Hydrodynamics and mass transfer of CO 2 in water in a tubular photobioreactor

Implementation of kLa-Based Strategy for Scaling Up Porphyridium purpureum (Red Marine Microalga) to Produce High-Value Phycoerythrin, Fatty Acids, and Proteins

Porphyridium purpureum is a well-known Rhodophyta that recently has attracted enormous attention because of its capacity to produce many high-value metabolites such as the pigment phycoerythrin and several high-value fatty acids. Phycoerythrin is a fluorescent red protein-pigment commercially relevant with antioxidant, antimicrobial activity, and fluorescent properties. The volumetric mass transfer coefficient (k_La) was kept constant within the different scaling-up stages in the present study. This scaling-up strategy was sought to maintain phycoerythrin production and other high-value metabolites by Porphyridium purpureum, using hanging-bag photobioreactors. The k_La was monitored to ensure the appropriate mixing and CO₂ diffusion in the entire culture during the scaling process (16, 80, and 400 L). Then, biomass concentration, proteins, fatty acids, carbohydrates, and phycoerythrin were determined in each step of the scaling-up process. The k_La at 16 L reached a level of 0.0052 s^-1, while at 80 L, a value of 0.0024 s^-1 was achieved. This work result indicated that at 400 L, 1.22 g L^-1 of biomass was obtained, and total carbohydrates (117.24 mg L^-1), proteins (240.63 mg L^-1), and lipids (17.75% DW) were accumulated. Regarding fatty acids production, 46.03% palmitic, 8.03% linoleic, 22.67% arachidonic, and 2.55% eicosapentaenoic acid were identified, principally. The phycoerythrin production was 20.88 mg L^-1 with a purity of 2.75, making it viable for food-related applications. The results of these experiments provide insight into the high-scale production of phycoerythrin via the cultivation of P. purpureum in an inexpensive and straightforward culture system.

CO2 biofixation and fatty acid composition of two indigenous Dunaliella sp. isolates (ABRIINW-CH2 and ABRIINW-SH33) in response to extremely high CO2 levels

Global warming, as a result of atmospheric CO₂ increase, is regarded as an important universal concern. Microalgae are considered as appropriate microorganisms for CO₂ assimilation. Here we aimed to investigate carbon biofixation ability of two indigenous isolates of Dunaliella spp. (ABRIINW-CH2 and ABRIINW-SH33) under elevated CO₂ concentrations of 10, 20, and 30% (v/v) as well as their lipid content, productivity, and fatty acid profile under adjusted pH conditions. The maximum biomass production and CO₂ biofixation rates were obtained under 10% CO₂. High CO₂ concentrations were favorable for the accumulation of lipids, lipid productivity, and polyunsaturated fatty acids formation. The highest lipid content and lipid productivity was obtained at 10% CO₂. The highest fraction of the fatty acids (FA) profile was allocated to omega-3 FAs at 20% CO₂. Accordingly, these isolates were able to tolerate extremely high CO₂ concentrations and present even enhanced growth as well as formation of valuable products.

Correlations between biochemical composition and biogas production during anaerobic digestion of microalgae and cyanobacteria isolated from different sources of Turkey

Twenty one species of microalgae and Cyanobacteria were isolated from different ecosystems in Turkey to investigate the relation between biochemical methane potential (BMP) and biochemical characterization. Since the highest dry weight (X), specific growth rate (µ) and maximum productivity (P_max) were obtained from the five species, identification of species and BMP tests with the composition analyzes were examined. BMP values were determined 308, 293, 242, 229 and 230 mLCH₄/gVS for Desertifilum tharense, Phormidium animale, Chlorella sp., Anabeana variabilis and Chlorophyta uncultured. The Pearson correlation and principal component analysis (PCA) were applied to extract and clarify the correlation between composition of species and their methane production. Pearson correlation shows that glucose, Kjeldahl nitrogen and chlorophyll are highly and positively correlated with BMP. PCA revealed that Chlorella sp., Chlorophyta uncultured and Desertifilum tharense were placed against Phormidium animale distinguished by its extreme and different profile because of Kjeldahl nitrogen and glucose content.

In situ biological CO2 fixation and wastewater nutrient removal with Neochloris oleoabundans in batch photobioreactor

Microalgae cultivation in wastewater media in phototrophic condition is a promising approach for integrated CO₂ biofixation and wastewater treatment. For this, Neochloris oleoabundans was used to investigate the tertiary treatment of wastewater along with CO₂ biofixation. In this investigation, biomass productivity, CO₂ biofixation rate and percentage of total nitrogen (TN) and total phosphorus (TP) removal from synthetic wastewater are considered under three different operating conditions: temperature, CO₂ feed concentration and nitrogen to phosphorus (NP) ratio in the media. Cultivation of N. oleoabundans was found to be highly temperature sensitive. With the increase of cultivation temperature from 25 to 45 °C, declining trends of biomass concentration, productivity and percentage of TN and TP removal were observed. Cultivation temperature of 25 °C was found to be most favorable in terms of biomass productivity, CO₂ biofixation rate, percentage of TN and TP removal of 92 (mg L^-1 day^-1), 145 (mg L^-1 day^-1), 100% and 32%, respectively. Arrhenius-type kinetic model was used and the model showed good agreement with the experimental findings. Activation energy for the active stage and decay stage was found to be [Formula: see text] = 88.8 kJ mol^-1 and [Formula: see text] = 8.4 kJ mol^-1, respectively. With the increase of CO₂ feed concentration, biomass productivity increased and the maximum biomass concentration and productivity was achieved at 6%. After that with the increase in CO₂, a declining trend was observed. With the increase of NP ratio from 1:1 to 2:1, both the biomass productivity and CO₂ biofixation were increased, but later were subsequently decreased with increase of NP ratio from 4:1 to 8:1. It is interesting that TP removal was increased with NP ratio and 100 percent of TP removal was achieved at 4:1 and 8:1 conditions.

CO2 utilization in the production of biomass and biocompounds by three different microalgae

The atmospheric CO₂ increase is considered the main cause of global warming. Microalgae are photosynthetic microorganisms that can help in CO₂ mitigation and at the same time produce value-added compounds. In this study, Scenedesmus obliquus, Chlorella vulgaris, and Chlorella protothecoides were cultivated under 0.035 (air), 5 and 10% (v/v) of CO₂ concentrations in air to evaluate the performance of the microalgae in terms of kinetic growth parameters, theoretical CO₂ biofixation rate, and biomass composition. Among the microalgae studied, S. obliquus presented the highest values of specific growth rate (μ = 1.28 d^-1), maximum productivities (P _max = 0.28 g L^-1d^-1), and theoretical CO₂ biofixation rates (0.56 g L^-1d^-1) at 10% CO₂. The highest oil content was found at 5% CO₂, and the fatty acid profile was not influenced by the concentration of CO₂ in the inflow gas mixture and was in compliance with EN 14214, being suitable for biodiesel purposes. The impact of the CO₂ on S. obliquus cells' viability/cell membrane integrity evaluated by the in-line flow cytometry is quite innovative and fast, and revealed that 86.4% of the cells were damaged/permeabilized in cultures without the addition of CO₂.