Selective degradation of the recalcitrant cell wall of Scenedesmus quadricauda CASA CC202

Algae biogas production focusing on operating conditions and conversion mechanisms - A review

Global warming is the result of traditional fuel use and manufacturing, which release significant volumes of CO₂ and other greenhouse gases from factories. Moreover, rising energy consumption, anticipated limitations of fossil fuels in the near future, and increased interest in renewable energies among scientists, currently increase research in biofuels. In contrast to biomass from urban waste materials or the land, algae have the potential to be a commercially successful aquatic energy crop, offering a greater energy potential. Here we discuss the importance of Anaerobic Digestion (AD) for enhanced biogas yield, characterization, and comparisons between algae pretreatment methods namely, mechanical, thermal, microwave irradiation, and enzymatic and catalytic methods. The importance of anaerobic digestion enhances biogas yield, characterization, and comparisons between mechanical, thermal, microwave irradiation, and enzymatic and catalytic treatment. Additionally, operational aspects such as algal species, temperature, C/N ratio, retention period, and particle size impact biofuel yield. The highest algal biogas yield reported was 740 mL/gVS, subtracted from Taihu de-oiled algae applying thermos-chemical pretreatment under conditions of temperature, time, and catalyst concentration of 70 °C, 3 h, and 6%, respectively. Another high yield of algal-based biogas was obtained from Laminaria sp. with mechanical pretreatment under temperature, time, and VS concentration of 38 ± 1 °C, 15 min, and 2.5% respectively, with a maximum yield of 615 ± 7 mL/g VS. Although biofuels derived from algae species are only partially commercialized, the feedstock for biogas might soon be commercially grown. Algae and other plant species that could be cultivated on marginal lands as affordable energy crops with the potential to contribute to the production of biogas are promising and are already being worked on.

Magnetic Immobilization and Growth of Nannochloropsis oceanica and Scenedasmus almeriensis

Microalgae are used in industrial and pharmaceutical applications. Their performance on biological applications may be improved by their immobilization. This study presents a way of cell immobilization using microalgae carrying magnetic properties. Nannochloropsis oceanica and Scenedasmus almeriensis cells were treated enzymatically (cellulase) and mechanically (glass beads), generating protoplasts as a means of incorporation of magnetic nanoparticles. Scanning electron microscopy images verified the successful cell wall destruction for both of the examined microalgae cells. Subsequently, protoplasts were transformed with magnetic nanoparticles by a continuous electroporation method and then cultured on a magnetic surface. Regeneration of transformed protoplasts was optimized using various organic carbon and amino acid supplements. Both protoplast preparation methods demonstrated similar efficiency. Casamino acids, as source of amino acids, were the most efficient compound for N. oceanica protoplasts regeneration in enzymatic and mechanical treatment, while for S. almeriensis protoplasts regeneration, fructose, as source of organic carbon, was the most effective. Protoplasts transformation efficiency values with magnetic nanoparticles after enzymatic or mechanical treatments for N. oceanica and S. almeriensis were 17.8% and 10.7%, and 18.6% and 15.7%, respectively. Finally, selected magnetic cells were immobilized and grown on a vertical magnetic surface exposed to light and without any supplement.

Nutritional Profiling and Preliminary Bioactivity Screening of Five Micro-Algae Strains Cultivated in Northwest Europe

This study aimed to map the nutritional profile and bioactivities of five microalgae that can be grown in Northwest Europe or areas with similar cultivation conditions. Next to the biochemical composition, the in vitro digestibility of carbohydrates, proteins, and lipids was studied for Chlamydomonas nivalis, Porphyridium purpureum, Chlorella vulgaris, Nannochloropsis gaditana, and Scenedesmus species biomass. These microalgae were also assessed for their ability to inhibit the angiotensin-1-converting enzyme (ACE-1, EC 3.4.15.1), which is known to play a role in the control of blood pressure in mammals. Large differences in organic matter solubility after digestion suggested that a cell disruption step is needed to unlock the majority of the nutrients from N. gaditana and Scenedesmus species biomass. Significant amounts of free glucose (16.4–25.5 g glucose/100 g dry algae) were detected after the digestion of C. nivalis, P. purpureum, and disrupted Scenedesmus. The fatty acid profiles showed major variations, with particularly high Ω-3 fatty acid levels found in N. gaditana (5.5 ± 0.5 g/100 g dry algae), while lipid digestibility ranged from 33.3 ± 6.5% (disrupted N. gaditana) to 67.1 ± 11.2% (P. purpureum). C. vulgaris and disrupted N. gaditana had the highest protein content (45–46% of dry matter), a nitrogen solubility after digestion of 65–71%, and the degree of protein hydrolysis was determined as 31% and 26%, respectively. Microalgae inhibited ACE-1 by 73.4–87.1% at physiologically relevant concentrations compared to a commercial control. These data can assist algae growers and processors in selecting the most suitable algae species for food or feed applications.