Absorber Tower as a Photobioreactor for Microalgae

Green microalgae were grown under natural light in a photobioreactor similar to a transparent plate absorber. A proper temperature was maintained through the control of evaporation and the minimization of convective heat waste. Carbon dioxide desorption was lower in comparison to its level during cultivation in open or covered ponds. A yield of 1 g/l per day and over 100 g/m² projection area was achieved.     

An analytical flat-plate photobioreactor with a spectrally attenuated light source for the incubation of phytoplankton under dynamic light regimes

An inexpensive and simple, analytical microalgal photobioreactor with a highly controllable, dynamic, spectrally attenuated light source is described. Spectral attenuation is achieved through the introduction of a variable thickness of CuSO₄ solution between the photobioreactor and a light source. The level of liquid is precisely determined via a computer-controlled peristaltic pump, which can be programmed to pump at a variety of rates. The resultant light fields consist of a wide range of irradiance intensities with concomitant spectral narrowing, which closely mimics modeled clear water attenuation patterns. Irradiance dynamics associated with virtually any mixing regime can be achieved. The culturing apparatus of the analytical photobioreactor is based on traditional flat-plate, photobioreactor design, but with several modifications: (1) The light path has been reduced to 1 cm to assure a uniform light field is experienced by all phytoplankton at relatively low cell densities; (2) carbon dioxide concentrations are kept constant through a negative feedback mechanism that pulses CO₂ into a constant air stream when culture media pH rises above a set point; (3) temperature is controlled in a similar manner, through the addition of cooling water to a water jacket in response to an increase in culture media temperature. This design is intended for use in photophysiological and bio- physical studies of microalgae under highly controlled culture conditions. It should prove easily adaptable to any number of more complex configurations.     

管道式光生物反应器的设计和性能

该文概述了管道式光生物反应器在设计上对性能的要求,对影响光生物反应器培养效率的各种生长条件如光能利用效率、CO2利用效率、环境温度、溶解氧等问题进行了探讨,指出高效并可自动调节的藻液循环混合系统对于高密度海藻培养是非常重要的,提出了能否自动清洗光生物反应器内壁是判断光生物反应器是否可用于工业化生产的关键。     

RATES OF PHOTOADAPTATION IN SEA ICE DIATOMS FROM MCMURDO SOUND,ANTARCTICA1

Sea ice microalgae are released from their relatively stable light environment to the water column seasonally, and any subsequent growth in a vertically mixed water column may depend, in part, on their photoadaptation rates. In this study we followed the time course of photoadaptation in natural sea ice algal communities from bottom ice and surface ice by measuring their photophysiological response to an artificial shift in the ambient irradiance field. Microalgae from under-ice habitats, were incubated under full sunlight (LL-HL) and microalgae from surface ice habitats were incubated under artificial light to mimic under-ice irradiance (HL-LL). During 3- to 4-day time course studies, opposite shifts in chlorophyll: carbon, α, P^B_m, and I_k were observed, depending on the direction of the irradiance change. First-order rate constants (k) ranged from 0.0067 to 0.29 h^?1 for photosynthetic parameters, although P^B_m did not always show a clear change over time. Rates of photoadaptation for ice algae are comparable to k values reported for temperate phytoplankton, suggesting that sea ice algae may be equally capable of adapting to the light conditions experienced in a vertically mixed water column. This study presents the first evidence that sea ice microalgae are physiologically capable of adapting to a planktonic life and thus could serve as a seed population for polar marine phytoplankton blooms.     

A new photobioreactor for continuous microalgal production in hatcheries based on external-loop airlift and swirling flow

This study deals with the scale of a new photobioreactor for continuous microalgal production in hatcheries. The combination of the state-of-art with the constraints inherent to hatcheries has turned the design into a closed, artificially illuminated and external-loop airlift configuration based on a succession of elementary modules, each one being composed of two transparent vertical interconnected columns. The liquid circulation is ensured pneumatically (air injections) with respect to a swirling motion (tangential inlets). A single module of the whole photobioreactor was built-up to scale its geometry (diameter and length) and to optimize its design (air sparger, tangential inlets). The volumetric productivities were predicted by modeling radiative transfer and growth of Isochrysis affinis galbana (clone Tahiti). The hydrodynamics of the liquid phase was modeled in terms of global flow behavior (circulation and mixing times, Péclet number) and of swirling motion decay along the column (Particle Image Velocimetry). The aeration performances were determined by overall volumetric mass transfer measurements. Continuous cultures of Isochrysis affinis galbana (clone Tahiti) were run in two geometrical configurations, generating either an axial or a swirling flow. Lastly, the definitive options of design are presented as well as a 120-L prototype, currently implemented in a French mollusk hatchery and commercialized.     

A PHYSIOLOGICAL TEST OF THE THEORY OF COMPLEMENTARY CHROMATIC ADAPTATION. I. COLOR MUTANTS OF A RED SEAWEED1

The physiological behavior of phycoerythrin-deficient mutants of the red seaweed Gracilaria tikvahiae (Mc-Lachlan 1979) is compared to that of their wild types. The mutants are phenotypically green while the wild types are red. Cloned scions were grown factorially at irradiances saturating and limiting to growth, and spectral distributions which were broadband (white) and narrowband (green). The green light field complements the absorptance spectrum of phycoerythrin. Experiments were performed in an outdoor continuous flow system. Physiological measurements included light-harvesting pigment composition, instantaneous photosynthesis-light relationships and growth. In all cases, the mutants performed as their wild type progenitors. Further, physiological responses occurring in no less than 8 days were dependent solely on irradiance (“intensity”), and were independent of spectral distribution (“color”). The data do not conform with the predictions of the theory of complementary chromatic adaptation for seaweeds.     

Photosynthetic characteristics of leaves developed at different irradiances and temperatures: an extension of the current hypothesis

Photosynthetic characteristics at high measurement irradiance were analyzed for single leaves of two C₃ and one C₄ species grown under twenty one combinations of irradiance level, irradiance duration, and air temperature in order to test the idea that photosynthetic characteristies developed by leaves in different environments are controlled by the daily amount of photosynthesis. Photosynthetic rates per unit area and mesophyll conductances at 25°C and air levels of CO₂ and O₂, and parameters for two photosynthesis models were used to characterize the photosynthetic properties of the leaves. Leaves with highest values of the photosynthetic parameters for each species were often developed in environments with irradiance levels below saturation for photosynthesis, and with only 12 hours of irradiance per day. Lower air temperature during growth increased the photosynthetic characteristics for a given irradiance regime. Photosynthetic characteristics had higher correlation coefficients with daily photosynthesis of mature leaves divided by 24-hour leaf elongation rates of young leaves, than with daily photosynthesis alone, indicating that photosynthetic characteristics may be related to a balance between photosynthesis and leaf expansion.     

Growth yield determination in a chemostat culture of the marine microalgaIsochrysis galbana

The growth yield of the PUFA-producing marine microalgaIsochrysis galbana ALII-4 grown in a light limited chemostat, was measured under a wide variety of conditions of incident irradiance (I _O ) and dilution rates (D). The experiments were conducted under laboratory conditions at 20 °C under continuous light. D ranged from 0.0024 to 0.0410 h^–1 at three intensities of Io (820, 1620 and 3270 µmol photon m^–2 s^–1) close to those found in outdoor cultures. A maximum efficiency _max = 0.616 g mol photon^–1 was obtained at I _O = 820 µmol photon m^–2 s^–1 and D = 0.030 h^–1 and the maximum capacity of the biomass to metabolize the light harvested was found to be 13.1 µmol photon g^–1 s^–1. Above this value, a significant drop in the system efficiency was observed. A new approach based in the averaged irradiance is used to assess the photon flux absorbed by the biomass.