfer of Resistance at Sublethal Concentrations].

In order to explore the conjugation of genes encoding extended-spectrum ß-lactamase (ESBL), ESBL-expressing P. aeruginosa and E.coli strains isolated from the wastewater of major hospitals in Singapore were used as donors. gfp-tagged E.coli SCC1 strains resistant to chloramphenicol (CHL) were chosen as recipients. Using response surface analysis, we detected and analyzed the induction of conjugal transfer under single-exposure and co-exposure of tetracycline (TC), sulfamethoxazole (SMZ), and ceftazidime (CAZ) at sublethal concentrations. It was found that the ESBL plasmid could be conjugal transferred from P. aeruginosa and E.coli strains to the recipient E.coli SCC1 strains at an average frequency of 0.0015 and 0.0042, respectively, without stress from inducing antibiotics, thus showing a low fitness cost and higher conjugal frequency between E.coli strains under the exposure of sub-MIC antibiotics. A significant conjugation between E.coli strains occurred under the single-exposure or co-exposure of a TC concentration of <0.03 mg·L-1 and a CAZ concentration of <0.002 mg·L-1, as inhibited by a sub-MIC level of TC. The conjugation between P. aeruginosa and E.coli strains was stimulated under the exposure of TC and CAZ with concentrations 5-times larger than the MIC, while no significant induction was detected from the sub-MIC antibiotics.

[Influence of Antibiotics on the Denitrification Process of Antibiotic Resistant Denitrifying Bacteria and the Analysis of Microbial Community Structure].

The removal rate of some antibiotics in urban sewage by conventional treatment is low, which leads to an increase in antibiotic resistant bacteria in natural water environments. To reduce the ecological harm of antibiotics to the water in towns, a risk control technique for degradation of microantibiotics by the co-metabolism of antibiotic resistant denitrifying bacteria was proposed. Using sodium acetate as an electron donor and maintaining the concentration of ofloxacin (OFLX) at 1 µg·g-1, gradually increasing the dominant growth of antibiotic degradation bacteria, denitrifying bacteria (DnB1), trace antibiotics and sodium acetate, and denitrifying bacteria (DnB2) with the presence of sodium acetate and nitrogen elements were cultured. The degradation effect of antibiotics through denitrification and the effects of antibiotics on denitrification of resistant denitrifying bacteria and the changes to the microbial community were investigated. The results showed that DnB2 had a significant degradation effect on OFLX compared to DnB1. The degradation to OFLX by DnB1 and DnB2 was 0.31 µg·g-1 and 16.14 µg·g-1, respectively. Increased OFLX concentration inhibited DnB1 denitrification activity in the short term. The denitrification process of DnB2 was less affected by OFLX. At the same time, high-throughput sequencing using the Illumina MiSeq platform was used. Based on the operational taxonomic unit information formed by the clustering of sequencing results, the diversity of each sample was compared and analyzed. The research results show that the relative abundance and diversity of the microbial community of DnB1 are higher than those of DnB2.

The enthalpies of formation for polychlorinated dibenzofurans with use of G3XMP2 model chemistry and density functional theory.

The standard gas-phase enthalpies of formation of polychlorinated dibenzofurans (PCDFs) have been predicted by using G3XMP2 model chemistry, density functional theory (DFT), and second-order Muller-Plesset (MP2) theory, coupled with isodesmic reactions. The results show a large difference between G3XMP2 and DFT methods with 6-31G(2df,p) and 6-311++G(3df,3pd) basis sets, while MP2/G3MP2Large calculations agree closely with G3XMP2. Two isodesmic reaction schemes are used for better prediction of formation enthalpies. The first (IR1) employs monochlorobenzene as a reference species and the second (IR2) employs polychlorinated benzenes as reference species. The relative stability of PCDFs is rationalized by positional interactions. While the Cl-substitution at position 1/9 leads to the most stable isomers, the simultaneous substitutions at positions 1 and 9 result in a strong repulsion between Cl atoms. Failure of DFT-B3LYP is due to the overestimation of o-ClCl repulsion. For 1,9-PCDFs, the torsion motions of the benzene rings have extremely low harmonic vibrational frequencies. Their contributions to entropy, heat capacity, and thermal corrections have been calculated by using the numerically evaluated energy levels. The PCDF isomer patterns are also discussed based on the calculated thermodynamic parameters.

Isolation and characterization of a new heterotrophic nitrifying Bacillus sp. strain.

OBJECTIVE: To characterize the heterotrophic nitrifying bacteria. METHODS: The bacteria were isolated from membrane bioreactor for treating synthetic wastewater using the method newly introduced in this study. Fluorescence in situ hybridization (FISH) was used to validate the nonexistence of autotrophic ammonia oxidizers and nitrite oxidizers. Batch tests were carried out to investigate the capability of heterotrophic nitrification by the pure culture. Phylogenetic analysis of the pure culture was performed. RESULTS: A heterotrophic nitrifier, named Bacillus sp. LY, was newly isolated from the membrane bioreactor system in which the efficiency of TN removal was up to 80%. After 24-day, incubation, the removal efficiency of COD by Bacillus sp. LY was 71.7%. The ammonium nitrogen removal rate after assimilation nearly ceased by Bacillus sp. LY was 74.7%. The phylogenetic tree of Bacillus sp. LY and the neighbouring nitrifiers were given. CONCLUSIONS: The batch test results indicate that Bacillus sp. LY can utilize the organic carbon as the source of assimilation when it grows on glucose and ammonium chloride medium accompanying the formation of oxidized-nitrogen. It also can denitrify nitrate while nitrifying. Bacillus sp. LY may become a new bacterial resource for heterotrophic nitrification and play a bioremediation role in nutrient removal.

Isolation of a new heterotrophic nitrifying Bacillus sp. strain.

A heterotrophic nitrifier, named Bacillus sp. LY, was newly isolated from a membrane bioreactor (MBR). Bacillus sp. LY could utilize the organic carbon as the source of assimilation when it grew on glucose and ammonium chloride medium companying the formation of oxidized-nitrogen. It also could denitrify nitrate while nitrification. After 24 days incubation, the removal efficiencies of the COD and TN by Bacillus sp. LY were 71.7% and 61.2%, respectively. The phylogenetic analysis of Bacillus sp. LY was performed and the phylogenetic tree of Bacillus sp. LY and the neighbouring nitrifiers was given. Bacillus sp. LY could become a new bacterial resource for heterotrophic nitrification and might play a bioremediation role for nutrient removal.

[Study progress on the mechanism of heterotrophic nitrification].

Nitrification plays an important role in the nitrogen cycle. Autotrophic bacteria have traditionally been regarded as the nitrifying agents. However, research in last few decades has established that a lot of heterotrophic microorganisms also make contribution to nitrification. Heterotrophic nitrification has become an issue for scientific research and environment management. In this overview, both the location of heterotrophic microorganisms and the methods of detection and isolation which take the polyphyletic nature of heterotrophic bacteria into account are briefly presented. The study on the mechanism which focuses on the enzymes, functional genes, electron transfer and metabolism pathway of heterotrophic nitrification are mainly reviewed. In the end, the problems lying in the research of the mechanism of the heterotrophic nitrification are proposed and future research directions are suggested.

Isolation and characterization of heterotrophic nitrifying bacteria in MBR.

The study presented the method for isolating the heterotrophic nitrifiers and the characterization of heterotrophic nitrification. Continuous tests via a membrane bioreactor (MBR) were operated under the controlled conditions to proliferate the nitrifiers. Heterotrophic nitrifying bacteria were isolated from the system in which the efficiency of total nitrogen (TN) removal was up to 80%. Since no autotrophic ammonium and nitrite oxidizers could be detected by fluorescence in situ hybridization (FISH), oxidized-N production was unlikely to be catalyzed by autotrophic nitrifiers during the heterotrophic nitrifiers' isolation in this study. The batch test results indicate that the isolated heterotrophic bacteria were able to nitrify. After 3 weeks incubation, the efficiencies of the COD removal by the three isolated bacterial strains B1, B2, and B3 were 52.6%, 71.7%, and 77.7%, respectively. The efficiencies of the TN removal by B1, B2, and B3 were 35.6%, 61.2% and 68.7%, respectively.

[Coupled Cytotoxicity of C60 Nano-Crystal Particle with Cu2+ to the Mouse Peritoneal Macrophage RAW 264.7].

This work evaluated the cytotoxicity effect of nC60 nano-crystal particle associated with Cu2+ by using mouse peritoneal microphage RAW264. 7 as the test cell line. The results showed that when exposed to nC60 of 6. 6 mg . L-1 and 9. 9 mg . L-1 for 24h, the cell viability decreased 45% and 70% , respectively, and had obvious time-response and dose-response. It was found that Cu2, could reduce the toxicity of nC60 on RAW 264. 7. The cell viability reduced to 25% when exposed to 6. 6 mg . L-1 nC60 with 2 mg . L-1 Cu2+, and reduced to 15% when exposed to 9. 9 mg . L-1 nC60 with 5 mg . L-1 Cu2+. The nC60 could adsorb Cu2+ and the adsorption isotherm was fitted to the Langmuir adsorptiqn isotherm. The adsprption of Cu2+ on the surface of nC60 may decrease the cytotoxicity nC60 on RAW 264.7.

[Phosphorus fractions, sorption characteristics and its release in the sediments of Yangtze Estuary Reservoir, China].

To analyze the sediment phosphorus (P) fractions and sorption characteristics and P release from sediment of reservoir in Yangtze estuary, the sediment was investigated during April, 2011 to January, 2012. Results of chemical fractionation analysis showed that total P (TP) content in sediment ranged from 535.07 to 910.9 mg x kg(-1), inorganic P (IP) was a dominant component of TP and the content of organic P (OP) was low. IP presented in the form of P bounded to calcium ( HCl-P) and dominated 75.57% of TP. The batch experiments showed that sediments had the maximum P adsorption capacity from 9.78 to 39.84 mg x kg(-1), sorption data fitted the modified Langmuir isotherm model. However, EPC0 ( equilibrium phosphorus concentration) in all sampling sites was higher than the soluble-reactive P concentration in water column, which was from 0.024-0.12 mg x L(-1). Accordingly, the sediments from those sampling sites would release phosphorus into the overlying water as a P release source. The maximum released amount from sediment was 11.03 mg x kg(-1) about 6 hours. Correlation between P released amount and NaOH-P was found (P < 0.01), and sediment P release would mainly originate from the NaOH-P, OP and HCl-P fraction. It is evident that the inherent phosphorus present in sediments would be a major threat to the water quality in Yangtze River estuary reservoir.

N2O and N2 production during heterotrophic nitrification by Alcaligenes faecalis strain NR.

A heterotrophic nitrifier, strain NR, was isolated from a membrane bioreactor. Strain NR was identified as Alcaligenes faecalis by Auto-Microbic system and 16S rRNA gene sequence analysis. A. faecalis strain NR shows a capability of heterotrophic nitrification and N(2)O and N(2) production as well under the aerobic condition. Further tests demonstrated that neither nitrite nor nitrate could be denitrified aerobically by strain NR. However, when hydroxylamine was used as the sole nitrogen source, nitrogenous gases were detected. With an enzyme assay, a 0.063 U activity of hydroxylamine oxidase was observed, while nitrate reductase and nitrite reductase were undetectable. Thus, nitrogenous gas was speculated to be produced via hydroxylamine. Therefore, two different metabolic pathways might exist in A. faecalis NR. One is heterotrophic nitrification by oxidizing ammonium to nitrite and nitrate. The other is oxidizing ammonium to nitrogenous gas directly via hydroxylamine.

[Removal of nickel from aqueous solutions using complexation-ultrafiltration process].

Polyacrylate (PAANa) and polyethylenimine (PEI) were used as complexing agents to combine with nickel ions. This complexation solution was transferred to the ultrafiltration cell and the separation by polyethersulfone (PES) ultrafiltration membranes was carried out under the pressure of 0.1 MPa. Effects of solution pH and polymer/Ni2+ mass ratio on nickel removal were investigated. The complex reaction equilibrium constants were calculated according to Langmuir isotherm model. Effects of concentration time on nickel removal and membrane flux were also studied. With PAANa as a polymer, the removal rate of nickel went the highest to 99.5% at pH 8 with PAANa/Ni2+ ratio of 5. When PEI was used, the removal rate of nickel ions went highest to 93.0% at pH 7 with PEI/Ni2+ ratio of 5. Best-fit complexation equilibrium constants at different pH values showed that pH 7 was most beneficial to the complex reaction. In addition, the number of nickel ions bound to a single monomer complexing agent increased with increase of pH value. During 12 h ultrafiltration process, the decline of membrane flux was less than 10% with PAANa as the complexing agent, while the membrane flux remains the same when PEI was used. The removal rates of Ni2+ kept constant with both complexing agents. Results showed that complexation-ultrafiltration can effectively remove nickel from aqueous solution at appropriate conditions.

Reactions of tetracycline antibiotics with chlorine dioxide and free chlorine.

Tetracyclines (TCs) are a group of widely used antibiotics that have been frequently found in the aquatic environment. The potential reactions of TCs with common water disinfection oxidants such as chlorine dioxide (ClO(2)) and free available chlorine (FAC) have not been studied in depth and are the focus of this study. The oxidation kinetics of tetracycline, oxytetracycline, chlorotetracycline and iso-chlorotetracycline by ClO(2) and FAC are very rapid (with large apparent second-order rate constants k(app) = 2.24 × 10(5)-1.26 × 10(6) M(-1) s(-1) with ClO(2) and k(app) = 1.12 × 10(4)-1.78 × 10(6) M(-1) s(-1) with FAC at pH 7.0) and highly dependent on pH. Species-specific rate constants are obtained by kinetic modeling that incorporates pH-speciation of TCs and the oxidants (for FAC), and reveal that TCs primarily react with ClO(2) and FAC by their unprotonated dimethylamino group and deprotonated phenolic-diketone group. The modest difference in reactivity among the four TCs toward the oxidants is consistent with expectation and can be explained by structural influences on the two reactive moieties. Product evaluation shows that oxidation of TCs by ClO(2) leads to (hydr)oxylation and breakage of TC molecules, while oxidation of TCs by FAC leads to chlorinated and (hydr)oxylated products without any substantial ring breakage. Results of this study indicate that rapid transformation of TCs by oxidants such as ClO(2) and FAC under water and wastewater treatment conditions can be expected.

[Isolation and characterazation of a carbazole-degrading bacterial strain].

A bacterial strain was isolated from soil samples using plate screening techniques. Results indicated this isolated were able to use carbazole as sole source of carbon and energy, simultaneously, including N-Methylcarbazole, 4-Hydroxycarbazole and 2,2'-Biphenol. It was identified as Flavobacterium sp. according to its morphology, and biochemical properties, and 16S rDNA sequence analysis. Utilization of carbazole by the isolates was confirmed by the increase in bacterial biomass and the decrease in substrate concentration in liquid cultures. The optimal pH and temperature for cell growth and carbazole degradation were 7.5 and 30 degrees C, respectively. Resting cells grown in Luria broth also showed activity for decomposing other heterocyclic compounds. In addition, biodegradation of carbazole was carried out with carbazole degrading strain KH-6. The results indicated that 90% of the carbazole could be degraded in the sterilized soil. And strain KH-6 could enhance the degradations of carbazole significantly.

Oxidation of fluoroquinolone antibiotics and structurally related amines by chlorine dioxide: Reaction kinetics, product and pathway evaluation.

Fluoroquinolones (FQs) are a group of widely prescribed antibiotics and have been frequently detected in the aquatic environment. The reaction kinetics and transformation of seven FQs (ciprofloxacin (CIP), enrofloxacin (ENR), norfloxacin (NOR), ofloxacin (OFL), lomefloxacin (LOM), pipemidic acid (PIP) and flumequine (FLU)) and three structurally related amines (1-phenylpiperazine (PP), N-phenylmorpholine (PM) and 4-phenylpiperidine (PD)) toward chlorine dioxide (ClO(2)) were investigated to elucidate the behavior of FQs during ClO(2) disinfection processes. The reaction kinetics are highly pH-dependent, can be well described by a second-order kinetic model incorporating speciation of FQs, and follow the trend of OFL > ENR > CIP âˆ¼ NOR âˆ¼ LOM > > PIP in reactivity. Comparison among FQs and related amines and product characterization indicate that FQs' piperazine ring is the primary reactive center toward ClO(2). ClO(2) likely attacks FQ's piperazinyl N4 atom followed by concerted fragmentation involving piperazinyl N1 atom, leading to dealkylation, hydroxylation and intramolecular ring closure at the piperazine moiety. While FQs with tertiary N4 react faster with ClO(2) than FQs with secondary N4, the overall reactivity of the piperazine moiety also depends strongly on the quinolone ring through electronic effects. The reaction rate constants obtained in clean water matrix can be used to model the decay of CIP by ClO(2) in surface water samples, but overestimate the decay in wastewater samples. Overall, transformation of FQs, particularly for those with tertiary N4 amines, could be expected under typical ClO(2) disinfection conditions. However, the transformation may not eliminate antibacterial activity because of little destruction at the quinolone ring.

[Comparison of the effect of solution environment on humic acid removal behavior with charged and traditional neutral ultrafiltration membranes].

Experiments were performed to evaluate the effect of solution environment (pH value, ionic strength and Ca2+) on humic acid removal and membrane fouling during filtration of humic acid through charge-modified regenerated (RC) ultrafiltration (UF) membrane and traditional unmodified neutral RC UF membrane. Results showed that: (1) the pH value changed the net charge on humic acid molecule and charged membrane through protonation effect, which further influenced the ultrafiltration behavior. When the solution pH value decreased from 7.5 to 3.5, the rejection coefficient of HA decreased from 92% to 79%, and the flux decline increased from 26% to 36% at 4 h filtration time on charged UF membrane; (23) the ionic strength influenced the ultrafiltration behavior through the change of humic acid molecule property and electrostatic shielding effect. In each solution with ionic strength of 0 mmol/L, 3 mmol/L and 100 mmol/L, the rejection coefficient decreased with the value of 92%, 87% and 48% respectively, and the flux decline increased with the value of 26%, 35% and 63% respectively at 4 h filtration time on charged membranes; (3) the effect of Ca2+ concentration on ultrafiltration behavior was due to the complementary effects of electrostatic shielding, Ca2+ bridge and the compact property of the cake layer. (4) the effect of pH value, ionic strength and Ca2+ concentration on the neutral membrane was similar to that on the charged membrane, but in different degrees. Results provide important guidance on the choice of appropriate solution environment when using charged ultrafiltration technology.

[Effect of charged ultrafiltration membrane on natural organic matter removal and membrane fouling].

With the deterioration of water pollution and stringency of water standards, ultrafiltration (UF) has become one of the best alternatives replacing conventional drinking water treatment technologies. However, UF is not very effectively to remove natural organic matter (NOM) due to the comparatively large pore size compared to the size of NOM. Fouling issue is another factor that restricts its widespread application. The rejection coefficient and flux decline during ultrafiltration of humic acid (HA) and raw water through neutral unmodified and negatively charge-modified regenerated cellulose (RC) membranes were investigated, and the analysis for membrane resistance was provided. The initial removal rate for HA is 59% and the flux decline is 32% on neutral unmodified RC membrane with MWCO of 100 x 10(3), while the initial removal rate for HA increases to 92% and the flux decline decreases to 25% on negatively charge-modified RC membrane. Compared to neutral unmodified RC membrane, the removal rate for NOM on negatively charge-modified RC membrane increases 20% and the flux decline decreases 12%. Results indicated that charged UF membrane could be an effective way for better removal of NOM and reduction of the membrane fouling due to the electrostatic interaction with the combination effect of membrane pore size.

[Removal of lead from aqueous solutions by complexation-ultrafiltration with chitosan].

Polyethersulphone (PES) membrane was chosen and chitosan was used as complexing agent to remove lead ions by complexation-ultrafiltration. Effects of solution pH, Pb2+/chitosan ratio, ionic strength and Ca2+ on the rejection coefficient of lead were investigated. The effect of concentration time on lead rejection coefficient and membrane flux was also studied. The value of pH was found to be the key parameter in the process of complexation-ultrafiltration. The rejection coefficient of lead goes high to over 99% at pH 6.0 with the Pb2+/chitosan ratio 0.25. The increase of ionic strength and Ca2+ is not beneficial to the lead removal by complexation-ultrafiltration. The chitosan-metal complex was acidified and then the chitosan was regenerated by diafiltration. The regenerated chitosan was used to remove Pb2+ by complexation-ultrafiltration, and the rejection coefficient of lead was found to be 96.2%, which shows no significant difference with that obtained on the fresh chitosan. Results showed that complexation-ultrafiltration can effectively remove lead from aqueous solutions and chitosan can be effectively regenerated.

Heterotrophic nitrogen removal by a newly isolated Acinetobacter calcoaceticus HNR.

Strain HNR, isolated from a Membrane Bioreactor (MBR), demonstrates a surprising ability to convert ammonium to nitrogen gas under aerobic conditions while growing heterotrophically. On the basis of phylogenetic analysis of the 16S rRNA gene sequence, strain HNR was related to Acinetobacter calcoaceticus (98.9% identity). Nitrogen balance during heterotrophic growth with 120mg/l of NH(4)(+)-N showed that 40.2% of NH(4)(+)-N was in the form of N(2) and 52.1% was found in biomass. Only a trace production was either nitrite or nitrate. Further tests demonstrated that nitrite and nitrate were not reduced by strain HNR under aerobic conditions. Neither nitrate reductase (NR) nor nitrite reductase (NiR) activity was detectable in the aerobic reaction mixtures. However, a 0.051 U activity of hydroxylamine oxidase (HAO) was observed. The nitrogen removal was speculated to be via a hydroxylamine intermediate instead of nitrite, which was different from the conventional nitrogen removal pathway.