Over 100‐nm‐Thick MoOx Films with Superior Hole Collection and Transport Properties for Organic Solar Cells

Herein, a novel and effective method to prepare n‐doped MoO_x films with highly improved conductivity is reported. The MoO_x films are readily prepared by spin‐coating an aqueous solution containing ammonium molybdate tetrahydrate and vitamin C (VC). As confirmed by UV–vis absorption, X‐ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy measurements, Mo(VI) is partially reduced to Mo(V) by VC, resulting in the n‐doping of MoO_x. The conductivity of the n‐doped MoO_x (H:V‐Mo) film can be enhanced by four orders of magnitude compared to pristine MoO_x (H‐Mo), that is, from 1.2 × 10⁻⁷ to 1.1 × 10⁻³ S m⁻¹. The device using a 10 nm H:V‐Mo anode interlayer (AIL) exhibits comparable photovoltaic performance to a poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate)‐modified device. More importantly, the hole transport and collection properties of the H:V‐Mo AILs show outstanding tolerance to thickness variation, that is, with increasing thickness of the H:V‐Mo AIL from 10 to 150 nm, the V _oc and fill factor values of the devices remain unchanged. The device based on the blade‐coated H:V‐Mo AIL also has a high power conversion efficiency of 10.6%. To the best of the authors' knowledge, this work demonstrates the first example to prepare metal oxide AILs with outstanding tolerance to thickness, which is promising for the future large‐area manufacturing.     

Proton exchange membrane and electrode surface areas as factors that affect power generation in microbial fuel cells

Power generation in microbial fuel cells (MFCs) is a function of the surface areas of the proton exchange membrane (PEM) and the cathode relative to that of the anode. To demonstrate this, the sizes of the anode and cathode were varied in two-chambered MFCs having PEMs with three different surface areas (A _PEM=3.5, 6.2, or 30.6 cm²). For a fixed anode and cathode surface area (A _An=A _Cat=22.5 cm²), the power density normalized to the anode surface area increased with the PEM size in the order 45 mW/m² (A _PEM=3.5 cm²), 68 mW/m² (A _PEM=6.2 cm²), and 190 mW/m² (A _PEM=30.6 cm²). PEM surface area was shown to limit power output when the surface area of the PEM was smaller than that of the electrodes due to an increase in internal resistance. When the relative cross sections of the PEM, anode, and cathode were scaled according to 2A _Cat=A_PEM=2A _An, the maximum power densities of the three different MFCs, based on the surface area of the PEM (A _PEM=3.5, 6.2, or 30.6 cm²), were the same (168±4.53 mW/m²). Increasing the ionic strength and using ferricyanide at the cathode also increased power output.     

THE MECHANISM OF DAYLENGTH PERCEPTION IN THE RED ALGA ACROSYMPHYTON PURPURIFERUM1

The red alga Acrosymphyton purpuriferum (J. Ag.) Sjöst. (Dumontiaceae) is a short day plant in the formation of its tetrasporangia. Tetrasporogenesis was not inhibited by 1 h night-breaks when given at any time during the long (16 h) dark period (tested at 2 h intervals). However, tetrasporogenesis was inhibited when short (8 h) main photoperiods were extended beyond the critical daylength with supplementary light periods (8 h) at an irradiance below photosynthetic compensation. The threshold irradiance for inhibition of tetrasporogenesis was far lower when supplementary light periods preceded the main photoperiod than when they followed it (<0.05 μmol·m⁻²·s⁻¹ vs. 3 μmol·m⁻²·s⁻¹). The threshold level also depended on the irradiance given during the main photoperiod and was higher after a main photoperiod in bright light than after one in dim light (threshold at 3 μmol·m⁻²·s⁻¹ after a main photoperiod at ca. 65 μmol·m⁻²·s⁻¹ vs. threshold at <0.5 μmol·m⁻²·s⁻¹ after a main photoperiod at ca. 35 μmol·m⁻²·s⁻¹). The spectral dependence of the response was investigated in day-extensions (supplementary light period (8 h) after main photoperiod (8 h) at 48 μmol·m⁻²·s⁻¹) with narrow band coloured light. Blue light (λ= 420 nm) was most effective, with 50% inhibition at a quantum-dose of 2.3 mmol·m⁻². However, yellow (λ= 563 nm) and red light (λ= 600 nm; λ= 670 nm) also caused some inhibition, with ca. 30% of the effectiveness of blue light. Only far-red light (λ= 710 nm; λ= 730 nm) was relatively ineffective with no significant inhibition of tetrasporogenesis at quantum-doses of up to 20 mmol·m⁻².     

Flexible and Stretchable Biobatteries: Monolithic Integration of Membrane‐Free Microbial Fuel Cells in a Single Textile Layer

The fabrication and performance of a flexible and stretchable microbial fuel cell (MFC) monolithically integrated into a single sheet of textile substrate are reported. The single‐layer textile MFC uses Pseudomonas aeruginosa (PAO1) as a biocatalyst to produce a maximum power of 6.4 µW cm^?2 and current density of 52 µA cm^?2, which are substantially higher than previous textile‐MFCs and are similar to other flexible paper‐based MFCs. The textile MFC demonstrates a stable performance with repeated stretching and twisting cycles. The membrane‐less single‐chamber configuration drastically simplifies the fabrication and improves the performance of the MFC. A conductive and hydrophilic anode in a 3D fabric microchamber maximizes bacterial electricity generation from a liquid environment and a silver oxide/silver solid‐state cathode reduces cathodic overpotential for fast catalytic reaction. A simple batch fabrication approach simultaneously constructs 35 individual devices, which will revolutionize the mass production of textile MFCs. This stretchable and twistable power device printed directly onto a single textile substrate can establish a standardized platform for textile‐based biobatteries and will be potentially integrated into wearable electronics in the future.     

KINETICS OF GROWTH AND DEATH IN ANABAENA FLOS-AQUAE (CYANOBACTERIA) UNDER LIGHT LIMITATION AND SUPERSATURATION

The kinetics of population growth and death were investigated in Anabaena flos-aquae (Lyngb.) Bréb grown at light intensities ranging from limitation to photoinhibition (5 W·m⁻² to 160 W·m⁻²) in a nutrient-replete turbidostat. Steady-state growth rate (μ, or dilution rate, D) increased with light intensity from 0.44·day⁻¹ at a light intensity of 5 W·m⁻² to 0.99·day⁻¹ at 20 W·m⁻² and started to decrease above about 22 W·m⁻², reaching 0.56·day⁻¹ at 160 W·m⁻². The Haldane function of enzyme inhibition fit the growth data poorly, largely because of the unusually narrow range of saturation intensity. However, it produced a good fit (P < 0.001) for growth under photoinhibition. Anabaena flos-aquae died at different specific death rates (γ) below and above the saturation intensity. When calculated as the slope of a v_x⁻¹ and D⁻¹ plot, where v_x and D are cell viability (or live cell fraction) and dilution rate, respectively; γ was 0.047·day⁻¹ in the range of light limitation and 0.103·day⁻¹ under photoinhibition. Live vegetative cells and heterocysts, either in numbers or as a percentage of the total cells, showed a peak at the saturation intensity and decreased at lower and higher intensities. The ratio of live heterocysts to live vegetative cells increased with intensity when light was limiting but decreased when light was supersaturating. In cells growing at the same growth rate, the ratio was significantly lower under light inhibition than under subsaturation and the cell N:C ratio was also lower under inhibition. The steady-state rate of dissolved organic carbon (DOC) production increased with light intensity. However, its production as a percentage of the total C fixation was lowest at the optimum intensity and increased as the irradiance decreased or increased. The rate and percentage was significantly higher under photoinhibition than limitation in cells growing at the same growth rate. About 22% of the total fixed carbon was released as DOC at the highest light intensity. No correlation was found between the number of dead cells and DOC.     

Investigating microbial fuel cell bioanode performance under different cathode conditions

A compact, three‐in‐one, flow‐through, porous, electrode design with minimal electrode spacing and minimal dead volume was implemented to develop a microbial fuel cell (MFC) with improved anode performance. A biofilm‐dominated anode consortium enriched under a multimode, continuous‐flow regime was used. The increase in the power density of the MFC was investigated by changing the cathode (type, as well as catholyte strength) to determine whether anode was limiting. The power density obtained with an air‐breathing cathode was 56 W/m³ of net anode volume (590 mW/m²) and 203 W/m³ (2160 mW/m²) with a 50‐mM ferricyanide‐based cathode. Increasing the ferricyanide concentration and ionic strength further increased the power density, reaching 304 W/m³ (3220 mW/m², with 200 mM ferricyanide and 200 mM buffer concentration). The increasing trend in the power density indicated that the anode was not limiting and that higher power densities could be obtained using cathodes capable of higher rates of oxidation. The internal solution resistance for the MFC was 5–6 Ω, which supported the improved performance of the anode design. A new parameter defined as the ratio of projected surface area to total anode volume is suggested as a design parameter to relate volumetric and area‐based power densities and to enable comparison of various MFC configurations. Published 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009     

Solid phase microbial fuel cell (SMFC) for harnessing bioelectricity from composite food waste fermentation: influence of electrode assembly and buffering capacity

Solid phase microbial fuel cells (SMFC; graphite electrodes; open-air cathode) were designed to evaluate the potential of bioelectricity production by stabilizing composite canteen based food waste. The performance was evaluated with three variable electrode-membrane assemblies. Experimental data depicted feasibility of bioelectricity generation from solid state fermentation of food waste. Distance between the electrodes and presence of proton exchange membrane (PEM) showed significant influence on the power yields. SMFC-B (anode placed 5 cm from cathode-PEM) depicted good power output (463 mV; 170.81 mW/m²) followed by SMFC-C (anode placed 5 cm from cathode; without PEM; 398 mV; 53.41 mW/m²). SMFC-A (PEM sandwiched between electrodes) recorded lowest performance (258 mV; 41.8 mW/m²). Sodium carbonate amendment documented marked improvement in power yields due to improvement in the system buffering capacity. SMFCs operation also documented good substrate degradation (COD, 76%) along with bio-ethanol production. The operation of SMFC mimicked solid-sate fermentation which might lead to sustainable solid waste management practices.     

The effect of physico-chemically immobilized methylene blue and neutral red on the anode of microbial fuel cell

A fast and cost effective immobilization of electron carriers, methylene blue (MB) and neutral red (NR) by pH shift was proposed to improve bioanodic performance. The adsorption of mediators onto the carbon cloth anode was verified using cyclic voltammogram (CV) and the effect of the immobilized mediators on acclimation, power density, and acetate removal of MFCs was investigated. A peak power density of P _max(MB) = 11.3 W/m³ was achieved over days 110 ∼ 120, as compared to P _max(Control) = 5.4 W/m³ and P _max(NR) = 3.1 W/m³ for the treated anode after 15 sequential fed-batch operations. The VFA removal rates however were similar for all MFC systems, ranging from 82 to 87%. It could be suggested that the increase in power density for the MB treated electrode resulted from an enhanced electron transport from exo-electrogenic bacteria. MB may also have a selective effect on the bacterial community during the start-up stage, increasing the voltage production and acetate removal from day 1 to 16. However, MFC with NR treated anode produced an initial voltage under 100 mV, with lower coulombic efficiency (CE). NR exhibited less favourable mediator molecule binding to the electrode surface, when subject to pH driven physico-chemical immobilization.     

Improving hydrogen production in microbial electrolysis cells through hydraulic connection with thermoelectric generators

Using alternative power sources to drive hydrogen production in microbial electrolysis cells (MECs) is important to implementation of MEC technology. Herein, thermoelectric generators (TEG) were to power MECs using simulated waste heat. With the MEC anolyte as a cold source for TEG, current generation of the MEC increased to 2.46 ± 0.06 mA and hydrogen production reached 0.14 m³ m⁻³ d^-1, higher than those of the TEG-MEC system without hydraulic connection (1.16 ± 0.07 mA and 0.07 ± 0.01 m³ m⁻³ d^-1). A high recirculation rate of 30 mL min^-1 doubled both current generation and hydrogen production with 10 mL min^-1, benefited from a stronger cooling effect that increased the TEG voltage output. However, the optimal recirculation rate was determined as 20 mL min^-1 because of comparable performance but potentially less energy requirement. Reducing anolyte hydraulic retention time to 4 h has increased hydrogen production to 0.25 ± 0.05 m³ m⁻³ d^-1 but decreased organic removal efficiency to 69 ± 2%. Adding three more TEG units that captured more heat energy further enhanced hydrogen production to 0.36 m³ m⁻³ d^-1. Those results have demonstrated a successful integration of TEG with MEC through both electrical and hydraulic connections for simultaneous wastewater treatment and energy recovery.     

Aerated Shewanella oneidensis in continuously fed bioelectrochemical systems for power and hydrogen production

We studied the effects of aeration of Shewanella oneidensis on potentiostatic current production, hydrogen production in a microbial electrolysis cell, and electric power generation in a microbial fuel cell (MFC). The potentiostatic performance of aerated S. oneidensis was considerably enhanced to a maximum current density of 0.45 A/m² or 80.3 A/m³ (mean: 0.34 A/m², 57.2 A/m³) compared to anaerobically grown cultures. Biocatalyzed hydrogen production rates with aerated S. oneidensis were studied within the applied potential range of 0.3–0.9 V and were highest at 0.9 V with 0.3 m³ H₂/m³ day, which has been reported for mixed cultures, but is ～10 times higher than reported for an anaerobic culture of S. oneidensis. Aerated MFC experiments produced a maximum power density of 3.56 W/m³ at a 200‐Ω external resistor. The main reasons for enhanced electrochemical performance are higher levels of active biomass and more efficient substrate utilization under aerobic conditions. Coulombic efficiencies, however, were greatly reduced due to losses of reducing equivalents to aerobic respiration in the anode chamber. The next challenge will be to optimize the aeration rate of the bacterial culture to balance between maximization of bacterial activation and minimization of aerobic respiration in the culture. Biotechnol. Bioeng. 2010;105: 880–888. © 2009 Wiley Periodicals, Inc.     

Boosting Ion Diffusion and Charge Transfer by Zincophilic Accordion Arrays to Achieve Ultrafast Aqueous Zinc Metal Batteries

A key challenge to apply aqueous zinc metal batteries (AZMBs) as next-generation energy storage device is to improve the rechargeability at high current densities, which is needed to circumvent slowly ion diffusion in anode and sluggish charge transfer of Zn²⁺. Herein, a zincophilic accordion array derived from MOF is developed as zinc host for simultaneously boosted ion diffusion and charge transfer. The designed host is prepared by etching and disproportionation reactions, the abundant zincophilic Sn sites with nano-size uniform disperse on accordion arrays nanosheets (Sn-AA). Then a composite Zn anode (Sn-AA@Zn) is obtained by compacting Sn-AA host with zinc power (Zn-P). The Sn-AA@Zn anode has an ultra-low activation energy (37.1 kJ mol⁻¹) and nucleation overpotential (10 mV), achieving fast charge transfer of Zinc deposition. In addition, the cycle life of the symmetric cell with Sn-AA@Zn anode exceeds 13 000 cycles at 50 mA cm⁻², which is 32 times than that of the Zn-P anode. And the full cell with Sn-AA@Zn anode and MnO₂ cathode maintains a capacity of 122 mAh g⁻¹ after 5000 cycles at 5 Ag⁻¹. Hopefully, the 3D anode based on Sn-AA@Zn accordion array and Zn-P has significantly improved the rechargeability of AZMB at high current density.     

Improved performance of membrane free single-chamber air-cathode microbial fuel cells with nitric acid and ethylenediamine surface modified activated carbon fiber felt anodes

Surface modifications of anode materials are important for enhancing power generation of microbial fuel cell (MFC). Membrane free single-chamber air-cathode MFCs, MFC-A and MFC-N, were constructed using activated carbon fiber felt (ACF) anodes treated by nitric acid and ethylenediamine (EDA), respectively. Experimental results showed that the start-up time to achieve the maximum voltages for the MFC-A and MFC-N was shortened by 45% and 51%, respectively as compared to that for MFC-AT equipped with an unmodified anode. Moreover, the power output of MFCs with modified anodes was significantly improved. In comparison with MFC-AT which had a maximum power density of 1304 mW/m², the MFC-N achieved a maximum power density of 1641 mW/m². The nitric acid-treated anode in MFC-A increased the power density by 58% reaching 2066 mW/m². XPS analysis of the treated and untreated anode materials indicated that the power enhancement was attributable to the changes of surface functional groups.     

Phytoplankton Primary Productivity and Population Efficiency Studies in a Prairie-Parkland Lake Near Edmonton,Alberta, Canada

The standing crop and primary productivity of a small eutrophic, prairie-parkland lake were measured. In general, both standing crops and primary productivity were large, 29.4 and 73.09 mg chlorophyll a m⁻³ and m⁻² and 78.71 and 196.77 mg C hr ⁻¹m⁻³ and m⁻² respectively. Productivity decreased with increasing depth, therefore, decreasing light intensity. Relations between productivity and chlorophyll a content, productivity and light intensity, phytoplankton productivity efficiency and light intensity, productivity and water temperature were investigated, as was the photosynthetic index. Experiments designed to determine the photosynthetic capacity of the phytoplankton distinguished between actively growing and senescent populations. The latter were present during the winter ice cover.     

COMPARISON OF INTRASPECIFIC VARIATIONS IN THE REPRODUCTION AND PHOTOSYNTHESIS OF AN UNDERSTORY HERB,ARNICA CORDIFOLIA

Intraspecific variations in the reproduction of individual ramets and monospecific patches of the understory herb Arnica cordifolia Hook. were compared with variations in photosynthesis and understory light conditions. Ramets and patches were compared from three microhabitats (open, intermediate, and shaded) that differed in daily integrated irradiance. Individual ramets from open microhabitats (> 12 MJ m⁻² d⁻¹) had 23% more total dry wt and produced twice as many seeds, when compared to ramets from shaded locations (< 5 MJ m⁻² d⁻¹). In addition, monospecific patches from open locations were 63% more dense, and estimates of seed and vegetative patch reproductive effort were 4 and 2 times greater, respectively, when compared to shaded plant patches. For all measurements, ramets and patches from intermediate understory locations (6–10 MJ m⁻² d⁻¹) were intermediate in reproductive capacity between those of open and shaded locations. In addition, A. cordifolia seeds from open microhabitats germinated significantly better (45%) than either intermediate or shaded location seeds under high light and only seeds from shaded microhabitats germinated (14%) in the dark. Compared to shaded location plants, the greater total dry weight and seed production of individual ramets and the greater estimated reproductive effort of patches from open locations corresponded to a greater maximum photosynthetic rate (16.9 μmoles m⁻² s⁻¹) and daily carbon gain (12.2 g m⁻² d⁻¹). Possibly, a greater photosynthetic capacity may make more photosynthetic resources available for reproduction by A. cordifolia plants in open locations. Thus, intraspecific variation in physiology may contribute to intraspecific variation in reproduction.     

Effect of light intensity and eye development on prey capture by larval striped bass Morone saxatilis

The efficacy of visual and non-visual feeding among pelagic striped bass Morone saxatilis larvae adapted to a turbid estuary was determined in the laboratory in clear water. Capture of Artemia salina (density 100 l⁻¹) was significantly affected by the interaction between age of larvae (range: 8–25 days post-hatch, dph) and light intensity (range: 0–10·6 μmol s⁻¹ m⁻² at the water surface). Visual feeding by larvae aged 9–11 dph was highest in dim light (0·086–0·79 μmol s⁻¹ m⁻²), with fish capturing up to 5 prey larva⁻¹ h⁻¹. As the larvae grew, prey capture in brighter light improved, associated with an increasing proportion of twin cone photoreceptors and improving ability of the retina to light- and dark-adapt. By age >22 dph, mean prey capture was greatest at highest light intensities (0·79 and 10·6 μmol s⁻¹ m⁻²) exceeding 100 prey larva⁻¹ h⁻¹. Incidence of feeding larvae generally improved as the larvae grew, reaching >80% in all light intensities from 16 dph onwards. The lower threshold for visual feeding, between 0·0084 and 0·03 μmol s⁻¹ m⁻², remained constant as the larvae grew, despite an increasing density of rod photoreceptors. Below this threshold, non-visual feeding was evident at a low rate (<6 prey larva⁻¹ h⁻¹) that was independent of larval age.     

Effects of inoculation strategy and cultivation approach on the performance of microbial fuel cell using marine sediment as bio-matrix

Aims: To investigate the effects of inoculation strategy and cultivation approach on the performance of microbial fuel cell (MFC). Methods and Results: A dual‐chamber sediment fuel cell was set up fed with glucose under batch condition. At day 30, the supernatant consortium was partly transferred and used as inoculum for the evaluation of cultivation approach. Power output gradually increased to 9·9 mW m^?2 over 180 days, corresponding to coulombic efficiency (CE) of 29·6%. Separated biofilms attached anode enabled power output and CE dramatically up to 100·9 mW m^?2 and over 50%, respectively, whereas the residual sediment catalysed MFC gave a poor performance. MFC catalysed by in situ supernatant consortium demonstrated more than twice higher power than MFC catalysed by the supernatant consortium after Fe(OH)₃ cultivation. However, the re‐generation of biofilms from the latter largely enhanced the cell performance. Conclusions: MFC exhibited a more efficient inducement of electroactive consortium than Fe(OH)₃ cultivation. MFC performance varied depending on different inoculation strategies. Significance and Impact of the Study: This is the first time to study cultivation approach affecting electricity generation. In addition, anodic limitations of mass and electron transfer were discussed through MFC catalysed by sediment‐based bio‐matrix.     

Highly Passivated n‐Type Colloidal Quantum Dots for Solution‐Processed Thermoelectric Generators with Large Output Voltage

Colloidal quantum dots (CQDs) are attractive materials for thermoelectric applications due to their simple and low‐cost processing; advantageously, they also offer low thermal conductivity and high Seebeck coefficient. To date, the majority of CQD thermoelectric films reported upon have been p‐type, while only a few reports are available on n‐type films. High‐performing n‐ and p‐type films are essential for thermoelectric generators (TEGs) with large output voltage and power. Here, high‐thermoelectric‐performance n‐type CQD films are reported and showcased in high‐performance all‐CQD TEGs. By engineering the electronic coupling in the films, a thorough removal of insulating ligands is achieved and this is combined with excellent surface trap passivation. This enables a high thermoelectric power factor of 24 µW m^?1 K^?2, superior to previously reported n‐type lead chalcogenide CQD films operating near room temperature (<1 µW m^?1 K^?2). As a result, an all‐CQD film TEG with a large output voltage of 0.25 V and a power density of 0.63 W m^?2 at ?T = 50 K is demonstrated, which represents an over fourfold enhancement to previously reported p‐type only CQD TEGs.     

Efficient Perovskite Photovoltaic‐Thermoelectric Hybrid Device

An efficient perovskite photovoltaic‐thermoelectric hybrid device is demonstrated by integrating the hole‐conductor‐free perovskite solar cell based on TiO₂/ZrO₂/carbon structure and the thermoelectric generator. The whole solar spectrum of AM 1.5 G is fully utilized with the ≈1.55 eV band gap perovskite (5‐AVA)_x(MA)_1?xPbI₃ absorbing the visible light and the carbon back contact absorbing the infrared light. The added thermoelectric generator improves the device performance by converting the thermal energy into electricity via the Seebeck effect. An optimized hybrid device is obtained with a maximum point power output of 20.3% and open‐circuit voltage of 1.29 V under the irradiation of 100 mW cm^?2.     

Kinetic modeling of light limitation and sulfur deprivation effects in the induction of hydrogen production with Chlamydomonas reinhardtii. Part II: Definition of model‐based protocols and experimental validation

Photosynthetic hydrogen production under light by the green microalga Chlamydomonas reinhardtii was investigated in a torus‐shaped PBR in sulfur‐deprived conditions. Culture conditions, represented by the dry biomass concentration of the inoculum, sulfate concentration, and incident photon flux density (PFD), were optimized based on a previously published model (Fouchard et al., 2009. Biotechnol Bioeng 102:232–245). This allowed a strictly autotrophic production, whereas the sulfur‐deprived protocol is usually applied in photoheterotrophic conditions. Experimental results combined with additional information from kinetic simulations emphasize effects of sulfur deprivation and light attenuation in the PBR in inducing anoxia and hydrogen production. A broad range of PFD was tested (up to 500 µmol photons m⁻² s⁻¹). Maximum hydrogen productivities were 1.0 ± 0.2 mL H₂/h/L (or 25 ± 5 mL H₂/m² h) and 3.1 mL ± 0.4 H₂/h L (or 77.5 ± 10 mL H₂/m² h), at 110 and 500 µmol photons m⁻² s⁻¹, respectively. These values approached a maximum specific productivity of approximately 1.9 mL ± 0.4 H₂/h/g of biomass dry weight, clearly indicative of a limitation in cell capacity to produce hydrogen. The efficiency of the process and further optimizations are discussed. Biotechnol. Bioeng. 2011;108: 2288–2299. © 2011 Wiley Periodicals, Inc.     

Dynamics of long-term continuous culture of Limnospira indica in an air-lift photobioreactor

MELiSSA (Microecological Life Support System Alternative) is a developing technology for regenerative life support to enable long-term human missions in Space and has developed a demonstration Pilot Plant. One of the components of the MELiSSA Pilot Plant system is an 83L external loop air-lift photobioreactor (PBR) where Limnospira indica (previously named Arthrospira sp. PC8005) is axenically cultivated in a continuous operation mode for long-periods. Its mission is to provide O₂ and consume CO₂ while producing edible material. Biological and process characterization of this PBR is performed by analysing the effect of two main variables, dilution rate (D) and PFD (Photon Flux Density) illumination. A maximum oxygen productivity () of 1.35 mmol l⁻¹ h⁻¹ is obtained at a D of 0.025 h⁻¹ and PFD of 930 µmol m⁻² s⁻¹. Photoinhibition can occur when a 1 g l⁻¹ cell density culture is exposed to PFD higher than 1700 µmol m⁻² s⁻¹. This process is reversible if the illumination is returned to dim light (150 µmol m⁻² s⁻¹), proving the cell adaptability and capacity to respond at different illumination conditions. Influence of light intensity in cell composition is also described. Specific photon flux density (qPFD) has a direct effect on phycobiliproteins and chlorophyll content causing a decrease of 62.5% and 47.8%, respectively, when qPFD increases from 6.1 to 19.2 µmol g⁻¹ s⁻¹. The same trend is observed for proteins and the opposite for carbohydrate content. Morphological and spiral structural features of L. indica are studied by confocal microscopy, and size distribution parameters are quantified. A direct effect between trichome width and CDW/OD ratio is observed. Changes in size distribution are not correlated with environmental factors, further confirms the adaptation capacity of the cells. The systematic analysis performed provides valuable insights to understand the key performance criteria of continuous culture in air-lift PBRs.