Process intensification for the enhancement of growth and chlorophyll molecules of isolated Chlorella thermophila: A systematic experimental and optimization approach.

In our current work, we have optimized six physicochemical parameters (light intensity, light period, pH, inoculum size, culture period, and salt concentration) toward growth and chlorophyll synthesis using isolated fresh water microalgae Chlorella thermophila [contains ∼6% (w/w on dry biomass basis) chlorophyll]. Here, both experimental and computational [Taguchi orthogonal array (TOA), artificial neural network (ANN), and genetic algorithm (GA)] approaches were employed for the process intensification. Results revealed that the content of biomass and chlorophyll were enhanced by 118% and 95%, respectively, with productivity enhancement of 30% for biomass and 61% for chlorophyll from the optimization of physicochemical parameters. Further, optimum light intensity was found to be 128 µmol m-2 s-1 after conducting experiments in optimized chemical and physicochemical conditions, contributing to the enhancement of productivity of 46% for biomass and 106% for chlorophyll. Urea was found to be the most effective nitrogen source with an increase of 70% and 160% biomass and chlorophyll productivity, respectively. Moreover, sucrose as a carbon source contributed to an increase of 97% and 264% biomass and chlorophyll productivity.

Transfer matrix optimization of a one-dimensional photonic crystal cavity for enhanced absorption of monolayer graphene.

The optical absorption enhancement of graphene is of significant interest due to its remarkable applications in optical devices. One of the most useful methods is placing graphene in an asymmetric Fabry-Perot cavity made of one-dimensional dielectric multilayers forming two mirrors. In that regard, using the transfer matrix method, we have explicitly calculated the required periodicity of the front photonic multilayer mirror to maximize the absorption in the graphene for any given combination of material types and number of layers. Then we studied the equivalence between these structural configurations and those with arbitrary periodicity but with defects, where the equivalence holds when ω=ξω0,ξ∈Z≥0. These defects are introduced via layer position alterations, based on which we propose an optimization algorithm to maximize absorption in structures having a cavity with an arbitrary periodicity. Numerical calculations are given for dielectric material combinations of TiO2/SiO2 and Ta2O5/SiO2, and to understand the behavior of these optimized structures for any general combination of material types, the mapping of their calculated front mirror periodicity for a range of refractive indices of the two material types has been studied.

Enhancement of growth and biomolecules (carbohydrates, proteins, and chlorophylls) of isolated Chlorella thermophila using optimization tools.

The production of multiple products from microalgae is essential for economic sustainability and the knowledge of optimum cultivation conditions for high growth and biomolecule synthesis of a microalgal strain is the prerequisite for its commercial production. In this work, optimization of nutrient concentrations for the cultivation of isolated Chlorella thermophila was performed by manipulating nine nutrients with the objectives of maximization of growth, carbohydrate, protein, and chlorophyll contents. Experiments were designed and effects of the parameters were studied using Taguchi orthogonal array (TOA). Experimental results of TOA were used for modeling artificial neural networks (ANN) followed by the optimization using genetic algorithm (GA) to find global optimal solutions. Results showed an increase of 36, 88, 36, and 88% for growth, carbohydrates, proteins, and chlorophylls, respectively, at optimal combinations of parameters given by TOA. Results obtained through the ANN-GA optimization were 9, 10, and 3% more compared to the TOA for biomass, carbohydrates, and chlorophylls, respectively with experimental verification. Nitrates and bicarbonate were found to play the most pivotal role in biomass and biomolecule synthesis of the isolated microalgal strain. Results of the current investigation can be used in the industrial scale-up for the production of multiple products using the biorefinery approach.

Priority-based multiple products from microalgae: review on techniques and strategies.

Microalgal biomass is composed of different valuable metabolites that can satisfy the requirements of renewable biofuels, alternative proteins, carbohydrates, and food grade natural colorants. Production of a specific product from microalgae has been proved to be economically infeasible on the commercial scale except for the production of high-value products (e.g. carotenoids and phycobiliproteins). Therefore, the simultaneous extraction of multiple products is essential to bring pragmatism for the production of biofuels, proteins, and carbohydrate derived products from microalgal biomass. In order to obtain multiple products, various strategies have been implemented using potential techniques of cell disruption and biomass fractionation based on the priorities of products. Conventional approaches of downstream processing have often proved to be inefficient in the case of integrated fractionation systems. This is attributable to the divergent nature of the intracellular metabolites of microalgae and their vulnerability toward the different chemicals and conditions of those downstream processes. However, three phase partitioning (TPP), aqueous two-phase separation, membrane separation, supercritical fluid extraction (SFE), and pressurized liquid extraction (PLE) are some of the advanced techniques which have been proved to be useful in this regard. Choice of cell disruption mechanisms is critical for several purposes, such as the selective release of metabolites into a suitable solvent, preservation of bioactivity of molecules and cost-savings. Unfortunately, consolidated report for the fractionation of priority-based products from microalgal biomass using these techniques is lacking. Therefore, in this review, we have critically discussed the different strategies for the priority-based multiple products by implementation of the advanced techniques.