Today there is a growing need to find an effective solution in terms of alternative and renewable energies, contamination of ecosystems, food and resource crisis.This leads us to ask ourselves a big question: what is the solution?There is no panacea for all problems, but something that comes close to it: the microalgae Chlorella vulgaris.Chlorella vulgaris is a Chlorophyta alga, commonly known as green algae, unicellular eukaryotic.The species is cosmopolitan of fresh waters (rivers, lakes and lagoons) and can be found in endosymbiosis with other organisms such as flatworms, ciliates and cnidarians of the genus Hydra.The microalga has a spherical shape with a diameter of 2-10 µm and is devoid of flagella.In addition to the deducible presence of chloroplasts rich in photosynthetic pigments, it shares several elements with the cells of higher plants (Fig. 1).Chlorella vulgaris is a mixotrophic organism, i.e. capable of adopting both an autotrophic and heterotrophic metabolism or a combination of them.Chlorella vulgaris reproduces by autosporulation, the most common form of asexual reproduction of algae.Four daughter cells with their own cell wall are formed from the mother cell.At the end of maturation, the four daughter cells are released thanks to the disintegration of the maternal cell wall whose remains will become the source of their nourishment.To date, given the growing need, the bioremediation potential of Chlorella vulgaris is the subject of increasingly targeted and in-depth studies.Of all the applications in terms of bioremediation, its ability to mitigate the effects of CO2 in the environment is certainly of greater interest.Chlorella vulgaris is in fact able to tolerate high levels of CO2 and convert it into O2 and biomass.A recent study by Mountourakis et al.(2021) has in fact observed that Chlorella vulgaris is not only able to tolerate CO2 concentrations higher than 40%, but that these concentrations represent an ideal growth condition in which there is an intensification of photosynthetic activity with a consequent increase in biomass. and oxygen production (Fig. 2).An incubation of the microalga at a light intensity greater than 50 μmol m-2 s-1 (corresponding to about 11 W m-2) at a CO2 concentration equal to 40% leads to a complete conversion of this into O2 over the arc 4-6 days.Furthermore, under these conditions the biomass of Chlorella vulgaris is quadrupled without the addition of further energy inputs into the system.In addition to CO2, Chlorella vulgaris is able to sequester large amounts of nutrients and contaminants from the environment, including heavy metals and nitrogen and phosphorus compounds.This makes Chlorella vulgaris a prominent species in wastewater treatments, such as civil and industrial wastewater or livestock manure.In the case of wastewater treated with Chlorella vulgaris, the phosphate content undergoes a reduction of 60% in the first 10 days of treatment and a reduction of nitrates by 84%.This makes this microalga of significant importance in the bioremediation of fertilizers.Chlorella vulgaris has a remarkable ability to absorb various heavy metals through the biosorption technique.This occurs because hydroxyl groups (-OH–) are present in the cell wall of the microalgae.These groups make the cellulose of the cell wall polar, which is therefore able to create bonds with the metal ions and to absorb them, sequestrating them from the environment.At this point Chlorella vulgaris carries out the detoxification process, where the heavy metals are converted into non-toxic forms.An alternative to detoxification is the isolation of these metals so that they do not interfere with cell metabolism.This is due to the formation of metal-protein complexes capable of accumulating in vacuoles.Among these proteins the most present, in general in microalgae, are metallothioneins and phytochelatins.Among the various heavy metals of considerable interest is lead.Dewi & Nuravivah (2018) observed that the absorption ability of Chlorella vulgaris is directly proportional to the concentration of Pb in the culture (Fig. 3).In any case, the more the adsorption of the metal increased, the more this led to growth interference.This was maximum at a lead concentration of 3 mg / l and minimum in the control and at 5 mg / l.Although still little studied, the phenomenon of the bioremediation of pesticides in water is of great interest.Further studies and investigations are needed, but it has been found that Chlorella vulgaris is able to remove different classes of pesticides from water mainly through the mechanisms of bioabsorption and biodegradation.Chlorella vulgaris also appears to have some potential in the bioremediation of radionuclide-contaminated water.However, this too is a little studied phenomenon and of which there is a very limited literature.The use of Chlorella vulgaris for the treatment of waste water in the textile sector is more well known.These waters have very varied characteristics, but they are all characterized by the presence of dyes, ammonia nitrogen, high presence of suspended solids and heavy metals.Due to these characteristics, these effluents can cause considerable damage to aquatic life leading to eutrophication phenomena, pH alteration and increased chemical and biochemical demands for oxygen.Different studies carried out both on a laboratory and industrial scale have revealed the excellent capabilities of Chlorella vulgaris in the treatment of these effluents.This microalgae is able to degrade azo dyes (60% -70% of the dyes used in the textile industry) into simpler organic compounds or CO2 through biosorption.It is hypothesized that the microalgae assimilates the dyes through adsorption and uses them to increase its biomass.Lim et al.(2010) observed a reduction in color in the range of 41.8 - 50% in waters treated with Chlorella vulgaris.Furthermore, they found a reduction in ammonia nitrogen of 44.4 - 45.1% and in COD of 38.3 - 62.3% (Fig. 4).The reduction in COD could be due to the production of oxygen by the microalgae.This would stimulate the degradation of the organic matter present in the waste water.The possibility of exploiting Chlorella vulgaris for the production of biofuels, bioethanol and biogas is also of growing interest.This is thanks to the starch and lipid content, abundantly present in the microalgae.Grown in particular stressful conditions, such as nitrogen, phosphorus and sulfur deficiency, the lipid or starch content of Chlorella vulgaris can reach 50 - 60% of its dry weight (Fig. 5).The same lipid profile can change depending on the growth conditions.Biofuels produced from microalgae are generally non-toxic and biodegradable.Furthermore, thanks to their high content of palmitic, palmitoleic, oleic and linoleic acids, they meet the European requirements for the production of biodiesel.The water and ash content is also in accordance with most biodiesel production regulations.From an efficiency point of view, the calorific value of biodiesel (38,000 kJ kg-1) is slightly lower than that of petroleum diesel (42,000 kJ kg-1).The production of bioethanol from starch is also relevant.This is hydrolyzed by the glucoamylase enzyme which converts it to simple sugars (d-glucose).The biomass is subsequently used as a substrate to which a yeast (Saccharomyces cerevisiae) is added which begins the glucose fermentation process.The product of this fermentation is ethanol.Despite the potential, corn is currently the main raw material for bioethanol production globally.The versatility and rapid growth rates of Chlorella vulgaris and microalgae generally lead to a higher production than other crops (soybean and rapeseed) by exploiting much smaller spaces.Suffice it to say that the production of oils in Chlorella vulgaris begins in 3-5 days, while a more traditional cultivation (eg corn) takes from 3 months to 3 years to start producing efficiently.The production of oils reaches 10-100 times higher with the same space compared to any other cultivation.Starch production, on the other hand, can reach 7-70 tons per hectare in a period of 150-250 days.Suffice it to say that with the same spaces and conditions, corn produces 4 tons.However, there are also some disadvantages.One of these is the limited possibility of concentrating excessive biomass.This is because in a culture the increase of biomass also reduces the penetration of light, thus inhibiting photosynthesis and growth.Furthermore, to date the management of microalgae crops still has quite high costs compared to conventional agriculture.The potential of Chlorella vulgaris in the production of biogas (biomethane) should also be considered.Sakarika & Kornaros (2019) measured the production of methane (Biochemical methane potential assays) from Chlorella vulgaris biomass inoculated with sludge from water treatment plants at different temperature conditions.In addition to microalgae, cellulose is used as a substrate.The results showed that the total methane production was considerably higher in Chlorella vulgaris (108.6 ± 3.7 ml CH4) than in cellulose (66.76 ± 1.47 ml CH4) under mesophilic conditions (37 ° C) (Fig. 6).However, the maximum potential of cellulose was shown in 30 days, while that of Chlorella vulgaris in 100. This is probably due to the greater difficulty of the microbiota in degrading the cell wall of the microalga.Despite the already extensive scientific literature regarding the potential of Chlorella vulgaris for the production of biofuels and bioenergy, further studies will have to be conducted.These in particular will have to be addressed to solving the main problems related to the use of microalgae, such as cost reduction.Like the best known Spirulina, erroneously called "alga" even if it is cyanobacteria ascribable to the Arthrospira genus, Chlorella vulgaris has excellent nutritional properties, which makes it excellent as a food additive or supplement and even as a food coloring.It has a broad spectrum of biomolecules whose function is essential for living organisms including proteins, lipids, carbohydrates, vitamins and minerals.Chlorella vulgaris has a total protein content of 42 - 58% of dry weight and its amino acid profile is in line, if not better, than that suggested by the World Health Organization (WHO) and the Food and Agricultural Organization (FAO). ) for human nutrition.The lipid content can vary from 5% to 40% of the dry weight, depending on the growth conditions, and is represented by glycolpids, oils, phospholipids and fatty acids.Under poor growing conditions, such as high CO2 levels and low nitrogen content, the content can even reach 58%.Depending on the applications, the fatty acid profile can change in relation to the growth conditions: mixotrophic conditions can lead to an accumulation of saturated and monounsaturated fatty acids such as palmitic acid, oleic acid, plamitoleic acid and stearic acid, content suitable for the production of biodisel.Under favorable growth conditions, Chlorella vulgaris has a preference for the accumulation of polyunsaturated fats, better for food use, such as linoleic acid.An important nutritional contribution in Chlorella vulgaris is represented by carbohydrates, which represent 12 - 55% of the dry weight.In any case, it should be noted that the highest concentration of carbohydrates is obtained in growth conditions in which the supply of nitrogen is limited.Starch is the most represented polysaccharide in Chlorella vulgaris.Of great importance is the polysaccharide β1 → 3 glucan of significant importance for health, as it has a function of containing blood levels of cholesterol and glucose, reducing the risk of onset of cardiovascular diseases.As for sugars, rhamnose is the most present (45 - 54%) followed by galactose (14-26%), xylose (7-19%), arabinose (2-9%), mannose (2-7%) ) and glucose (1-4%).Chlorella vulgaris is also an important source of minerals and vitamins.Worthy of note is the potassium content, an element involved in muscle contraction and transmission of nerve impulses, in protein synthesis, in carbohydrate metabolism and in the regulation of the balance of fluids and minerals between the inside and outside of the cells.The magnesium content is also important, an element with an important contribution in muscle contraction, nervous activity and energy metabolism (processes of storage, transfer and use of energy).Another particularly represented element is zinc, involved in numerous metabolic processes including the synthesis of biomolecules, as well as a cofactor of the superoxide dismutase enzyme which carries out a protective activity against oxidative processes.Also present iron, calcium and other trace elements.The vitamin profile is also important and is linked, therefore alterable, to the growth conditions.Chlorella vulgaris has a rather complete spectrum: vitamin A, involved in cell growth and differentiation, vitamin B, essential for enzymatic activity in metabolic processes, and vitamins C and E which perform an antioxidant activity.By way of example, the following table shows different vitamin profiles found in different studies:Pigments are also worth mentioning.Chlorophyll (a and b) is the most abundant pigment in Chlorella vulgaris and can reach 2% of dry weight.Abundant is also the content of phaeophytin and carotenoids including β-carotene, astaxanthin, canthaxanthin, violaxanthin and lutein.Pigments perform important antioxidant, regulatory and protective activities and are involved in the prevention of chronic diseases, particularly cardiovascular ones.The versatility of Chlorella vulgaris would therefore make it possible to use it for the solution of different current problems.For this to happen, further targeted studies and, finally, a more complex reconversion of the industrial apparatus will be necessary.Despite current limitations, this "small" microalgae could therefore represent a key resource for the future.Enter your e-mail address to subscribe to this blog, and receive notifications of new posts by e-mail.