Jiří Doucha

Utilization of flue gas for cultivation of microalgae (Chlorella sp.) in an outdoor open thin-layer photobioreactor.

Flue gas generated by combustion of natural gas in a boiler was used for outdoor cultivation of Chlorella sp. in a 55 m2 culture area photobioreactor. A 6 mm thick layer of algal suspension continuously running down the inclined lanes of the bioreactor at 50 cm s−1 was exposed to sunlight. Flue gas containing 6–8% by volume of CO2 substituted for more costly pure CO2 as a source of carbon for autotrophic growth of algae. The degree of CO2 mitigation (flue gas decarbonization) in the algal suspension was 10–50% and decreased with increasing flue gas injection rate into the culture. A dissolved CO2 partial pressure (pCO2) higher than 0.1 kPa was maintained in the suspension at the end of the 50 m long culture area in order to prevent limitation of algal growth by CO2. NOX and CO gases (up to 45 mg m−3 NOX and 3 mg m−3 CO in flue gas) had no negative influence on the growth of the alga. On summer days the following daily net productivities of algae [g (dry weight) m−2] were attained in comparative parallel cultures: flue gas = 19.4–22.8; pure CO2 = 19.1–22.6. Net utilization (η) of the photosynthetically active radiant (PAR) energy was: flue gas = 5.58–6.94%; pure CO2 = 5.49–6.88%. The mass balance of CO2 obtained for the flue gas stream and for the algal suspension was included in a mathematical model, which permitted the calculation of optimum flue gas injection rate into the photobioreactor, dependent on the time course of irradiance and culture temperature. It was estimated that about 50% of flue gas decarbonization can be attained in the photobioreactor and 4.4 kg of CO2 is needed for production of 1 kg (dry weight) algal biomass. A scheme of a combined process of farm unit size is proposed; this includes anaerobic digestion of organic agricultural wastes, production and combustion of biogas, and utilization of flue gas for production of microalgal biomass, which could be used in animal feeds. A preliminary quantitative assessment of the microalgae production is presented.

Microalgae—novel highly efficient starch producers

The freshwater alga Chlorella, a highly productive source of starch, might substitute for starch‐rich terrestrial plants in bioethanol production. The cultivation conditions necessary for maximizing starch content in Chlorella biomass, generated in outdoor scale‐up solar photobioreactors, are described. The most important factor that can affect the rate of starch synthesis, and its accumulation, is mean illumination resulting from a combination of biomass concentration and incident light intensity. While 8.5% DW of starch was attained at a mean light intensity of 215 µmol/(m2 s1), 40% of DW was synthesized at a mean light intensity 330 µmol/(m2 s1). Another important factor is the phase of the cell cycle. The content of starch was highest (45% of DW) prior to cell division, but during the course of division, its cellular level rapidly decreased to about 13% of DW in cells grown in light, or to about 4% in those kept in the dark during the division phase. To produce biomass with high starch content, it is necessary to suppress cell division events, but not to disturb synthesis of starch in the chloroplast. The addition of cycloheximide (1 mg/L), a specific inhibitor of cytoplasmic protein synthesis, and the effect of element limitation (nitrogen, sulfur, phosphorus) were tested. The majority of the experiments were carried out in laboratory‐scale photobioreactors, where culture treatments increased starch content to up to about 60% of DW in the case of cycloheximide inhibition or sulfur limitation. When the cells were limited by phosphorus or nitrogen supply, the cellular starch content increased to 55% or 38% of DW, respectively, however, after about 20 h, growth of the cultures stopped producing starch, and the content of starch again decreased. Sulfur limited and cycloheximide‐treated cells maintained a high content of starch (60% of DW) for up to 2 days. Sulfur limitation, the most appropriate treatment for scaled‐up culture of starch‐enriched biomass, was carried out in an outdoor pilot‐scale experiment. After 120 h of growth in complete mineral medium, during which time the starch content reached around 18% of DW, sulfur limitation increased the starch content to 50% of DW. Biotechnol. Bioeng. 2011; 108:766–776.

Productivity, CO2/O2 exchange and hydraulics in outdoor open high density microalgal (Chlorella sp.) photobioreactors operated in a Middle and Southern European climate

Two variants of open photobioreactors were operated at surface-to-volume ratios up to 170 m−1. The mean values for July and September obtained for photobioreactor PB-1 of 224 m2 culture area (length 28 m, inclination 1.7%, thickness of algal culture layer 6 mm), operated in Třeboň (49∘N), Czech Republic, were: net areal productivity, Pnet = 23.5 and 11.1 g dry weight (DW) m−2 d−1; net photosynthetic efficiency (based on PAR – Photosynthetic Active Radiation), η = 6.48 and 5.98%. For photobioreactor PB-2 of 100 m2 culture area (length 100 m, inclination 1.6%, thickness of algal culture layer 8 mm) operated in Southern Greece (Kalamata, 37∘N) the mean values for July and October were: Pnet = 32.2 and 18.1 g DW m−2 d−1, η = 5.42 and 6.07%. The growth rate of the alga was practically linear during the fed-batch cultivation regime up to high biomass densities of about 40 g DW L−1, corresponding to an areal density of 240 g DW m−2 in PB-1 and 320 g DW m−2 in PB-2. Night biomass loss (% of the daylight productivity, PL) caused by respiration of algal cells were: 9–14% in PB-1; 6.6–10.8% in PB-2. About 70% of supplied CO2 was utilized by the algae for photosynthesis. The concentration of dissolved oxygen (DO) increased from about 12 mg L−1 at the beginning to about 35 mg L−1 at the end of the 100 m long path of suspension flow in PB-2 at noon on clear summer days. Dissipation of hydraulic energy and some parameters of turbulence in algal suspension on culture area were estimated quantitatively.

Bioaccumulation and toxicity of selenium compounds in the green alga Scenedesmus quadricauda

BackgroundSelenium is a trace element performing important biological functions in many organisms including humans. It usually affects organisms in a strictly dosage-dependent manner being essential at low and toxic at higher concentrations. The impact of selenium on mammalian and land plant cells has been quite extensively studied. Information about algal cells is rare despite of the fact that they could produce selenium enriched biomass for biotechnology purposes.ResultsWe studied the impact of selenium compounds on the green chlorococcal alga Scenedesmus quadricauda. Both the dose and chemical forms of Se were critical factors in the cellular response. Se toxicity increased in cultures grown under sulfur deficient conditions. We selected three strains of Scenedesmus quadricauda specifically resistant to high concentrations of inorganic selenium added as selenite (Na2SeO3) – strain SeIV, selenate (Na2SeO4) – strain SeVI or both – strain SeIV+VI. The total amount of Se and selenomethionine in biomass increased with increasing concentration of Se in the culturing media. The selenomethionine made up 30–40% of the total Se in biomass. In both the wild type and Se-resistant strains, the activity of thioredoxin reductase, increased rapidly in the presence of the form of selenium for which the given algal strain was not resistant.ConclusionThe selenium effect on the green alga Scenedesmus quadricauda was not only dose dependent, but the chemical form of the element was also crucial. With sulfur deficiency, the selenium toxicity increases, indicating interference of Se with sulfur metabolism. The amount of selenium and SeMet in algal biomass was dependent on both the type of compound and its dose. The activity of thioredoxin reductase was affected by selenium treatment in dose-dependent and toxic-dependent manner. The findings implied that the increase in TR activity in algal cells was a stress response to selenium cytotoxicity. Our study provides a new insight into the impact of selenium on green algae, especially with regard to its toxicity and bioaccumulation.

The chlorococcalean alga Chlorella in animal nutrition: a review

Unicellular freshwater microalgae of the genus Chlorella are characterised by a relative ease of cultivation, high productivity and high content of proteins and other valuable components. However, the alga is too expensive to use widely as a protein supplement in animal feed. Nevertheless, in many experiments, it was found that even a very low, economically acceptable addition of Chlorella biomass to animal feed can positively influence growth and performance. This is due to the presence of pigments, antioxidants, provitamins, vitamins and a growth substance known as the Chlorella Growth Factor (CGF), which can stimulate or enhance the immune system, increase feed intake and utilisation and promote reproduction; the use of Chlorella biomass might therefore increase the value of animal products for human consumption. Significant results were also achieved in the use of Chlorella biomass as a carrier of organically bound selenium and iodine that play a substantial role in the thyroid hormone regulation in an organism.

High Density Outdoor Microalgal Culture

Despite the common use of open raceway pond technology for algae production, the system has many serious drawbacks resulting in low productivities and relatively high production costs. The key to higher yields and a cheaper product rests with the lowering of culture volume by decreasing the thickness of the algal layer exposed to the light. The higher the culture surface-to-volume ratio (S/V), the higher the culture density and the lower the cost of handling and harvesting. Basic parameters (light, temperature, mixing, carbon dioxide, oxygen, nutrition) affecting algal productivity in thin-layer (TL) photobioreactor have been assessed. In a low volume of vigorously mixed culture, utilization of light energy and algal yields are increased. Production costs are reduced to about one fifth (20 %) compared to raceways ponds.

CO2 and O2 gas exchange in outdoor thin-layer high density microalgal cultures

Two thin layer culture units operated as batch cultures with the algaChlorella kessleri were used in gas exchange experiments. The mass transfer coefficient Kg [g m−2 h−1 kPa−1] of O2 and CO2 desorption from culture surface decreased with increasing culture temperature. Between 60–70% of supplied CO2 was used for algal growth. It was estimated that the length of growth surface may be extended to about 50 m, without additional saturation by CO2. On average 1.35 g CO2 was consumed by the alga per 1 g of produced O2. Net CO2 consumption (RCO2) and O2 production (RO2) were not inhibited by irradiance. RO2 did not decrease (in some cases it even increased) along the culture surface, despite increased accumulation of O2. Measurement of pO2 where the culture leaves the reactor before being pumped back onto the illuminated surface, correlated with O2 production and CO2 consumption and may be used to monitor the reactors growth performance.

What kind of lamp for the cultivation of algae

AbstractA method for quantitative evaluation of light sources from the point of their suitability for algal cultivation is described. Two parameters are used for the evaluation: (1)amount of photons emitted in the spectral region absorbed by algae per consumed unit of electrical energy;(2)fraction of photons intercept by the algae that got effectively transformed into chemical energy. The value of parameter (2) depends on the emission spectrum of the light source, the absorption spectrum of the algae, quantum capacity of the algae and on conditions of cultivation.The method permits the assessment of the differences in algal productivity under light of various light sources with respect to other recent methods for comparison.

Erratum to: Outdoor open thin-layer microalgal photobioreactor: potential productivity

Figure 1 shown in the article does not represent real timecourse of algal growth in the photobioreactor during one fedbatch growth cycle. It was constructed as an ideal growth curve to estimate the maximum productivity using selected data obtained during clear summer days. Not included in the curve is the lower growth rate of the culture at the beginning of the curve. This would prolong the length of the cycle up to 12– 14 days and decreases the average daily net areal productivity in course of the growth cycle to about 29 g m d. Still, under ideal climate and growth conditions, yields of 80–100 t of dried Chlorella biomass per 1 ha area could be theoretically reached for a 300-day cultivation season. One of the major goals of algal biotechnology is to prove experimentally that such high biomass yields can be achieved in Chlorella strains with high starch content (50 % in biomass).

Beneficial or Toxic Effects of Selenium on Green Algae and Their Application as Nutrient Supplements or Bio-remediators

Selenium is an essential element in many organisms, with beneficial roles for animal health, but it can also be a dangerous toxin. Research into these two paradoxical faces of selenium is reviewed in relation to unicellular species of microalgae. Recent information on algal selenoproteins in general, and selenium-containing enzymes in particular, will be described, as well as the bioaccumulation of different forms of selenium in algae. In this review, we will also consider the impact of selenium on algal growth and other cellular events: firstly from the point of its toxicity, including research into selenium-resistant algal strains and their possible use for remediation of selenium contaminated environments. Secondly, we will examine case examples of selenium-enriched algae as a source of organic selenium with health benefits for different domestic animals.