Thin-layer Photobioreactor Research Articles

Optimization of thin-layer photobioreactors for the production of microalgae by integrating fluid-dynamic and photosynthesis rate aspects

Optimization of thin-layer photobioreactors for the production of microalgae by integrating fluid-dynamic and photosynthesis rate aspects

Cultivation of the PHB-producing cyanobacterium Synechococcus leopoliensis in a pilot-scale open system using nitrogen from waste streams

PHB-producing cyanobacteria may provide the raw material for bio-based and biodegradable plastics. To commercialize photoautotrophic PHB production, their cultivation needs to be scaled up in open systems and to reduce costs and increase sustainability, nutrients must be obtained from waste streams. Here, the feasibility of these steps was verified. Different PHB-producing cyanobacteria were compared in laboratory-scale cultivations using either water from recirculating aquaculture systems or pre-processed liquid digestate as nutrient sources. Then, Synechococcus leopoliensis was cultivated in an open thin-layer photobioreactor (18 m2, 200 L), were growth in mineral Z-medium was again compared to said waste streams. All cultivations were successful. Cultivation in mineral medium resulted in both the highest final biomass yield (6 g L−1) and productivity (0.7 g L−1 d−1). Both waste stream-based media showed lower biomass yields and productivities (2 g L−1 and 0.25–0.3 g L−1 d−1). However, due to differences in the cultivation conditions (e.g., temperature, nutrient supply), final biomass yield and productivity do not represent the performance of the cultivations adequately. Relative parameters such as nitrogen and energy conversion ratios indicate that cultivation with aquaculture water suffered from insufficient nitrogen supply to the culture, whereas the use pre-processed liquid digestate resulted in a substantial loss of nitrogen due to volatilization. All cultivations in the open system were continued in the laboratory, where cultures were starved for ten days under nutrient-depleted conditions (without nitrogen, phosphorus, or both). While PHB accumulation occurred, concentrations were comparatively low (< 1%dw). The comparison of the results suggests that PHB yields were influenced more by the initial cultivation condition than by the specific type of nutrient depletion. Thus, while the cultivation with waste streams in an open system is feasible, environmental parameters seem to influence PHB yields considerably and must be considered for the optimization of the complete process.

The alga Bracteacoccus bullatus (Chlorophyceae) isolated from snow, as a source of oil comprising essential unsaturated fatty acids and carotenoids

A unicellular alga isolated from snow in the Sierra Nevada Mountains (Spain) was characterised using a polyphasic approach. Comparative analysis of ITS2 rDNA secondary structures identified the new culture (CCALA 1120 Cepák and Lukavský Nova Hedwigia 94:163–173, 2012) as being conspecific with Bracteacoccus bullatus (Chlorophyceae). For the first time this study documented sexual reproduction as the pairing of gametes and also an-isogamy. Strain CCALA 1120 had a temperature optimum of growth about 21 °C and an irradiance optimum above 160 µmol photons m−2 s−1. It was cultivated in pilot-plant scale, using an open thin-layer photobioreactor in a greenhouse with only partial temperature control. After harvest, a high proportion of fatty acids was found (15.3% of dry mass) with linoleic (18:2ω-6) 18.3% and α-linolenic acids (18:3ω-3) 17.4% being the most abundant. Monounsaturated fatty acids accounted for about 30% with oleic (18:1ω-9) and vaccenic acids (18:1 ω-7) as the most prominent. The ratio of PUFA ω-6/ω-3 was 1:1.16, i.e. near to the ideal ratio of 1:1, as recommended by the World Health Organization. Biomass production was 2.67 g m–2 day−1 of dry weight, i.e. 0.2 g L−1 day−1. At the end of growth phase, total carotenoids made up 10.1 mg L−1. These results indicate that B. bullatus is suitable for production of a vegetable oil at lower temperatures (12–18 °C) and comprising a high content of unsaturated fatty acids.

Critical assessment of the filamentous green microalga Oedocladium carolinianum for astaxanthin and oil production

The filamentous microalga Oedocladium carolinianum that was isolated from soil was found to be capable of producing large amounts of astaxanthin under stress culture conditions. When the culture conditions were optimized, the maximum specific growth rate of 0.37 d−1 and the maximum biomass concentration of 10.12 g L−1 were obtained after 18 days of cultivation in 1-liter glass columns (inner diameter: 5 cm) under laboratory conditions. When subjected to culture conditions of nitrogen starvation and 2 g L−1 NaCl-induced salinity stress, however, the cells produced up to 3.91% w/w astaxanthin and a high astaxanthin productivity of 24.2 mg L−1 d−1 was obtained. Analysis by HPLC-MS revealed that the majority of astaxanthin was in fatty acid esterified forms with a typical molecular ratio of free, monoester and diester astaxanthin of 1:18:81. The biosynthesis of astaxanthin coincided with that of fatty acids, and the total fatty acid content reached 40% w/w or more. The technical feasibility of mass culture of O. carolinianum was tested in a 7000-L inclined thin-layer photobioreactor and a 10,000-L tubular photobioreactor in a greenhouse. This demonstrated that O. carolinianum grew rapidly in a nitrogen replete BG-11 culture medium and the maximum biomass concentrations obtained in the inclined thin-layer photobioreactor and tubular photobioreactor were 3.74 g L−1 and 3.07 g L−1 respectively, resulting in maximum biomass productivities of 276 mg L−1 d−1 and 198 mg L−1 d−1, respectively. Although small populations of a few zooplankton species occurred in the two types of photobioreactors, none grazed on O. carolinianum and they grazed on invading unicellular microalgae instead. It was therefore concluded that O. carolinianum is a promising microalga for sustainable co-production of astaxanthin and fatty acids.

Cultivation of microalgae at high-density with pretreated liquid digestate as a nitrogen source: Fate of nitrogen and improvements on growth limitations

A liquid digestate rich in ammonium nitrogen (8.3 g L−1) was collected from an agricultural biogas plant and supplied to microalgae cultures as their only nitrogen source. Chlorella vulgaris was cultivated for up to 21 days, both under controlled conditions in laboratory-scale glass-column photobioreactors as well as outdoors in an open pilot-scale thin-layer photobioreactor. By systematically addressing issues associated with the use of liquid digestate (i.e., turbidity, nutrient imbalance, ammonium toxicity, and acidification), microalgae were robustly cultivated at a high density and cultures achieved a net biomass dry weight of between 10 and 14 g L−1, and a productivity of up to 0.93 g L−1 d−1 (93% of maximum expectation). Cultivation in the thin-layer photobioreactor achieved areal productivities between 7 and 10 g m−2 d−1. Water acidification due to the uptake of ammonium by microalgae was prevented by a controlled addition of NaOH. A detailed mass balance showed that, despite high removal efficiencies (approximately 3% of the supplied nitrogen remained in the medium), microalgae assimilated only 40–60% of the supplied nitrogen and, consequently, a large amount of nitrogen was lost to the atmosphere.

Modelling and pH Control in Raceway and Thin-Layer Photobioreactors for Wastewater Treatment

One of the most critical variables in microalgae-related processes is the pH; it directly determines the overall performance of the production system especially when coupling with wastewater treatment. In microalgae-related wastewater treatment processes, the adequacy of pH has a large impact on the microalgae/bacteria consortium already developing on these systems. For cost-saving reasons, the pH is usually controlled by classical On/Off control algorithms during the daytime period, typically with the dynamics of the system and disturbances not being considered in the design of the control system. This paper presents the modelling and pH control in open photobioreactors, both raceway and thin-layer, using advanced controllers. In both types of photobioreactors, a classic control was implemented and compared with a Proportional–Integral (PI) control, also the operation during only the daylight period and complete daily time was evaluated. Thus, three major variables already studied include (i) the type of reactors (thin-layers and raceways), (ii) the type of control algorithm (On/Off and PI), and (iii) the control period (during the daytime and throughout the daytime and nighttime). Results show that the pH was adequately controlled in both photobioreactors, although each type requires different control algorithms, the pH control being largely improved when using PI controllers, with the controllers allowing us to reduce the total costs of the process with the reduction of CO2 injections. Moreover, the control during the complete daily cycle (including night) not only not increases the amount of CO2 to be injected, otherwise reducing it, but also improves the overall performance of the production process. Optimal pH control systems here developed are highly useful to develop robust large-scale microalgae-related wastewater treatment processes.

The light/dark cycle of microalgae in a thin-layer photobioreactor

A numerical study of the motion of algal cells in a representative thin-layer-cascade (TLC) photobioreactor is presented. The goal is to determine the time scale associated with the light/dark (L/D) cycle seen by the cells during their turbulent motion in the liquid culture. Owing to the limited reliability of the available numerical results which deal with time-averaged quantities and thus lack time-resolved information, the present study is based upon the Direct Numerical Simulation of the Navier-Stokes equations, a reliable but consequently expensive numerical approach which does not incur in turbulence modelling errors. Indeed, the simulation is successfully validated in terms of averaged velocity with experimental data. The availability of full temporal information allows algae cells to be followed in time along their trajectories. A large number (up to a million) of tracers is placed in the flow to mimic the algae cell. Their trajectories are statistically studied and linked to the turbulent mixing. Results indicate that, in a typical TLC reactor designed to mimic an experimental setup, cells undergo an L/D cycle with a time scale in the range 0.1–2 s. Such time scale, albeit much longer than the typical time scale of the photosynthesis, significantly benefits the productivity of the algae compared to a steady illumination.

Year-long production of Scenedesmus almeriensis in pilot-scale raceway and thin-layer cascade photobioreactors

Biomass of Scenedesmus almeriensis was produced outdoors for 12 months using three different photobioreactor designs. Optimum dilution rates to achieve the highest biomass productivities were 0.2 day−1 for raceways and 0.3 day−1 for thin-layer reactors. Biomass productivities achieved using thin-layer cascade photobioreactors during the months of higher photosynthetic activity reached 30–35 g/m2·day, higher than those obtained using raceways during the same period: 20–25 g/m2·day. Photosynthetic efficiency was lower in spring/summer when compared to autumn/winter, suggesting that a larger share of the solar energy that reaches the culture in spring/summer is not used for microalgal growth. During summer, culture temperature reached 40 °C in thin-layer photobioreactors, which demonstrates the importance of selecting microalgal strains able to resist these conditions. Photoinhibition was not observed at incident irradiances up to 1600 μE/m2·s. However, dissolved oxygen values were especially high in thin-layer photobioreactors during this time of the year. They reached maximum values of 400% and showed an inhibitory effect on microalgal growth.

Co-cultivation of microalgae in aquaculture water: Interactions, growth and nutrient removal efficiency at laboratory- and pilot-scale

Microalgae biotechnology is of increasing importance and a central application concerns the treatment of wastewater. Here, its implementation in a recirculating aquaculture system (RAS) to lower the discharge of wastewater is studied. To better cope with external variations in culture conditions, a co-cultivation of two species of microalgae, Chlorella vulgaris and Tetradesmus obliquus, was used to obtain a more reliable and robust culture and was compared to monocultures. This approach was tested using RAS water both under sterile and non-sterile conditions at laboratory scale and then compared to a co-culture at pilot-scale in an open thin-layer photobioreactor. Performance of cultures was tested in terms of microalgae growth and nutrient removal efficiency. Furthermore, to better understand the interaction between environmental variables and each microalgae species, their relative frequencies in co-cultures as well as the presence of protozoa and bacteria were monitored. All growth experiments were carried out successfully and, unlike in a previous study, no crashes were observed. However, shifts in species frequency in co-cultures indicated that the two species were differentially affected by cultivation conditions. Despite nutrient limitation, the pilot-scale cultivation had a high productivity (13.3 g m−2 d−1) and final dry weight (11.1 g l−1) after 29 days and demonstrated its suitability for RAS water treatment.

Comparison of lipid productivity of Parachlorella kessleri heavy-ion beam irradiation mutant PK4 in laboratory and 150-L mass bioreactor, identification and characterization of its genetic variation

Parachlorella kessleri (formerly Chlorella kessleri) can accumulate high levels of both starch and lipids that can be used for the production of bioethanol and biodiesel, respectively. We mutagenized P. kessleri by heavy-ion beam irradiation and obtained a biotechnologically promising mutant strain, PK4, for further improvement of lipid productivity in comparison with wild type [1]. PK4 reached two times the optical density and accumulated 2.6 times as much starch in complete urea-phosphate (UP) media compared to tris-acetate-phosphate (TAP) media under laboratory conditions. Similarly to wild type, PK4 accumulated only negligible amounts of lipids in complete UP media. PK4 accumulated more lipids (WT: 1.17 g L−1, PK4: 1.75 g L−1) and accumulated lipids faster than WT after dilution of the UP media (WT; 0.22 g L−1 day−1, PK4; 0.43 g L−1 day−1). The productivity of PK4 was analyzed in mass culture using a 150-L thin-layer photo bioreactor housed in a temperature and light-uncontrolled glass greenhouse. The PBR consisted of two glass plates (each 6 m long and 1 m wide) at an inclination of 1.6%, arranged in a meandering path and connected with a trough. The culture was diluted four-fold with water on day 7 post-inoculation to ensure prompt nutrient limitation in the UP media. Lipid accumulation in PK4 was significantly induced so that it accumulated 66% of lipid per dry weight. Under 150-L mass cultivation conditions, PK4 showed high biomass productivity (0.82 g L−1 day−1) and high lipid productivity (0.59 g L−1 day−1). In addition, the whole genome of PK4 was sequenced to clarify the genetic variation upon heavy-ion-beam irradiation by comparison with the reference genome of WT. As a result, genetic differentiation of PK4 was found at three genes encoding endo-1,4-β-mannanase, an ATP/ADP transporter, and an elicitor response protein.

High-density cultivation of microalgae continuously fed with unfiltered water from a recirculating aquaculture system

Water from recirculating aquaculture systems (RAS) has been shown to be a suitable growth medium for microalgae and their cultivation can, therefore, be used to reduce RAS emissions. However, while efficient wastewater treatment is possible, the nutrient content of RAS water limits attainable microalgae biomass densities to 1–2 g l−1 at best, which requires frequent harvesting of microalgae. We have taken advantage of the constant evaporation of water from an open thin-layer photobioreactor (200 l volume, 18 m2 illuminated surface, artificial supply of CO2) to continuously add water from RAS to a microalgae culture and thereby provide nutrients for continued growth while evaporating all water. To test for a possible inhibitory effect of RAS water on microalgae growth, components of mineral medium were omitted stepwise in subsequent cultivations and replaced by RAS water as the only source of nutrients. This approach showed that microalgae can be grown successfully for up to three weeks in RAS water without additional nutrients and that high (20 g l−1) biomass densities can be attained. While growth in wastewater did not reach productivities measured in mineral medium, analysis of growth data suggested that this reduction was not due to an inhibitory effect of the RAS water but due to an insufficient supply rate of nutrients, even though RAS water contained up to 158 mg l−1 NO3-N. It is, therefore, concluded that this method can be used to fully treat the wastewater discharge of a RAS. Furthermore, because both water evaporation from and microalgae growth in the photobioreactor correlated positively with each other due to their shared dependency on solar radiation, supply of nutrients continuously adjusts to changes in demand. It is estimated that the area of a photobioreactor required to treat all emissions of a RAS requires approximately 6.5 times the area of the latter.

Study of cultivation and growth rate kinetic for mixed cultures of local microalgae as third generation (G-3) bioethanol feedstock in thin layer photobioreactor

The increasing use of fossil fuels causes the depletion in supply and contributes to climate change by GHG emissions into the atmosphere. Microalgae indicate as renewable and sustainable energy sources as they have a high potential for producing large amounts of biomass for third-generation biofuels (bioethanol and biodiesel) feedstock. However, there are several parameters which should be considered for microalgae cultivation, such as environmental conditions, medium composition and microalgae species. The aim of this research was to study cultivation of mixed microalgae cultures (Glagah consortium and Arthrospira maxima) in a thin layer photobioreactor. Farmpion medium, Bold’s Basal Medium (BBM) and Thoriq Eko Arief (TEA) medium were investigated as cultivation medium for bioethanol feedstock for 7 days. The results showed that the highest dry weight concentration of microalgae was in Farmpion medium (0.35 mg/ml) and the highest carbohydrate concentration of microalgae was in BBM (0.14 mg/ml). Thus, the optimum medium of microalgae cultivation for bioethanol feedstock was BBM because of the highest carbohydrate-dry weight ratio (0.88). In addition, mathematical approach by using Contois model was used to find out the growth rate of microalgae cultivation in each medium.

Pilot cultivation of the green alga Monoraphidium sp. producing a high content of polyunsaturated fatty acids in a low-temperature environment

A cold-adapted strain of Monoraphidium (Selenastraceae, Chlorophyta) isolated from an Antarctic ice-covered lake was tested for polyunsaturated fatty acids (PUFAs) production. The strain was successfully cultivated in an outdoor 150L thin-layer photobioreactor under early winter conditions of Central Europe, where the average temperature was 10.0°C and the average intensity of PAR 32μmolm−2s−1. The growth rate over the 22days of the pilot cultivation reached a value of 0.341day−1 and lipid productivity was 162mgL−1day−1. The proportion of the 16:4 and 18:4 acids was up to 19.1% and/or 34.7% of total fatty acids that resulted in a productivity of these acids of 27.5 and 43.7mgL−1day−1, respectively, which is one order of magnitude higher than previously reported values. These characteristics make this strain a prospective candidate for low-temperature biotechnology.

The role of light and nitrogen in growth and carotenoid accumulation in Scenedesmus sp.

To study the regulation of carotenoid biosynthesis and accumulation, the microalga Scenedesmus sp. might represent an alternative model microorganism to the well established Haematococcus pluvialis or Dunaliella salina. Scenedesmus sp. strain CCALA 1074 can produce high levels of carotenoids, mainly lutein, over all growth phases. In exponentially growing cultures, total carotenoids and lutein accumulated to levels of up to 1 and 0.75% DW, respectively. In early stationary phase, total carotenoids increased to 2.3% DW; lutein however remained unchanged and additional minor ketocarotenoids such as astaxanthin, echinenone and a number of unidentified carotenoid species were also present. Nitrate-limited cultures were supplemented either with nitrate or complete growth medium in early stationary phase and were cultivated either in light or in darkness. As expected, in light, cells started to divide and cultures grew; surprisingly however, in darkness, cell division was blocked after supplementation, independent of the nutrient added. Carotenoid synthesis also only proceeded in the light, whereas, in darkness, carotenoid content remained constant. When cultivated in an outdoor thin-layer photobioreactor (PBR), the greatest increase in carotenoid accumulation occurred under conditions of nitrogen sufficiency and high light. These results suggest that in Scenedesmus sp., light is a critical factor in the accumulation of carotenoids, and nitrogen availability plays only a minor role.

Elevated production of carotenoids by a new isolate of Scenedesmus sp.

A newly isolated strain of Scenedesmus sp. was tested for carotenoid production. In the laboratory, the strain accumulated total carotenoids to a relative cellular content of more than 2% DW. Very high carotenoid productivity (max. up to 20mgL−1d−1) of Scenedesmus sp. was achieved due to its high specific growth rate (μmax 2.7d−1) and biomass productivity (max. up to 2gL−1d−1). Moreover the strain showed a high tolerance to elevated temperatures with only a moderate decrease in the final biomass at 38°C and 40°C compared to 30°C; there were no statistical differences in maximal specific growth rates between temperatures. Scenedesmus sp. was successfully grown in an outdoor 150L thin-layer photobioreactor, achieving a maximal specific growth rate of 1.44d−1 and a maximal biomass productivity of 1.3gL−1d−1. After 16d it accumulated 1.86% DW of total carotenoids with an overall carotenoid productivity of 9mgL−1d−1. Excellent growth, high carotenoid production and thermotolerance make this strain a prospective candidate for biotechnological production of carotenoid-rich biomass. The possibility of using the genus Scenedesmus as an alternative to well-established carotenoid producing microalgae is discussed.

Energy-positive wastewater treatment with microalgae: raceways coupled to thin layer photobioreactors

Energy-positive wastewater treatment with microalgae: raceways coupled to thin layer photobioreactors

The microalga Parachlorella kessleri––A novel highly efficient lipid producer

The alga Parachlorella kessleri, strain CCALA 255, grown under optimal conditions, is characterized by storage of energy in the form of starch rather than lipids. If grown in the complete medium, the cultures grew rapidly, producing large amounts of biomass in a relatively short time. The cells, however, contained negligible lipid reserves (1-10% of DW). Treatments inducing hyperproduction of storage lipids in P. kessleri biomass were described. The cultures were grown in the absence or fivefold decreased concentration of either nitrogen or phosphorus or sulfur. Limitation by all elements using fivefold or 10-fold diluted mineral medium was also tested. Limitation with any macroelement (nitrogen, sulfur, or phosphorus) led to an increase in the amount of lipids; nitrogen limitation was the most effective. Diluted nutrient media (5- or 10-fold) were identified as the best method to stimulate lipid overproduction (60% of DW). The strategy for lipid overproduction consists of the fast growth of P. kessleri culture grown in the complete medium to produce sufficient biomass (DW more than 10 g/L) followed by the dilution of nutrient medium to stop growth and cell division by limitation of all elements, leading to induction of lipid production and accumulation up to 60% DW. Cultivation conditions necessary for maximizing lipid content in P. kessleri biomass generated in a scale-up solar open thin-layer photobioreactor were described.

Production of lipids in 10 strains of Chlorella and Parachlorella, and enhanced lipid productivity in Chlorella vulgaris

We tested 10 different Chlorella and Parachlorella strains under lipid induction growth conditions in autotrophic laboratory cultures. Between tested strains, substantial differences in both biomass and lipid productivity as well as in the final content of lipids were found. The most productive strain (Chlorella vulgaris CCALA 256) was subsequently studied in detail. The availability of nitrates and/or phosphates strongly influenced growth and accumulation of lipids in cells by affecting cell division. Nutrient limitation substantially enhanced lipid productivity up to a maximal value of 1.5g l(-1)day(-1). We also demonstrated the production of lipids through large-scale cultivation of C. vulgaris in a thin layer photobioreactor, even under suboptimal conditions. After 8days of cultivation, maximal lipid productivity was 0.33g l(-1)day(-1), biomass density was 5.7g l(-1) dry weight and total lipid content was more than 30% dry weight. C. vulgaris lipids comprise fatty acids with a relatively high degree of saturation compared with canola oil offering a possible alternative to the use of higher plant oils.

Outdoor open thin-layer microalgal photobioreactor: potential productivity

We have previously estimated the productivity and photosynthetic efficiency of the microalga Chlorella sp. grown in an outdoor open thin-layer photobioreactor under climate conditions typical of the Middle European region, i.e. with many days unsuitable for intensive growth of algae (cloudy and rainy days, low air temperature, low solar PAR input).To estimate the real potential productivity of the bioreactor, we collected data on algae yields obtained during clear summer day periods. Cultivation was performed in fed-batch cycles in a bioreactor with a 224 m2 culture area (length 28 m, slope 1.7%), and a 6–7 mm-thick layer of algal culture. The suspension volume in the bioreactor was 2,000 L. The mean values found for Třeboň (49°N), Czech Republic, as an average of several sunny summer cultivation periods in July, were: net areal productivity, Pnet = 38.2 g dry weight (DW) m-2 day-1; net volumetric productivity, Pvol, = 4.3 g algal DW L-1 day-1, photosynthetic efficiency (based on PAR), ηnet = 7.05%. The peak values were: Pnet about 50 g (DW) m-2 day-1, ηnet about 9%. Algal growth rate was practically linear up to high biomass densities (40–50 g DW L-1, corresponding to an areal density of 240–300 g DW m-2), at which point the culture was harvested. The concentration of dissolved oxygen increased from about 10 mg L-1 at the beginning to about 23 mg L-1 at the end of culture area at noon. Use of the above-described technology for economical production of bioethanol is proposed.

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. NO X and CO gases (up to 45 mg m−3 NO X 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.