•All boiling regimes were clearly observed for all experiments performed in initial sample temperature range 600–900 °C.•Highest cooling rate of 166.21 °C/sec is achieved with wide square fin structured surface.•An enhancement of 47.1, 50.3, 60.1 and 67.1% in burnt out heat for wide square fin structured surface has been achieved.•A sharp increase in heat transfer coefficient is observed when cooling process enter into nucleate boiling regime.•Boiling Number for pyramid narrow fin and square wide fine is higher than smooth flat surface.The objective of the study is to enhance heat transfer performance of stainless steel structured surfaces with different geometries at different initial sample temperature (Ts) under air-water spray having constant spray parameters. Seven sample structured surfaces has been used. Square wide fin (Sq-W), square narrow fin (Sq-N), straight wide fin (Str-W), straight narrow fin (Str-N), pyramid wide pins (Py-W), pyramid narrow fin (Py-N) were machined on the top surface of the stainless steel cylindrical blocks. A smooth reference surface (FL) was also machined to be used as base line. Top surface diameter of each block was 27 mm and bottom surface diameter was 25 mm. The height, H of each cylinder was 12.5 mm. Each cylinder was providing with two thermocouple holes of 2 mm diameter at different geometrical locations. Square narrow fin (Sq-N) surface, gives maximum enhanced surface area (AE) of 1689.1 mm2 with an AE/AS ration of 2.9. Nozzle to surface distance (y) spray angle (θ) and fluid temperature (Tf) are fixed to 25 mm, 0° and 23.5 °C. Commercial inverse heat conduction solver INTEMP was used to estimate the time-varying surface heat flux and surface temperature of the quenched samples. It was determined that geometry of structured surfaces has significant effect on heat transfer rate. Burnout heat flux (qb) and critical heat flux (qc) showed significant increase for Sq-W at all tested sample temperatures with respect to smooth reference surface. The qc for Py-N is 85.5% and 58.3% higher than Sq-W at Ts = 800 °C and Ts = 900 °C respectively. The highest cooling rate of 166 °C/sec was achieved with sample Sq-W for Ts = 900 °C. In addition, heat transfer coefficient (h) increases gradually with decreasing surface super heat (ΔT). A sharp increase in heat transfer coefficient is observed when cooling process enters into nucleate boiling regime. Boiling Number, Bo for FL is smaller than for Py-N and Sq-W which is another way to see better heat performance of these two structured surfaces; making them better choice for high temperature safety applications.The objective of the study is to enhance heat transfer performance of stainless steel structured surfaces with different geometries at different initial sample temperature (Ts) under air-water spray having constant spray parameters. Square fin, straight fin and pyramid fin (2 geometries each) are machined on stainless steel blocks. A smooth reference surface (FL) is used as base line. Commercial inverse heat conduction solver INTEMP is used to estimate the time-varying surface heat flux and surface temperature. Burnout heat flux (qb) and critical heat flux (qc) showed significant increase for wide square fin (Sq-W) sample at all tested sample temperatures with respect to smooth reference surface. The highest cooling rate of 166 °C/sec was achieved with Sq-W sample for Ts = 900 °C. In addition, heat transfer coefficient, h increases gradually with decreasing surface super heat (ΔT). A sharp increase in heat transfer coefficient is observed when cooling process enter into nucleate boiling regime. Wide square fin structured surface showed h-curve sharp increase in nucleate boiling regime earlier than other tested samples. Boiling Number (Bo) for pyramid narrow fin (Py-N) and square wide fin (Sq-W) is higher than smooth flat surface (FL).

•A novel photothermal biomaterial doped with LaB6 NPs named as GSCML was prepared.•The proposed biomaterial can improve PSB biofilm development and H2 production.•The biofilm growth rate and H2 production rate were greatly enhanced.•Temperature increase and light intensity of light transmitted through the biomaterial can be controlled.•The biomaterial is applicable for large-scale PSB immobilization and H2 production.A novel photothermal biomaterial, designated GeO2-SiO2-Chitosan-Medium-LaB6 (GSCML), was prepared to improve photosynthetic bacteria (PSB) biofilm development and hydrogen production performance. This biomaterial employed spectral beam splitting technology to increase the overall utilization of the incident light spectrum, which LaB6 nanoparticles (NPs) mainly absorb light at approximately 380–510 and 660–780 nm and convert it into heat energy; the transmit light is around 590 nm for PSB growth. The temperature increased, and the luminous intensity of the light transmitted through the prepared biomaterial are controlled by adjusting the LaB6 NPs' content. The average biofilm growth rate and hydrogen production rate of the biofilm on the created biomaterial were 0.05 mg/cm2/day and 2.92 mmol/h/m2, which were 3.4 and 4.1 times higher than those of the glass slide, respectively. The properties of the GSCML biomaterial provide advantages for applications in immobilized cell technologies and photobioreactors.

•A novel BPBR using LGP as light guider and biofilm support material was proposed.•The surface of LGP was modified with SCM to improve the biocompatibility and roughness.•The LGP can enhance the luminous intensity and avoid shielding effects.•The proposed BPBR can effectively improve PSB biofilm formation and H2 production.A novel biofilm photobioreactor (BPBR) using light guide plate (LGP) as light guider and biofilm support material was proposed to improve the hydrogen production. To further improve the biocompatibility and roughness of LGP surface, it was modified with SiO2-chitosan-medium (SCM) biomaterial. The luminous intensity on the surface of LGP and SCM-LGP were 10.1 W/m2 and 7.8 W/m2, respectively, much higher than that (2.8 W/m2) of the traditional polymethyl methacrylate (PMMA) flat-plate. The hydrogen production rate (HPR) of the BPBRs using LGP and SCM-LGP were 8.9 mmol/h/m2 and 11.6 mmol/h/m2, which were 0.62 and 1.11 times higher than that of the traditional BPBR using PMMA, respectively. In addition, the biofilm analysis including SEM and dry biofilm density showed that SCM-LGP was more suitable for the formation of biofilms relative to LGP and PMMA. These results suggested that the proposed BPBRs have great potential for immobilized cell technologies and biohydrogen production.

•A gas distributor was designed based on CO2 bubbles rising behaviors.•CO2 bubbles influenced zone was controlled by the structure of gas distributor.•Optimized holes’ diameter and spacing of gas distributor was 0.5 mm and 1.5 mm.•Biomass productivity increased by 83.44% with the optimized gas distributor.Dynamic behavior of bubbles would significantly affect CO2 mass transfer and may cause microalgae cells uneven distribution due to the bubble carrying effect. To improve microalgae growth, the gas distributor and aeration conditions was optimized according to the bubble rising behavior. The CO2 bubble rising trajectory is similar to a Zigzag. The amplitude and wavelength of the Zigzag, which reflected the influenced zone of microalgae suspension in horizontal direction and disturbance intensity on culture, respectively, was controlled by the structure of gas distributor and aeration conditions. An optimized round gas distributor that full of holes with an inner diameter of 0.5 mm and spacing of 1.5 mm was designed. When cultivated with the optimized gas distributor aerating 5% CO2 gas at 0.250 vvm, the maximum biomass concentration of Chlorella pyrenoidosa achieved 2.88 g L−1, increased by 83.44% compared to that of 1.57 g L−1cultivated with the commercial micro-bubbles aerator.Download high-res image (81KB)Download full-size image

•The interaction of light and nitrate were optimized to boost lipid productivity.•Higher light intensity induced more lipid synthesis in the PW-PBR.•Simultaneously enhanced microalgae growth and lipid accumulation was achieved.•The maximum lipid content and lipid yield reached 41.66% and 2200.25 mg L−1.•Proportions of MUFA and C18:1 increased with the rising light intensity.Interval between adjacent planar waveguides and light intensity emitted from waveguide surface were the primary two factors affecting light distribution characteristics in the planar waveguide flat-plate photobioreactor (PW-PBR). In this paper, the synergy effect between light and nitrate in the PW-PBR was realized to simultaneously enhance microalgae growth and lipid accumulation. Under an interval of 10 mm between adjacent planar waveguides, 100% of microalgae cells in regions between adjacent waveguides could be illuminated. Chlorella vulgaris growth and lipid accumulation were synchronously elevated as light intensities emitted from planar waveguide surface increasing. With an identical initial nitrate concentration of 18 mM, the maximum lipid content (41.66% in dry biomass) and lipid yield (2200.25 mg L−1) were attained under 560 μmol m−2 s−1, which were 86.82% and 133.56% higher relative to those obtained under 160 μmol m−2 s−1, respectively. The PW-PBR provides a promising way for microalgae lipid production.Download high-res image (270KB)Download full-size image

High heat transfer performance of spray cooling on structured surface might be an additional measure to increase the safety of an installation against any threat caused by rapid increase in the temperature. The purpose of present experimental study is to explore heat transfer performance of structured surface under different spray conditions and surface temperatures. Two cylindrical stainless steel samples were used, one with pyramid pins structured surface and other with smooth surface. Surface heat flux of 3.60, 3.46, 3.93 and 4.91 MW/m2 are estimated for sample initial average temperature of 600, 700, 800 and 900 °C, respectively for an inlet pressure of 1.0 MPa. A maximum cooling rate of 507 °C/s was estimated for an inlet pressure of 0.7 MPa at 900 °C for structured surface while for smooth surface maximum cooling rate of 356 °C/s was attained at 1.0 MPa for 700 °C. Structured surface performed better to exchange heat during spray cooling at initial sample temperature of 900 °C with a relative increase in surface heat flux by factor of 1.9, 1.56, 1.66 and 1.74 relative to smooth surface, for inlet pressure of 0.4, 0.7, 1.0 and 1.3 MPa, respectively. For smooth surface, a decreasing trend in estimated heat flux is observed, when initial sample temperature was increased from 600 to 900 °C. Temperature-based function specification method was utilized to estimate surface heat flux and surface temperature. Limited published work is available about the application of structured surface spray cooling techniques for safety of stainless steel structures at very high temperature scenario such as nuclear safety vessel and liquid natural gas storage tanks.

•PTFE emulsion was sprayed onto the glass surface to change its wettability.•Bubbles adhered on the treated surface leaded to a porous biofilm microstructure.•Maximum biomass concentration increased by 16.86% on the treated surface.•Biomass concentration reached to 177.89 g/m2 on surface with 64° contact angle.Microalgae biofilm that adhered on the supporting material surface has a potential of high biomass productivity. The characteristics of material surface are very important for the microalgae growth, especially, the wettability. To improve the growth of microalgae biofilm, polytetrafluoroethylene (PTFE) emulsion was sprayed onto the glass surface to change its wettability in the study. The experimental results indicated that the microstructure of Scenedesmus obliquus biofilm on the treated glass surface was more porous due to the enhanced bubble adhesion. Favorable porous structure in the S. obliquus biofilm could enhance the nutrients and CO2 mass transfer to the microalgae cells within biofilm for more biomass accumulation. Therefore, the biofilm biomass production increased by 16.86%–122.03 g/m2 on the surface with a contact angle of 64° compared with that of 104.42 g/m2 on the untreated surface. Subsequently, flow rate of pre-mixed medium and inlet height of the photobioreactor was optimized. The maximum areal biomass concentration of S. obliquus biofilm on the PTFE-glass surface with a contact angle of 64° achieved 177.89 g/m2 with the mean growth rate of 9.88 g/m2/d in a photobioreactor with 2.5 cm inlet height under 3.5 ml/min of pre-mixed medium flow rate.

Indirect biophotolysis hydrogen production by microalgae is vigorously studied due to both hydrogen production and CO2 fixation. CO2 capture and fixation by microalgae as the first and most important step greatly affects microalgae growth, organics accumulating and then hydrogen production. In this process, CO2 gas is always pumped into photobioreactors in the form of bubbles whose dynamic behaviors CO2 transmission greatly affect the distribution and growth of microalgae. In this work, therefore, the dynamic behaviors of CO2 bubbles in bubble column photobioreactor were visually studied and the effect of inlet CO2 concentration, blast orifice size and gas flow rate on the microalgal distribution and growth were also analyzed. It was found that abundant microalgal cells and cells community were adsorbed on the bubble surface and rose with the rising bubble because of the bubble carrying, resulting in the enrichment of microalgae at the top of the microalgae suspension. Moreover, the non-uniform distributions of microalgal cells along the photobioreactor became more serious with the growth of microalgae. In addition, parametric study indicated that higher inlet CO2 concentration, smaller blast orifice size and larger gas flow rate gave rise to more serious bubble carrying, leading to higher microalgae cell density at the top of the microalgae suspension. The optimal operational conditions for the microalgae growth were 5% (V/V) in the inlet CO2 concentration, 20 μm in the blast orifice size and 20 ml/min in the gas flow rate. These findings will be a helpful for the optimized design and operation of photobioreactors.

•Biofilm growth was monitored and controlled in real time.•Uneven distribution of biofilm in the photobioreactore was improved.•A loose biofilm structure with high hydrogen production activity was obtained.•Obtained a high Bio-hydrogen production concentration and production rate.To improve biofilm activity and obtain a high hydrogen production performance of biofilm photobioreactor (BPBR), the biofilm growth on the fiber-optic surface was optimized by using a multi-sensor measurement system, plus biofilm thickness automatic control device. The proposed measurement system consisted of three types of sensors, i.e. biofilm thickness sensors, biomass concentration sensor and fiber Bragg grating temperature sensors, respectively, to monitor biofilm growth and distribution, cell adsorption/detachment rates, cell metabolic heat production and distribution in time-dependent tests. The biofilm thickness was controlled in real time using the designed biofilm control device and the information obtained from the biofilm sensors. The biofilm, in the improved BPBR, showed a loose structure and high hydrogen production activity. The H2 concentration and H2 production rate reached a high level of 45 μg/mL and 2.72 mmol/L/h, respectively, for the improved BPBR; these values were 1.73 times and 1.49 times those of the unimproved BPBR, respectively.

The lattice Boltzmann method is adopted to simulate hydrodynamics and mass transfer accompanying with biochemical reaction in a channel with cylinder bundle, which is the scenario of biohydrogen production by photosynthetic bacteria in the biofilm attached on the surface of cylinder bundle in photobioreactor. The effects of cylinder spacing, Reynolds number and cylinder arrangement are investigated. The numerical results reveal that highest glucose concentration and the lowest hydrogen concentration are obtained at the front of the first row cylinders for all cases. The staggered arrangement leads to an increment in average drag coefficient, Sherwood number and consumption efficiency of substrate under a given condition, and the increment in Sherwood number reaches up to 30 %, while that in drag coefficient is around 1 %, moreover, the increment in consumption efficiency reaches the maximum value of 12 %. The results indicate that the staggered arrangement is beneficial to the mass transfer and biochemical reaction.

A new simple fiber-optic evanescent wave sensor was created to accurately monitor the growth and hydrogen production performance of biofilms. The proposed sensor consists of two probes (i.e., a sensor and reference probe), using the etched fibers with an appropriate surface roughness to improve its sensitivity. The sensor probe measures the biofilm growth and change of liquid-phase concentration inside the biofilm. The reference probe is coated with a hydrophilic polytetrafluoroethylene membrane to separate the liquids from photosynthetic bacteria Rhodopseudomonas palustris CQK 01 and to measure the liquid concentration. We also developed a model to demonstrate the accuracy of the measurement. The biofilm measurement was calibrated using an Olympus microscope. A linear relationship was obtained for the biofilm thickness range from 0 to 120 μm with a synthetic medium under continuous supply to the bioreactor. The highest level of hydrogen production rate occurred at a thickness of 115 μm.

A microstructured fiber Bragg grating (MSFBG) was created to accurately and simultaneously monitor the cell growth of photosynthetic bacteria (PSB) Rhodopseudomonas palustris CQK 01 and the temperature in a photobioreactor. The proposed sensor was made from an FBG unit that was separated into three regions, an unperturbed region, and two etched regions with smooth surfaces. The unperturbed grating region was employed to monitor the temperature. To eliminate the effects of the liquid concentration and temperature on the biomass, a polyimide–silica hybrid membrane was created and coated on an etched grating region to separate the liquids from the PSB; that is, this thinned region was developed to analyze the liquid concentration and temperature. Another etched grating region with a smaller diameter was used to determine the response to the temperature, biomass, and liquid concentration. In addition, two models were also presented to demonstrate accurate simultaneous measurement of the biomass and temperature. We discovered that the MSFBG sensor can rapidly and accurately determine the difference in the Bragg wavelength shifts caused by changes in the temperature, biomass, and liquid-phase concentration. The measured biomass is highly correlated with the real cell growth, with a correlation of 0.9438; the hydrogen production rate and temperature difference from metabolic heat production reached 1.97 mmol/L/h and 2.8 °C, respectively, in the PSB culture.

•A new method for operating MFCs in alkaline substrates is proposed.•The proposed operation method can enhance the electrochemical activity of biofilms.•The MFC operated by substrates with varying pH generates the highest performance.•The MFC operated with varying substrate pH shows the highest coulombic efficiency.The characteristics of electricity generation and COD removal of dual-chamber microbial fuel cells (MFCs) operated with alkaline substrates were studied. Substrates with constant pH of either 7 or 9 as well as varying pH in a cycle of 7-8-9-8-7 were used. MFCs operated with these substrates were denoted as MFC-pH7, MFC-pH9 and MFC-pHV, respectively. The experimental results indicate that the MFC-pHV can generate the highest performance of 2554 ± 159 mW/m2. Cyclic voltammetry (CV), active biomass and electrochemical impedance spectroscopy (EIS) measurements were conducted and these results suggested that the MFC-pHV had the highest electrochemical activity per unit biomass and the lowest internal resistance, which together contributed to the improved power output of the MFC-pHV. In addition, compared with the other two MFCs operated at fixed pH values, the COD removal efficiency of the MFC-pHV was improved due to the stronger adaptation to the varying pH-environment.

•A new BPBR with a GeO2–SiO2–chitosan-medium- (GSCM-) coated hollow optical fiber was proposed.•The physicochemical properties of the GSCM-coated fiber were investigated.•The biofilm and its' hydrogen production performance were investigated.•The BPBR yielded fairly stable long-term performance with a high hydrogen production rate.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.

•The light decay and cell inactivation are considered in the biofilm formation.•The roughness and thickness of the biofilm increase but the porosity decreases time.•The optimal growth conditions for the PSB biofilm formation are achieved.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.

•The bioreaction process in a porous granule Immobilized PSB-Cell is simulated.•A lattice Boltzmann model combined with multi-block strategy is established.•The illumination intensity of 6000 lx leads to a best hydrogen production performance.•The effect of permeability and influent velocity on bioreaction is significant.•The porosity of porous media has less impact on flow and mass transfer.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.

•A composite anode comprising GFB and GG was proposed.•The MFC using the composite anode showed a long start-up time.•Active biomass content on the anode of the MFC was increased by combination.•The peak power density of the MFC was improved by combination.In this study, a composite electrode combined of a graphite fiber brush and carbon granules (MFC-GFB/GG) was adopted as the anode of a tubular microbial fuel cell (MFC). Compared with an MFC with graphite granules (MFC-GG) and an MFC with a graphite fiber brush (MFC-GFB), MFC-GFB/GG showed a longer lag time during the start-up process, while it reached the highest operating voltage at 50 Ω. Furthermore, during the stable operation, the MFC-GFB/GG achieved the highest power density of 66.9 ± 1.6 W m−3, which was about 5.3 and 1.2 times as that of MFC-GG and MFC-GFB, respectively. The highest performance of the MFC-GFB/GG can be attributed to the highest active biomass content on the electrode and the smallest internal resistance of the MFC. The optimum COD concentration was found to be 500 mg COD L−1 for MFC-GFB/GG.

•A new support material SiO2-Chitosan-Medium was proposed.•The physicochemical properties of the support material were investigated.•The average H2 production rates of the biofilms were investigated. The new support material increased the H2 production rate of the photobioreactor.To enhance bacterial adhesion and biofilm activity, a new support material named as SiO2-Chitosan-Medium Sol is proposed for hydrogen production by photosynthetic bacteria. The physicochemical properties of the support material are comparatively investigated with other four different materials in terms of topography, surface energy and composition. And the biocompatibilities to Rhodoseudomonas palustris CQK 01 for these five support materials are experimentally studied by quantifying the initially adhered cell numbers, biofilm dry-weights, protein and polysaccharide in EPS of the biofilms and the average H2 production rates. Experimental results show that the proposed support material shows favorable properties like rough surface, amine group and nutrients. The new support material enhances the cell adhesion capacity, reduces the biofilm formation time and improves the biofilm activity. The average H2 production rate of the bioreactor with proposed support material was improved by 80% compared with the rate of the bioreactor with the unmodified material.

For improving photo-biohydrogen production, a novel gas bubble column photobioreactor with Ar gas sparging was developed for biohydrogen production by purple non-sulfur phototrophic bacteria, Rhodoseudomonas palustris CQK-01. The dissolved hydrogen concentration was in-situ measured by a hydrogen microsensor. Experimental results demonstrated that Ar gas sparging dramatically decreased the dissolved hydrogen concentration, resulting in an improvement in the photo-biohydrogen production performance. Furthermore, effects of the gas flow rate and the time interval of gas sparging were investigated. The results showed that with an increase in the gas flow rate, the hydrogen production performance increased initially due to the reduced dissolved hydrogen concentration and enhanced mass transport, and then it decreased as a result of an increased shear stress. Meanwhile, the short sparging time interval resulted in a low accumulation of dissolved hydrogen in the bioreactor, hence high hydrogen production performance. The optimal hydrogen production rate (5.86 mmol/l/h) and hydrogen yield (3.38 mol H2/mol glucose) were obtained at the gas flow rate of 10 ml/min, respectively.Highlights► The dissolved hydrogen concentration was in-situ measured by a hydrogen microsensor. ► Effects of the spare gas flow rate and the sparging time interval were investigated. ► The short sparging time interval resulted in a low accumulation of dissolved hydrogen in the bioreactor.

A two-dimensional model is developed to describe the photosynthetic bacteria (PSB) biofilm formation on the solid surface in a flat-panel photobioreactor. The diffusion-reaction equations and cellular automata (CA) rule along with the previously obtained growth kinetics parameters of PSB are used to simulate the coupled mass transport and biochemical reaction as well as the biomass growth. With this model, the effects of the illumination intensity, pH value and initial inoculation on the formed biofilm morphology, porosity, roughness and thickness are investigated. Numerical results show that the biofilm porosity and thickness continuously decreases and increases during the PSB biofilm formation process, respectively, while the surface roughness reaches a stable value after a certain time. The optimal conditions for the PSB biofilm formation are the initial inoculation of 500, and the illumination intensity of 5000 lx and pH value of 7.0.Highlights► The diffusion-reaction equations and cellular automata (CA) rules are combined. ► The effects of optical intensity, pH value and initial inoculation are investigated. ► Some variables are determined by fitting experimental data. ► The optimal conditions were determined.

A one-dimensional two-phase flow and transport model is presented for a packed bed photobioreactor with transparent gel granules containing immobilized photosynthetic bacterial cells. The inherently coupled two-phase flow and mass transport, along with the biochemical reactions occurring in the photobioreactor are taken into account. The source term in the species conservation equation of the substrate is derived from a local transport model for a single gel granule. Model predictions of the glucose consumption efficiency and hydrogen production rate are in good agreement with experimental data. The results show that the photoinhibition of immobilized cells appears at incident light intensities higher than 6000 lux. It is the most suitable for photo-hydrogen production under neutral conditions and 30 °C of the influent substrate solution. Moreover, a high influent substrate solution flow rate results in a large hydrogen production rate due to the improved substrate transport from the bulk solution to gel granules.

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 (μmax) 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.Highlights► Effects of operation variables on kinetic characteristics of H2 production were investigated. ► The kinetic parameters of H2 production by PSB were obtained. ► The modified Monod equation as functions of operation variables is established. ► These models on H2 production describe positive and negative effects of operation variables.

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.Highlights► The lattice Boltzmann method is used to simulate the biochemical reaction. ► The effects of Re number on mass transfer are investigated by Sherwood number. ► Increasing Re will decrease the concentration extension along X- and Y-directions. ► The highest hydrogen concentration is obtained at the back of the cylinder. ► Increasing Re results in decreasing substrate consumption efficiency.

Numerical simulation of injection of polyethylene fluid in a variable cross-section nano-channel was carried out using the molecular dynamics method. The effects of the nano-channel cross-section and the external force on the rheological behavior and structural properties of the polyethylene fluid were investigated. It was found that an absorbed layer appeared near the wall and the thickness of the absorbed layer increased with increasing cone angle of the nano-channel. The injection distance of the polyethylene fluid decreased with increasing cone angle and decreasing external force. In the nano-channel with cone angle 45°, polyethylene particles uniformly filled the whole channel and were stretched along the flow direction. Uniaxial stretching of particles was enhanced when the external force was strengthened, which facilitates injection of the polyethylene fluid into the nano-channel.

A two-dimensional two-phase mass transport model has been developed to predict methanol and water crossover in a semi-passive direct methanol fuel cell with an air-breathing cathode. The mass transport in the catalyst layer and the discontinuity in liquid saturation at the interface between the diffusion layer and catalyst layer are particularly considered. The modeling results agree well with the experimental data of a home-assembled cell. Further studies on the typical two-phase flow and mass transport distributions including species, pressure and liquid saturation in the membrane electrode assembly are investigated. Finally, the methanol crossover flux, the net water transport coefficient, the water crossover flux, and the total water flux at the cathode as well as their contributors are predicted with the present model. The numerical results indicate that diffusion predominates the methanol crossover at low current densities, while electro-osmosis is the dominator at high current densities. The total water flux at the cathode is originated primarily from the water generated by the oxidation reaction of the permeated methanol at low current densities, while the water crossover flux is the main source of the total water flux at high current densities.

Potassium persulfate aqueous solution without pH adjustment is used as the cathodic electron acceptor in a two-chamber microbial fuel cell (MFC) in the present study. The performance of the MFC with K2S2O8 solution is evaluated and compared with that of K3Fe(CN)6 solution. The results show that the maximum power density of the K3Fe(CN)6 used MFC doubled that with K2S2O8 solution when fresh aqueous solution is used. However, a significant increase in electrical power generation is observed in the case of the MFC with K2S2O8 solution after 2-day operation under an external resistance of 1000 Ω. This improvement can be attributed mainly to the increased cathode performance as a result of the hydrolysis of the persulfate ion in aqueous solution. It is demonstrated that persulfate can be used as an effective cathodic electron acceptor due to its unique capability of self pH adjustment.

To investigate the electrocatalytic performance of PtRu nanoparticles supported on multi-walled carbon nanotubes (MWCNTs) with different lengths and diameters, X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and cyclic voltammetry experiments were conducted. It is demonstrated that the length and diameter of MWCNTs play an important role in the electrocatalytic performance of PtRu catalysts. The co-existence of amorphous carbon impurities on the MWCNT10-2 support lowered the accessible surface area of the PtRu nanoparticles, hampered the dispersion of the PtRu nanoparticles, and induced the formation of a low degree of PtRu alloy, thus lowered the electrocatalytic performance of the PtRu/MWCNT10-2 catalyst for methanol oxidation. The highest mass-specific activity of PtRu/MWCNT3050-2 results from a highly accessible PtRu surface and a good dispersion of PtRu particles. Our experimental results also demonstrate that the tube length of MWCNT samples has little effect of the surface area specific activity of the PtRu/MWCNT catalyst, whereas the PtRu nanoparticles supported on the MWCNT samples with large tube diameter tends to exhibit a higher surface area specific activity for methanol oxidation reaction. This result is suggested to be the combined effects of a high degree of PtRu alloying and the high electronic conductivity of these MWCNT samples.

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.

The present study reports on experimental investigations of the dynamic behavior of CO2 gas bubbles and the performance of a 9 cm2 transparent direct methanol fuel cell (DMFC). The movement of CO2 gas bubbles in the anode channel subjected to a flow of aqueous methanol solution was visualized. A series of parametric studies was carried out to evaluate the effects on the CO2 gas bubbles dynamics as well as the cell performance. It was observed that the pores around the corner of the channel ribs and the intersection of the carbon cloth fibres were favorable sites for the emergence of CO2 gas bubbles. The growth and coalescence of CO2 gas bubbles resulted in gas slugs blocking the channel and the pores in porous diffusion layer as well. Then the gas slugs were pushed by the aqueous methanol solution flow to detach and sweep downstream, clearing all the existing small bubbles on the porous diffusion layer surface. The processes of emergence, growth, coalescence, detachment, and sweeping of the gas bubbles were found to occur periodically. High flow rates of the aqueous methanol solution resulted in small discrete CO2 gas bubbles and short gas slugs. Increasing temperature of the methanol solution increased the quantity of CO2 gas bubbles. More CO2 gas bubbles and large gas slugs appeared in the channels with increasing pressure difference between the anode and the cathode. The cell performance was improved with increasing aqueous methanol flow rates, feed temperature, feed concentration, and the pressure difference between the anode and the cathode.

•A novel four-layer D-shaped step-index fiber-optic sensor is developed.•Background noise is suppressed using black paint doped with carbon nanotubes.•We check effects of coating thickness and refractive indices on sensors sensitivity.•Sensors sensitivity is evaluated using glucose and IgG analytes.•Proposed sensor shows a high sensitivity and accuracy for detection of IgG antibody.We present a novel four-layer structure consisting of bottom, second, third, and surface layers in the sensing region, for a D-shaped step-index fiber-optic evanescent wave (FOEW) sensor. To reduce the background noise, the surface of the longitudinal section in the D-shaped region is coated with a light-absorbing film. We check the morphologies of the second and surface layers, examine the refractive indices (RIs) of the third and surface layers, and analyze the composition of the surface layer. We also investigate the effects of the thicknesses and RIs of the third and surface layers and the LA film on the light transmission and sensitivity of the FOEW sensors. The results highlight the very good sensitivity of the proposed FOEW sensor with a four-layer structure, which reached −0.077 (μg/l)−1 in the detection of the target antibody; the sensitivity of the novel FOEW sensor was 7.60 and 1.52 times better than that of a conventional sensor with a core–cladding structure and an FOEW sensor with a three-layer structure doped with GeO2. The applications of this high-sensitivity FOEW sensor can be extended to biodefense, disease diagnosis, and biomedical and biochemical analysis.

The photo bioreaction combined with flow and mass transfer is simulated with pore-scale lattice Boltzmann (LB) method, which is the scenario of a bioreactor filled with a porous granule immobilized photosynthetic bacteria cells for hydrogen production. The quartet structure generation set (QSGS) is used to generate porous structure of the immobilized granule. The effects of porosity of the immobilized granule on flow and concentration fields as well as the hydrogen production performance are investigated. Higher porosity facilitates the substrate solution smoothly flowing through the porous granule with increasing velocity, and thus results in higher product concentration inside the immobilized granule. Additionally, the substrate consumption efficiency increases, while hydrogen yield slightly decreases with increasing porosity, and they tend to stable for the porosity larger than 0.5. Furthermore, the LB numerical results have a good agreement with the experimental results. It is demonstrated that the pore-scale LB simulation method coupling with QSGS is available to simulate the photo hydrogen production in the bioreactor with porous immobilized granules.