A novel culture medium designed for the simultaneous enhancement of biomass and lipid production by Chlorella vulgaris UTEX 26

Enhancing microalgal lipid accumulation for biofuel production

Microalgae have high lipid accumulation capacity, high growth rate and high photosynthetic efficiency which are considered as one of the most promising alternative sustainable feedstocks for producing lipid-based biofuels. However, commercialization feasibility of microalgal biofuel production is still conditioned to the high production cost. Enhancement of lipid accumulation in microalgae play a significant role in boosting the economics of biofuel production based on microalgal lipid. The major challenge of enhancing microalgal lipid accumulation lies in overcoming the trade-off between microalgal cell growth and lipid accumulation. Substantial approaches including genetic modifications of microalgal strains by metabolic engineering and process regulations of microalgae cultivation by integrating multiple optimization strategies widely applied in industrial microbiology have been investigated. In the present review, we critically discuss recent trends in the application of multiple molecular strategies to construct high performance microalgal strains by metabolic engineering and synergistic strategies of process optimization and stress operation to enhance microalgal lipid accumulation for biofuel production. Additionally, this review aims to emphasize the opportunities and challenges regarding scaled application of the strategic integration and its viability to make microalgal biofuel production a commercial reality in the near future.

Removal of carbon and nitrogen in wastewater from a poultry processing plant in a photobioreactor cultivated with the microalga Chlorella vulgaris

This study evaluates the removal of COD and nitrogen from poultry wastewater in photobioreactors. Cell growth, the effect of light intensity (3200, 9800, and 12000 lux) and air flow (1.6, 3.2, and 4.8 L min^-1) as a source of CO₂ in bold basal medium and wastewater with different concentrations of COD were evaluated. The growth kinetics were modeled by using the Gompertz model and logistic model for both culture media. COD removals of up to 95% were achieved, and poultry wastewater was found to be a viable growing medium for Chlorella vulgaris. Finally, the wastewater met Mexican standards, and biomass was obtained with products valued as lipids (3.2 g lipid/100 g biomass) and proteins (342.94 mg L^-1). The culture was found to have a dilatory behavior, and the rheological models of Ostwald de Waele, Ostwald de Waele linealized and Herschel Bulkley were utilized, showing a laminar behavior.

Co-cultivation of microalga and xylanolytic bacterium by a continuous two-step strategy to enhance algal lipid production

To enhance microalgal lipid production, canonical two-step cultivation strategy that by transferring the microalgal cells grown in nutrient-replete medium to nutrient-depleted medium is widely used. However, the harvesting step during the transfer raises the production cost. To avoid the harvesting step, this study developed a continuous two-step (CTS) cultivation strategy. In the strategy, Chlorella sacchrarophila was grown in bioreactor while a xylanolytic bacterium Cellvibrio pealriver grown in an inner bag that embedded in the bioreactor; after the first-step co-cultivation, the inner bag is removed which then start the second-step cultivation of C. sacchrarophila. Based on the strategy, the lipid production was determined as 825.34-929.79 mg·L^-1, which were 1.7-1.9 times higher than that of cultivation in canonical two-step strategy using glucose as feedstock. During the CTS strategy, the co-cultivation using xylan as feedstock promotes the microalgal growth and the removal of inner bag produces nutrient-depleted condition for enhancing microalgal lipid production.

Insights into the physiology of Chlorella vulgaris cultivated in sweet sorghum bagasse hydrolysate for sustainable algal biomass and lipid production

Supplementing cultivation media with exogenous carbon sources enhances biomass and lipid production in microalgae. Utilization of renewable organic carbon from agricultural residues can potentially reduce the cost of algae cultivation, while enhancing sustainability. In the present investigation a medium was developed from sweet sorghum bagasse for cultivation of Chlorella under mixotrophic conditions. Using response surface methodology, the optimal values of critical process parameters were determined, namely inoculum cell density (O.D.₇₅₀) of 0.786, SSB hydrolysate content of the medium 25% v/v, and zero medium salinity, to achieve maximum lipid productivity of 120 mg/L/d. Enhanced biomass (3.44 g/L) and lipid content (40% of dry cell weight) were observed when the alga was cultivated in SSB hydrolysate under mixotrophic conditions compared to heterotrophic and photoautotrophic conditions. A time course investigation revealed distinct physiological responses in terms of cellular growth and biochemical composition of C. vulgaris cultivated in the various trophic modes. The determined carbohydrate and lipid profiles indicate that sugar addition to the cultivation medium boosts neutral lipid synthesis compared to structural lipids, suggesting that carbon flux is channeled towards triacylglycerol synthesis in the cells. Furthermore, the fatty acid profile of lipids extracted from mixotrophically grown cultures contained more saturated and monosaturated fatty acids, which are suitable for biofuel manufacturing. Scale-up studies in a photobioreactor using SSB hydrolysate achieved a biomass concentration of 2.83 g/L consisting of 34% lipids and 26% carbohydrates. These results confirmed that SSB hydrolysate is a promising feedstock for mixotrophic cultivation of Chlorella and synthesis of algal bioproducts and biofuels.

Microalgae: A Promising Source of Valuable Bioproducts

Microalgae are a group of autotrophic microorganisms that live in marine, freshwater and soil ecosystems and produce organic substances in the process of photosynthesis. Due to their high metabolic flexibility, adaptation to various cultivation conditions as well as the possibility of rapid growth, the number of studies on their use as a source of biologically valuable products is growing rapidly. Currently, integrated technologies for the cultivation of microalgae aiming to isolate various biologically active substances from biomass to increase the profitability of algae production are being sought. To implement this kind of development, the high productivity of industrial cultivation systems must be accompanied by the ability to control the biosynthesis of biologically valuable compounds in conditions of intensive culture growth. The review considers the main factors (temperature, pH, component composition, etc.) that affect the biomass growth process and the biologically active substance synthesis in microalgae. The advantages and disadvantages of existing cultivation methods are outlined. An analysis of various methods for the isolation and overproduction of the main biologically active substances of microalgae (proteins, lipids, polysaccharides, pigments and vitamins) is presented and new technologies and approaches aimed at using microalgae as promising ingredients in value-added products are considered.

Impact of Cultivation Condition and Media Content onChlorella vulgaris Composition

Microalgae are a source material in food, pharmacy, and cosmetics industries for producing various products including high-protein nutritional supplements, synthetic pharmaceuticals, and natural colors. A promising algal source for such productions is Chlorella vulgaris which contains a considerable protein content. Similar to other microalgae, its desirability is minimal nutrient requirements since they are unicellular, photosynthetic, and fast-growing microorganisms. Another propitious option to be produced by C. vulgaris is biodiesel, since it is rich in oil too. Besides, algal well thriving in presence of increased amount of carbon dioxide makes them a practicable alternative biofuel resource without some problems of the traditional ones. At the same time, C. vulgaris is also a promising source for nutraceuticals such as amino acids, vitamins, and antioxidants. This review aims to discuss the conditions need to be observed for achieving a favorable growth efficiency of the C. vulgaris, as well as targeted productions such as biomass, antioxidant, and biofuel. Additionally, different approaches to induce any specific production are also considered comprehensively.

Biomass and lipid production from Chlorella vulgaris UTEX 26 cultivated in 2 m3 raceway ponds under semicontinuous mode during the spring season

A Chlorella vulgaris UTEX 26 semicontinuous culture was implemented in 2000 L raceways with M medium during spring season at greenhouse conditions. Areal biomass productivities between 20 and 26 g m^-2 d^-1 were reached on the third day. The maximal areal lipid productivity obtained was 6.1 g m^-2 d^-1 and an increment in the saturated fatty acids (SFA) proportion (C14-C18) was favored in comparison with the fatty acids obtained with M medium in photobioreactors of 1 L and photoperiod light:darkness 12:12 h. After the eighth day of the culture or biomass concentrations above 0.25 g L^-1, the microalgal cultures were prone to contamination by ciliates and amoebae, due to the sugars excreted by C. vulgaris UTEX 26. The periodical addition of NH₄HCO₃ to the microalgal culture maintained the ammonium concentration between 25 and 50 mg L^-1, which contributed to diminish the contamination risks by protozoa.

Assessment of Chlorella vulgaris and indigenous microalgae biomass with treated wastewater as growth culture medium

The aim of the present work was to evaluate the feasibility of microalgae cultivation using secondary treated domestic wastewater. Two Chlorella vulgaris strains (CICESE and UTEX) and an indigenous consortium, were cultivated on treated wastewater enriched with and without the fertilizer Bayfolan®. Biomass production for C. vulgaris UTEX, CICESE and the indigenous consortium grown in treated wastewater was 1.167±0.057, 1.575±0.434 and 1.125±0.250g/L, with a total lipid content of 25.70±1.24, 23.35±3.01and 20.54±1.23% dw, respectively. The fatty acids profiles were mainly composed of C16 and C18. Regardless of the media used, in all three strains unsaturated fatty acids were the main FAME (fatty acids methyl esters) accumulated in a range of 45-62%. An enrichment of treated wastewater with Bayfolan® significantly increased the production of biomass along with an increase in pigments and proteins of ten and threefold, respectively.