Evaluation of Pre-Chlorinated Wastewater Effluent for Microalgal Cultivation and Biodiesel Production

Taxonomic, Physiological, and Biochemical Characterization of Asterarcys quadricellularis AQYS21 as a Promising Sustainable Feedstock for Biofuels and ω-3 Fatty Acids

Asterarcys quadricellularis strain AQYS21, a green microalga isolated from the brackish waters near Manseong-ri Black Sand Beach in Korea, shows considerable potential as a source of bioactive compounds and biofuels. Therefore, this study analyzed the morphological, molecular, and biochemical characteristics of this strain; optimized its cultivation conditions; and evaluated its suitability for biodiesel production. Morphological analysis revealed characteristics typical of the Asterarcys genus: spherical to ellipsoidal cells with pyrenoid starch plates and mucilage-embedded coenobia. Additionally, features not previously reported in other A. quadricellularis strains were observed. These included young cells with meridional ribs and an asymmetric spindle-shaped form with one or two pointed ends. Molecular analysis using small-subunit rDNA and tufA sequences confirmed the identification of the strain AQYS21. This strain showed robust growth across a wide temperature range, with optimal conditions at 24 °C and 88 µmol m-2s-1 photon flux density. It was particularly rich in ω-3 α-linolenic acid and palmitic acid. Furthermore, its biodiesel properties indicated its suitability for biodiesel formulations. The biomass of this microalga may serve as a viable feedstock for biodiesel production and a valuable source of ω-3 fatty acids. These findings reveal new morphological characteristics of A. quadricellularis, enhancing our understanding of the species.

Transcriptomic and fatty acid analyses of Neochloris aquatica grown under different nitrogen concentration

In this study, we characterized the fatty acid production in Neochloris aquatica at transcriptomics and biochemical levels under limiting, normal, and excess nitrate concentrations in different growth phases. At the stationary phase, N. aquatica mainly produced saturated fatty acids such as stearic acid under the limiting nitrate concentration, which is suitable for biodiesel production. However, it produced polyunsaturated fatty acids such as α-linolenic acid under the excess nitrate concentration, which has nutritional values as food supplements. In addition, RNA-seq was employed to identify genes and pathways that were being affected in N. aquatica for three growth phases in the presence of the different nitrate amounts. Genes that are responsible for the production of saturated fatty acids were upregulated in the cells grown under a limiting nitrogen amount while genes that are responsible for the production of polyunsaturated fatty acid were upregulated in the cells grown under excess nitrogen amount. Further analysis showed more genes differentially expressed (DEGs) at the logarithmic phase in all conditions while a relatively steady trend was observed during the transition from the logarithmic phase to the stationary phase under limiting and excess nitrogen. Our results provide a foundation for identifying developmentally important genes and understanding the biological processes in the different growth phases of the N. aquatica in terms of biomass and lipid production.

Impact of wastewater cultivation on pollutant removal, biomass production, metabolite biosynthesis, and carbon dioxide fixation of newly isolated cyanobacteria in a multiproduct biorefinery paradigm

The impact of wastewater cultivation was studied on pollutant removal, biomass production, and biosynthesis of high-value metabolites by newly isolated cyanobacteria namely Acaryochloris marina BERC03, Oscillatoria sp. BERC04, and Pleurocapsa sp. BERC06. During cultivation in urabn wastewater, its pH used to adjust from pH 8.0 to 11, offering contamination-free cultivation, and flotation-based easy harvesting. Besides, wastewater cultivation improved biomass production by 1.3-fold when compared to control along with 3.54-4.2 gL^-1 of CO₂ fixation, concomitantly removing suspended organic matter, total nitrogen, and phosphorus by 100%, 53%, and 88%, respectively. Biomass accumulated 26-36% carbohydrates, 15-28% proteins, 38-43% lipids, and 6.3-9.5% phycobilins, where phycobilin yield was improved by 1.6-fold when compared to control. Lipids extracted from the pigment-free biomass were trans-esterified to biodiesel where pigment extraction showed no negative impact on quality of the biodiesel. These strains demonstrated the potential to become feedstock of an integrated biorefinery using urban wastewater as low-cost growth media.

Cultivating microalgae in wastewater for biomass production, pollutant removal, and atmospheric carbon mitigation; a review

Water shortage is one of the leading global problems along with the depletion of energy resources and environmental deterioration. Recent industrialization, global mobility, and increasing population have adversely affected the freshwater resources. The wastewater sources are categorized as domestic, agricultural and industrial effluents and their disposal into water bodies poses a harmful impact on human and animal health due to the presence of higher amounts of nitrogen, phosphorus, sulfur, heavy metals and other organic/inorganic pollutants. Several conventional treatment methods have been employed, but none of those can be termed as a universal method due to their high cost, less efficiency, and non-environment friendly nature. Alternatively, wastewater treatment using microalgae (phycoremediation) offers several advantages over chemical-based treatment methods. Microalgae cultivation using wastewater offers the highest atmospheric carbon fixation rate (1.83 kg CO₂/kg of biomass) and fastest biomass productivity (40-50% higher than terrestrial crops) among all terrestrial bio-remediators with concomitant pollutant removal (80-100%). Moreover, the algal biomass may contain high-value metabolites including omega-3-fatty acids, pigments, amino acids, and high sugar content. Hence, after extraction of high-value compounds, residual biomass can be either directly converted to energy through thermochemical transformation or can be used to produce biofuels through biological fermentation or transesterification. This review highlights the recent advances in microalgal biotechnology to establish a biorefinery approach to treat wastewater. The articulation of wastewater treatment facilities with microalgal biorefinery, the use of microalgal consortia, the possible merits, and demerits of phycoremediation are also discussed. The impact of wastewater-derived nutrient stress and its exploitation to modify the algal metabolite content in view of future concerns of cost-benefit ratios of algal biorefineries is also highlighted.

Isolation and selection of growth medium for freshwater microalgae Asterarcys quadricellulare for maximum biomass production

The use of microalgae biomass as a suitable alternative feedstock for biofuel production has been promoted in the field of green biotechnology. In this present study, the microalgae were isolated from freshwater samples. The predominant strain was screened from the samples and grown in four different growth media, including modified Bold's Basal Medium (BBM), modified CFTRI medium, BG11 medium and CHU medium, to find the suitable growth medium to enrich biomass production. In total three microalgae colonies were identified based on their colony morphology microscopically by using a light microscope. The predominant strain was confirmed as Asterarcys quadricellulare using 18S rRNA sequencing. The growth of microalgae was investigated based on parameters like dry weight, pigment composition such as chlorophyll a, chlorophyll b, carotenoid and lipid content in the microalgae. Among the four different media, modified BBM medium showed maximum dry weight (1.44 ± 0.015 g/L), chlorophyll a (23.07 ± 0.049 mg/L), chlorophyll b (16.76 ± 0.010 mg/L), carotenoid (8.92 ± 0.031 mg/L) and lipid content (375 ± 0.020 mg/L) on the 25th day of culture. The gas chromatography mass spectrometry (GC/MS) analysis showed the presence of major fatty acids stearic acid, palmitic acid and oleyl alcohol in the microalgae. Therefore the high lipid content and fatty acid profiles of Asterarcys quadricellulare are becoming a promising suitable strain for biofuel production with modified BBM medium.

High production of carotenoids by the green microalga Asterarcys quadricellulare PUMCC 5.1.1 under optimized culture conditions

Since carotenoids are important as natural colorants, antioxidants, neutraceutics and pharmaceutics, the aim of the present study was to find a new good source of these pigments. We hereby report a green microalga Asterarcys quadricellulare PUMCC 5.1.1 as a new and good producer of carotenoids. The organism produced 35±1.75 μg carotenoids mg-1 dry biomass during stationary phase in control cultures. The growth and carotenoids production by the test microalga were optimized by varying nutrient growth media, pH, nitrogen and phosphate source, salinity, light quality, intensity and duration. The optimized conditions for carotenoid production were: Bold basal (BB) medium with pH 8.5, containing with10 mM nitrate, 3.5 mM phosphate and 0.17 mM salinity and illuminated with blue light with 60 μmol m-2 s-1 photon flux light intensity. Cultivation of cultures in the above mentioned optimized conditions resulted in nearly 3.0 fold increase in carotenoid production compared to the control cultures grown in unmodified BB medium. Using HPTLC, four carotenoids have been identified as β-carotene, lutein, astaxanthin and canthaxanthin. Further, carotenoids were also separated and purified by flash chromatography and the amounts of purified carotenoids were determined by HPLC. The organism produced 47.0, 28.7, 15.5 and 14.0 μg β-carotene, lutein, astaxanthin and canthaxanthin mg-1 dry biomass, respectively, under optimized conditions. The amount of total carotenoids (118 μg mg-1 dry biomass) produced by Asterarcys quadricellulare PUMCC 5.1.1 under optimized culture conditions was significantly higher than control cultures. Thus, this microalgal strain is a promising candidate for carotenoid production at commercial level.