A study on performance characteristics of granular-media trickling filters

Mass transfer within microbial films is described using Monod type biological kinetics in terms of the properties of packing material and the feed solution. For this purpose computer techniques have been first developed for the numerical evaluation of the normalized biofilm mathematical model. A second-order partial differential equation describing the mechanism of dispersion phenomena inside the liquid layer is then solved to determine the mass transfer coefficient. The application of the theory to experimental data reported in literature has also been demonstrated using the values of mass transfer coefficients and the computer programs developed.     

A Sunscreen-Based Photocage for Carbonyl Groups

Photolabile protecting groups (PPGs) have been exploited in a wide range of chemical and biological applications, due to their ability to provide spatial and temporal control over light-triggered activation. In this work, we explore the concept of a new photocage compound based on the commercial UVA/UVB filter oxybenzone (OB; 2-hydroxy-4-methoxybenzophenone) for photoprotection and controlled release of carbonyl groups. The point here is that oxybenzone not only acts as a mere PPG, but also provides, once released, UV photoprotection to the carbonyl derivative. This design points to a possible therapeutic approach to reduce the severe photoadverse effects of drugs containing a carbonyl chromophore.     

Success and failure of colloidal approaches in adhesion of microorganisms to surfaces

Biofilms are communities of cells attached to surfaces, their contributions to biological process may be either a benefit or a threat depending on the microorganism involved and on the type of substrate and environment. Biofilm formation is a complex series of steps; due to the size of microorganisms, the initial phase of biofilm formation, the bacterial adhesion to the surface, has been studied and modeled using theories developed in colloidal science. In this review the application of approaches such as Derjaguin, Landau, Verwey, Overbeek (DLVO) theory and its extended version (xDLVO), to bacterial adhesion is described along with the suitability and applicability of such approaches to the investigation of the interface phenomena regulating cells adhesion. A further refinement of the xDLVO theory encompassing the brush model is also discussed. Finally, the evidences of phenomena neglected in colloidal approaches, such as surface heterogeneity and fluid flow, likely to be the source of failure are defined.     

The role of conditioning film formation and surface chemical changes on Xylella fastidiosa adhesion and biofilm evolution

Biofilms are complex microbial communities with important biological functions including enhanced resistance against external factors like antimicrobial agents. The formation of a biofilm is known to be strongly dependent on substrate properties including hydrophobicity/hydrophilicity, structure, and roughness. The adsorption of (macro)molecules on the substrate, also known as conditioning film, changes the physicochemical properties of the surface and affects the bacterial adhesion. In this study, we investigate the physicochemical changes caused by Periwinkle wilt (PW) culture medium conditioning film formation on different surfaces (glass and silicon) and their effect on X. fastidiosa biofilm formation. Contact angle measurements have shown that the film formation decreases the surface hydrophilicity degree of both glass and silicon after few hours. Atomic force microscopy (AFM) images show the glass surface roughness is drastically reduced with conditioning film formation. First-layer X. fastidiosa biofilm on glass was observed in the AFM liquid cell after a period of time similar to that determined for the hydrophilicity changes. In addition, attenuation total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy supports the AFM observation, since the PW absorption spectra increases with time showing a stronger contribution from the phosphate groups. Although hydrophobic and rough surfaces are commonly considered to increase bacteria cell attachment, our results suggest that these properties are not as important as the surface functional groups resulting from PW conditioning film formation for X. fastidiosa adhesion and biofilm development.     

Comparative study of pretreatment methods for the determination of metals in atmospheric aerosol by electrothermal atomic absorption spectrometry

A comparative study of pretreatment methods for the determination of 10 elements (As, Cd, Pb, V, Ni, Mn, Cr, Cu, Fe, Al) in atmospheric aerosols by electrothermal atomic absorption spectrometry (ETAAS) was conducted. For the digestion of the particulates collected in filters, six methods were compared using a mixture of HNO₃ and HF with or without the addition of various oxidative agents (HClO₄ or H₂O₂) or acids (HCl). The comparative study was performed using loaded cellulose filter samples, which were digested in Parr bombs and heated in a conventional oven at 170 °C for 5 h. The extraction efficiency and blanks were compared and it was proved that the digestion method using only HNO₃–HF extracted most of the metals and gave the lowest blanks. The HNO₃–HF mixture was selected for the development of an improved microwave digestion method specific for aerosol-loaded filters. The operating parameters were optimized, so that quantitative recovery of the reference materials NIST 1649a urban dust and NIST 1648 urban particulate matter was achieved. The blank of cellulose and teflon filters were also determined and compared. Teflon filters present the lowest blanks for all the elements. The obtained limits of detection for each type of filters were adequate for environmental monitoring purposes. ETAAS instrumental operation was also optimized for the compensation and the elimination of interferences. The temperature optimization was performed for each metal in every type of filter and optimized parameters are proposed for 10 elements.     

生物膜电极在以苯酚为燃料的微生物燃料电池中的应用

以苯酚为燃料, 生物膜电极为负极, Ti/SnO₂-Sb₂O₅/PbO₂电极为正极, 构建了双室微生物燃料电池. 利用微电流驯化法和自然驯化法分别制备了生物膜电极, 研究了微生物的挂膜方法、 挂膜时间和负极基底材料种类对微生物燃料电池产电能力的影响. 结果表明, 微电流驯化法优于自然驯化法, 微电流驯化法制备的生物膜电极更利于电池的产电; 微生物的挂膜时间为8 d时, 电池的产电能力最高, 其最大输出功率密度达到39 mW/m²; 不同基底材料生物膜电极所组建的微生物燃料电池产电能力高低顺序为碳毡>石墨>钛网>泡沫钛.     

A comparison of some electronic filters for use in noise suppression circuitry of HPLC detectors

Summary Four electronic filters suitable for baseline noise suppression in HPLC detectors were compared for their response and peak distortion characteristics under conventional HPLC conditions. The filters were designed to be white noise equivalent and the types of filter used were lag, lag-lag, critically damped lag and chain, these being representative of common, simple filter configurations. These filters were evaluated for speed of response to an optical step input signal and also for the effects of their level of noise suppression on peak height, retention time, peak asymmetry and apparent column efficiency. The critically damped lag filter was superior to the other filters in almost all respects and its use considerably enhanced detector performance.     

Solid ink-printed filter paper as a green adsorbent material for the solid-phase extraction of UV filters from water samples

This work describes the development of a new green solid-phase extraction approach, which is based on the use of low-cost extraction discs composed of plain filter papers that are covered with a synthetic wax-like coating. The filter papers are printed in a commercial solid ink printer, which dispenses a synthetic wax-like ink on the surface of the paper, to cover the hydrophilic cellulose fibre matrix with an interface of lipophilic domains where non-polar analytes can partition through hydrophobic interactions. The modified paper filters were used to extract hydrophobic organic compounds from water samples following the customary procedure of solid-phase extraction without sorbent preconditioning and needless of high-vacuum sources. As a proof-of-concept application, a series of non-polar organic UV filters were used as model analytes to optimise the extraction parameters and evaluate the performance of the method in spiked water samples. Based on this principle, a new sample preparation platform with low environmental footprint has been developed that enables extraction to be carried out using low-cost, environmental benign and non-toxic conventional materials. The advantages and disadvantages of the method, alongside with its future prospects towards the development of custom-made ‘printed extraction kits’, are envisioned and discussed.     

Solving nonlinear reaction–diffusion problem in electrostatic interaction with reaction-generated pH change on the kinetics of immobilized enzyme systems using Taylor series method

A mathematical model of electrostatic interaction with reaction-generated pH change on the kinetics of immobilized enzyme is discussed. The model involves the coupled system of non-linear reaction–diffusion equations of substrate and hydrogen ion. The non-linear term in this model is related to the Michaelis–Menten reaction of the substrate and non-Michaelis–Menten kinetics of hydrogen ion. The approximate analytical expression of concentration of substrate and hydrogen ion has been derived by solving the non-linear reactions using Taylor’s series method. Reaction rate and effectiveness factor are also reported. A comparison between the analytical approximation and numerical solution is also presented. The effects of external mass transfer coefficient and the electrostatic potential on the overall reaction rate were also discussed.

     

微生物燃料电池中生物膜成长对电池电化学性能的影响

以大肠杆菌为接种体,葡萄糖为基质,在1 000 Ω恒外阻下生成电活性生物膜,研究了生物膜的形成对电池电化学行为的影响。应用循环伏安、阻抗测试、极化分析、输出功率和阳极电势来考察其电化学表现。研究结果表明,随着生物膜完全成熟,阳极极化电阻减小66.5%,阳极电势逐渐降低,最大输出功率密度增加260%。     

Investigations on the Angle-Dependent Dip Coating Technique (ADDC) for the Production of Optical Filters

Angle-dependent dip coating (ADDC) is a modified dip coating technique that offers advantages for the production of optical interference filters. In contrast to conventional dip coating (DC), the substrate is withdrawn from the coating solution under an angle of inclination. Thereby, the two surfaces of the substrate are coated with individual film thicknesses. An experimental setup for ADDC has been built and the decisive process influences on coating thicknesses have been evaluated. In order to gain full control over the individual layer thicknesses, reaching from 20 nm to 160 nm, it is necessary to vary the following process parameters: lifting speed, angle of inclination and concentration of the dipping solution. The results of coating experiments prove the advantages of ADDC over DC. A first example aims at reducing the number of coating steps: an ADDC long pass filter produced in 10 coating steps reaches the same optical performance as a conventional DC filter made in 16 steps. A second example demonstrates the possibility to improve quality: a commercial DC beam splitter can be improved with respect to the flatness of transmission and reflection curves when being produced in 4 steps by ADDC instead of 8 steps by DC. Furthermore, ADDC offers the possibility to fabricate even narrow band pass filters, which are naturally difficult to obtain by conventional DC.     

Evidence of Substrate Melting of NiCr Particles on Stainless Steel Substrate by Experimental Observation and Simulations

Single NiCr splats were plasma-sprayed onto a polished stainless steel substrate held at room temperature. The splat-substrate interface was characterized by focused ion beam and transmission electron microscopy. The frequent observation of NiO particles, particularly in pores within the splat, and at the periphery of splat, suggests that the principal oxidation process occurs at the substrate surface, where the splats are exposed to a water vapor-rich environment. It was also observed that the splat adhered well in some locations where elemental-diffusion and jetting of the substrate occurred, suggestive of substrate melting. A three-dimensional numerical model was developed to simulate the impact of a splat onto a substrate. The simulation shows that the observation of the central pore in the splat and the phenomenon of substrate melting may occur. Based on these results, the effect of water release on oxide formation and splat morphology can be explained.     

Real-time monitoring of induced adaptation of redox active Escherichia coli biofilm by EQCM-controlled extracellular redox environment

In this paper we report the anaerobic Escherichia coli biofilm formation on solid substrate under redox-controlled extracellular environment by an electrochemical quartz crystal microbalance (EQCM) method. Both biomass and electrochemical activity were monitored in situ. Larger biomass was yielded under redox-controlled condition comparing with natural biofilm growth, which was also confirmed by optical observation. Surface-colonizing cells responded more sensitively to their redox environment than planktonic cells. Cyclic voltammogram (CV) obtained during the time course of biofilm development indicates the emergence of redox active phenotype under redox-controlled condition but not in natural condition. Our results suggest an effective means to control biofilm development with desired metabolic adaptation and also to in situ monitor the biomass yield and the emergent catalytic property simultaneously.     

Biofilm inhibition and antimicrobial action of lipopeptide biosurfactant produced by heavy metal tolerant strain Bacillus cereus NK1

Biosurfactants are worthful microbial amphiphilic molecules with efficient surface-active and biological properties applicable to several industries and processes. Among them lipopeptides represent a class of microbial surfactants with increasing scientific, therapeutic and biotechnological interests. A heavy metal tolerant Bacillus strain has been isolated and the biofilm inhibition and antimicrobial activity of biosurfactant produced by the strain have been studied. Biosurfactant production was confirmed by the conventional screening methods including hemolytic activity, drop collapsing test, oil displacement test, emulsification and lipase production assays. The biosurfactant produced by this strain was a lipopeptide and exhibited strong surface activity. The biosurfactant has been characterized using FTIR, TLC and HPLC. The minimum active dose of this biosurfactant when compared with the other chemical surfactants was found as 0.150±0.06 μg. The critical micelle concentration was found to be 45 mg/l. The biosurfactant was found to be stable and active over a wide range of pH, temperature and NaCl concentration. It was also able to emulsify a wide range of hydrocarbons and oils thereby extending its application for the bioremediation of oil contaminated sites. The biosurfactant exhibited significant reduction in biofilm formation by pathogens and showed potent antimicrobial activity against various gram positive, gram negative bacteria and fungi. Agar diffusion assay for heavy metal resistance showed that the isolate was resistant to ferrous, lead and zinc. Considering the biofilm inhibition and antimicrobial property of biosurfactant, it can be utilized as a potential therapeutic molecule for numerous microbial infections. The heavy metal resistance of the strain can also be harnessed as an invaluable biological tool for in situ bioremediation.     

Recurrent neural network based hybrid model for reconstructing gene regulatory network

One of the exciting problems in systems biology research is to decipher how genome controls the development of complex biological system. The gene regulatory networks (GRNs) help in the identification of regulatory interactions between genes and offer fruitful information related to functional role of individual gene in a cellular system. Discovering GRNs lead to a wide range of applications, including identification of disease related pathways providing novel tentative drug targets, helps to predict disease response, and also assists in diagnosing various diseases including cancer. Reconstruction of GRNs from available biological data is still an open problem. This paper proposes a recurrent neural network (RNN) based model of GRN, hybridized with generalized extended Kalman filter for weight update in backpropagation through time training algorithm. The RNN is a complex neural network that gives a better settlement between biological closeness and mathematical flexibility to model GRN; and is also able to capture complex, non-linear and dynamic relationships among variables. Gene expression data are inherently noisy and Kalman filter performs well for estimation problem even in noisy data. Hence, we applied non-linear version of Kalman filter, known as generalized extended Kalman filter, for weight update during RNN training. The developed model has been tested on four benchmark networks such as DNA SOS repair network, IRMA network, and two synthetic networks from DREAM Challenge. We performed a comparison of our results with other state-of-the-art techniques which shows superiority of our proposed model. Further, 5% Gaussian noise has been induced in the dataset and result of the proposed model shows negligible effect of noise on results, demonstrating the noise tolerance capability of the model.     

Nonlinear deformation of a ferrofluid droplet in a uniform magnetic field

This paper reports experimental and numerical results of the deformation of a ferrofluid droplet on a superhydrophobic surface under the effect of a uniform magnetic field. A water-based ferrofluid droplet surrounded by immiscible mineral oil was stretched by a magnetic field parallel to the substrate surface. The results show that an increasing flux density increases the droplet width and decreases the droplet height. A numerical model was established to study the equilibrium shape of the ferrofluid droplet. The governing equations for physical fields, including the magnetic field, are solved by the finite volume method. The interface between the two immiscible liquids was tracked by the level-set method. Nonlinear magnetization was implemented in the model. Comparison between experimental and numerical results shows that the numerical model can predict well the nonlinear deformation of a ferrofluid droplet in a uniform magnetic field.     

Precise and Sensitive Water Soluble Ion Extraction Method for Aerosol Samples Collected on Polytetrafluoroethylene Filters

Abstract

The widely used aerosol collection filters composed of polytetrafluoroethylene (Teflon) present a problem in the extraction of water soluble ions from the collection surface due to the hydrophobic nature of the Teflon. A method is presented for the extraction and analysis of water soluble ions from Teflon aerosol filters which is efficient and sensitive. This method uses a direct application of ethanol to the filter surface to decrease the surface tension of the filter and allow a dilute HC10, solution to contact the collection surface and extract any water soluble ions. This study compares this extraction method with other extraction methods currently being used. The results obtained from the extraction of water soluble ions from the Teflon filters were also compared to the results obtained from quartz filters collected on a colocated high volume sampler. From these studies, it is concluded that the hydrophobic nature of the Teflon filters makes the complete dissolution of water soluble ions exceptionally difficult and that the prewetting of the Teflon filters with ethanol minimizes dissolution and extraction problems.     

Kinetics of batch production of single-cell protein from cheese whey

A kinetic model for single-cell protein batch fermentation was developed using the numerical simultaneous integration approach of the fourth-order Runge-Kutta method. The model takes into account the effect of substrate inhibtion, maintenance energy, and cell death on the cell growth and substrate utilization during the fermentation process. The theoretical results obtained from the model compared well with the experimental data. The model was used to study the effect of the initial substrate concentration on the lag period, fermentation time, specific growth rate, population size, and cell productivity of batch fermentation. Increasing the initial substrate concentration increased the lag period and fermentation time and decreased the specific growth rate and cell yield. The growth limiting substrate concentration was 2.9 g/L, whereas the growth inhibiting substrate concentration was 69.0 g/L. Increasing the initial substrate concentration above 150 g/L significantly decreased the yeast population size.     

Influence of Different Redox Conditions on the Biodegradation of the Pesticide Metabolites Phenol and Chlorophenols

Abstract

The fate and behaviour of phenol and monochlorophenols during bankfiltration and underground passage with variable redox conditions were investigated. A model ecosystem was used consisting in laboratory filter columns filled with natural underground material and operated with natural aerobic and anaerobic groundwater to create different redox situations.

The test substances (phenol, 2-chlorophenol, 3-chlorophenol, 4-chlorophenol) were added continuously to the infiltrating water and their concentration in the filter effluents determined. Beside the redox conditions other factors known to affect microbial degradation processes like the substrate concentration and the underground material were varied stepwise.

Phenol was degraded under both, aerobic and anaerobic conditions. The presence of oxygen is more favourable to degradation; no lag phase was observed under aerobic conditions. In a sulfate reducing environment, phenol could only be degraded after microbial adaptation. The length of the lag phase was strongly influenced by the substrate concentration and the undergroundmaterial. Prior contact with phenol resulted in a shorter lag phase.

Monochlorophenols behaved almost persistent in the model system. Degradation could only be observed in a test filter that provided a more active microbial population due to prior adaptation to phenol and a more favourable underground material.     

A silicon sensor for measurement of liquid flow and thickness of fouling biofilms

A silicon sensor for the measurement of the flow velocity and thickness of a flouling biofilm was designed and fabricated. Using micro-machining in silicon, small and thermally-insulated sensor areas could be constructed. A physical model was worked out showing that with a double-chip method, both flow velocity and biofilm thickness can be measured. Experiments showed that this method gave a smaller accuracy in thickness measurements compared to a single-chip method at constant flow velocity. The accuracy in thickness measurement was ±0.5 for the single-chip method at ±3.5 μm for the double-chip method. The accuracy in flow velocity measurement decreased at increased film thickness, from about ±10% of the measured value at zero film thickness to about ±30% of the measured value at 20μm film thickness. A pilot experiment studying biofilm development in sea water over a period of 48 days is also presented.