A Comparative Study of Scenedesmus dimorphus Cultured with Synthetic and Actual Wastewater

This study compared the growth of the microalgae Scenedesmus dimorphus in synthetic wastewater and actual wastewater under different cultivation conditions, in terms of nitrogen and phosphorus availability, wastewater quality, light condition and CO2 addition. The results show that the form of nitrogen source had a significant effect on the growth of microalgae. Urea as a nitrogen source increased the growth rate of S. dimorphus significantly, while the high concentration of inorganic nitrogen inhibited the growth. When phosphate was 4 mg/L and pH was 7, the growth of S. dimorphus was the greatest. The bacteria in actual wastewater not only promote the growth of microalgae but also facilitate the formation of flocs, which is conducive to biomass harvest. With the increase in light intensity and light duration, S. dimorphus showed primarily an increasing and then a decreasing trend. Higher light intensity was required in actual wastewater than in synthetic wastewater, which may be due to the barrier effect of wastewater turbidity. S. dimorphus grew well in both kinds of wastewater with the addition of 2% CO2.

Mass transfer characteristics and biological effect of flue gas during microalgae culture

Not only carbon dioxide (CO2) but also air pollutants, such as sulfur oxides (SOx) and nitrogen oxides (NOx), are present in flue gas, and their reasonable and effective utilization is conducive to reducing the cost of microalgal biomass production. By utilizing simulated flue gas, the absorption characteristics of different components in transfer units were explored. The results showed that the presence of SO2 decreased the absorptivity of CO2, which reduced the concentration of the available carbon source for microalgal cells in the culture medium at the same pH value. Moreover, the presence of high-concentration oxygen (O2) in flue gas could improve the absorptivity of nitric oxide (NO). Scenedesmus dimorphus was cultured by using sulfur- or nitrogen-deficient culture media. The results showed that SOx and NOx in flue gas did not significantly influence the growth and biochemical compositions of microalgal cells when these gases were dissolved in water. Based on the above results and the metabolic kinetics of microalgal cells for nutrient elements, an adjustment strategy for the initial gas source when culturing microalgae with flue gas is proposed: (1) flue gas should be partially desulfurized so that the SOx and CO2 concentrations after desulfurization satisfy a certain relationship with the components; and (2) denitrification should not be performed because flue gas can be oxidized before utilization to increase the rate of utilization of NO.

Antifungal and Antioxidant Potential of Methanolic Extracts from Acorus calamus L., Chlorella vulgaris Beijerinck, Lemna minuta Kunth and Scenedesmus dimorphus (Turpin) Kützing

Plant extracts are an important alternative to antibiotics, which are ever more restricted because of their developing microbial resistance and some adverse effects that have been observed following frequent application. The aim of the present study was to determine the antifungal and antioxidant activity of the methanolic extracts of Acorus calamus, Chlorella vulgaris, Lemna minuta and Scenedesmus dimorphus. The antifungal activity of the extracts against strains of Aspergillus flavus, Aspergillus parasiticus, Aspergillus ochraceus, Aspergillus niger, Aspergillus carbonarius, Fusarium graminearum, Fusarium oxysporum, Penicillium chrysogenum and Alternaria alternata was evaluated via the agar well diffusion method. The antioxidant activity of the extracts was measured through the determination of three parameters—total phenolic content, total flavonoid content and radical scavenging potential (determined through UV/Vis analysis). A. calamus extracts had the highest antimicrobial activity against eight fungal strains, followed by the C. vulgaris, L. minuta and S. dimorphus extracts, which were inhibitory against two to three strains. Among the extracts from the species studied, the extract from S. dimorphus showed the highest antioxidant potential, as determined via the DPPH (1,1’-diphenyl-2-picrylhydrazil-radical) method. This correlated to its high total phenolic and flavonoid content. From A. calamus and L. minuta, methanolic extracts were obtained that exhibited similar values of the aforementioned parameters, followed by C. vulgaris extracts, which showed the lowest antioxidant activity. Based on the Pearson correlation coefficients, the impacts of the total phenolic content and the total flavonoid content on radical scavenging capacity are similar, and flavonoids were a significant part of the total phenolic compounds extracted from the plant materials studied.

Paraphysoderma sedebokerense Infection in Three Economically Valuable Microalgae: Host Preference Correlates with Parasite Fitness

The blastocladialean fungus Paraphysoderma sedebokerense parasitizes three microalgae species of economic interest: Haematococcus pluvialis, Chromochloris zofingiensis and Scenedesmus dimorphus. For the first time, we characterized the developmental stages of isolated fungal propagules in H. pluvialis co-culture, finding a generation time of 16 h. We established a patho-system to compare the infection in the three different host species for 48 h, with two different setups to quantify parameters of the infection and parameters of the parasite fitness. The prevalence of the parasite in H. pluvialis and C. zofingiensis cultures was 100%, but only 20% in S. dimorphus culture. The infection of S. dimorphus not only reached lower prevalence but was also qualitatively different; the infection developed preferentially on senescent cells and more resting cysts were produced, being consistent with a reservoir host. In addition, we carried out cross infection experiments and the inoculation of a mixed algal culture containing the three microalgae, to determine the susceptibility of the host species and to investigate the preference of P. sedebokerense for these microalgae. The three tested microalgae showed different susceptibility to P. sedebokerense, which correlates with blastoclad’s preference to the host in the following order: H. pluvialis > C. zofingiensis > S. dimorphus.

Freshwater pond microalgae for biofuel: Strain isolation, identification, cultivation and fatty acid content

Perdana BA, Dharma A, Zakaria IJ, Syafrizayanti. 2021. Freshwater pond microalgae for biofuel: Strain isolation, identification, cultivation, and fatty acid content. Biodiversitas 22: 505-511. Microalgae have capability to produce fatty acid for biofuel, drugs, and nutraceutical foods development. This study was carried out to obtain a new strain candidate for fatty acid production. The methods were used in this study include isolation of microalgae species from freshwater ponds of Andalas University, Padang, Indonesia. Molecular identification of microalgae was carried out with specific 18S rRNA primer, F-P73, and R-P47. Microalgae growth was measured by cell density and optical density method using various wavelengths (400, 500, and 680 nm). Total lipid was extracted using Bligh & Dyer method. Fatty acid analyses were conducted using gas chromatography-mass spectroscopy. Microalgae were isolated i.e Chlorella emersonii MAUA001, Mychonastes rotundus MAUA002, Scenedesmus dimorphus MAUA003, and Scenedesmus armatus MAUA004. The result exhibited M. rotundus was the highest lipid content, it was about 28.8% biomass weight. Fatty acid profiles of microalgae were dominated by monounsaturated (MUFA) and saturated fatty acid (SFA). The highest content of fatty acid species found in C. emersonii with octadecenoic acid (C18:1) was 47.74% total lipid. This work showed that C. emersonii has potential as biodiesel due to high saturated fatty acid.