Microalgae Cultivation Process Research Articles

Non-invasive monitoring of microalgae cultivations using hyperspectral imager

AbstractHigh expectations are placed on microalgae as a sustainable source of valuable biomolecules. Robust methods to control microalgae cultivation processes are needed to enhance their efficiency and, thereafter, increase the profitability of microalgae-based products. To meet this need, a non-invasive monitoring method based on a hyperspectral imager was developed for laboratory scale and afterwards tested on industrial scale cultivations. In the laboratory experiments, reference data for microalgal biomass concentration was gathered to construct 1) a vegetation index-based linear regression model and 2) a one-dimensional convolutional neural network model to resolve microalgae biomass concentration from the spectral images. The two modelling approaches were compared. The mean absolute percentage error (MAPE) for the index-based model was 15–24%, with the standard deviation (SD) of 13-18 for the different species. MAPE for the convolutional neural network was 11–26% (SD = 10–22). Both models predicted the biomass well. The convolutional neural network could also classify the monocultures of green algae by species (accuracy of 97–99%). The index-based model was fast to construct and easy to interpret. The index-based monitoring was also tested in an industrial setup demonstrating a promising ability to retrieve microalgae-biomass-based signals in different cultivation systems.

Numerical study of microalgae cultivation process in a batch liquid foam-bed photobioreactor using CFD approach

Microalgae have different uses as feedstock of beneficial chemicals such as polysaccharides, carotenoids, and polyunsaturated fatty acids. Furthermore, they have been applied in the renewable energy, food, agriculture and feed industries, and in wastewater treatment. The growth and cultivation of microalgae are highly regarded by researchers worldwide. So, a variety of systems and designs have been used to cultivate microalgae. A research team recently proposed a new experimental design of photobioreactors based on a liquid foam flow at Wageningen University in the Netherlands. In this study, a numerical study of hydrodynamics and mass transfer of this novel system was conducted using computational fluid dynamics (CFD). This method is based on the simultaneous solution of transfer equations including hydrodynamic equations, mass transfer, cell growth, and radiation transport equation. The simulation was performed in an unsteady and three-dimensional state in COMSOL 5.5 software. The flow regime was considered laminar and mixture model and transport dilution species physics were used to model the behavior of two-phase fluid. Manual geometry grid generation was performed after defining the velocity and concentration boundaries. The number of optimal meshes was determined to be approximately 1.2 × 105 using the mesh independence test. The simulation results were validated according to the concentration-time curve. The cell density, 22 g l−1, is minimal in the center. The maximum biomass is 30.9 g l−1 at the bed wall after 80 h at 1446 μmol photon. m−2. s−1 light flux for the minimal cell density.

Effect of High Cell Density to Lipid Content Microalgae Chlorella vulgaris on Photoautotrophic Cultivation

Chlorella vulgaris is one of microalgae types that has essential ingredients beneficial tohumans, such as being a source of good lipid. Chlorella sp. have high lipid content, up to30%, under autotrophic conditions considered as a promising candidate for commercial lipidproduction due to its fast growth and easy cultivation. High cell density sedimentation can beinvestigated as a starving method in cultivation to make microalgae conditions less favorablein obtaining nutrient to lipid accumulation. Starving is one of the stress conditions carried outwith the aim of reducing nutrients in the microalgae cultivation process. The aim of this studywas to determine the effect of high cell density on increasing lipid content in Chlorellavulgaris. The results of this study showed that high cell density method affected theproductivity of Chlorella vulgaris biomass. The data obtained were analyzed using ANOVAα=0.05. The highest productivity and lipid content was obtained from the control sample witha biomass value of 0.36±0.03 g/l and a lipid content of 56.2±4.6% (P<0.05). The conclusionof this study is high cell density may not increase the production of lipid content fromChlorella vulgaris

Microalgae Production on Biogas Digestate in Sub-Alpine Region of Europe—Development of Simple Management Decision Support Tool

In a one-and-a-half-year study conducted in the ALS6 region in Europe (Ljubljana, Slovenia), the cultivation of microalgae in anaerobic digestate from food waste, mainly Scenedesmus dimorphus and Scenedesmus quadricauda, was investigated in three ponds (1260 L each) under a greenhouse. The effects of changing digestate quality and quantity as well as seasonal fluctuations on the productivity of the microalgae were investigated in three stages: Learning/Design (SI), Testing (SII), and Verification/Calibration (SIII). A decision support tool (DST) was developed using easy-to-measure parameters such as pH, temperature, electrical conductivity, mineral nitrogen forms and physical, biological parameters (OD, delayed fluorescence intensity). To control optimal pond operation, we proposed the photosynthetic culture index (PCI) as an early indicator for necessary interventions. Flocculation and nitrite levels (above 3 mg NO2-N L−1) were signals for the immediate remediation of the algae culture. Under optimal conditions in summer SIII, an average algal biomass production of 11 ± 1.5 g m−2 day−1 and a nitrogen use efficiency of 28 ± 2.6 g biomass/g N-input were achieved with the developed DST. The developed DST tool was, in this study, successfully implemented and used for the cultivation of microalgae consortia predominated by Scenedesmus dimorphus and S. quadricauda with biogas digestate. DST offers the possibility to be modified according to producers’ specific needs, facility, digestate and climate conditions, and as such, could be used for different microalgae cultivation processes with biogas digestate as a food source.

Interchangeable modular design and operation of photo-bioreactors for Chlorella vulgaris cultivation towards a zero-waste biorefinery

This study explores diverse cultivation modes for Chlorella vulgaris within a biorefinery at pilot scale that produces both biodiesel by transesterification of waste frying oils and syngas by gasification of organic wood waste. Given microalgae's comparatively modest biofuel yield relative to principal biorefinery products, the microalgae cultivation process is designed on the biofuels production rates. Liquid and gaseous waste streams are recycled inside the biorefinery: crude glycerol is mixed with wood to enhance the quality of syngas, wastewater is fed to microalgae so as flue gas. Also, the oil extracted from microalgae contributes to produce biodiesel and the waste cells are gasified.Considering that the optimal fit for each cultivation mode varies with the shape of the reactor, we propose a modular approach to assemble them in batteries of tubular, bubble flow, and airlift reactors, and present an operating design criterion that can fulfill the mass balance of the plant by adding/transforming the number of units inside the different batteries. Methods to adjust the operating conditions and control the operating parameters are also discussed.The designed configurations were operated recycling nominal waste streams of about 30 L d−1 of wastewater and 90 Nm3 h−1 of flue gas. Results confirm that the most advantageous one, in terms of volume per recycled waste streams, is a battery of 16 airlift reactors, operating in mixotrophic mode, with growing rate of 0.427 d−1, yield of 3.06, glycerol conversion 39 %, CO2 removal 64 % of inlet 6–10 %(mol) concentration. The same nominal waste streams can also be managed by 40 tubular reactors in almost heterotrophic conditions coupled with 12 bubble columns in autotrophic conditions; working respectively at growing rates of 0.395 d−1 and 0.362 d−1 and yields of 2.94 and 2.84. The battery of tubular reactors reached a glycerol conversion of 45 % and the array of bubble columns removed about 51 % of inlet 12–20 %(mol) CO2 concentration. A complete comparison is reported also in terms of dimensionless numbers and pumping/mixing requirements.

Bioenergy production from swine wastewater based on a combined process of anaerobic dynamic membrane reactor and microalgae cultivation: Feasibility and performance

Enhanced methane production and sustainable reduction of pollutants from anaerobic digestate are crucial for swine wastewater treatment. In this study, anaerobic dynamic membrane bioreactor (AnDMBR) was introduced to enhance methane production, then microalgae were cultivated on the digestate for nutrients recovery and lipid production. Results showed that pollutants can be effectively removed under various hydraulic retention time (HRT) conditions during long-term operation. Methanogenesis was enhanced with the reduction of HRT from 20 days to 10 days (0.23 L-CH4/g-CODremoved), but inhibited by shortening HRT to 5 days (0.09 L-CH4/g-CODremoved). Ammonia and phosphate in the digestate were effectively removed after microalgae cultivation. In addition, the highest microalgal biomass and lipid productivity (1.7 g/L and 17.5 mg/(L·d), respectively) were obtained using digestate ratio of 20 %, while microalgal growth was seriously restricted at high digestate content (>50 %). This work provides a prospective pathway for pollutants control and energy production from swine wastewater through integrating of AnDMBR technology with microalgae cultivation.

Upstream bioprocessing of Spirulina platensis microalgae using rainwater and recycle medium from post-cultivation for C-phycocyanin production

BackgroundThe cultivation of microalgae represents a water-intensive process, prompting the need to reduce its water footprint and explore alternative water sources. Therefore, this research work aims to investigate the growth of Spirulina by recycling the culture medium obtained from the post-cultivation process and substituting rainwater resources for the preparation of the culture medium. MethodsThe effect of pre-treatment methods, specifically microfiltration and UV-light was investigated. These methods were applied to treat the recycled medium and rainwater resources used for Spirulina cultivation. Biomass concentration, biomass productivity and phycocyanin accumulation of Spirulina were examined to assess the Spirulina growth under different pre-treatment conditions. Significant FindingsAfter three cultivation cycles in the recycled medium, biomass productivity decreased from 0.2246 to 0.0802 g/L/d which might be due to high salinity and biological pollutants that inhibit Spirulina growth. However, different pre-treatment methods using microfiltration and UV-light on the recycling medium were found to be effective in increasing biomass productivity from 0.1395 to 0.1861 g/L/d. Additionally, the use of rainwater for Spirulina cultivation was explored. Applying pre-treatment methods to the rainwater, biomass productivity was further improved from 0.3211 to 0.3837 g/L/d. These findings suggest that the use of pre-treatment methods and alternative rainwater resources can improve the biomass productivity of Spirulina and potentially reduce the environmental impact throughout the microalgae cultivation process.

Microalgae Photobioreactor for Carbon Dioxide Fixation and Production of Biofuel Feedstock

Microalgae cultivation is considered fit to the concept of green economy, in which greenhouse gases (GHG’s) mitigation and production of valuable substances is performed simultaneously. Carbon dioxide consumption by the algal cells reduces GHG’s emission to the atmosphere, while biomass conversion to biofuel feedstock supports the concept of circular economy of microalgae cultivation process. In this study, Chlorella sp. was cultivated in a Multi Tubular Airlift Photobioreactor (MTAP) system with a total volume of about 600 L. The result of a thirteen days batch culture showed the ability of the system to fix 1.57 g CO2 L-1 day-1. At the last day of experiment, 600 L MTAP showed biomass production of 0.35 g L-1 and 18% oil from cell dry weight was observed. This research showed the ability of 600 L MTAP to absorb 942 g CO2 and produce 37.8 g oil as biofuel feedstock. Compared to other experiments, percentage of oil in this experiment (18% from cell dry weight) was in the average range from other experiments (of about 10 – 40% from cell dry weight). However, this MTAP showed higher performance than other systems (mostly below 1 g CO2 L-1 day-1) in CO2 fixation rate.

Robust fractional control based on high gain observers design (RNFC) for a Spirulina maxima culture interfaced with an advanced oxidation process

Abstract In this article, the theory of fractional control and state estimation applied to biological science is studied, particularly in hybrid wastewater treatment. For nonlinear systems with stable and known states, an interconnected fractional robust control design with high gain state estimation is proposed to generate a control insensitive to nutritional perturbations originated by an advanced oxidation process in a microalgae culture. An online study is proposed for the mineralization of glyphosate and its feedback in a microalgae cultivation process where through the designed control the light dynamics is manipulated to robustly and automatically regulate the biomass signal provided by an analog sensor and nutrient estimation via state observers. In the literature, there are few results developed with real-time results. This work is a multidisciplinary study with online results where the performance and improvement of the proposed complex process are concluded.

Life cycle assessment (LCA) of marine microalgae cultivation and harvesting process for the Indian context

Microalgae cultivation is one of the emerging CO2 mitigation technologies and converting it into valuable products. The present study evaluates the environmental impacts of marine microalgae's cultivation and harvesting process with a cradle-to-gate approach from an Indian context. The algal cultivation site of 1000 acres is assumed to be located near the Indian coastal area. The life cycle inventory (LCI) data related to the site was assumed based on the literature. The functional unit (FU) for the present study was one kg of dried algae. The evaluation showed that the algal-based technology could mitigate about 1.28 kg CO2 eq./kg algae produced. Among all the impacts, marine aquatic ecotoxicity potential (MAETP) was found to be the most significant one, at 612 kg 1,4-dichlorobenzene (DCB) eq./kg algae. The major contributor to MAETP was the source of electricity. To take into account the uncertainties in the LCI, a scenario analysis was performed with the lower and higher possible process data. The global warming potential (GWP) for 35 g/m2 day productivity was −1.34 kg CO2 eq./kg algae, and for 15 g/ m2 day was −1.11 kg CO2 eq. against −1.28 kg CO2 eq. for the base case. For harvesting the feed concentration of 0.25 g/L, GWP was −0.98 kg CO2 eq./kg algae, and for 0.75 g/L, GWP was −1.39 kg CO2 eq./kg algae. For the consumption change of ±50% in electricity, the change in GWP was ± 13.85%. Further, a scenario analysis based on the source of electricity was evaluated. Replacing 25%, 50%, and 100% of Indian mixed grid electricity with solar-based electricity resulted in improvement in CO2 mitigation by 6%, 12%, and 24%, respectively. Additionally, a significant improvement in MAETP and human toxicity potential (HTP) was observed, with a reduction in MAETP by 20%, 40%, and 80% and HTP by 17%, 35%, and 70% for 25%, 50%, and 100% solar-based electricity respectively.

Microalgal bioactive metabolites as promising implements in nutraceuticals and pharmaceuticals: inspiring therapy for health benefits.

The rapid increase in global population and shrinkage of agricultural land necessitates the use of cost-effective renewable sources as alternative to excessive resource-demanding agricultural crops. Microalgae seem to be a potential substitute as it rapidly produces large biomass that can serve as a good source of various functional ingredients that are not produced/synthesized inside the human body and high-value nonessential bioactive compounds. Microalgae-derived bioactive metabolites possess various bioactivities including antioxidant, anti-inflammatory, antimicrobial, anti-carcinogenic, anti-hypertensive, anti-lipidemic, and anti-diabetic activities, thereof rapidly elevating their demand as interesting option in pharmaceuticals, nutraceuticals and functional foods industries for developing new products. However, their utilization in these sectors has been limited. This demands more research to explore the functionality of microalgae derived functional ingredients. Therefore, in this review, we intended to furnish up-to-date knowledge on prospects of bioactive metabolites from microalgae, their bioactivities related to health, the process of microalgae cultivation and harvesting, extraction and purification of bioactive metabolites, role as dietary supplements or functional food, their commercial applications in nutritional and pharmaceutical industries and the challenges in this area of research.Graphical abstract

Exploring the Pivotal Significance of Microalgae-Derived Sustainable Lipid Production: A Critical Review of Green Bioenergy Development

The persistent fight against global environmental threats and energy catastrophe is currently a major concern for the economic development of bioenergy across the entire country. Hence, traditional fuel-based reserves are overburdened to cope with the rapid energy crisis, necessitating an urgent need for an innovative carbon-neutral green-energy resource. In order to address these critical bottlenecks, microalgae with incredible metabolic versatility have paved the way for a pivotal attention towards sustainable biofuel production. However, due to high operational costs and low lipid productivity, the microalgae-based biofuel resource is still in its infancy. As a result, this problem can be overcome by incorporating engineered microalgal strains which can pave the way for significant lipid augmentation for biofuel production. Thus, our current review depicts an in-depth understanding of a multi-omics approach to microalgae, the broad scope of self-sustaining microalgae cultivation, lipid-extraction strategies, and conversion processes to improve economic commercialization in the bioenergy framework. The present review also provides a detailed analysis of the international and national status of bioenergy development by several federal agencies.

Development of algorithms for prediction of the technological process

This article discusses the development of algorithms for predicting and automatically controlling the process of microalgae cultivation. For the operational management of production, it is necessary to be able to evaluate the values of the criterion during the process for short periods of time and predict the influence of control actions on the optimality criterion. Since the cultivation process can be carried out in periodic or continuous modes, it is necessary to consider the possibilities and conditions for choosing the optimality criterion. For continuous mode, when at each moment of time the state of the process is determined only by the parameters of the state and does not depend on the state of the process at previous moments of time, an estimation instant can be used. In this case, the criterion will have the meaning of the instantaneous value of the process productivity, referred to profit. In this case, it is a criterion that is directly related to the profit of the considered class of objects. Therefore, it is expedient to choose an optimality criterion in the form of a target product maximization problem. It follows from this expression that for N cultivators connected in series, the total residence time T = 1/λN must be distributed equally among all cultivators, if individually they have the same volume.

Implementation of mathematical models and algorithms in task control of the microalgae cultivation processes

This article considers the implementation of mathematical models and algorithms in the problems of controlling the process of chlorella cultivation. When building a control system, the following tasks are solved: collecting and primary processing of information, predicting the course of technological processes, optimizing regime parameters, managing a technological process, etc. One of the necessary conditions for the optimal conduct of the process of cultivating microorganisms is automatic control of the quality and composition of nutrients at the inlet, as well as control of the output indicators of the process. The frequency of solving control problems is set depending on the technological features, the control object, the mode of introducing the process, and also on the availability of a complex of technical means. As a result of the implementation of the proposed control system, the maximum ratio of the concentration of chlorella from its average value decreased by 23.8%. Thus, the control system for the cultivation of chlorella provides timely forecasting of the course of the technological process and the formation of control actions using a computing device, which contributes to an increase in the productivity of the cultivator by 8-12%.

A Comparative Analysis of Environmental Impacts of Operational Phases of Three Selected Microalgal Cultivation Systems

In recent years, microalgal biomass cultivation has been growing in importance, not only related to the production of alternative foods and nutritional supplements but also for its usage for energy purposes or as a natural solution for wastewater treatment. Regarding these cases, the practical potential associated with the circular economy is evident. However, this is not an option for microalgal food and supplements due to strict hygiene requirements for microalgae cultivation used for these purposes. Currently, the most common cultivation options for microalgae include phototrophic cascades, photobioreactors, and heterotrophic fermenters. Generally, the higher requirements for the purity of the resulting biomass, the higher the consumption of energy and nutrients needed. These are the main operational parameters that significantly shape the total environmental and economic performance of microalgae cultivation processes. The comparative Life Cycle Assessment (LCA) of environmental aspects in the operational phases of three selected cultivation systems, located in the Czech Republic and used for pure microalgae biomass production, confirmed that the impacts of these systems in the assessed categories are fundamentally dependent on the amount of electricity needed and nutrient consumption, as well as their sources. For this reason, the heterotrophic fermenter was evaluated as being the most damaging in the comparison of the three cultivation systems, while the phototrophic cascade showed a lower total environmental impact by 15% and the flat photobioreactor was lower still, by 95%, mainly due to energy production from biomass. The major impact categories observed were climate change, depletion of fossil fuels, human toxicity, and freshwater and marine ecotoxicity. The environmental impacts of microalgae cultivation systems could be further reduced if cycling practices, such as process water recycling and reprocessing of generated sewage sludge, were addressed.

Life Cycle Assessment (Lca) of Marine Micro-Algae Cultivation and Harvesting Process for the Indian Context

Life Cycle Assessment (Lca) of Marine Micro-Algae Cultivation and Harvesting Process for the Indian Context

Cattle wastewater as a low-cost supplement augmenting microalgal biomass under batch and fed-batch conditions

The utilization of costly chemical fertilizers and large freshwater requirements make the microalgae cultivation process uneconomical and highly unsustainable. To address this challenge, the present study aimed to integrate cattle wastewater (CW) (alternate for fertilizers) with domestic sewage wastewater (DSW) (substitute for freshwater) to cultivate Chlorella thermophile. To maximize the biomass yield, in-depth nutrient consumption patterns in both batch and fed-batch cultivation conditions were analyzed. Out of the eight (1%–4.5%) different CW feed concentrations tested during the batch cultivation, 2.5% CW set gave the highest biomass yield (2.17 g L−1), which was almost double the yield obtained using Bold Basal Medium (1.24 g L−1) and DSW without any CW addition (1.22 g L−1). However, the biomass yield declined with CW> 2.5%, and the ammonium (NH4+) inhibitory effect was observed. To address the (NH4+) toxicity challenge and further enhance the biomass yield, fed-batch experiments were designed with an intermittent CW feeding based on nutrient (NH4+) consumption pattern. The fed-batch cultivation resulted in twofold increased biomass yield (4.52 g L−1) in comparison to the batch process. The nutrient consumption pattern inferred that the (NH4+) concentration greater than 600 mg L−1 during the logarithmic phase was inhibitory for Chlorella thermophila cells. On biomass characterization, a significant improvement in protein content with CW addition was observed. The FAME analysis of the derived lipid stated its competitive biofuel quality with up-gradation of C:16 and C:18 groups. Based on the obtained results, projection analysis for an integrated rural model demonstrated the technology's potential for sustainable water management with valuable resource recovery.

The feasibility of immobilized Chlorella vulgaris cultivated in palm oil mill effluent for lipid and fatty acid methyl ester production

The abundance of palm oil mill effluent (POME) in Malaysia had exposed an opportunity for the researchers to replace the common culture for microalgae cultivation process. However, the small size of microalgae bring difficulties in the separation process from the culture medium. Thus, immobilization technique had been implemented in this study to simplify the separation process of microalgae Chlorella vulgaris. A new immobilized C. vulgaris consisted of combination matrix (sodium alginate (SA), calcium alginate (CA) and sodium carboxymethyl cellulose (CMC)) with volumetric ratio (Matrix:Microalgae) 0.3:1 were utilized in this experiment. The feasibility of POME as a cultivation medium was determined by cultivating the immobilized C. vulgaris in different concentration of POME (20–100%). Two types of media were explored in this study which were POME mixed with distilled water (DW) (0–80%) and POME mixed with Bold Basal Medium (BBM) (0–80%). Based on the cell density result, the medium with 20% POME + 80% DW and 40% POME + 60% BBM medium performed the highest number of cells with 1.63 × 109 cells/mL and 0.59 × 109 cells/mL, respectively. Meanwhile, the the POME mixture medium showed the potential as a cultivation medium for the immobilized microalgae. The lipid extracted from immobilized microalgae beads cultivated in BBM media were the highest with 48.03 ± 3.7%, followed by 20% POME + 80% DW (38.14 ± 2.2%) and the lowest by 40% POME + 60% BBM media (32.93 ± 2.8%). Besides, the FAME produced from oil extracted using immobilized microalgae biomass cultured in POME mixture medium showed a good quality of oil. Thus, the oil produced revealed the potential for biodiesel production.

Carbon dioxide delivery and resulting biomass separation in microalgae cultivation using triethanolamine

ABSTRACT This study investigates a novel use of triethanolamine (TEA), a well-known carbon dioxide (CO2) – capturing chemical, to simultaneously deliver CO2 and separate microalgae biomass from the growth media in microalgae cultivation processes. For this purpose, the growth and nutrient utilization rates of Chlorella sp., were monitored at different concentrations of TEA saturated with 15% of CO2 in a gas mixture. In addition, the total inorganic carbon content in the growth media was followed in order to estimate the CO2 delivery rates. The highest growth and nutrient utilization rates occurred at 20 and 30 mM TEA concentrations, which results in 2.5-fold increase in biomass production rate at these TEA concentrations. More than 85% of the produced biomass was successfully separated from the medium by flotation facilitated by the release of oxygen and CO2 gases to the air from the oversaturated growth media, as well as the surfactant characteristics of TEA.

Bacterial-algal coupling system for high strength mariculture wastewater treatment: Effect of temperature on nutrient recovery and microalgae cultivation

In the present study, bacterial-algal coupling system, an integration process of acidogenic fermentation and microalgae cultivation was used for high strength mariculture wastewater (HSMW) treatment, resource recovery and low-cost biomass production. The effect of temperature on Chlorella vulgaris (C. vulgaris) cultivation was investigated with culture medium of acidogenic liquid. The results showed that acidogenic liquid could be used as culture medium for C. vulgaris and higher biomass was obtained compared to control. The acidogenic liquid obtained at initial pH of 8 was the most suitable culture medium for C. vulgaris growth due to befitting C/N and considerable volatile fatty acids. Moreover, the optimum temperature for C. vulgaris cultivation was 25 °C and the removal efficiency of chemical oxygen demand (COD) and NH4+-N from acidogenic liquid could reach 94.4% and 68.8%, respectively. The outcome could create an innovative value chain with environmental sustainability and economic feasibility in aquaculture industry.