Mohammad Ali Mohammad Mirzaie

Microalgae Dunaliella salina has been recognized as an effective source of β-carotene. To elevate the productivity of this species, light has been served as an important induction factor, in this regard, a new idea was inspired as designing a red-to-blue wavelength shifting system based on the growth rate and cell behavior. A photobioreactor was exposed to two panels of flashing red and blue LEDs. At the commencement of the stationary phase, the wavelength shifting was applied and red LEDs were replaced with blue ones. Maximum β-carotene content of 10 mg.g⁻¹ was obtained; at least 300% higher than the content in the controlled system (flashing red and blue light to the end of growth).

Simple, applicable electrodes are the main features of electrochemical biosensors. Production of such electrodes using a time-consuming and non-expensive method was the aim of this study. According to this purpose, three-dimensional graphene foam (3DGF) was produced successively as an interconnected porous network of the high intrinsic surface area via a self-assembly method. Using Ag pastes as substrate, free-standing 3DGF electrodes as well as other graphene-based electrodes were prepared simply with high conductivity and desired electrochemical features. Any kind of additives including enzymes or functional groups or even, other nanomaterials as a hybrid was not used in the electrodes provided longer stability and less preparation time. A low cathodic current of -4.3 mA was measured in cyclic voltammograms (CV) of such small 3DGF electrodes (100 times less than previously reported glassy carbon (GC)-based electrodes). Non-enzymatic detection of H2O2 was clearly illustrated by a remarkable drop of the cathodic current, about 1.2 mA. Besides, the amperometric response of the 3DGF electrode certified the excellent reduction toward hydrogen peroxide with a correlation coefficient of more than 98 %. The reusability of the 3DGF electrode was confirmed by less than 3 % deviation in the cathodic current of particular electrodes after washing and repetitive use.

Chlorella vulgaris (C. vulgaris) microalga was investigated as a new potential feedstock for the production of biodegradable lubricant. In order to enhance microalgae lipid for biolubricant production, mixotrophic growth of C. vulgaris was optimized using statistical analysis of Plackett–Burman (P-B) and response surface methodology (RSM). A cheap substrate-based medium of molasses and corn steep liquor (CSL) was used instead of expensive mineral salts to reduce the total cost of microalgae production. The effects of molasses and CSL concentration (cheap substrates) and light intensity on the growth of microalgae and their lipid content were analyzed and modeled. Designed models by RSM showed good compatibility with a 95% confidence level when compared to the cultivation system. According to the models, optimal cultivation conditions were obtained with biomass productivity of 0.123 g L⁻¹ day⁻¹ and lipid dry weight of 0.64 g L⁻¹ as 35% of dry weight of C. vulgaris. The extracted microalgae lipid presented useful fatty acid for biolubricant production with viscosities of 42.00 cSt at 40°C and 8.500 cSt at 100°C, viscosity index of 185, flash point of 185°C, and pour point of −6°C. These properties showed that microalgae lipid could be used as potential feedstock for biolubricant production.

Growth of Chlorella vulgaris and its lipid production were investigated under autotrophic, heterotrophic, and mixotrophic conditions. Cheap agricultural waste molasses and corn steep liquor from industries were used as carbon and nitrogen sources, respectively. Chlorella vulgaris grew remarkably under this agricultural waste medium, which resulted in a reduction in the final cost of the biodiesel production. Maximum dry weight of 2.62 g L⁻¹ was obtained in mixotrophic growth with the highest lipid concentration of 0.86 g L⁻¹. These biomass and lipid concentrations were, respectively, 140% and 170% higher than autotrophic growth and 300% and 1200% higher than heterotrophic growth. In mixotrophic growth, independent or simultaneous occurrence of autotrophic and heterotrophic metabolisms was investigated. The growth of the microalgae was observed to take place first heterotrophically to a minimum substrate concentration with a little fraction in growth under autotrophic metabolism, and then the cells grew more autotrophically. It was found that mixotrophic growth was not a simple combination of heterotrophic and autotrophic growth.