Indoor Photobioreactor Research Articles

Unveiling the anti-proliferative and pro-thermogenic activity of Staurosirella pinnata (Bacillariophyta) bioproducts

Biorefinery co-products obtained from biomass of the field isolated diatom Staurosirella pinnata have been investigated for their bioactivity on selected human and murine cell lines. Biomass grown in indoor photobioreactor, collected at the stationary phase, was subjected to methanolic extraction to produce a crude extract, sequentially fractionated (hydrophilic-hydrophobic gradient) to obtain six fractions (A4, A5, A7; B4, B5, B6). Fractions' bioactivity was tested on BRAFwt and BRAFV600E human melanoma cell lines, compared to normal keratinocytes. All fractions showed cytotoxic activity, but only fraction A4 showed a remarkable cell-type selectivity, with cell death induction up to 70 % on melanoma cells. Further characterization allowed to identify and purify four apocarotenoids from fraction A4, representing the first report of such class of compound s in mass cultivated diatoms. In addition, fraction A5 resulted to be a mixture of oxylipins and fraction B4 of purine nucleosides, with adenosine as main component. Residual biomass was further processed to obtain an enriched lipidic extract, characterized by a high content of poly-unsaturated fatty acids. Anti-diabetic and anti-obesity activities were assessed by evaluating the expression levels of key proteins involved into thermogenesis (UCP1), lipolysis (Perilipin, HSL660), and mitochondrial dynamics (pDRP1, VDAC), on murine white adipocyte cell line. Overall, the data here reported confirmed S. pinnata as a platform for the discovery and purification of bioactive compounds with biomedical potential, and the biorefinery pipeline allow their combined isolation, thus advancing the sustainability of diatom exploitation for the discovery and production of bioactive molecules.

Cultivation of Pseudochlorella pringsheimii for biodiesel production in a scalable indoor photobioreactor: case studies from Egypt

BackgroundEnhancement of lipid accumulation is the major strategy to improve the commercial feasibility of microalgae as a source for biodiesel production. Pseudochlorella pringsheimii (Formally was named as Chlorella ellipsoidea) green microalgae strain was chosen with respect to their ability as a potential source to produce high lipids content, could be used for the production of biofuel, which can be an alternative renewable energy source instead of fossil fuels. ResultsInitially, the Pseudochlorella pringsheimii microalgae was evaluated on the basis of tested at Lab scales 2 L by applicable different nutrient individual of N, P, Fe conditions in BBM medium concentrations for choosing the best concentrations induce lipid contents and productivity to cultivate in large scale in the 2000 L PBR. The suitable concentrations of nutrients with highest lipid contents were obtained under deficient of nitrogen (1.25 gL−1, limited N) and phosphorus (0.1 mg L−1, limited P) coupled with high iron concentration (10 mg L, rich Fe) and CO2 (6%). Therefore, their collective of nutrients was applied to culture of microalgae cells at large scale in 2000 L photobioreactor (PBR model), which, this techniques was used to quantify high lipid contents (25% w/w) and high lipid productivity (74.07 mgL−1 day−1). The inducted lipid conversion to biodiesel via transestrification process was 91.54 ± 1.43%. The fatty acid methyl esters (FAMEs profile by means of GC/MS resulted in C16:0, C18:1, C18:2, C18:3 as a main constituents. With regard to physical–chemical property (such as density, kinematic viscosity, gravity, and certain number), the Pseudochlorella pringsheimii biodiesel have biofuel properties, in accordance with appropriate biodiesel properties, as ASTM and EU standards, that thereby referring to high quality biodiesel. ConclusionsPseudochlorella pringsheimii cultured in large scale in photobioreactor under stress condition have a high potential of lipids production with high quality of FAMEs that can be used as a promising biodiesel fuel. It has also a potential to be applied for commercialization based on the techno-economic and environmental impacts. Highlights*Pseudochlorella pringsheimii showed a high potential of lipids 25% lipid accumulation.*Pseudochlorella pringsheimii could be cultured at large scale in potobioreactor, as potential feedstock for biodiesel production.*Bodiesel FAME contains C 16:0, C 18:1 and C 18:2 as a maim FAM.*N, P starvation collective with high Fe3+was the main driver behind lipid accumulation.*Pseudochlorella pringsheimii biodiesel have appropriate biodiesel properties, as ASTM and EU standards.*C. ellipsoidea can be used as a potential feedstock for biodiesel production.

Outdoor annual algae productivity improvements at the pre-pilot scale through crop rotation and pond operational management strategies

The Development of Integrated Screening, Cultivar Optimization, and Verification Research (DISCOVR) collaborative consortium operated pre-pilot scale outdoor ponds to deliver much-needed multi-year, long-term and consistent, algae cultivation data relevant to understanding the current state of technology in terms of expected seasonal algae biomass productivity. Over the course of four years from 2018 to 2021, twelve identical 4.2 m2 mini-ponds were run in triplicate sets to test strains and operational strategies demonstrated in small-, indoor photobioreactors, in pursuit of increasing overall algae areal productivity and projected farm yield. Fourteen different cultivars derived from a strain screening pipeline were tested. Through deliberate seasonal crop rotation and improvements in operational strategies, annual biomass productivity increased from 11.6 to 17.6 g m−2 day−1, a > 50 % increase over the 2018 baseline. Both brackish and marine strains were included and four out of the fourteen strains consistently yielded high productivity across multiple years; brackish strains Monoraphidium minutum (26BAM) and Scenedesmus obliquus (UTEX393), and marine strains Tetraselmis striata (LANL1001) and Picochlorum celeri (TG2). These freely available datasets, which represent nearly complete annual daily coverage of cultivation metrics including weather, pond temperature and pH, nutrients, and productivity, are unique in the public domain and seek to fill agronomic and operational knowledge gaps to help in the eventual commercialization of algal biofuels and bioproducts.

Complete N and P removal from hydroponic greenhouse wastewater by Tetradesmus obliquus: A strategy for algal bioremediation and cultivation in Nordic countries

Agricultural wastewaters are a major source of pollution in nature. Here, agricultural wastewaters from a commercial hydroponic greenhouse were used to cultivate the microalga Tetradesmus obliquus sp. NIVA-CHL107 in order to assess its bioremediation ability and evaluate the potential held in biomass derived from wastewater. The batch cultivation trials were performed using a pilot scale indoor photobioreactor equipped with LEDs. The culture achieved 100 % removal efficiency of N and P and a maximum dry weight (DW) of 6.2 g L−1. At the exponential phase of growth, the biomass had a protein content of 45–50 % of DW and a carbohydrate fraction representing 20 % of DW. At the stationary phase, the carbohydrates increased to 60 % of DW. The PUFA content was higher during the exponential phase, representing >65 % of total fatty acids. Throughout the cultivation, the predominant carotenoids were lutein and β-carotene. The Tetradesmus obliquus sp. NIVA-CHL107 was demonstrated to be a suitable candidate for an algal biorefinery designed for hydroponic wastewater treatment and a multi-product pipeline.

Optimisation and growth kinetic analysis of Microalgae, Arthrospira platensis in 2-L Photobioreactors

In recent years, photoautotrophic microalgae are widely recognised due to their diverse yet significant natural values, particularly in healthcare, including pharmaceuticals, cosmetics and feedstock industries. One of the most exploited blue-green microalgae, Arthrospira sp. has been addressed as a potent superfood. However, the microalgal mass-production requires suitable inoculum strain and controlled cultivation conditions for enhanced growth performance. Hence, this study aimed to maximise biomass of Arthrospira platensis chosen strain in a 2 litres indoor photobioreactor under three different parameters which were aeration rate, light intensity and pH of the medium. In the present study, a comparative study of growth performance between helical (S1) and straight form (S2) of A. platensis was conducted and the results revealed that morphological differences did not affect growth performances. Meanwhile, the optimisation based on the parameters studied shows that cultivation of A. platensis with aeration of 0.5 L/min and medium of pH 9.0 yielded the highest biomass production which were 1.500 ± 0.049 g/L. Under different light intensity, A. platensis produced the highest biomass and maximum specific growth rate of 1.142 ± 0.037 g/L and 0.716 ± 0.018 1/day, respectively when cultivated under irradiance of 6000 Lux. In conclusion, compared to before optimisation, biomass and maximum specific growth rate after optimisation was 137% and 24% increased, respectively.

Biomass and pigment production for Arthrospira platensis via semi-continuous cultivation in photobioreactors: Temperature effects.

This study describes the response of Arthrospira platensis to a variety of temperature conditions as reflected in variations of photosynthetic parameters, pigmentation, and biomass productivity in indoor photobioreactor (PBR) cultivations. These experiments are designed to better understand the impact of temperature, seasonal variations, and acclimation effects on outdoor biomass production. The irradiance level and temperature range (20-39°C) are chosen to enable modeling of semi-continuous operation of large-scale outdoor PBR deployments. Overall, the cultivations are quite stable with some pigment-related instabilities after prolonged high-temperature exposure. Changes in productivity with temperature, as reflected in measured photosynthetic parameters, are immediate and mainly attributable to the temperature dependence of the photosaturation parameter, a secondary factor being variation in pigment content on a longer time scale corresponding to turnover of the culture population. Though pigment changes are not accompanied by significant changes in productivity, prolonged exposure at 35°C and above yields a clear degradation in performance. Productivities in a semi-continuous operation are quantitatively reproduced with a productivity model incorporating photosynthetic parameters measured herein. This study confirms the importance of temperature for biomass and pigment production in Arthrospira cultivations and provides a basis for risk assessments related to temperature mitigation for large-scale outdoor cultivations.

Design of batch algal cultivation systems and ranking of the design parameters

In this article, we developed a process to design batch algal cultivation systems consisting of outdoor ponds, indoor photobioreactors (PBRs), outdoor PBRs, and indoor ponds for both freshwater and industrial wastes (wastewater and flue gas). We considered pH, temperature, light conditions, carbon, nutrients, inhibitors, mixing, and O2 degassing as design parameters and sequentially ranked them according to the necessity of cultivation conditions. Although each set of conditions warrants a unique design according to the requirements, some scenarios were common for every system, i.e., microalgae species, temperature, pH, light, size, shape, and material were always ranked before nutrients, and mixing technique and inhibitors were consistently ranked after nutrients. Light and temperature for outdoor conditions, pH for ponds, and nitrogen and phosphorus were deemed noncontrollable. Ponds do not require material for construction; O2 degassing and the selection of microalgae were always ranked first; and SOx and NOx were considered only for industrial flue gas. We constructed cultivation models of Chlorella vulgaris (C. vulgaris) for Bangkok based on the developed designs of algal cultivation systems. Monod’s model (mathematical model) and simulations by SuperPro Designer software using the optimum parameter values predicted a maximum algal productivity of 0.0114–0.0381 and 0.11–0.7 g/l/day (open pond and PBR, respectively), bioremediation of 52–70% and 81–90% (open pond and PBR; only wastewater), and CO2 biofixation of < 1% (only PBR). A comparison between the results found in this study and the literature on C. vulgaris suggests that both Monod’s model and simulation software can predict algal productivity and bioremediation, but they are not recommended for CO2 biofixation.

Indoor and outdoor cultivation of Chlorella vulgaris and its application in wastewater treatment in a tropical city—Bangkok, Thailand

This study was carried out to assess the effectiveness of algal growth cultivated in photobioreactors (PBRs) in different conditions in a tropical environment, i.e., indoor and outdoor conditions with wastewater in Bangkok. The PBRs were inoculated with pure Chlorella vulgaris, and the cultivation was conducted in housing state wastewater. The productivity of C. vulgaris was found to be 0.0960 g/l/d in a pH-controlled outdoor PBR with pH in between 7.0 and 8.0, 0.0618 g/l/d in outdoor PBR with no control, and 0.0131 g/l/d in indoor pH-controlled PBR (with a fixed pH of 7.5). Chlorella vulgaris did not show growth in indoor PBR with no pH control. Indoor PBRs consumed 232 to 270 times more energy and needed 25 to 57 times more capital cost, and 3.8 to 16.8 times more operating cost than that of outdoor PBRs. Outdoor PBRs showed better nutrient removal efficiency of housing state wastewater than that of the wastewater treatment plant, i.e., 100% removal of biological oxygen demand, chemical oxygen demand, total phosphorus and more than 96% removal of total nitrogen; However, required time and energy consumption were more in outdoor PBRs. The possibility of improving the process performance by controlling pH, by supplying CO2 from additional source, and by supplying continuous aeration appears as an attractive option. Although precautions should be taken for CO2 supply, high concentration CO2 caused a significant drop in pH and an increase of total dissolved solids. Light transmission efficiency of PBR material polyethylene terephthalate material was 85.45% to 92.08%, and efficiency decreased with the increase in light intensity.

A feasibility study of utilizing hydrothermal liquefaction derived aqueous phase as nutrients for semi-continuous cultivation of Tetraselmis sp.

The feasibility of substituting 50% nutrients by aqueous phase liquid (APL), derived from hydrothermal liquefaction of Tetraselmis sp. biomass, in a semi-continuous cultivation of Tetraselmis sp. was studied. Growth experiments were conducted in indoor photobioreactor and outdoor raceway tank for three consecutive cycles. At the end of exponential growth pahse, 75% of the culture was harvested, and the supernatant was returned to the cultivation system. For control cultures, fresh nutrients were added; however, for the experimental cultures, an appropriate volume of APL was added to replace half of the nutrients. Either indoor or outdoor, the growth rate and biomass yield in APL-added cultures were either equal or slightly better compared to control culture; although APL had little to no effect on the metabolite content of Tetraselmis sp., metabolites profile of Tetraselmis sp. varied between APL-added and control cultures. Nevertheless, 50% nutrients requirements for microalgae cultivation could be replaced by APL.

Continuous production of biohydrogen from oil palm empty fruit bunch hydrolysate in tubular photobioreactors

Production of hydrogen by the photosynthetic bacterium Rhodobacter sphaeroides was compared in continuously operated tubular photobioreactors illuminated by natural outdoor sunlight (0.15–66 klux; diurnal cycle) and constant indoor artificial light (10 klux; tungsten lamps). In both cases the operating temperature was 35 °C and the organic carbon source was an acid hydrolysate of oil palm empty fruit bunch (EFB), an agroindustrial waste. In the outdoor photobioreactor, under the best production conditions, the daytime feeding rate of the mixed carbon substrate was 48 mL h−1 and the average pseudo-steady state hydrogen production rate was 36 mL H2 L−1 medium h−1. The cumulative hydrogen production was 430 mL H2 L−1 medium. For the indoor photobioreactor fed at the same rate as the outdoor system, the steady state average hydrogen production rate was 43 mL H2 L−1 h−1 and the cumulative hydrogen production was 517 mL H2 L−1 medium. Reducing the feed rate to less than 48 mL h−1, enhanced the biomass concentration, but reduced hydrogen production in both bioreactors. The sunlight-based cumulative hydrogen production was only about 17% less compared to the artificially lit system, but required only 22% of the electrical energy.

Full-scale validation of an algal productivity model including nitrogen limitation

Accurate predictions of algal productivity under nutrient-limiting conditions are needed to assess the economics of full-scale algal cultivation for the developing markets of food, feed, and at longer term, green chemistry and biofuel. In particular, predicting pigments production from micro-algae is a critical milestone in the assessments of high-value chemicals production from micro-algae. This study validates a mathematical model predicting algal biomass productivity in outdoor raceway ponds under nitrogen-limiting conditions. The model was first validated from experimental data collected during Dunaliella salina cultivation in indoor photobioreactors and accounts for the impact of light, temperature, and nitrogen concentration on algal productivity (overall accuracy on algal concentration of ±2.7 mg L−1, N = 48). The model was then validated against data collected in outdoor raceway ponds over a period of 2 years, representing a total of 111 days of cultivation. Biomass and extracellular nitrogen concentrations predictions were accurate within ±0.055 g L−1 (N = 69) and ±0.0024 g L−1 (N = 26), respectively. Model inaccuracies were mostly due to measurement errors and uncertainties on model inputs. Measured carotenoids concentrations were found proportional to the biomass concentrations in the outdoor raceway ponds. By coupling this linear correlation to the productivity model, predicted carotenoids concentrations were in good agreement with experimental data (accuracy within ±0.0046 g L−1, N = 55). The mathematical model developed in this study has therefore the potential to refine previous assessments of algal cultivation for biofuels and pigments production.

Potential of wastewater treating Chlorella minutissima for methane enrichment and CO2 sequestration of biogas and producing lipids

An algal biorefinery approach is today's need for commercialization of microalgal biodiesel production. In the present study, an indoor photobioreactor with Chlorella minutissima was evaluated to upgrade biogas produced from anaerobic digestion of cow dung. The potential of C. minutissima was assessed in two different growth media viz. BG 11 and wastewater. The significant CO2 absorption reported by C. minutissima was in the range of 75–85.4% at 1296 μmol m−2s−1 of light intensity and 0.33 vol per volume per minute (vvm) gas flows. The present study demonstrated that there is an increase in methane content from 63.5 to 86.4% in the effluent biogas. The highest biomass productivity was observed at 1296 μmol m−2 s−1 light intensity with the same gas flow and the productivity of 0.18 gL−1 and 2.2 gL−1 in the BG11 medium and wastewater respectively. Further, we reported that total lipid content based on dry biomass of C. minutissima were 22.4% and 26% in the BG11 medium and wastewater, respectively. The gross calorific value of treated biogas was also higher (8.15 kWh m−3 and 8.63 kWh m−3) in both BG11 and wastewater, respectively.

The Diatom Staurosirella pinnata for Photoactive Material Production.

A native isolate of the colonial benthic diatom Staurosirella pinnata was cultivated for biosilica production. The silicified cell walls (frustules) were used as a source of homogeneous and structurally predictable porous biosilica for dye trapping and random laser applications. This was coupled with the extraction of lipids from biomass showing potential to fabricate photoactive composite materials sustainably. The strain was selected for its ease of growth in culture and harvesting. Biosilica and lipids were obtained at the end of growth in indoor photobioreactors. Frustules were structurally characterized microscopically and their chemistry analyzed with Fourier Transform Infrared Spectroscopy. Frustule capacity of binding laser dyes was evaluated on a set of frustules/Rhodamine B (Rho B) solutions and with respect to silicon dioxide and diatomite by Fluorescence Spectroscopy demonstrating a high affinity for the organic dye. The effect of dye trapping property in conveying Rho B emission to frustules, with enhancement of scattering events, was analyzed on Rho B doped polyacrylamide gels filled or not with frustules. Amplified spontaneous emission was recorded at increasing pump power indicating the onset of a random laser effect in frustule filled gels at lower power threshold compared to unfilled matrices.

Biophotonic perception on Desmodesmus sp. VIT growth, lipid and carbohydrate content

Constant and fluctuating light intensity significantly affects the growth and biochemical composition of microalgae and it is essential to identify suitable illumination conditions for commercial microalgae biofuel production. In the present study, effects of light intensities, light:dark cycles, incremental light intensity strategies and fluctuating light intensities simulating different sky conditions in indoor photobioreactor on Desmodesmus sp. VIT growth, lipid and carbohydrate content were analyzed in batch culture. The results revealed that Desmodesmus sp. VIT obtained maximum lipid content (22.5%) and biomass production (1.033g/L) under incremental light intensity strategy. The highest carbohydrate content of 25.4% was observed under constant light intensity of 16,000lx and 16:08h light:dark cycle. The maximum biomass productivity of Desmodesmus sp. VIT (53.38mg/L/d) was occurred under fluctuating light intensity simulating intermediate overcast sky condition.

Assessment of a Novel Algal Strain Chlamydomonas debaryana NIREMACC03 for Mass Cultivation, Biofuels Production and Kinetic Studies.

A novel microalgae strain Chlamydomonas debaryana (KJ210856) was isolated from a freshwater lake of Punjab, India, and cultivated considering climatic sustainability and inherent adaptability concern. C. debaryana was grown in a 30-L indoor photobioreactor to study the mass cultivation prospect and biofuel potential. Physicochemical characterization of biomass and the lipid was performed with effect to nitrogen stress. It showed a higher biomass yield (1.58±0.02gL(-1), dry weight) and twofold increase in lipid yield (552.78±9mgL(-1)) with 34.2±0.19% lipid content under nitrogen deficient condition. Strikingly, increase in triglycerides achieved with nitrogen depletion containing over 96% of total fatty acids (C 14, C 16, and C 18). Proximate and ultimate analysis suggested the presence of relatively higher volatile matter and carbon-hydrogen ratio. Furthermore, lower moisture and ash content signified C. debaryana biomass has promising features towards biofuel applications. The pyrolytic behavior of the whole biomass was also studied using thermogravimetric analyzer (TGA) and kinetic parameters were estimated using different methods. Promising growth rate and lipid yield leading to feasible biofuel feed stock production in indoor photobioreactor along with autosediment potential of cells validates C. debaryana NIREMACC03, a potential strain for mass cultivation.

Batch Growth of Chlorella Vulgaris CCALA 896 versus Semi-Continuous Regimen for Enhancing Oil-Rich Biomass Productivity

The aim of this study was to induce lipid accumulation in Chlorella cells by creating stressful growth conditions. Chlorella vulgaris CCALA 896 was grown under various batch growth modes in basal and modified BG-11 and Kolkwitz culture broths, using a continuous light regimen of 150 µE/m2/s, at 30 °C. In order to perform the experiments, two indoor photobioreactor shapes were used: a cylindrical glass photobioreactor (CGPBR) with a working volume of 350 mL, and a flat glass photobioreactor (FGPBR) with a working volume of 550 mL. Stress-eliciting conditions, such as nitrogen and phosphorous starvation, were imposed in order to induce lipid accumulation. The results demonstrated that more than 56% of the lipids can be accumulated in Chlorella biomass grown under two-phase batch growth conditions. The highest biomass productivity of 0.30 g/L/d was obtained at the highest nominal dilution rate (0.167 day−1) during a semi-continuous regimen, using a modified Kolkwitz medium. During the pH-stress cycles, the amount of lipids did not increase significantly and a flocculation of Chlorella cells was noted.

Up-scaling aquaculture wastewater treatment by microalgal bacterial flocs: From lab reactors to an outdoor raceway pond

Sequencing batch reactors with microalgal bacterial flocs (MaB-floc SBRs) are a novel approach for photosynthetic aerated wastewater treatment based on bioflocculation. To assess their technical potential for aquaculture wastewater treatment in Northwest Europe, MaB-floc SBRs were up-scaled from indoor photobioreactors of 4 L over 40 and 400 L to a 12 m(3) outdoor raceway pond. Scale-up decreased the nutrient removal efficiencies with a factor 1-3 and the volumetric biomass productivities with a factor 10-13. Effluents met current discharge norms, except for nitrite and nitrate. Flue gas sparging was needed to decrease the effluent pH. Outdoor MaB-flocs showed enhanced settling properties and an increased ash and chlorophyll a content. Bioflocculation enabled successful harvesting by gravity settling and dewatering by filtering at 150-250 μm. Optimisation of nitrogen removal and biomass valorisation are future challenges towards industrial implementation of MaB-floc SBRs for aquaculture wastewater treatment.

Optimal design of scalable photo-bioreactor for phototropic culturing of Haematococcus pluvialis

The unicellular green microalgae, Haematococcus pluvialis, has been examined as a microbial source for the production of astaxanthin, which has been suggested as a food supplement for humans and is also prescribed as an ingredient in eye drops because of its powerful anti-oxidant properties. In this study, we estimated the effects of the slope of a V-shaped bottom design, the volumetric flow rate of air, height/diameter (H/D) ratio, and diameter of an air sparger on the performance of a photo-bioreactor. These parameters were selected because they are recognized as important factors effecting the mixing that produces increased cell density in the reactor. The mixing effect can be measured by changes in optical density in the bioreactor over a period of time. A 6 L indoor photo-bioreactor was prepared in a short time period of 24 h for the performance study. A bioreactor designed with a V-shaped bottom with a slope of 60° showed an optical density change of 0.052 at 680 nm, which was sixfold less than the change in a photo-bioreactor designed with a flat bottom. Studies exploring the effects of bioreactor configuration and a porous metal sparger with a 10 μm pore size showed the best performance at an H/D ratio of 6:1 and a sparger diameter of 1.3 cm, respectively. The optimal rate of air flow was 0.2 vvm. The indoor culture of microalgae in the photo-bioreactor was subsequently carried for an application study using the optimal values established for the important factors. The indoor culture system was composed of a light source controlled according to cell phase, a carbon dioxide feeder, a bag-type reactor with an H/D ratio of 6:1, and a temperature controller. Results demonstrated the efficient production of microalgal cells and astaxanthin in the amounts of 2.62 g/L and 78.37 mg/L, respectively, when using adequate hydrodynamic mixing. Furthermore, the optimal design of a photo-bioreactor can be applied for the phototropic culturing of other microalgae for mass production.

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

AbstractMicroalgal 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 (ka) 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).

On the nitrogen and phosphorus removal in algal photobioreactors

This study shows results of nitrogen and phosphorus removal by microalgae (tertiary treatment) in a prototype of tubular photobioreactor tested under controlled and uncontrolled conditions. The wastewater was the supernatant coming from a secondary settler of a municipal wastewater activated sludge treatment plant without nitrification and denitrification units. The algal biomass was directly selected from the supernatant and it was principally composed of genus Scenedesmus (autochthonous algae). All the experiments evaluated both nitrogen and phosphorus removal and biomass and lipid production. A satisfactory nutrients removal – about 99.9% for the nitrogen and phosphorus – and a specific biomass productivity of 0.25 g/l d have been obtained in the indoor photobioreactor; less satisfactory results have been reached in the outdoor photobioreactor because of ambient condition instability and limiting nutrients concentration.