Influences of carbon and nitrogen sources and metal ions on the heterotrophic culture of Scenedesmus sp. LX1

Nitrogen and phosphorus removal performance of sequential batch operation for algal cultivation through suspended-solid phase photobioreactor

Nitrogen (N) and phosphorus (P) absorbed by algae in the suspended-solid phase photobioreactor (ssPBR) have emerged as an efficient pathway to purify the effluent of wastewater treatment plants (WWTPs). However, the key operational parameters of the ssPBR need to be optimized. In this study, the stability of the system after sequential batch operations and the efficiency under various influent P concentrations were evaluated. The results demonstrated that the ssPBR maintained a high N/P removal efficiency of 96 % and 98 %, respectively, after 5 cycles. When N was kept at 15 mg/L and P ranged from 1.5 to 3.0 mg/L, the system yielded plenty of algae products and guaranteed the effluent quality that met the discharge standards. Notably, the carriers were a key contributor to the high metabolism of algae and high performance. This work provided theoretical ideas and technical guidance for effluent quality improvement in WWTPs.

Simultaneous bioremediation of Disperse orange-2RL Azo dye and fatty acids production by Scenedesmus obliquus cultured under mixotrophic and heterotrophic conditions

Several types of green photosynthetic microalgae can grow through the process of heterotrophic growth in the dark with the help of a carbon source instead of the usual light energy. Heterotrophic growth overcomes important limitations in the production of valuable products from microalgae, such as the reliance on light, which complicates the process, raises costs, and lowers the yield of potentially useful products. The present study was conducted to explore the potential growth of green microalga Scenedesmus obliquus under mixotrophic and heterotrophic conditions utilizing Disperse orange 2RL Azo dye as a carbon source to produce a high lipid content and the maximum dye removal percentage. After 7 days of algal growth with dye under mixotrophic and heterotrophic conditions with varying pH levels (5, 7, 9, and 11), KNO₃ concentrations (1, 1.5, 2, and 3 g/L), and dye concentrations (20, 40, and 60 ppm); dye removal percentage, algal dry weight, and lipid content were determined. The results showed that the highest decolorization of Disperse orange 2RL Azo dye (98.14%) was attained by S. obliquus in heterotrophic medium supplemented with glucose at the optimal pH 11 when the nitrogen concentration was 1 g/L and the dye concentration was 20 ppm. FT-IR spectroscopy of the dye revealed differences in peaks position and intensity before and after algal treatment. S. obliquus has a high concentration of oleic acid, which is enhanced when it is grown with Disperse orange 2RL Azo dye, making it ideal for production of high-quality biodiesel. In general, and in the vast majority of instances, heterotrophic cultivation is substantially less expensive, easier to set up, and requires less maintenance than mixotrophic cultivation. Heterotrophic cultivation allows for large-scale applications such as separate or mixed wastewater treatment along with biofuel production.

Selection of a suitable photosynthetically active microalgae strain for the co-cultivation with mammalian cells

Preventing hypoxic zones in 3D bioprinted mammalian cell-laden constructs using an internal oxygen supply could enable a more successful cultivation both in vitro and in vivo. In this study, the suitability of green microalgae as photosynthetic oxygen generators within bioprinted constructs was evaluated by defining and investigating important parameters for a successful co-culture. First, we assessed the impact of light–necessary for photosynthesis–on two non-light adapted mammalian cell types and defined red-light illumination and a temperature of 37°C as essential factors in a co-culture. The four thermotolerant microalgae strains Chlorella sorokiniana, Coelastrella oocystiformis, Coelastrella striolata, and Scenedesmus sp. were cultured both in suspension culture and 3D bioprinted constructs to assess viability and photosynthetic activity under these defined co-culture conditions. Scenedesmus sp. proved to be performing best under red light and 37°C as well as immobilized in a bioprinted hydrogel based on alginate. Moreover, the presence of the antibiotic ampicillin and the organic carbon-source glucose, both required for mammalian cell cultures, had no impact on bioprinted Scenedesmus sp. cultures regarding growth, viability, and photosynthetic activity. This study is the first to investigate the influence of mammalian cell requirements on the metabolism and photosynthetic ability of different microalgal strains. In a co-culture, the strain Scenedesmus sp. could provide a stable oxygenation that ensures the functionality of the mammalian cells.

Enhancing growth and oil accumulation of a palmitoleic acid-rich Scenedesmus obliquus in mixotrophic cultivation with acetate and its potential for ammonium-containing wastewater purification and biodiesel production

A palmitoleic acid-rich Scenedesmus obliquus strain SXND-02 was isolated from ammonium-containing wastewater. Biomass and lipid production were examined for this microalgal strain in photoautotrophic, heterotrophic, and mixotrophic cultivations, respectively, in order to extend its application in wastewater purification coupled with production of valued bio-products. Among the tested conditions, the microalga had better growth and higher lipid accumulation in mixotrophy. NH₄Cl inhibited the microalgal growth in photoautotrophic cultivation. However, NaAc alleviated this inhibition in both heterotrophy and mixotrophy. Using 7 g L^-1 NaAc and 0.5 g L^-1 NH₄Cl as carbon and nitrogen sources significantly increased the algal biomass and lipid yields under mixotrophic cultivation, with the highest levels up to 1.0 g L^-1 and 59.88%, respectively. Fatty acid profiling indicated that palmitoleic acid was 23% in the S. obliquus SXND-02 under mixotrophic condition, which was about 21-fold higher than that in the control S. obliquus. Furthermore, this microalgal strain was tested in the chicken farm wastewater (CFW) containing high ammonium. Compared with other treatments, the S. obliquus SXND-02 cultivated in the 1/2 CFW + NaAc medium produced larger amounts of biomass (2.18 g L^-1) and lipids (50.22%), and simultaneously higher removal rates of total nitrogen (TN) (80%), total ammonium nitrogen (TAN) (68%), total phosphate (TP) (82%), biological oxygen demand (BOD) (86%) and chemical oxygen demand (COD) (89%) from wastewater. The present data indicate that this excellent microalga can be used in mixotrophic cultivation for wastewater purification coupled with commercial production of valued biomass and high-quality algal oils.

Synergistic effect of growth conditions and organic carbon sources for improving biomass production and biodiesel quality by the microalga Choricystis minor var. minor

In the search for microalgae species with potential for biodiesel production, Choricystis minor var. minor has been seen as a promising source of biomass due to its high lipid content and the satisfactory characteristics of its fatty acid methyl esters (FAMEs). For this reason, the objective of this study was to investigate the synergistic effect of growth conditions and organic carbon sources on cultivation of this microalga. To do so, experimental cultivations were conducted in photoautotrophic, heterotrophic and mixotrophic metabolisms using glucose, fructose, glycerol or sucrose - in growth conditions that use organic carbon. Thus, growth parameters of the cultures were evaluated and at the end of the cultivations, FAMEs yield and profile were determined by gas chromatography, the efficiency of carbon conversion into biomass was evaluated and a microbial analysis was conducted. Regarding growth conditions, the findings have confirmed that, regardless of the organic carbon source used, the heterotrophic and mixotrophic metabolisms can present advantages over the photoautotrophic one. In addition, biomass production was higher with the use of glucose than with other organic carbon sources, regardless of growth condition (heterotrophic or mixotrophic). Moreover, cultivations with the addition of CO₂ have converted carbon into biomass less efficiently. On the other hand, photoautotrophic cultures presented the lowest bacterial load. In comparison to photoautotrophic and mixotrophic, heterotrophic cultures have led to lower FAMEs content and higher yields of unsaturated fatty acids. The most satisfactory FAMEs profile for biodiesel production was obtained with mixotrophic growth using fructose.

Assessing the robust growth and lipid-accumulating characteristics of Scenedesmus sp. for biodiesel production

In the present investigation, different salts of nitrogen and carbon sources were tested for their potential to boost biomass and lipid content in Scenedesmus sp. IITRIND2. Among the nitrogen sources, ammonium bicarbonate/nitrate cultures showed maximum dry cell weight (DCW) of ~ 1.8 g/L and lipid yield (~ 40%) while the addition of C6 sugars (glucose and mannose) and sodium acetate enhanced the DCW (~ 3 g/L) and lipid accumulation (~ 40%) compared with disaccharides, C4 and C5 sugars. On evaluating the synergistic effects of the nitrogen and carbon sources, maximum DCW (3.66 g/L) was obtained in ammonium bicarbonate + sodium acetate cultures with a lipid yield of 37.15%. The fatty acid profile of the derived biodiesel was similar to that of plant oils. The results clearly established the robust capability of the novel microalga to efficiently adapt, sustain, and grow in different carbon and nitrogen sources along with high lipid productivity, making it a potential source for biodiesel production.