The problem of the excessive CO₂ emitted into the atmosphere is one of the significant problems for the modern world and ecology. This article examines the dynamics of carbon dioxide absorption from thermal power plants, TPP, and waste gases by three types of microalgae, the most typical for the Russian Federation: Chlorella kessleri, Chlorella vulgaris, and Chlorella sorokiniana. The exhaust gases of the TPP contain up to 39% carbon dioxide. In this work, the rate of absorption of carbon dioxide from model exhaust gases with a CO₂ content of up to 39% was studied. As a result of the study, a species of microalgae (Chlorella vulgaris) was identified, characterized by the maximum rate of absorption of CO₂ = 0.412 g/L·day and the maximum volume of CO₂ utilized in 1 day = 8.125 L. The conducted research proved the possibility of utilizing a large content (up to 39%) of carbon dioxide from the exhaust gases of the TPP with the help of microalgae of the genus Chlorella. A scheme for the utilization of CO₂ with the help of microalgae is also proposed, which meets the principles of a circular economy (closed cycle).

This paper considers modern sorption materials for wastewater treatment. The literature data on wastewater treatment with materials based on graphene and chitosan are presented. The production and application of composite sorbents is discussed. It is shown that a promising application of graphene oxide (GO) as a filler enhances the mechanical and sorption properties of the polymer matrix. The biopolymer chitosan (Ch) is a challenging matrix for GO, having unique sorption, chelate-forming, ion-exchange, and complex-forming properties. Composite adsorbents based on graphene oxide and chitosan have a high extraction efficiency of heavy and radioactive metals, dyes, and pharmaceutical compounds dorzolamide and tetracycline. GO-Ch composites with various ratios of chitosan and graphene oxide (2–7%) were formed by drop granulation. The composites obtained were investigated in terms of the ability to extract copper cations from the effluents, and it was shown that the composite having the content of GO:Ch = 55.5:44.5% (by mass in dry granules) had the best sorption and mechanical properties. This sample had high purification efficiency from copper cations (96%) and the required mechanical properties (attrition ≤ 0.4%, grindability ≤ 4%). For this sample, the influence of various factors (pH, sorbent dosage, temperature, and time of sorption) on sorption processes were studied. The best conditions for the sorption processes by the GO-Ch sorbent were determined. The sorbent dosage was 20 g/L, the sorption time was 20 min, and the temperature was 20 ± 2 °C, pH = 7. The adsorption isotherm was plotted and the maximum sorption capacity of copper cations A = 58.5 mg/g was determined. Microstructural and infrared (IR) spectroscopy studies of GO-Ch composites showed the presence of a porous surface and OH- and C=O functional groups. A mechanism for the extraction of copper cations due to physical sorption of the porous surface by GO-Ch composites, and due to chemisorption processes by functional groups, was proposed. The sorption properties for methylene blue and iodine absorption, and the specific surface area of the GO-Ch samples, were determined. The spent sorbent is proposed to be used as a soil improver.

This article explores the feasibility of producing biohydrogen from microalgae following their use in wastewater purification from food industry facilities and the removal of high levels of carbon dioxide (CO₂) from the air. The authors investigated various methods for disrupting the cell membranes of microalgae and their impact on biohydrogen yield. The microalgae biomass obtained after wastewater and air purification underwent pre-treatment using physicochemical and chemical methods, including microwave radiation, acid treatment, and thermal treatment. The highest hydrogen production occurred during thermal and acid treatments of biomass with the addition of starch (44.24 mL/L of suspension). The use of microwave radiation for processing did not yield significant results. A comparison of the biohydrogen values obtained from untreated and treated biomass revealed that treatment enhances biohydrogen yield.

Microalgae have attracted growing interest all around the world due to their potential applications in multiple sectors of industry, such as energetics, nutraceuticals, pharmaceuticals, agriculture, and ecology. Concepts of biorefinery of microalgae lipids for biodiesel production coupled with other applications have been suggested in several studies. However, very few studies focus on overcoming the degree of unsaturation of microalgae lipids using methods of fractionation. This study presents a method for obtaining two oil fractions from microalgae Chlorella sorokiniana suitable for food and biofuels via urea complex formation with further production of a long-chain PUFA concentrated oil suitable for the nutraceutical industry. A DHA–EPA-rich fraction was obtained from the dry microalga biomass using a succession of extraction, urea-complexation, fractionation, and esterification with glycerol. Analytical and organoleptic methods were used to assess the quality of the final product. Results show that the urea-complexation method allowed the obtaining of two lipid fractions with different fatty acid profiles. The urea complexed fraction (UCF) contained a majority of saturated fatty acids (54.46%); thus, it could find applications in the biofuels or food industry. The non-urea complexed fraction (NUCF) was rich in polyunsaturated fatty acids (PUFA) (81.00%), especially long-chain PUFA with 16.52% EPA and 35.08% DHA. The recovery rates of EPA and DHA in the NUCF reached 59% and 87.14%, respectively. Finally, the physicochemical and organoleptic characteristics of the DHA–EPA oil concentrate were determined and found conform to the norms recommended by the WHO/FAO standards for edible oils and the Russian State Standard GOST 1129-2013.

The application of microalgae biomass of Chlorella sorokiniana as environmentally friendly biosorbents for removing potentially toxic elements (PTE) from water and as a source of biofuel has been thoroughly studied. In this paper, we investigate its physicochemical properties infrared spectroscopy (IR spectra), microstructure, adsorption properties); we have managed to isolate the lipid complex, which amounted to 20% of dry biomass. Studies of the lipid complex showed that 80.02% of lipids are unsaturated fatty acids (C18:1, C18:2, C18:3). Additionally, we have investigated the efficiency of using the residual biomass obtained after lipid extraction for water purification from rare-earth metals (REM) and PTE. To increase the sorption properties of residual biomass, its thermal modification was carried out and sorption materials based on heat-treated residual biomass and chitosan were created. The physicochemical and mechanical properties of the obtained sorption materials were studied. The total sorption capacity was 31.9 mg/g for REM and 349.7 mg/g for PTE. Moreover, we propose a new method for the disposal of spent sorbents as additional fuel. Spent sorbents can be considered to be biofuel in terms of energy content (20.7 MJ*kg⁻¹). The results of this study provide the basis for increased use of microalgae.