Hierarchical stringent response behaviors of activated sludge system to stressed conditions.

The stringent response of activated sludge systems to either stressed or harmful environments is important for the stable operation of activated sludge, which is examined by taking copper ion (Cu2+) as a stress model in this study. When weak stress was employed (Cu2+ ≤ 2.5 mg/L), the N-acyl-homoserine lactones (AHLs) of C6-, C8-, and C10-HSL increased by 30 %, 13 %, and 127 %, respectively, while the redox sensor green (RSG) intensity decreased by 28 %. Encountering the increased stress (2.5 mg/L < Cu2+ ≤ 5 mg/L), bacteria concentration in the supernatant increased by 87 %. However, the respiration rates of autotrophic and heterotrophic bacteria (SOURa and SOURh) and adenosine triphosphate decreased by 52 %, 18 %, and 27 %, respectively, and the flocs disintegrated with a diameter decreasing from 57 to 51 µm. When the stress became more serious (Cu2+ > 5 mg/L), the respiration rates continued to decline, but the quasi-endogenous respiration ratio (Rq/t) increased from 31 % to 47 %. Negligible changes occurred in the endogenous respiration rate (SOURe), adenosine diphosphate, and adenosine monophosphate. Based on these results, a hierarchical stringent response model of the activated sludge system to stressed conditions was proposed, and these responses were evaluated by respirogram. The initial response to weak stress was related to the most sensitive signals of quorum sensing and RSG intensity, well described by the quasi-endogenous respiration rate. The adaptive response to increased stress was the proactive migrations of low- and high-nucleic-acid bacteria to the supernatant, causing the looseness and even disintegration of sludge flocs, well described by SOURa, SOURh, and Rq/t. The lethal response to lethal stress was related to endogenous metabolic processes, well described by SOURe. This work provides new insights into understanding the stringent response of activated sludge systems to some stressed conditions. It helps to regulate the stability of activated sludge systems with respirogram technology.

Cobalt, nickel and iron embedded chitosan microparticles as efficient and reusable catalysts for Heck cross-coupling reactions.

Cobalt, nickel and iron are efficient catalysts for numerous chemical and biological reactions, but they are hardly immobilized on solid matrixes due to their relatively weak chelation with the surface molecules. We have employed a co-electrospraying coupling with glutaraldehyde cross-linking technique to prepare cobalt (Co2+), nickel (Ni2+) and iron (Fe2+) catalyst embedded chitosan microparticles (M@MicroCS) (M = Co, Ni and Fe). The Co@MicroCS beads exhibited excellent catalytic activity for the Heck cross-coupling reactions of aromatic iodides with alkenes. Moreover, the Co@MicroCS bead catalyst could be even reused at least for five times without significant loss of the catalytic activities. The average diameter of the free volume holes for the porous Co@MicroCS beads was determined to be much larger than the size of the reactant and product molecules, allowing them to freely migrate through the catalytic sites inside the chitosan beads. These results clearly indicate that the Heck reactions catalyzed by the Co@MicroCS beads primarily occurs inside the porous chitosan beads. Taken together, we have demonstrated a straightforward approach to prepare efficient and recyclable heterogeneous catalysts derived from the first-row transition metal catalysts by entrapping them inside the chitosan microparticles.

Removal of heavy metal chromium using cross-linked chitosan composite nanofiber mats.

Uniform chitosan composite nanofiber mats (CS/PAAS) containing 4.0 wt% polyacrylic acid sodium loading have been prepared by electrospinning, followed by annealing at elevated temperature to improve solvent resistance and mechanical strength. The CS/PAAS nanofiber mats have been characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and tensile strength analysis. The prepared nanofiber mats have been shown to be much better than the pristine chitosan powder to adsorb the chromium (VI) ion. SEM-Energy dispersive X-ray spectroscopic (SEM-EDS) and positron annihilation lifetime spectroscopic (PALS) analysis show that Cr(VI) ion can freely permeate into the composite nanofiber and coordinate with the internal chitosan chain molecules. The adsorption abilities of these cross-linked CS/PAAS nanofiber mats are dependent on the chitosan contents as well as N-atom basicity of the chitosan chain. The adsorption capacity toward Cr(VI) ion was improved to 78.92 mg/g after modification of the chelating ligands for the cross-linked CS/PAAS composite nanofibers.

[Preparation and performance characterization of pseudo-ginseng entrapped in crosslinked chitosan/polyacrylic acid/poly(ethylene oxide) nanofibrous membrane].

OBJECTIVE: To prepare the cross-linked chitosan/poly(acrylic acid)/poly (ethylene oxide) nanofibrous membrance loaded with pseudo-ginseng and to determine its characteristics. METHODS: Pseudo-ginseng entrapped in chitosan, poly (acrylic acid), poly (ethylene oxide) nanofibrous membrane loaded with pseudo-ginseng was prepared by electrospinning and thermal treatment method. The surface morphology of fiber membrane was observed by scanning electron microscopy and the chemical structures were characterized by infrared spectroscopy; the thermal decomposition temperature was analyzed by the thermogravimetric analysis. UV-Vis spectra were used to evaluate the in vitro release properties. RESULTS: The average diameter of the prepared nanofibrous particles was (181 ± 71) nm. The tensile strength of fiber membrane increased by 35.3% and the decomposition temperature increased from 197℃ to 208℃ after crosslinking. Compared with casting film, the structure of fiber membrane increased the release rate and the overall amount of active components from pseudo-ginseng. CONCLUSION: The preparation of chitosan fiber loaded with pseudo-ginseng is simple and the dispersion of pseudo-ginseng is homogeneous. This fibrous pseudo-ginseng exhibited good release performance, providing a new Chinese medicine formulation.

Palladium-catalyzed reductive homocoupling of aromatic halides and oxidation of alcohols.

Palladium-catalyzed reductive homocoupling of aromatic halides can be performed in alcohol solutions without any auxiliary reducing reagents. Pd(dppf)Cl(2) [dppf = 1,1'-bis(diphenylphosphino)ferrocene] has been shown as the most effective catalyst among the palladium catalysts screened for the model reductive homocoupling of iodobenzene in alcoholic solutions. The reduction of iodobenzene is stoichiometrically coupled with the oxidation of solvent alcohol (3-pentanol). The X-ray photoelectron spectroscopic (XPS) studies clearly indicate that the oxidation of solvent alcohol molecules is involved with the in situ regeneration of the reductive Pd(0)(dppf) active species, indicating that the solvent alcohol also reacts as a reducing reagent for the reductive homocoupling of aromatic halides. Elimination of the external reducing reagents will simplify the product separation and purification. Base is essential for the success of the Pd(dppf)Cl(2)-catalyzed redox reaction as 2 molar equiv of base is needed to neutralize the acid byproduct formed. Biaryls are the predominant products for the Pd(dppf)Cl(2)-catalyzed reductions of the unsubstituted aromatic halides in 3-pentanol solution, whereas the dehalogenation products are predominant for the Pd(dppf)Cl(2)-catalyzed reductions of the substituted aromatic halides. The reaction mechanisms have been discussed for the palladium-mediated concomitant reduction of aromatic halides and oxidation of alcohols without any auxiliary reductants and oxidants.