Differences in adaptation to light and temperature extremes of Chlorella sorokiniana strains isolated from a wastewater lagoon

Efficient supply with carbon dioxide from flue gas during large scale production of microalgae: A novel approach for bioenergy facades

The efficiency of using enriched CO2 from flue gas for large scale production of the green microalgae Chlorella sorokiniana in a bioenergy facade was studied. Using a membrane device, the enrichment of CO2 from heating system flue gas in the low pressure product gas was up to 49 vol% and the CO2 recovery was 62 %. With a static mixer the re-compressed product gas was applied to the culture medium with mean losses during cultivation of only 24 %. Thereby the pH could be maintained at a mean of 6.2 and a temperature always below 28 °C, both optimal for growth of Chlorella sorokiniana. Although PAR solar radiation during midday always exceeded 1000 µmol m-2 s-1 mean photosynthetic efficiency was 0.54 g mol-1. Results indicate that the chosen approach for CO2 supply overcomes the problem of CO2 losses and allows for a more economic and sustainable microalgae production in a bioenergy facade.

Bioengineering strategies of microalgae biomass for biofuel production: recent advancement and insight

Algae-based biofuel developed over the past decade has become a viable substitute for petroleum-based energy sources. Due to their high lipid accumulation rates and low carbon dioxide emissions, microalgal species are considered highly valuable feedstock for biofuel generation. This review article presented the importance of biofuel and the flaws that need to be overcome to ensure algae-based biofuels are effective for future-ready bioenergy sources. Besides, several issues related to the optimization and engineering strategies to be implemented for microalgae-based biofuel derivatives and their production were evaluated. In addition, the fundamental studies on the microalgae technology, experimental cultivation, and engineering processes involved in the development are all measures that are commendably used in the pre-treatment processes. The review article also provides a comprehensive overview of the latest findings about various algae species cultivation and biomass production. It concludes with the most recent data on environmental consequences, their relevance to global efforts to create microalgae-based biomass as effective biofuels, and the most significant threats and future possibilities.

Growth of microalgae adapted to high-light temperature conditions in different types of wastewater

To obtain microalgae strains adapted to wastewater in the Mediterranean region, microalgae present in the Nile River were cultivated at both high-light temperature (HLT) and low-light temperature (LLT) conditions. It was found that the species which became dominant under HLT was chlorophyta of the genus Scenedesmus. In contrast, under LLT, bacillariophyta became dominant. The microalgae strain (Scenedesmus arcuatus) was subsequently isolated and cultivated in different types of primary treated wastewater under HLT and LLT conditions. The different types of primary treated wastewater were black water (BW), grey water (GW), and sewage water (SW). Growth rates reached during the exponential phase at HLT using GW, BW, and SW were between 0.38 and 0.4 (day-1). At LLT, 1.5-2.7 folds of lower growth rates were determined due to limitation by CO2. Removal of COD and inorganic N and P from sewage wastewater reached up to 88, 96, and 100%, respectively. Results thus indicate that microalgae adapted to the climate conditions can be efficiently used for COD removal and nutrient recovery from wastewater in the Mediterranean.

Carbon capture and biocatalytic oxygen production of photosystem II from thylakoids and microalgae on nanobiomaterials

Enhanced carbon capture and oxygen production via water splitting was observed by controlling the plasmon-induced resonance energy transfer (PIRET) for photosystem II (PSII) in thylakoid extracts and spirulina assembled on gold nanoparticle (AuNP) dimer arrays. The two types of vertical (V) and horizontal (H) AuNP dimer arrays were uniformly inserted inside pore diameter-controlled templates. Based on the theoretical calculations, the longitudinal mode of the H AuNP dimer array was found to be sensitive to the nanogap distances between the two AuNPs in resonance with the absorption at P680 of the PSII. The longitudinal modes that interacted with P680 of PSII increased from the V to the H conformer. The optical properties from the H AuNP dimer array caused overlapping absorbance and photoluminescence with PSII, and the H AuNP dimer arrays exhibited a significant increase in carbon capture and oxygen generation rates in comparison with those of the bare PSII protein complex under light irradiation via the controlled PIRET process.

Heavy Metals Exacerbate the Effect of Temperature on the Growth of Chlorella sp.: Implications on Algal Blooms and Management

With the accelerated urbanization and rapid development of the industrial and agricultural sectors, concern about the pollution of water environments is becoming more widespread. Algal blooms of varying sizes are becoming increasingly frequent in lakes and reservoirs; temperatures, nutrients, heavy metals, and dissolved oxygen are the factors that influence algal bloom occurrence. However, knowledge of the combined effect of heavy metals and temperature on algal growth remains limited. Thus, this study investigated how specific concentrations of heavy metals affect algal growth at different temperatures; to this end, two heavy metals were used (0.01 mg/L Pb2+ and 0.05 mg/L Cr6+) at three incubation temperatures (15, 25, and 30 °C) with the alga Chlorella sp. A higher incubation temperature contributed to a rise in soluble proteins, which promoted algal growth. The density of algal cells increased with temperature, and catalase (CAT) decreased with increasing temperature. Chlorella sp. growth and catalase activity were optimal at 30 °C (algal cell density: 1.46 × 107 cell/L; CAT activity: 29.98 gprot/L). Pb2+ and Cr6+ significantly promoted Chlorella sp. growth during incubation at 25 and 30 °C, respectively. At specific temperatures, 0.01 mg/L Pb2+ and 0.05 mg/L Cr6+ promoted the production of soluble proteins and, hence, the growth of Chlorella sp. The results provide a useful background for the mitigation and prevention of algal blooms.

Blue-green light is required for a maximized fatty acid unsaturation and pigment concentration in the microalga Acutodesmus obliquus

Blue-green light is known to maximize the degree of fatty acid (FA) unsaturation in microalgae. However, knowledge on the particular waveband responsible for this stimulation of FA desaturation and its impact on the pigment composition in microalgae remains limited. In this study, Acutodesmus obliquus was cultivated for 96 h at 15°C with different light spectra (380-700 nm, 470-700 nm, 520-700 nm, 600-700 nm, and dark controls). Growth was monitored daily, and qualitative characterization of the microalgal FA composition was achieved via gas chromatography coupled with electron impact ionization mass spectrometry (GC-EI/MS). Additionally, a quantitative analysis of microalgal pigments was performed using high-performance liquid chromatography with diode array detection (HPLC-DAD). Spectra that included wavelengths between 470 and 520 nm led to a significantly higher percentage of the polyunsaturated fatty acids (PUFA) 18:3 and 16:4, compared to all other light conditions. However, no significant differences between the red light cultivations and the heterotrophic dark controls were observed for the FA 18:3 and 16:4. These results indicate, that exclusively the blue-green light waveband between 470 and 520 nm is responsible for a maximized FA unsaturation in A. obliquus. Furthermore, the growth and production of pigments were impaired if blue-green light (380-520 nm) was absent in the light spectrum. This knowledge can contribute to achieving a suitable microalgal pigment and FA composition for industrial purposes and must be considered in spectrally selective microalgae cultivation systems.