Effect of organic carbon,C:N ratio and light on the growth and lipid productivity of microalgae/cyanobacteria coculture

Current culture methods based on monocultures under phototrophic regimes are prone to contamination, predation, and collapse. Native cultures of multiple species are adapted to the local conditions and are more robust against contamination and predation. Growth, lipid and biomass productivity of a Louisiana native coculture of microalgae (Chlorella vulgaris) and cyanobacteria (Leptolyngbya sp.) in heterotrophic and mixotrophic regimes were investigated. Dextrose and sodium acetate at C:N ratios of 15:1 and 30:1 under heterotrophic (dark) and mixotrophic (400 μmol m^?2 s^?1) regimes were compared with autotrophic controls. The carbon source and C:N ratio impacted growth and biomass productivity. Mixotrophic cultures with sodium acetate (C:N 15:1) resulted in the highest mean biomass productivity (156 g m^?3 d^?1) and neutral lipid productivity (24.07 g m^?3 d^?1). The maximum net specific growth rate (U) was higher (0.97 d^?1) in mixotrophic cultures with dextrose (C:N 15:1) but could not be sustained resulting in lower total biomass than in mixotrophic cultures with acetate (C:N 15:1), with a U of 0.67 d^?1. The ability of the Louisiana coculture to use organic carbon for biomass and lipid production makes it a viable feedstock for biofuels and bioproducts.     

Impact of light quality and quantity on growth rate kinetics of Selenastrum capricornutum

Microalgal biomass produced in indoor photobioreactors can be used as inoculum for large‐scale outdoor cultures or directly for the production of high‐value bioproducts due to the higher control of these cultures compared with outdoor systems. One of the main costs of indoor microalgal cultures is the illumination. This work can be used as a basis for the optimization of the light source for indoor microalgal biomass production, based on the light source type, irradiance, productivity, growth rate, attenuation coefficients, and contaminant growth on the reactor's side‐walls. Four commercially available near 400‐W artificial light sources for microalgal cultures (metal halide (MH), high‐pressure sodium (HPS), Son Agro^®, and fluorescent) were compared. The light elevation and the surface scalar irradiance were shown to have a linear relationship. The attenuation coefficient in air (k_a) was highest with Son Agro^®. A linear partition of the attenuation coefficient between the water and biomass and an exponential relationship between average scalar irradiance and depth were found. An empirical overall scalar attenuation coefficient for each light source was obtained. The lowest maximum observed growth rate was obtained with fluorescent light (0.98 d^?1) and the highest with Son Agro^® (2.39 d^?1). The highest growth on the reactor's wall was obtained with Son Agro^®. Further studies resulted in a higher maximum specific growth rate and optimum irradiance for HPS (2.37 d^?1 and 460 μmol s^?1 m^?2) compared with those observed with MH (1.73 d^?1 and 391 μmol s^?1 m^?2).     

Growth model for raceway pond cultivation of Desmodesmus sp. MCC34 isolated from a local water body

Biofuel production by microalgae has the advantage of higher biomass productivity over land crops. The selection of potential microalgae depends on the growth in outdoor mass cultivation during different seasons, which can be predicted by a mathematical model. Here, freshwater green algae were isolated from a local water body in Pilani, Rajasthan, India (geographical coordinates: 28°22′N 75°36′E) and characterized by microscopy and ribosomal RNA analysis. The strain was submitted to the Indian Agricultural Research Institute's microbial culture collection (IARI, India) and identified as Desmodesmus sp. MCC34. This strain, along with a fresh water green algae (Chlorella minutissima), two marine green algae species (Dunaliella salina and Dunaliella tertiolecta) and two nitrogen fixing cyanobacteria (Nostoc muscorum and Anabaena doliolum), were screened for lipid productivity and growth kinetics under culture room and raceway pond conditions. Desmodesmus sp. MCC34 showed the highest specific growth rate (0.26 day^?1), biomass production (1.9 g L^?1) and lipid productivity (103 mg L^?1 day^?1). The optimal temperature and saturating light intensity for maximal growth of Desmodesmus sp. MCC34 were 35 °C and 75 μmol m^?2 s^?1 with molar extinction coefficient of 0.22 m² g^?1, respectively. Desmodesmus sp. MCC34 was then subjected to outdoor cultivation in a 20‐m long raceway pond for 18 days during March and November 2013. The areal biomass productivity and volumetric biomass productivity were 13946.23 kg ha^?1 year^?1 and 56.94 mg L^? 1day^?1 during the month of March, decreasing to 6262.28 kg ha^?1 year^?1 and 25.57 mg L^? 1day^?1 during the month of November. A mathematical model was constructed to explain the relationship between biomass production and growth parameters such as temperature, light intensity and nutrient concentration. The productivity values predicted with the proposed model correspond well with the experimental data, suggesting the validity of the model.     

Growth and biomass productivity of Scenedesmus vacuolatus on a twin layer system and a comparison with other types of cultivations

Scenedesmus is a genus of microalgae employed for several industrial uses. Industrial cultivations are performed in open ponds or in closed photobioreactors (PBRs). In the last years, a novel type of PBR based on immobilized microalgae has been developed termed porous substrate photobioreactors (PSBR) to achieve significant higher biomass density during cultivation in comparison to classical PBRs. This work presents a study of the growth of Scenedesmus vacuolatus in a Twin Layer System PSBR at different light intensities (600 μmol photons m⁻² s⁻¹ or 1000 μmol photons m⁻² s⁻¹), different types and concentrations of the nitrogen sources (nitrate or urea), and at two CO₂ levels in the gas phase (2% or 0.04% v/v). The microalgal growth was followed by monitoring the attached biomass density as dry weight, the specific growth rate and pigment accumulation. The highest productivity (29 g m⁻² d⁻¹) was observed at a light intensity of 600 μmol photons m⁻² s⁻¹ and 2% CO₂. The types and concentrations of nitrogen sources did not influence the biomass productivity. Instead, the higher light intensity of 1000 μmol photons m⁻² s⁻¹ and an ambient CO₂ concentration (0.04%) resulted in a significant decrease of productivity to 18 and 10–12 g m⁻² d⁻¹, respectively. When compared to the performance of similar cultivation systems (15–30 g m⁻² d⁻¹), these results indicate that the Twin Layer cultivation System is a competitive technique for intensified microalgal cultivation in terms of productivity and, at the same time, biomass density.

     

Uptake of inorganic and organic nutrient species during cultivation of a Chlorella isolate in anaerobically digested dairy waste

A natural assemblage of microalgae from a facultative lagoon system treating municipal wastewater was enriched for growth in the effluents of an anaerobic digester processing dairy waste. A green microalga with close resemblance to Chlorella sp. was found to be dominant after multiple cycles of sub‐culturing. Subsequently, the strain (designated as LLAI) was isolated and cultivated in 20× diluted digester effluents under various incident light intensities (255–1,100 µmoles m^?2 s^?1) to systematically assess growth and nutrient utilization. Our results showed that LLAI production increased with increasing incident light and a maximum productivity of 0.34 g L^?1 d^?1 was attained when the incident irradiance was 1,100 µmoles m^?2 s^?1. Lack of growth in the absence of light indicated that the cultures did not grow heterotrophically on the organic compounds present in the medium. However, the cultures were able to uptake organic N and P under phototrophic conditions and our calculations suggest that the carbon associated with these organic nutrients contributed significantly to the production of biomass. Overall, under high light conditions, LLAI cultures utilized half of the soluble organic nitrogen and >90% of the ammonium, orthophosphate, and dissolved organic phosphorus present in the diluted waste. Strain LLAI was also found to accumulate triacylglycerides (TAG) even before the onset of nutrient limitation and a lipid productivity of 37 mg‐TAG L^?1 d^?1 was measured in cultures incubated at an incident irradiance of 1,100 µmoles m^?2 s^?1. The results of this study suggest that microalgae isolates from natural environments are well‐suited for nutrient remediation and biomass production from wastewater containing diverse inorganic and organic nutrient species. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:1336–1342, 2016     

The influence of light on copper‐limited growth of an oceanic diatom,Thalassiosira oceanica (Coscinodiscophyceae)

Thalassiosira oceanica (CCMP 1005) was grown over a range of copper concentrations at saturating and subsaturating irradiance to test the hypothesis that Cu and light were interacting essential resources. Growth was a hyperbolic function of irradiance in Cu‐replete medium (263 fmol Cu′ · L^?1) with maximum rates achieved at 200 μmol photons · m^?2 · s^?1. Lowering the Cu concentration at this irradiance to 30.8 fmol Cu′ · L^?1 decreased cellular Cu quota by 7‐fold and reduced growth rate by 50%. Copper‐deficient cells had significantly slower (P < 0.0001) rates of maximum, relative photosynthetic electron transport (rETR_max) than Cu‐sufficient cells, consistent with the role of Cu in photosynthesis in this diatom. In low‐Cu medium (30.8 fmol Cu′ · L^?1), growth rate was best described as a positive, linear function of irradiance and reached the maximum value measured in Cu‐replete cells when irradiance increased to 400 μmol photons · m^?2 · s^?1. Thus, at high light, low‐Cu concentration was no longer limiting to growth: Cu concentration and light interacted strongly to affect growth rate of T. oceanica (P < 0.0001). Relative ETR_max and Cu quota of cells grown at low Cu also increased at 400 μmol photons · m^?2 · s^?1 to levels measured in Cu‐replete cells. Steady‐state uptake rates of Cu‐deficient and sufficient cells were light‐dependent, suggesting that faster growth of T. oceanica under high light and low Cu was a result of light‐stimulated Cu uptake.     

Characterization of a model cyanobacterium Synechocystis sp. PCC 6803 autotrophic growth in a flat‐panel photobioreactor

We characterized the photoautotrophic growth of glucose‐tolerant Synechocystis sp. PCC 6803 in a flat‐panel photobioreactor running on a semicontinuous regime under various lights, temperatures, and influx carbon dioxide concentrations. The maximum reached growth rate was 0.135 h^?1, which corresponds to a doubling time of 5.13 h—a growth speed never reported for Synechocystis before. Saturating red light intensity for the strain was 220–360 μmol(photons) m^?2 s^?1, and we did not observe any photoinhibition up to 660 μmol(photons) m^?2 s^?1. Synechocystis was able to grow under red light only; however, photons of wavelengths 405–585 and 670–700 nm further improved its growth. Optimal growth temperature was 35°C. Below 32°C, the growth rates decreased linearly with temperature coefficient (Q₁₀) 1.70. Semicontinuous cultivation is known to be efficient for growth characterization and optimization. However, the assumption of correct growth rates calculation—culture exponential growth—is often not fulfilled. The semicontinuous setup in this study was operated as a turbidostat. Accurate online OD measurements with high time‐resolution allowed fast and reliable growth rates determination. Repeating diluting frequencies (up to 18 dilutions per day) were essential for rapid growth stability evaluation. The presented setup provides improvement to previously published semicontinuous characterization strategies by decreasing experimental time requirements and maintaining the culture in exponential growth phase throughout the entire characterization procedure.     

Survival in low light: photosynthesis and growth of a red alga in relation to measured in situ irradiance

Reduced light availability for benthic primary producers as a result of anthropogenic activities may be an important driver of change in coastal seas. However, our knowledge of the minimum light requirements for benthic macroalgae limits our understanding of how these changes may affect primary productivity and the functioning of coastal ecosystems. This knowledge gap is particularly acute in deeper water, where the impacts of increased light attenuation will be most severe. We examined the minimum light requirements of Anotrichium crinitum, which dominates near the maximum depth limit for macroalgae throughout New Zealand and Southern Australia, and is a functional analog of rhodophyte macroalgae in temperate low‐light (deep‐water) habitats throughout the world. These data show that A. crinitum is a shade‐adapted seaweed with modest light requirements for the initiation of net photosynthesis (1.49–2.25 μmol photons · m^?2 · s^?1) and growth (0.12–0.19 mol photons · m^?2 · d^?1). A. crinitum maintains high photosynthetic efficiency and pigment content and a low C:N ratio throughout the year and can maintain biomass under sub‐compensation (critical) light levels for at least 5 d. Nevertheless, in situ photon flux is less than the minimum light requirement for A. crinitum on at least 103 d per annum and is rarely sufficient to saturate growth. These findings reinforce the importance of understanding the physiological response of macroalgae at the extremes of environmental gradients and highlight the need to establish minimum thresholds that modification of the subtidal light environment should not cross.     

Agricultural encroachment: implications for carbon sequestration in tropical African wetlands

Tropical wetlands have been shown to exhibit high rates of net primary productivity and may therefore play an important role in global climate change mitigation through carbon assimilation and sequestration. Many permanently flooded areas of tropical East Africa are dominated by the highly productive C₄ emergent macrophyte sedge, Cyperus papyrus L. (papyrus). However, increasing population densities around wetland margins in East Africa are reducing the extent of papyrus coverage due to the planting of subsistence crops such as Colocasia esculenta (cocoyam). In this paper, we assess the impact of this land use change on the carbon cycle and in particular the impacts of land conversion on net ecosystem carbon dioxide exchange. Eddy covariance techniques were used, on a campaign basis, to measure fluxes of carbon dioxide over both papyrus and cocoyam dominated wetlands located on the Ugandan shore of Lake Victoria. Peak rates of net photosynthetic CO₂ assimilation, derived from monthly diurnal averages of net ecosystem exchange, of 28–35 μmol CO₂ m^?2 s^?1 and 15–20 μmol CO₂ m^?2 s^?1 were recorded in the papyrus and cocoyam wetlands, respectively, whereas night‐time respiratory losses ranged between 10 and 15 μmol CO₂ m^?2 s^?1 at the papyrus wetland and 5–10 μmol CO₂ m^?2 s^?1 at the cocoyam site. The integration of the flux data suggests that papyrus wetlands have the potential to act as a sink for significant amounts of carbon, in the region of 10 t C ha^?1 yr^?1. The cocoyam vegetation assimilated ~7 t C ha^?1 yr^?1 but when carbon exports from crop biomass removal were accounted for these wetlands represent a significant net loss of carbon of similar magnitude. The development of sustainable wetland management strategies are therefore required to promote the dual wetland function of crop production and the mitigation of greenhouse gas emissions especially under future climate change scenarios.     

Photosynthetic efficiency of Chlorella sorokiniana in a turbulently mixed short light‐path photobioreactor

To be able to study the effect of mixing as well as any other parameter on productivity of algal cultures, we designed a lab‐scale photobioreactor in which a short light path (SLP) of (12 mm) is combined with controlled mixing and aeration. Mixing is provided by rotating an inner tube in the cylindrical cultivation vessel creating Taylor vortex flow and as such mixing can be uncoupled from aeration. Gas exchange is monitored on‐line to gain insight in growth and productivity. The maximal productivity, hence photosynthetic efficiency, of Chlorella sorokiniana cultures at high light intensities (1,500 μmol m^?1 s^?1) was investigated in this Taylor vortex flow SLP photobioreactor. We performed duplicate batch experiments at three different mixing rates: 70, 110, and 140 rpm, all in the turbulent Taylor vortex flow regime. For the mixing rate of 140 rpm, we calculated a quantum requirement for oxygen evolution of 21.2 mol PAR photons per mol O₂ and a yield of biomass on light energy of 0.8 g biomass per mol PAR photons. The maximal photosynthetic efficiency was found at relatively low biomass densities (2.3 g L^?1) at which light was just attenuated before reaching the rear of the culture. When increasing the mixing rate twofold, we only found a small increase in productivity. On the basis of these results, we conclude that the maximal productivity and photosynthetic efficiency for C. sorokiniana can be found at that biomass concentration where no significant dark zone can develop and that the influence of mixing‐induced light/dark fluctuations is marginal. © 2010 American Institute of Chemical Engineers Biotechnol. Prog., 2010     

Temperature‐dependent phagotrophy and phototrophy in a mixotrophic chrysophyte

The roles of temperature and light on grazing and photosynthesis were examined for Dinobryon sociale, a common freshwater mixotrophic alga. Photosynthetic rate was determined for D. sociale adapted to temperatures of 8, 12, 16, and 20°C under photosynthetically active radiation light irradiances of 25, 66, and 130 μmol photons · m^?2 · s^?1, with concurrent measurement of bacterial ingestion at all temperatures under medium and high light (66 and 130 μmol photons · m^?2 · s^?1). Rates of ingestion and photosynthesis increased with temperature to a maximum at 16°C under the two higher light regimes, and declined at 20°C. Although both light and temperature had a marked effect on photosynthesis, there was no significant difference in bacterivory at medium and high irradiances at any given temperature. At the lowest light condition (25 μmol photons · m^?2 · s^?1), photosynthesis remained low and relatively stable at all temperatures. D. sociale acquired the majority of carbon from photosynthesis, although the low photosynthetic rate without a concurrent decline in feeding rate at 8°C suggested 20%–30% of the carbon budget could be attributed to bacterivory at low temperatures. Grazing experiments in nutrient‐modified media revealed that this mixotroph had increased ingestion rates when either dissolved nitrogen or phosphorus was decreased. This work increases our understanding of environmental effects on mixotrophic nutrition. Although the influence of abiotic factors on phagotrophy and phototrophy in pure heterotrophs and phototrophs has been well studied, much less is known for mixotrophic organisms.     

Synechococcus sp. (PTCC 6021) cultivation under different light irradiances—Modeling of growth rate-light response

Synechococcus sp. (PTCC 6021), a cyanobacterium species, was cultivated in an internally illuminated photobioreactor. The reactor was designed to achieve a monoseptic cultivation of the species. The goal was to study the growth–irradiance behavior of Synechococcus sp. (PTCC 6021). To accomplish this, different initial light irradiances were implemented inside the photobioreactor and the growth of the cells was monitored. It was observed that cell growth increased with higher light intensity until the photoinhibition occurrence at light irradiance higher than 250?μE?m^?2?s^?1. The maximum OD₆₀₀, maximum growth rate, and biomass productivity increased, and hence the extinction coefficient decreased, with the increase in light irradiance before photoinhibition. The maximum optical density (OD₆₀₀) of 5.91 was obtained with irradiance below 250?μE?m^?2?s^?1 during a growth period of 80 days. The modified Monod function could model the growth–irradiance of cells with satisfactory agreement with the experimental data. The comparison of growth–irradiance of the studied species with other photosynthetic organisms showed the same trend as for cyanobacteria with photoinhibition.     

PHOTOINHIBITION OF MECHANICALLY STIMULABLE BIOLUMINESCENCE IN THE AUTOTROPHIC DINOFLAGELLATE CERATIUM FUSUS (PYRROPHYTA)1

Ceratium fusus (Ehrenb.) Dujardin was exposed to light of different wavelengths and photon flux densities (PFDs) to examine their effects on mechanically stimulable bioluminescence (MSL). Photoinhibition of MSL was proportional to the logarithm of PFD. Exposure to I μmol photons·m^?2s^?1 of broadband blue light (ca. 400–500 nm) produced near-complete photoinhibition (≥90% reduction in MSL) with a threshold at ca. 0.01 μmol photons·m^?2·s^?1. The threshold of photoinhibition was ca. an order of magnitude greater for both broadband green (ca. 500–580 nm) and red light (ca. 660–700 nm). Exposure to narrow spectral bands (ca. 10 nm half bandwidth) from 400 and 700 nm at a PFD of 0.1 μmol photons·m^?2·s^?1 produced a maximal response of photoinhibition in the blue wavelengths (peak ca. 490 nm). A photoinhibition response (≥ 10%) in the green (ca. 500–540 nm) and red wavelengths (ca. 680 nm) occurred only at higher PFDs (1 and 10 μmol photons·m^?2·s^?1). The spectral response is similar to that reported for Gonyaulax polyedra Stein and Pyrocystis lunula Schütt and unlike that of Alexandrium tamarense (Lebour) Balech et Tangen. The dinoflagellate's own bioluminescence is two orders of magnitude too low to result in self-photoinhibition. The quantitative relationships developed in the laboratory predict photoinhibition of bioluminescence in populations of C. fusus in the North Atlantic Ocean.     

Effects of flashing light-emitting diodes on algal biomass productivity

To reduce power consumption and enhance algal biomass productivity in a thin flat-plate bioreactor (called a sliver tank bioreactor), flashing (pulsing) light was used. Biomass productivity and power consumption were monitored in controlled experiments using various photon flux levels, including a constant (non-flashing) flux of 75 μmol photons m^?2 s^?1 and three flashing experiments with photon fluxes of 375, 275, and 175 μmol photons m^?2 s^?1. Flashing experiments were performed at 10 kHz and a duty cycle of 20 %. A sliver tank bioreactor with a chamber width of 6.4 mm was used for its short optical path. Data from the experiments where light was flashed with a photon flux of 375 μmol photons m^?2 s^?1 indicated 9.6 % less power and 2.86 times the biomass productivity compared to the constant photon flux experiments. Similar results were obtained for the other flashing light regimes, which had lower biomass yields but also less input power per unit biomass produced, indicating that a large fraction of the continuously applied photons are shed or wasted, even at levels approximately 1/30th the intensity of full sun.     

Productivity of Chlorella sorokiniana in a short light‐path (SLP) panel photobioreactor under high irradiance

Maximal productivity of a 14 mm light‐path panel photobioreactor under high irradiance was determined. Under continuous illumination of 2,100 µmol photons m^?2 s^?1 with red light emitting diodes (LEDs) the effect of dilution rate on photobioreactor productivity was studied. The light intensity used in this work is similar to the maximal irradiance on a horizontal surface at latitudes lower than 37°. Chlorella sorokiniana, a fast‐growing green microalga, was used as a reference strain in this study. The dilution rate was varied from 0.06 to 0.26 h^?1. The maximal productivity was reached at a dilution rate of 0.24 h^?1, with a value of 7.7 g dw m^?2 h^?1 (m² of illuminated photobioreactor surface) and a volumetric productivity of 0.5 g dw L^?1 h^?1. At this dilution rate the biomass concentration inside the reactor was 2.1 g L^?1 and the photosynthetic efficiency was 1.0 g dw mol photons. This biomass yield on light energy is high but still lower than the theoretical maximal yield of 1.8 g mol photons^?1 which must be related to photosaturation and thermal dissipation of absorbed light energy. Biotechnol. Bioeng. 2009; 104: 352–359 © 2009 Wiley Periodicals, Inc.     

Temperature response of photosynthetic light‐ and carbon‐use characteristics in the red seaweed Gracilariopsis lemaneiformis (Gracilariales,Rhodophyta)

The red seaweed Gracilariopsis is an important crop extensively cultivated in China for high‐quality raw agar. In the cultivation site at Nanao Island, Shantou, China, G. lemaneiformis experiences high variability in environmental conditions like seawater temperature. In this study, G. lemaneiformis was cultured at 12, 19, or 26°C for 3 weeks, to examine its photosynthetic acclimation to changing temperature. Growth rates were highest in G. lemaneiformis thalli grown at 19°C, and were reduced with either decreased or increased temperature. The irradiance‐saturated rate of photosynthesis (P_max) decreased with decreasing temperature, but increased significantly with prolonged cultivation at lower temperatures, indicating the potential for photosynthesis acclimation to lower temperature. Moreover, P_max increased with increasing temperature (~30 μmol O₂ · g^?1FW · h^?1 at 12°C to 70 μmol O₂ · g^?1FW · h^?1 at 26°C). The irradiance compensation point for photosynthesis (I_c) decreased significantly with increasing temperature (28 μmol photons · m^?2 · s^?1 at high temperature vs. 38 μmol photons · m^?2 · s^?1 at low temperature). Both the photosynthetic light‐ and carbon‐use efficiencies increased with increasing growth or temperatures (from 12°C to 26°C). The results suggested that the thermal acclimation of photosynthetic performance of G. lemaneiformis would have important ecophysiological implications in sea cultivation for improving photosynthesis at low temperature and maintaining high standing biomass during summer. Ongoing climate change (increasing atmospheric CO₂ and global warming) may enhance biomass production in G. lemaneiformis mariculture through the improved photosynthetic performances in response to increasing temperature.     

Using CO2 to enhance carbon capture and biomass applications of freshwater macroalgae

A major limiting factor in the development of algae as a feedstock for the bioenergy industry is the consistent production and supply of biomass. This study is the first to access the suitability of the freshwater macroalgal genus Oedogonium to supply biomass for bioenergy applications. Specifically, we quantified the effect of CO₂ supplementation on the rate of biomass production, carbon capture, and feedstock quality of Oedogonium when cultured in large‐scale outdoor tanks. Oedogonium cultures maintained at a pH of 7.5 through the addition of CO₂ resulted in biomass productivities of 8.33 (±0.51) g DW m^?2 day^?1, which was 2.5 times higher than controls which had an average productivity of 3.37 (±0.75) g DW m^?2 day^?1. Under these productivities, Oedogonium had a carbon content of 41–45% and a higher heating value of 18.5 MJ kg^?1, making it an ideal biomass energy feedstock. The rate of carbon fixation was 1380 g C m^?2 yr^?1 and 1073.1 g C m^?2 yr^?1 for cultures maintained at a pH of 7.5 and 8.5, and 481 g C m^?2 yr^?1 for cultures not supplemented with CO₂. This study highlights the potential of integrating the large‐scale culture of freshwater macroalgae with existing carbon waste streams, for example coal‐fired power stations, both as a tool for carbon sequestration and as an enhanced and sustainable source of bioenergy.     

Light History Influences the Response of Fluvial Biofilms to Zn Exposure

Fluvial biofilms are subject to multistress situations in natural ecosystems, such as the co‐occurrence of light intensity changes and metal toxicity. However, studies simultaneously addressing both factors are rare. This study evaluated in microcosm conditions the relationship between short‐term light intensity changes and Zn toxicity on fluvial biofilms with long‐term photoacclimation to different light conditions. Biofilms that had long‐term photoacclimation to 25 μmol photons · m^?2 · s^?1 (low light [LL] biofilms), 100 μmol photons · m^?2 · s^?1 (medium light [ML] biofilms), and 500 μmol photons · m^?2 · s^?1 (high light [HL] biofilms) were characterized by different structural (Chlorophyll‐a [Chl‐a], total biomass‐AFDW, EPS, algal groups, and diatom taxonomy) and physiological attributes (ETR‐I curves and photosynthetic pigments). HL biofilms showed higher light saturation intensity and a higher production of xanthophylls than LL biofilms. In contrast, LL biofilms had many structural differences; a higher proportion of diatoms and lower AFDW and EPS contents than ML and HL biofilms. A clear effect of light intensity changes on Zn toxicity was also demonstrated. Zn toxicity was enhanced when a sudden increase in light intensity also occurred, mainly with LL biofilms, causing higher inhibition of both the Φ′_PSII and the Φ_PSII. A decoupling of NPQ from de‐epoxidation reaction (DR) processes was also observed, indicating substantial damage to photoprotective mechanisms functioning in biofilms (i.e., xanthophyll cycle of diatoms) due to Zn toxicity. This study highlights the need to take into account environmental stress (e.g., light intensity changes) to better assess the environmental risks of chemicals (e.g., metals).     

Outdoor pilot-scale production of Botryococcus braunii in panel reactors

In this paper, the outdoor production of Botryococcus braunii in pilot-scale panel reactors (0.4?m³) is studied under uncontrolled conditions at a location close to the Atacama Desert (Chile). Discontinuous experiments were performed on different dates to determine the feasibility of the culture and the influence of environmental conditions on the system yield. Data showed that solar radiation is a major parameter in determining system yield, the average irradiance inside the culture determining both the growth rate and biomass productivity. A maximum specific growth rate of 0.09?day^?1 and biomass productivity of 0.02?g?L^?1?day^?1 (dry weight) were measured in discontinuous mode, at an average irradiance of 60?μE?m^?2?s^?1. With respect to lipids, a productivity of 2.5?mg?L^?1?day^?1 was obtained under favourable growth conditions; no accumulation of lipids at the stationary phase was observed. To confirm this behaviour, a semicontinuous culture was performed at 0.04?day^?1 in a larger reactor (1?m³). In this experiment, the biomass concentration and productivity was 0.3?g?L^?1 and 0.015?g?L^?1?day^?1, respectively. The lipid content and productivity was 15.6% and 2.4?mg?L^?1?day^?1, respectively, the mean average irradiance inside the reactor being 60?μmol photons?m^?2?s^?1. The light path of the reactor determines the light availability, thus determining also the biomass concentration and productivity of the reactor once the dilution rate is fixed. Experimentally, biomass productivity of 0.015?g?L^?1?day^?1 was determined for a light path of 0.15?m, but this can be increased by more than three times for a light path of 0.1?m. These data confirm that this alga can be produced outdoors in a secure form, the culture yield improving when optimal conditions are applied, the data reported here establishing the starting point for the development of the process.     

Effect of blue and red-orange LEDs on the growth and biochemical profile of Chlamydomonas reinhardtii

Light management methods are considered effective to enhance the quantum yield and photosynthetic efficiency and promote the biomass and nutrient production; however, light saturation and inhibition restrain further improvement. This work studies the effect of light mixing on algal light saturation/inhibition, growth kinetics, and biochemical profile. The green alga Chlamydomonas reinhardtii was cultivated with batch culture under an LED light panel with multiple spectra options. Different combinations of blue (B) and red-orange (RO) light intensities were tested with blue light ranging from 45 to 65 μmol photons m^?2 s^?1 and red-orange light ranging from 45 to 205 μmol photons m^?2 s^?1. Results reveal that the mixed blue and red-orange light significantly improved the growth kinetics and relieved the light saturation under blue light and the light inhibition under the red-orange light. The maximum specific growth rate, biomass concentration, and productivity increased by 22, 50, and 57%, respectively, compared with the results under the red-orange light. The lipid and protein synthesis were observed to be promoted under mixed light with relatively low red-orange light intensities (45 and 105 μmol photons m^?2 s^?1) and repressed at high red-orange light intensities (155 and 205 μmol photons m^?2 s^?1). The carbohydrate content did not change.