A simulation on PSB biofilm formation with considering cell inactivation

A differential-discrete mathematical model is developed to predict the photosynthetic bacteria (PSB) Rhodopseudomonas palustris CQK 01 biofilm formation. In this model, with the consideration of the light decay in the photobioreactor, PSB inactivation and cellular automata (CA) rules along with the previously obtained growth kinetics parameters of PSB are used to simulate biofilm growth. With this model, the effects of illumination intensity, pH value and initial inoculation on the biofilm morphology, active cell biomass as well as some characteristic parameters such as porosity, roughness and thickness is investigated. Numerical results show that cell inactivation occurs within the biofilm and the biofilm morphology varies with the operating conditions. Moreover, the roughness and thickness increase, but the porosity decreases as the biofilm grows. The amount of active cells is increasing with time. It is also found that the optimal conditions for PSB biofilm formation are the illumination intensity of 6000 lx, the initial inoculation of 60 and the substrate solution pH value of 7.0.     

Photo-hydrogen production rate of a PVA-boric acid gel granule containing immobilized photosynthetic bacteria cells

The polyvinyl alcohol (PVA)-boric acid gel granule facilitates the light penetration and mass transport as it has the features of the transparency and adequate porous structure. In this work, a hydrogen production bioreactor with the indigenous photosynthetic bacteria (PSB) Rhodopseudomonas palustris CQK 01 immobilized in a PVA-boric acid gel granule is developed to enhance the rate of photo-hydrogen production. Particular attention is paid to exploring the effects of illumination wavelength and intensity, as well as the effects of concentration, flow rate, pH, and temperature of influent substrate solution on the hydrogen production rate. The immobilized PSB gel granule exhibited the maximum hydrogen production rate of 3.6 mmol/g cell dry weight/h in all tests. The experimental results show that the hydrogen production rate of an immobilized PSB granule illuminated at 590 nm is distinctly higher than that at 470 and 630 nm. Photo-inhibition of the gel granule occurs as the long-wavelength illumination intensity exceeds 7000 lux. In addition, there exists an optimal pH of 7.0 and temperature of 30 °C for PSB immobilized in the granule to produce hydrogen. More importantly, the feasibility of PSB immobilized in the PVA-boric acid gel granule for the enhancement of the photo-hydrogen production is demonstrated.     

Effect of culture conditions on the kinetics of hydrogen production by photosynthetic bacteria in batch culture

Biochemical kinetic characteristics of photo-fermentative hydrogen production were experimentally and numerically investigated to optimize the photo-fermentation hydrogen-producing process in this work. It is found that a maximum specific growth rate of 0.26 h⁻¹ was achieved under the optimal conditions of illumination intensity 6000 lux, 30 °C culture temperature and pH 7.0 of culture medium. These experimental results also led to an empirical formula of the maximum specific microbial growth rate (μ_max) as a function of illumination intensity, pH and temperature. With the empirical formula, the modified Monod equation along with the kinetic equations for biomass growth, glucose consumption and hydrogen production is then developed to simulate the photofermentation hydrogen-producing process. The modeling results are in good agreements with the experimental data, indicating that the developed kinetic models are able to objectively describe the characteristics of hydrogen production by PSB under different culture conditions.     

Bubble behavior and photo-hydrogen production performance of photosynthetic bacteria in microchannel photobioreactor

A transparent microchannel photobioreactor was manufactured to visualize the colony formation of photosynthetic bacteria (PSB), Rhodopseudomonas palustris CQK 01, as well as the biogas bubble behavior within the microstructure. The results showed that the formation of PSB colony in the interior of microchannels can be divided into four stages: bacteria absorption, bacteria reproduction, morphological transformation and colony formation. It was founded that the microchannel vents immobilized by PSB colony was the favorable sites for the emergence of biogas bubbles. In this work, the effects of substrate concentration and flow rate of the influent solution as well as illumination wavelength and intensity on the photo-hydrogen production performance of the bioreactor were also investigated. The microchannel photobioreactor exhibited a maximal hydrogen production rate of 1.48 mmol/g cell dry weight/h, maximal hydrogen yield of 0.91 mol H₂/mol glucose in all tests at an optimal inlet medium flow rate of 2.8 ml/h and substrate concentration of 50 mmol/l. In addition, photobioreactor showed a highest performance of hydrogen production and substrate consumption at 590 nm illumination wavelength and 5000 lx illumination intensity.     

Biofilm affected characteristics of porous structures

Formation of biofilm within a porous matrix reduces the pore size and the total open space of the system, altering the porosity and permeability of the medium. This change in the pore size distribution can be quantified by expressing the porous structure with a proper geometrical model. A set of pertinent multispecies biofilm models is used to arrive at the dynamic biofilm thickness distribution. The obtained results are utilized within a modified Kozeny–Carman framework to establish permeability and porosity distribution during the biofilm formation. The biofilm thickness and the obtained permeability profile for a special microorganism, Pseudomonas aeruginosa, are compared with available experimental data. The potential reasons attributing to the differences between the numerical and experimental data are discussed.     

Performance of a groove-type photobioreactor for hydrogen production by immobilized photosynthetic bacteria

The biofilm technique has been proved to be an effective cell immobilization method for wastewater biodegradation but it has had restricted use in the field of photobiological H₂ production. In the present study, a groove-type photobioreactor was developed and it was shown that a groove structure with large specific surface area was beneficial to cell immobilization and biofilm formation of the photosynthetic bacteria on photobioreactor surface as well as light penetration. A series of experiments was carried out on continuous hydrogen production in the groove-type photobioreactor illuminated by monochromatic LED lights and the performance was investigated. The effects of light wavelength, light intensity, inlet glucose concentration, flow rate and initial substrate pH were studied and the results were compared with those obtained in a flat panel photobioreactor. The experimental results show that the optimum operational conditions for hydrogen production in the groove-type photobioreactor were: inlet glucose concentration 10 g/L, flow rate 60 mL/h, light intensity 6.75 W/m², light wavelength 590 nm and initial substrate pH 7.0. The maximum hydrogen production rate, H₂ yield and light conversion efficiency in the groove-type photobioreactor were 3.816 mmol/m²/h, 0.75 molH₂/molglucose and 3.8%, respectively, which were about 75% higher than those in the flat panel photobioreactor.     

Mathematical model for gas–liquid two-phase flow and biodegradation of a low concentration volatile organic compound (VOC) in a trickling biofilter

A theoretical model is established for predicting the biodegradation of a low concentration volatile organic compound (VOC) in a trickling biofilter. To facilitate the analysis, the packed bed is simplified to a series of straight capillary tubes covered by the biofilm in which the liquid film flow on the surface of biofilm and the gas core flow in the center of tube. The theoretical formulas to calculate liquid film thickness in the capillary tube are obtained by simultaneously solving a set of hydrodynamic equations representing the momentum transport behaviors of the gas–liquid two-phase flow under co-current flow and counter-current flow. Subsequently, the mass transport equations are respectively established for the gas core, liquid film, and biofilm with considering the mass transport resistance in the liquid film and biofilm, the biochemical reaction in the biofilm, and the limitation of oxygen to biochemical reaction. Meanwhile, the surface area of mass transport in the capillary tube is modified by introducing the active biofilm surface area, namely the specific wetted surface area available for biofilm formation. The predicted purification efficiencies of VOC waste gas are found to be in good agreement with the experimental data for the trickling biofilters packed with ?8 mm, ?18 mm, and ?25 mm ceramic spheres under the gas–liquid co-current flow mode and counter-current flow mode. It has been revealed that for a fixed inlet concentration of toluene, the purification efficiency of VOC waste gas decreases with the increase in the gas and liquid flow rate, and increases with the increase in the specific area of packed materials and the height of packed bed. Additionally, it is found that there is an optimal porosity of packed bed corresponding to the maximal purification efficiency.     

Application of finite-difference time domain to dye-sensitized solar cells: The effect of nanotube-array negative electrode dimensions on light absorption

We examine the light absorbing behavior of dye-sensitized solar cells (DSCs) having cathodes (negative electrodes) comprised of highly ordered TiO₂ nanotube arrays using the electromagnetic computational technique, finite-difference time domain (FDTD). The highly ordered nanotube arrays, grown using anodic oxidation of titanium foils or thin films, feature an open end with the other end fixed on a dense oxide layer (barrier layer). The numerical simulation model is comprised of nanotube arrays on a transparent conducting glass substrate under front-side illumination. In the FDTD analysis, a transverse electromagnetic (TEM) wave is incident onto a N719 dye-coated nanotube array initially passing through the barrier layer; light that emerges from the nanotubes is reflected by a perfectly conducting layer (perfect electric conductor—PEC) boundary that simulates the effect of the DSC platinum counter electrode. An observation plane placed between the electromagnetic source and DSC detects the intensity of both the incident wave and the wave returning back from the DSC structure. The absorbance and transmittance spectra are determined in the wavelength range 300–700 nm as a function of nanotube-array dimensions including length, pore size, barrier layer thickness, and surface roughness while keeping the wall thickness constant at 12 nm. The validity of the computational simulations is experimentally verified. A significant increase in the light absorption by the dye-coated nanotubes was observed for increasing nanotube length; smaller pore sizes, and increased surface roughness. Changes in the barrier layer thickness had a negligible effect on the absorbance spectrum. Our efforts demonstrate FDTD to be a broadly applicable technique capable of guiding design of an optimal DSC architecture.     

High-performance biofilm photobioreactor based on a GeO2–SiO2–chitosan-medium-coated hollow optical fiber

To improve hydrogen production performance, this paper describes a novel approach for fabricating a biofilm photobioreactor by adsorption of the photosynthetic bacteria (PSB) Rhodopseudomonas palustris CQK 01 on a hollow optical fiber (HOF) with a GeO₂–SiO₂–chitosan medium (GSCM) coating. The composition of the coating is analyzed using Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The biocompatibility of the GSCM-coated HOF and the PSB in the hungry condition are examined. We also quantitatively investigate the biofilm dry weight; protein, polysaccharide, bacteriochlorophyll, carotenoid, and ATP contents of the biofilm cell; and average H₂ production rates. The GSCM-coated HOF exhibits enhanced the biofilm biomass, improved the biofilm activity, and an increased H₂ production rate. The proposed photobioreactor yielded fairly stable long-term performance with a hydrogen production rate of 2.65 mmol/L/h, which is 1.56 and 1.51 times higher than those of photobioreactors with an uncoated HOF and with a fiber having a roughened surface obtained by wrapping it in wire mesh, respectively.     

Synthesis of biofilm resistance characteristics against antibiotics

A phenomenological model for the biofilm resistance against biocide activity is analyzed in this work. The effect of different biofilm physical attributes when exposed to antibiotic treatment is investigated. Pertinent aspects affecting the biofilm resistance characteristics such as transport of the bulk fluid within the reactor, diffusive-reactive transport of the dissolved phase into the biofilm, convective-reactive transport of particulate phase, dynamic biofilm thickness, cell detachment, extracellular polymeric substance (EPS) production and persister cell formation are analyzed and incorporated in the presented model. Microbial survival fraction is correlated in terms of pertinent non-dimensional groups from biofilm and bulk fluid governing equations and the effect of persister cell formation on the biofilm response to biocide disinfection is demonstrated. To the authors’ best knowledge, the current model is the first comprehensive model that considers several physical attributes simultaneously and presents a set of correlations to predict the microbial survival of a biofilm subject to the biocide treatment.     

Lattice Boltzmann simulation of substrate flow past a cylinder with PSB biofilm for bio-hydrogen production

Based on hydrogen production by photosynthetic bacteria (PSB) in biofilm bioreactor, in the present study, a substrate solution with specific inlet concentration flowing past a circular cylinder with biochemical reaction in an attached thin PSB biofilm is numerically simulated by applying the lattice Boltzmann method (LBM). A non-equilibrium extrapolation method is employed to handle the velocity and concentration curved boundary. The model is validated by available theoretical and numerical results in terms of the drag and lift coefficients and concentration profiles. The good agreement demonstrated that LBM is an effective method to simulate nonlinear biochemical reaction systems with curved boundary. The velocity profile and concentration distributions of the substrate and hydrogen are determined, and the effect of Reynolds number on mass transfer characteristics is also discussed by introducing Sherwood number. The simulation results show that for both the substrate and product the concentration extension along X- and Y-directions decrease with increasing Reynolds number. The highest hydrogen concentration is obtained at the back of the cylinder. Furthermore, increasing Reynolds number results in decreasing substrate consumption efficiency, while hydrogen yield almost keeps a steady value.     

Lattice Boltzmann simulation of substrate solution through a porous granule immobilized PSB-cell for biohydrogen production

A bioreaction system of substrate solution through a porous granule immobilized photosynthetic bacteria-cell for photobiohydrogen production is simulated by the lattice Boltzmann model coupled with a multi-block strategy. The effects on flow and mass transfer are investigated by illumination intensity, influent velocity, permeability and porosity of porous granule. Additionally, hydrogen production performance including hydrogen yield and substrate consumption efficiency is evaluated. The numerical results indicate that the hydrogen yield and substrate consumption efficiency achieve maximum under illumination intensity of 6000 lx. The permeability and influent velocity have significant impact on flow and concentration fields. Moreover, with increasing permeability, the hydrogen yield increases, while the substrate consumption efficiency decreases, and with increasing influent velocity, both the hydrogen yield and consumption efficiency decrease. With increasing porosity, the hydrogen yield slightly decreases and the substrate consumption efficiency increases, and they tend to be stable when the porosity is over 0.5.     

Experimental study on behavior of initial frost crystal formation under lower water vapor pressures

This paper studies the fashion in which the initial ice crystals form on the surface under lower water vapor pressures. The fashion affects greatly the ensuing frost growth. A unique fashion of ice crystal formation was observed. Some kind of unknown surface property, but not roughness and maybe more microscopic than roughness, determined the possibility of the surface to induce frosting. There were a limited number of sites with such kind of property on the surface. Improving the conditions of those sites is possible to avoid or delay the induction of deposition.     

Negative plate macropore surfaces in lead-acid batteries: Porosity, Brunauer-Emmett-Teller area, and capacity

We propose an explanation for the production of an electrochemically active area during the electrochemical formation of lead-acid battery negative plates based on solid-state reactions. Our proposal is supported by experimental data. This study includes a critical review of the literature on charge/discharge mechanisms, porosity, and BET area. The critical review, through the latter two parameters, indicates the existence of both macro and micropores in positive plates, but only macropores in negative plates, with characteristic surface roughness. In the present paper the surface sulfation of the precursor is controlled using various acidic, neutral and alkaline solutions during an electrochemical formation process that does not include soaking. Our results confirm that variable roughness can be produced at the negative plate macropore surfaces. The morphological changes produced by different formation conditions are assessed by measuring the macroporosity, BET area, and capacity of single negative plates. Based on these concepts, a method was developed and applied to measure independently the contributions of geometrical surface macroporosity and roughness to the negative plate capacity.     

基于响应曲面法的厨余发酵产氢条件优化研究

利用响应曲面法优化厨余发酵产氢条件。以初始pH、物料比和碳氮比为自变量,培养7天的产氢量为因变量,采用Box-Behnken(BB)设计,研究各自变量及其交互作用对厨余发酵产氢效果的影响。以模拟得到的二次多项式回归方程的预测模型为基础,得到物料比为10%、50%和90%,最佳反应条件下的产氢量(VS)分别为35.49,49.12,48.39 ml/g,远高于单因素实验的最高值34.21,46.36,45.21 ml/g,试验结果为厨余发酵产氢技术应用提供了技术参数。     

Study of Hydrate Formation Kinetics in Petroleum Pipes by the Phase Field

We report the influence of phase field parameters on the modeling of gas hydrates formation. Also, the interface of the surface tension, super-cooling, and homogeneous and heterogeneous nucleation on the interface morphology and growing kinetics is evaluated. The mathematical model consists of simultaneous energy and phase field equations and is solved using the finite volume method. Results indicated that decreasing the surface tension leads to an increase of interface roughness and higher interface instability. It is also observed that an increase in the surface tension occurs together with an increase of surface thickness and lower growing kinetics. In this case, to promote the hydrate growth, it is necessary to impose a super-cooling of 2 K. Regarding homogeneous and heterogeneous nucleation, two conditions were simulated: a random distribution of nuclei, where the evolution of hydrate formation shows the occurrence of coalescence and the growing kinetics of coalesced was lightly decreased in comparison to the isolated portions of the hydrate; and heterogeneous nucleation along all the extension of the wall, where hydrate grows inward, the liquid region by mean of a homogeneous advance of the interface. In this paper, a model is reported that can be used to predict the hydrate growth process and asses parameters that are difficult to obtain experimentally.     

Photovoltage dependence on film thickness and type of illumination in nanoporous thin film electrodes according to a simple diffusion model

A simple model predicting the value of the open-circuit voltage at semiconductor nanostructured electrodes under steady-state conditions is presented. The model assumes that diffusion is the main driving force for electron transport. Analytical expressions are derived showing that the electron concentration near the back contact not only depends on the illumination intensity, light absorption coefficient, electron lifetime and diffusion coefficient for electrons, but also on the film thickness and type of illumination, either through the electrolyte or through the substrate. The behavior predicted by the model is contrasted with literature experimental results concerning TiO₂ dye-sensitized solar cells.     

On a Thermodynamic Theory of Porous Cosserat Elastic Shells

This paper presents a theory for porous thermoelastic shells using the model of Cosserat surfaces and the Nunziato–Cowin theory for materials with voids. To describe the porosity of the thin body, we introduce two scalar fields: one field accounts for the changes in volume fraction along the middle surface of the shell, and the other field characterizes the porosity variations along the shell's thickness. First, we postulate the principles of thermodynamics for these two-dimensional continua and we obtain the equations of the nonlinear theory. Then, we consider the linearized theory and prove the uniqueness of solution to the boundary initial value problem with no definiteness assumption on the constitutive coefficients. Finally, we consider the deformation of isotropic and homogeneous shells and determine the constitutive coefficients for Cosserat surfaces, by comparison with the results obtained from the three-dimensional approach to shell theory.     

Computations of the optical properties of metal/insulator-composites for solar selective absorbers

Solar selective absorbers are very useful for photo thermal energy conversion. The absorbers normally consist of thin films (mostly composite), sandwiched between the antireflection layer and (base layer on) a metallic substrate, selectively absorbing in the solar spectrum and reflecting in the thermal spectrum. The optical performance of the absorbers depends on the thin film design, thickness, surface roughness and optical constants of the constituents. The reflectivity of the underlying metal and porosity of the antireflection coating plays important roles in the selectivity behavior of the coatings. Computer simulations, applying effective medium theories, have been used to investigate the simplest possible design for composite solar selective coatings. A very high solar absorption is achieved when the coating has a non-uniform composition in the sense that the refractive index is highest closest to the metal substrate and then gradually decreases towards the air interface. The destructive interference created in the visible spectrum has increased the solar absorption to 98%. This paper also addresses the optical performance of several metals/dielectric composites like Sm, Ru, Tm, Ti, Re, W, V, Tb, Er in alumina or quartz on the basis of their refractive indices. The antireflection coating porosity and surface roughness has been analyzed to achieve maximum solar absorption without increasing the thermal emittance. Antireflection layer porosity is a function of dielectric refractive index and has nominal effect on the performance of the coating. While, up to the roughness of 1×10⁻⁷ m RMS, the solar absorption increases and for higher roughness, the thermal emittance increases only.     

Experimental investigation of anodized/ spray pyrolysed nanoporous structure on heat transfer augmentation

This paper analyzes the effects of nanoporous surface on heat transfer temperaments of assorted thermal conducting materials. A phenomenal proposal of wielding the surface roughness to ameliorate the heat transfer rate has been discovered. The maximum increase of heat transfer rate procured by nanoporous layers is 133.3% higher than the polished bare metals of surface roughness 0.2 μm. This plays an imperative role in designing compact refrigeration systems, chemical and thermal power plants. Experimental results picture a formidable upswing of 58.3% heat transfer in chemically etched metals of surface roughness 3 μm, 133.3% in nanoporous surface of porosity 75–95 nm formed by electrochemical anodization, and porosity of 40–50 nm formed by spray pyrolysis increases the heat transfer by 130%. Effects of porosity, flow velocity and scaling on the energy transfer are also scrutinized. This paper also analyzes the multifarious modes of nanoporous fabrication, to contrive both prodigious and provident system.