Characteristics of Membrane Fouling in an Anaerobic-(Anoxic/Oxic)~n-MBR Process

The characteristics of membrane fouling and cleaning, in a hybrid MBR process, was investigated. Under the condition of sub-critical flux operation, a characteristic three-stage trans-membrane pressure （TMP） profile is observed as time passes. The initially extended period of slow pressure rise, followed by a somewhat faster rise, is then sup- planted by a sudden transition to rapid pressure rise. Membrane cleaning experiments and SEM examination make it apparent that the rapid TMP rise is mainly caused by the accumulation of a surface cake layer, which is a reversible fouling that can be removed by tap water washing. Fouling caused by a gel layer, which is an irreversible fouling, can be removed efficiently by chemical cleaning. NaC10 can oxidize the gel layer, which is formed mainly of macromo-lecular organic substances. The HC1 can remove inorganic particles formed by Ca^2＋, Mg^2＋ ions etc. The sequence of chemicals used in membrane cleaning has an influence on the cleaning result. The effect of the NaC1O＋HC1 cleaning procedure is superior to that of the HCI＋NaC1O one. Particle size distribution measurements （PSD） reveal that fine particles are inclined to deposit or attach on the membrane surface, or in the membrane pores, and caused rapid fouling.

Start-up and contaminants removal characteristics of aerobic granules-membrane bioreactor at low temperature

In order to understand the effect of low temperature on the formation process of aerobic granules and contaminants removal characteristics,the aerobic granules-membrane bioreactor (AGS-MBR) has been started up and operated at low temperature using the carbon resource of sodium acetate. Aerobic granules cultivated in AGS-MBR possess smooth surface and compact structure in morphology as well as better settling property and higher biomass after 38 days. The average parameters of aerobic granules are: diameter 3. 1 mm,wet density 1. 041 g/mL,sludge volume index 42. 35 mL/g and settling velocity 20. 6 - 45. 2 cm/min. During the start-up of AGS-MBR,the respectively average contaminants removal efficiencies at low temperature are 91. 9% for chemical oxygen demand (COD) ,89. 2% for NH4 + -N and 86. 3% for PO43- -P,and the overgrowth of filamentous bacteria has been well controlled. In addition,the hollow fiber microfiltration (MF) membrane fouling is light and the regime membrane layer is capable of enhancing membrane filtration as well as the average growth of trans-membrane pressure (TMP) is 1. 07 kPa/d. Compared with the conventional cultivation of aerobic granules,the sludge granulation time significantly decreases from 73 days to 38 days by the application of microfiltration membrane at low temperature.

Trans-membrane controlling of an amphiphilic metalloporphyrin

In order to perform a transfer process of the porphyrin moiety across membrane media, an amphiphilic porphyrin 5,10,15-tri(4-hydroxyphenyl)-20-(4-hexadecyloxy-phenyl) porphyrin (P1) and its metalloporphyrin (P1Zn) were selected to be solubilized in cetyltrimethyl ammonium bromide (CTAB) micellar solutions. By taking advantage of the microenvironment sensitivity of their Soret band, UV-Vis spectra were used to study the dependence of location of the porphyrins in CTAB micellar media on the bulk pH value or the salt concentration of bulk solutions. The red shift of the Soret band, the decrease of its absorbance and the increase of the full width at half-maximum (FWHM) of P1Zn and P1 with pH titration process from neutral to weak basicity were attributed to the transfer process of the porphyrin moiety from the inner core to the outer surface of the micelles. In the pH sensitive area of the Soret band of P1Zn and P1, the blue shift of the Soret band, the increase of its absorbance and decrease of FWHM

A NEW MODEL AND IMPROVED CABLE FUNCTION FOR REPRESENTING THE ACTIVATING PERIPHERAL NERVES BY A TRANSVERSE ELECTRIC FIELD DURING MAGNETIC STIMULATION

Objective Previous studies of peripheral nerves activation during magnetic stimulation have focused almost exclusively on the cause of high external parallel electric field along the nerves, whereas the effect of the transverse component has been ignored. In the present paper, the classical cable function is modified to represent the excitation of peripheral nerves stimulated by a transverse electric field during magnetic stimulation. Methods Responses of the Ranvier nodes to a transverse-field are thoroughly investigated by mathematic simulation. Results The simulation demonstrates that the excitation results from the net inward current driven by an external field. Based on a two-stage process, a novel model is introduced to describe peripheral nerves stimulated by a transverse-field. Based on the new model, the classical cable function is modified. Conclusion Using this modified cable equation, the excitation threshold of peripheral nerves in a transverse field during MS is obtained. The modified cable equation can be used to represent the response of peripheral nerves by an arbitrary electric field.

Description of a Putative Oligosaccharyl:S-Layer Protein Transferase from the Tyrosine <i>O</i>-Glycosylation System of <i>Paenibacillus alvei</i>CCM 2051^T

Surface (S)-layer proteins are model systems for studying protein glycosylation in bacteria and simultaneously hold promises for the design of novel, glyco-functionalized modules for nanobiotechnology due to their 2D self-assembly capability. Understanding the mechanism governing S-layer glycan biosynthesis in the Gram-positive bacterium Paenibacillus alvei CCM 2051T is necessary for the tailored glyco-functionalization of its S-layer. Here, the putative oligosaccharyl:S-layer protein transferase WsfB from the P. alvei S-layer glycosylation gene locus is characterized. The enzyme is proposed to catalyze the final step of the glycosylation pathway, transferring the elongated S-layer glycan onto distinct tyrosine O-glycosylation sites. Genetic knock-out of WsfB is shown to abolish glycosylation of the S-layer protein SpaA but not that of other glycoproteins present in P. alvei CCM 2051T, confining its role to the S-layer glycosylation pathway. A transmembrane topology model of the 781-amino acid WsfB protein is inferred from activity measurements of green fluorescent protein and phosphatase A fused to defined truncations of WsfB. This model shows an overall number of 13 membrane spanning helices with the Wzy_C domain characteristic of O-oligosaccharyl:protein transferases (O-OTases) located in a central extra-cytoplasmic loop, which both compares well to the topology of OTases from Gram-negative bacteria. Mutations in the Wzy C motif resulted in loss of WsfB function evidenced in reconstitution experiments in P. alvei ΔWsfB cells. Attempts to use WsfB for transferring heterologous oligosaccharides to its native S-layer target protein in Escherichia coli CWG702 and Salmonella enterica SL3749, which should provide lipid-linked oligosaccharide substrates mimicking to some extent those of the natural host, were not successful, possibly due to the stringent function of WsfB. Concluding, WsfB has all features of a bacterial O-OTase, making it the most probable candidate for the oligosaccharyl:S-layer protein transferase of P. alvei, and a promising candidate for the first O-OTase reported in Gram-positives.

Fouling mechanisms in the early stage of an enhanced coagulation-ultrafiltration process

We investigated the fouling performances of ultrafiltration （UF） membrane for treating in-line coagulated water in an enhanced coagulation-UF hybrid process. Then we analyzed the fouling mechanisms in the early stage of UF using mathematical models and microscopy observation methods. Finally, we discussed the impact of aeration on membrane fouling in this paper. The results showed that a two-stage of trans-membrane pressure （-TMP） profile during the operation of enhanced coagulation-UF membrane was observed, and the relationship between permeability and operation time fitted well with a logarithmic curve. Membrane pores blocking and cake filtration were confirmed as main membrane fouling mechanisms using the mathematical models. The two stages of membrane fouling mechanisms were further deduced, namely, the membrane pore narrowing followed by the formation of cake layer. Membrane autopsy analysis using scanning electron microscopy （SEM） images of the membrane surface sampled from different filtration cycles also confirmed the mechanisms of pores blocking and cake filtration. Moreover, according to the variations of the permeability and membrane fouling resistance, aeration was able to mitigate and control the membrane fouling to a certain extent, but the optimization of aeration conditions still needs to be studied.

Relationship between sludge settleability and membrane fouling in a membrane bioreactor

The evolution of activated sludge settleability and its relationship to membrane fouling in a submerged mem-brane bioreactor were studied at a lab-scale equipment fed with synthetic wastewater.It was found that sludge volume index(SVI)gradually increased and the sludge settleability was reduced,which was caused by the propagation of filamentous bacteria.With increasing SVI,the average increasing rate of trans-membrane pressure increased,the stable filtration period was shortened,and the two stages(smooth stage and accelerating stage)of the trans-membrane pressure were more obvious.At the same time,the increasing rate of trans-membrane pressure at the smooth stage decreased and the rate at the accelerating stage increased with SVI,respectively.The observation by using scanning electronic microscopes showed the cake layer with loose structure and large thickness formed on the membrane surface due to the appearance of filamentous bacteria and high SVI in sludge.Influence of the sludge settleability on the trans-membrane pressure was related to the structure and thickness of the cake layer on the membrane.

Selective pseudosolubilization capability of Pseudomonas sp. DG17 on n-alkanes and uptake mechanisms analysis

Pseudosolubilized ability of Pseudomonas sp. DG17 on n-alkanes, role of biosurfactants in n-octadecane uptake and trans-membrane transport mechanism of n- octadecane were studied by analyzing amount of pseudo- solubilized oil components in water phase, and the fraction of radiolabeled ~4C n-octadecane in the broth and cell pellet. GC-MS results showed that pseudosolubilized oil components were mainly C12 to C28 of n-alkanes. In n- octadecane broth, pseudosolubilized n-octadecane could be accumulated as long as faster than mineralization maximum concentration of cane achieved to 45.37 mg. L pseudosolubilized rate was rate of substrate, and the pseudosolubilized n-octade- 1. All of these results showed that Pseudomonas sp. DG17 mainly utilized alkanes by directly contacting with pseudosolubilized small oil droplets in the water phase. Analysis of 14C amount in cell pellet revealed that an energy-dependent system mainly controlled the trans-membrane transport of n- octadecane.

Construction of a Caco-2/EAhy926 cell tandem compound model and its application in mechanism study of nanoparticle transcytosis

Based on the physiological structure of the intestine, a Caco-2/EAhy926 tandem compound model was constructed in order to simulate the intestinal-vascular barrier. This model was applied in the study of transcytosis of nanoparticles, and it was compared with the traditional intestinal cell model in the whole study. Briefly, Fe3O4 nanoparticles with a size about 30 nm were used as model nanoparticles, which remained steady during transcytosis. The nanoparticles hardly had cytotoxicity to Caco-2 cells and EAhy926 cells within the incubation concentrations. The cell tandem model was established by connecting upper Caco-2 monolayer and lower EAhy926 monolayer. Based on the FD4 permeability or TEER, all cell models remained integrity within certain period of culture time. The expression of Claudin-4 or VE Cadherin demonstrated the presence of tight junctions. The intact morphology of microfilament F-actin indicated the favorable intracellular connection. It was found that the two-layer cell tandem model created a bigger barrier for the transcytosis of FD4 than Caco-2 and EAhy926 monolayer models, and the translocation of Fe3O4 nanoparticles showed a similar pattern. Interestingly, we found that the main barrier of tandem model for nanoparticles was caused by the upper Caco-2 cell monolayer, while the lower layer of EAhy926 monolayer remained high permeability. Generally, the cell tandem compound model established here enabled us to evaluate the impact of both intestinal epithelial and endothelial layer on transcytosis, and it might provide a novel approach to study bio-nano interaction in the intestine.