Flat Panel Reactor Research Articles

H-Glass Supported Hybrid Gold Nano-Islands for Visible-Light-Driven Hydrogen Evolution.

Flat panel reactors, coated with photocatalytic materials, offer a sustainable approach for the commercial production of hydrogen (H2) with zero carbon footprint. Despite this, achieving high solar-to-hydrogen (STH) conversion efficiency with these reactors is still a significant challenge due to the low utilization efficiency of solar light and rapid charge recombination. Herein, hybrid gold nano-islands (HGNIs) are developed on transparent glass support to improve the STH efficiency. Plasmonic HGNIs are grown on an in-house developed active glass sheet composed of sodium aluminum phosphosilicate oxide glass (H-glass) using the thermal dewetting method at 550°C under an ambient atmosphere. HGNIs with various oxidation states (Au0, Au+, and Au-) and multiple interfaces are obtained due to the diffusion of the elements from the glass structure, which also facilitates the lifetime of the hot electron to be ≈2.94ps. H-glass-supported HGNIs demonstrate significant STH conversion efficiency of 0.6%, without any sacrificial agents, via water dissociation. This study unveils the specific role of H-glass-supported HGNIs in facilitating light-driven chemical conversions, offering new avenues for the development of high-performance photocatalysts in various chemical conversion reactions for large-scale commercial applications.

A custom 3D printed paddlewheel improves growth in flat panel photobioreactor.

One of the main challenges with using flat panel photobioreactors for algal growth is uneven mixing and settling of cells in corners, especially when bubbling is the only method used for mixing. In order to improve mixing in our flat panel reactor, we designed a custom paddlewheel. Paddlewheels are frequently used in outdoor algae raceway ponds to improve mixing and we are taking advantage of the same principle for mixing in the reactor. The paddlewheel is easily integrated into our PSI FMT150 1-L flat panel photobioreactor and is printed on a 3D printer using high temperature poly lactic acid (HT-PLA). With the inclusion of an annealing step, the paddlewheel is autoclavable. Addition of the paddlewheel in the reactor minimized cell settling and improved algal growth, as evidenced by a nearly 40% increase in oxygen production rates. Nutrient dispersion and utilization in the culture was also improved as evidenced by a corresponding 38% decrease in CO2 concentration. The paddlewheel device presented here is a cost-effective method for improving algal growth in a flat panel photobioreactor.

Shear stress computation in a millimeter thin flat panel photobioreactor: Numerical design validated by experiments

Flat panels are the most spread type of photobioreactors for studying light effects on a microalgae culture. Their low thickness, usually between 1 and 3cm, aims at ensuring light homogeneity across the culture. Yet because optical density has to remain very low, studies are still limited to low cell density cultures. To alleviate this problem, even thinner photobioreactors can be designed. Nevertheless, thin flat panel reactors are very prone to induce high shear stress. This work aimed at designing a new millimeter thin panel photobioreactor to study light effects on Chlorella and Scenedesmus genera. We proposed a numerical workflow that is capable of assessing the shear stress intensity in such a reactor. The numerical predictions were validated at three different levels: 2D preliminary simulations were able to reproduce bubble commonly known behaviors; close to the nozzle, the predictions were successfully confronted to shadowgraphy experimental reference; at the mini bioreactor scale, experimental and numerical mixing were found to be close. After these throughout validations, shear stress intensity in the photobioreactor was calculated over 1000 Lagrangian tracers. The experienced shear stress was agglomerated at the population level. From the computed shear stress, it was possible to choose the minimal reactor thickness that would not hinder cell growth.

Optimization of outdoor cultivation of the marine microalga Nannochloropsis gaditana in flat-panel reactors using industrial exhaust flue gases

The market for microalgae is substantial and currently expanding. To meet this demand, it is necessary to demonstrate the feasibility of large-scale biomass production over long periods. This study aims to demonstrate the feasibility and sustainability of a semi-industrial process for the outdoor cultivation of the microalga Nannochloropsis gaditana in flat-panel reactors using flue gases on demand from a coal-fired power plant. To this end, four secondary objectives were defined: (i) To generate an accurate estimate of the annual average biomass production using this process; (ii) To determine how the production rate and the biochemical composition of the biomass vary with the weather conditions over the course of a year; (iii) To reduce operational costs by developing a new culture medium based on natural seawater enriched with agricultural fertilizers; and (iv) To increase the productivity yield by optimizing the air flow rate in outdoor flat-panel reactors. This research is relevant because it fills an information gap in the available literature regarding experimentation with outdoor microalgae culture, on a semi-industrial scale, using flue gases, for a period of 2 full years. Results showed that biomass production and growth rate range from 0.040 ± 0.022 g (dry weight) L−1 d−1 and 0.088 ± 0.044 d−1 to 0.078 ± 0.033 g dwt L−1 d−1 and 0.179 ± 0.079 d−1, respectively, depending on the environmental conditions. Protein and lipid content range from 34.4 ± 8.163 to 43.5 ± 13.250% dry weight and from 12.5 ± 2.243 to 14.4 ± 0.936% dwt, respectively. The culture was maintained during a complete cycle of two years, with the stated conditions, and demonstrated the technical feasibility and sustainability of the process.

Comparison of the photoactivity of TiO2 coatings using a flat panel reactor and FTIR to monitor the CO2 evolution rate

A system designed to continuously monitor the gas phase for the UV irradiation of flat panels of organic coatings has been modified to compare the photocatalytic degradation of organic pollutants using TiO2 functional coatings. TiO2 was formulated into pastes and was coated onto various stainless steel and glass fibre meshes. The photoactivity was determined by monitoring the photodegradation of acetone and following the rate of CO2 evolution using FTIR spectroscopy. The kinetics were compared to the photoinduced degradation of indigo carmine, followed by UV–vis spectroscopy to determine whether the CO2 evolution method is a viable, rapid alternative to photodegradation monitoring. A correlation was established between the two methods by determining the rate constants of the decolourisation of indigo carmine and CO2 evolution, demonstrating that such a method can be used as a rapid assessment of the photoactivity of photocatalytic coatings.

Overall development of a bioprocess for the outdoor production of Nannochloropsis gaditana for aquaculture

In this paper, a systematic methodology is shown for the scaling-up of Nannochloropsis gaditana production for aquaculture uses. First, an adequate culture medium was developed, prepared using fertilizers instead of pure chemicals. Subsequently, the performance of N. gaditana was modelled as a function of average irradiance; this model being validated in continuous culture experiments. The model was used to determine the optimal dilution rate as well as the expected biomass concentration and productivity at optimal conditions. Finally, outdoor experiments were performed to confirm the model's validity and to determine optimal conditions at real production step. Biomass productivity values of up to 0.08 g L−1 day−1 were obtained at an optimal dilution rate of 0.25 per day in 0.2 m wide flat-panel reactors using culture medium containing 0.4 g/L NO−3 and 0.034 g/L·PO4−3. Fish trials with Atlantic Salmon demonstrated that the inclusion of produced biomass into fed increase the final weight up to 5%, thus confirming the adequacy of the biomass produced for aquaculture uses. The growth model and the scaling-up strategy proposed here are necessary to develop real industrial-scale processes capable of supplying microalgal biomass to the aquaculture markets, which in turn require a guaranteed supply and quality of the raw materials provided.

Nitrification by microalgal-bacterial consortia for ammonium removal in flat panel sequencing batch photo-bioreactors

Ammonium removal from artificial wastewater by microalgal-bacterial consortia in a flat-panel reactor (FPR1) was compared with a microalgae-only flat-panel reactor (FPR2). The microalgal-bacterial consortia removed ammonium at higher rates (100±18mgNH4+-NL−1d−1) than the microalgae (44±16mgNH4+-NL−1d−1), after the system achieved a stable performance at a 2days hydraulic retention time. Nitrifiers present in the microalgae-bacteria consortia increased the ammonium removal: the ammonium removal rate by nitrifiers and by algae in FPR1 was, respectively, 50(±18) and 49(±22)mgNH4+-NL−1d−1. Apparently ammonium removal by algae was not significantly different between FPR1 and FPR2. The activity of the nitrifiers did not negatively affect the nitrogen uptake by algae, but improved the total ammonium removal rate of FPR1.

Enhancement in lipid content of Chlorella sp. MJ 11/11 from the spent medium of thermophilic biohydrogen production process

The present study investigates the effect of spent media of acetogenic dark fermentation for mixotrophic algal cultivation for biodiesel production. Mixotrophic growth conditions were optimized in culture flask (250mL) using Chlorella sp. MJ 11/11. Maximum lipid accumulation (58% w/w) was observed under light intensity, pH, nitrate and phosphate concentration of 100μmolm−2s−1, 7, 2.7mM and 1.8mM, respectively. Air lift (1.4L) and flat panel (1.4L) reactors were considered for algal cultivation. Air lift showed significant improvement in biomass and lipid production as compared to flat panel reactor. The results could help in development of sustainable technology involving acetogenic hydrogen production integrated with sequential mitigation of spent media by algal cultivation for improved energy recovery.

Outdoor pilot production of Nannochloropsis gaditana: Influence of culture parameters and lipid production rates in flat-panel photobioreactors

This work is the last of a series of three papers. The previous ones were performed in tubular photobioreactors and raceways. In the present work, the outdoor continuous production of Nannochloropsis gaditana in flat-panel reactors is studied over a two-year period, analysing the influence of the dilution rate imposed in addition to the nitrate and phosphate supplied. Maximum biomass and lipid yields of 0.19g/lday and 38.0mg/lday were obtained when operating at a dilution rate of 0.351/day and concentrations of 10.0mMNO3− and 0.8mMPO43− in the culture medium. By decreasing the specific nitrate input (below 2mmolN/gday), and exposing the culture to moderate light availability and temperature, the volumetric productivity of saturated and monounsaturated fatty acids increased to 10.0mg/lday. The specific nitrate input, together with other important parameters such as the average irradiance, temperature and dilution rate were used to develop a model describing this species' behaviour. The model is a powerful tool for further improvement and scaling-up of this technology.

Comparison of four outdoor pilot-scale photobioreactors.

BackgroundMicroalgae are a potential source of sustainable commodities of fuels, chemicals and food and feed additives. The current high production costs, as a result of the low areal productivities, limit the application of microalgae in industry. A first step is determining how the different production system designs relate to each other under identical climate conditions. The productivity and photosynthetic efficiency of Nannochloropsis sp. CCAP 211/78 cultivated in four different outdoor continuously operated pilot-scale photobioreactors under the same climatological conditions were compared. The optimal dilution rate was determined for each photobioreactor by operation of the different photobioreactors at different dilution rates.ResultsIn vertical photobioreactors, higher areal productivities and photosynthetic efficiencies, 19–24 g m−2 day−1 and 2.4–4.2 %, respectively, were found in comparison to the horizontal systems; 12–15 g m−2 day−1 and 1.5–1.8 %. The higher ground areal productivity in the vertical systems could be explained by light dilution in combination with a higher light capture. In the raceway pond low productivities were obtained, due to the long optical path in this system. Areal productivities in all systems increased with increasing photon flux densities up to a photon flux density of 30 mol m−2 day−1. Photosynthetic efficiencies remained constant in all systems with increasing photon flux densities. The highest photosynthetic efficiencies obtained were; 4.2 % for the vertical tubular photobioreactor, 3.8 % for the flat panel reactor, 1.8 % for the horizontal tubular reactor, and 1.5 % for the open raceway pond.ConclusionsVertical photobioreactors resulted in higher areal productivities than horizontal photobioreactors because of the lower incident photon flux densities on the reactor surface. The flat panel photobioreactor resulted, among the vertical photobioreactors studied, in the highest average photosynthetic efficiency, areal and volumetric productivities due to the short optical path. Photobioreactor light interception should be further optimized to maximize ground areal productivity and photosynthetic efficiency.

Use of wavelength-selective optical light filters for enhanced microalgal growth in different algal cultivation systems

This work is to use thin film nano-materials as light filters to selectively transmit certain wavelengths from natural sunlight to algal culture. A red light filter (620–710nm) and blue filter (450–495nm) were evaluated. Algae were grown in flasks, flat panel reactors, and rotating algal biofilm (RAB) system. It was found that the light filters did not improve algal growth in flask cultures, probably due to the additional reflection of light by the glass wall of the flasks. However, the light filters significantly (P<0.05) improved biomass yield (13–34%) in flat panel reactors and biomass productivity (70–100%) in RAB system, depending on the growth mode and lighter filters. Such improvements may be due to the eliminating the ultra-violet (UV) damaging the cellular structure. The biomass compositions did not change significantly among different light-filter cultures (P>0.05). The research shows a great potential of using light filters to improve microalgal growth.

Assessment of the CO2 fixation capacity of Anabaena sp. ATCC 33047 outdoor cultures in vertical flat-panel reactors

The extent of biological CO2 fixation was evaluated for outdoor cultures of the cyanobacterium Anabaena sp. ATCC 33047. Culture conditions were optimized indoors in bubble-column photochemostats operating in continuous mode, subjected to irradiance cycles mimicking the light regime outdoors. Highest values achieved for CO2 fixation rate and biomass productivity were 1 and 0.6gL−1day−1, respectively. The comparison among different reactors operating simultaneously – open pond, horizontal tubular reactor and vertical flat-panel – allowed to assess their relative efficiency for the outdoor development of Anabaena cultures. Despite the higher volumetric CO2 fixation capacity (and biomass productivity) exhibited by the tubular photobioreactor, yield of the flat-panel reactor was 50% higher than that of the tubular option on a per area basis, reaching values over 35g CO2 fixed m−2d−1. The flat-panel reactor actually represents a most suitable system for CO2 capture coupled to the generation of valuable biomass by Anabaena cultures.

Performance of a flat panel reactor in the continuous culture of microalgae in urban wastewater: Prediction from a batch experiment

A laboratory-scale flat panel photobioreactor was operated for the continuous growth of Scenedesmus obliquus and consequent removal of nutrients in wastewater. This study develops a simple model by which biomass values in continuous operation can be predicted from kinetic growth parameters obtained from a shorter batch experiment. Based on this study, biomass concentrations and productivities in continuous operation can be successfully predicted as a function of the specific hydraulic retention time (HRT) assumed. Considerable biomass production and nutrient uptake from wastewater were achieved in the experiment. Optimum operating conditions for the reactor depend on the particular objective: the maximization of biomass production and carbon dioxide biofixation involves a HRT of 2μ−1 (specific growth rate), whereas efficient nutrient removal involves a HRT as close as possible to μ−1 (as long as discharges comply fully with the parameters set); alternatively biomass intended for biodiesel or biogas production would involve a HRT>2μ−1.

On Energy Balance and Production Costs in Tubular and Flat Panel Photobioreactors

Reducing mixing in both flat panel and tubular photobioreactors can result in a positive net energy balance with state-of-the-art technology and Dutch weather conditions. In the tubular photobioreactor, the net energy balance becomes positive at velocities &lt; 0.3 ms-1, at which point the biomass production cost is 3.2 €/kg dry weight. In flat panel reactors, this point is at an air supply rate &lt; 0.25 vol vol-1 min-1, at which the biomass production cost is 2.39 €/kg dry weight. To achieve these values in flat panel reactors, cheap low pressure blowers must be used, which limits the panel height to a maximum of 0.5 m, and in tubular reactors the tubes must be hydraulically smooth. For tubular reactors, it is important to prevent the formation of wall growth in order to keep the tubes hydraulically smooth. This paper shows how current production costs and energy requirement could be decreased.

Hydrogen production using Rhodobacter sphaeroides (O.U. 001) in a flat panel rocking photobioreactor

Photofermentative hydrogen production is challenged by the photobioreactor design that can overcome poor light penetration, agitation and temperature control. Flat panel reactors have been reported to have several advantages over other reactors. But they are limited to a suitable type of agitation system when using it for hydrogen production. The aim of the present study is to develop and improve a flat panel reactor that can overcome the problem of agitation with a rocking motion. Studies with Rhodobacter sphaeroides O.U. 001 resulted in a cumulative hydrogen production of 492 ± 10 mL with maximum production rate of 11 mL L −1 h −1, substrate (malic acid) conversion efficiency of 44.4% and light conversion efficiency of 3.31%. The mixing time of the reactor was found to be around 17 s with a power input of 100–275 W/m 3. Though the entire reactor was in motion the energy spent for the rocking motion was found to be quite low.

Comparison of two reactor concepts for anoxygenic H 2 production by Rhodobacter capsulatus

In the contribution at hand two main concepts of photobioreactors are considered: the flat-panel reactor and the tubular reactor. Both reactors are investigated under outdoor conditions in Germany in the summer time for their applicability for H 2 production by means of purple non-sulphur bacteria Rhodobacter capsulatus. The experiments are performed as fed batch. The performance of a photobioreactor is evaluated in terms of H 2 productivity per IRS (illuminated reactor surface). It is demonstrated that both reactors could be operated stable for several weeks with comparable H 2 productivities. The mean hydrogen productivity for the panel and the tubular reactor is 3690 ml H 2/(m IRS 2 d) and 3350 ml H 2/(m IRS 2 d) respectively. While approximately 8 m 2 of the illuminated reactor surface of the panel reactor can be installed on 1 m 2 of ground space, the relation of the illuminated reactor surface to the ground area for the tubular reactor is approximately 1–1.

Novel flat panel reactor for monitoring photodegradation

A closed system incorporating FTIR continuous monitoring of the gas phase and a novel gas cell for the UV irradiation of flat panels of organic coatings is described. This has been used to probe various aspects of the photocatalysed degradation of TiO2 pigmented polymer films under UVA illumination. The flat panel cell is machined from a single block of aluminium and is specifically designed to minimise dead volumes, enable rapid gas mixing and be suitable for the investigation of flat coupons of material up to 220 × 100 mm in size. The cell incorporates a gas input and output channel in its base feeding and fed by small bore holes drilled in such a way as to maximise the exhaustive effects on the contents of the cell. To demonstrate the effectiveness of the design the effect of TiO2 pigment photoactivity on the rates of degradation of a commercial acrylic emulsion paint using commercial photostable TiO2 grades is reported. In testing using this new reactor configuration it has been possible to correlate photoactivities obtained over periods of several thousand hours Xenon Arc exposure, which is the most reliable test currently available. The test cell has also been used to evaluate other coating components. Using unplasticised PVC films we have found that the rate of photogenerated CO2 falls by up to 40% when a simple molecular UV absorber (2 hydroxybenzophenone) is added at levels of up to levels of 1.5% per hundred resin (PHR). Beyond this there is little further reduction in photoactivity. Finally the test cell has been used to investigate the effects of TiO2 loading on the rates of CO2 evolution from irradiated unplasticised PVC films pigmented with 0–70 PHR TiO2. The initial rate of photodegradation (over 100 min) follows a linear trend to increased CO2 evolution rates up to 50 PHR TiO2. There is a transition to a secondary rate after the production of 1.8 mmol m-2 of CO2 suggesting that after a set amount of degradation there is a change in the reaction rate. This rate is still proportional to the concentration of TiO2. It is likely that this is due to a combination of acid catalysis and the generation of porosity in the irradiated surface, the latter enabling greater oxygen access to the irradiated TiO2.

Optimization of biomass, vitamins, and carotenoid yield on light energy in a flat-panel reactor using the A-stat technique

Acceleration-stat (A-stat) cultivations in which the dilution rate is continuously changed at a constant acceleration rate, leading to different average light intensities inside the photobioreactor, can supply more information and reduce experimental time compared with chemostat cultivations. The A-stat was used to optimize the biomass and product yield of continuous cultures of the microalgae D. tertiolecta in a flat-panel reactor. In this study, four different accelerations were studied, a pseudo steady state was maintained at acceleration rates of 0.00016 and 0.00029 h(-2) and results were similar to those of the chemostat. An increase in the acceleration rate led to an increase in the deviation between results obtained in the A-stat and in the chemostats. We concluded that it is advantageous to use the A-stat instead of chemostats to determine culture characteristics and optimize a specific photobioreactor. The effect of average light intensity inside the photobioreactor on the production of vitamins C and E, lutein, and beta-carotene was studied using the A-stat. The highest concentrations of these products were 3.48 +/- 0.46, 0.33 +/- 0.06, 5.65 +/- 0.24, and 2.36 +/- 0.38 mg g(-1), respectively. These results were obtained at different average light intensities, showing the importance of optimizing each product on light intensity.