Improving ‘Lipid Productivity’ in Microalgae by Bilateral Enhancement of Biomass and Lipid Contents: A Review

Strain selection and adaptation of a fungal-yeast-microalgae consortium for sustainable bioethanol production and wastewater treatment from livestock wastewater

This study explores the potential of strain selection and adaptation for developing a fungi-yeast-microalgae consortium capable of integrated bioethanol production and livestock wastewater treatment. We employed a multi-stage approach involving isolation and strain selection/adaptation of these consortiums. The study started with screening some isolated fungi to grow on the cellulosic biomass of the livestock wastewater (saccharification) followed by a fermentation process using yeast for bioethanol production. The results revealed that Penicillium chrysogenum (Cla) and Saccharomyces cerevisiae (Sc) produced a remarkable 99.32 ppm of bioethanol and a concentration of glucose measuring 0.56 mg ml- 1. Following the impact of fungi and yeast, we diluted the livestock wastewater using distilled water and subsequently inoculated Nile River microalgae into the wastewater. The findings demonstrated that Chlorella vulgaris emerged as the dominant species in the microalgal community. Particularly, the growth rate reached its peak at a 5% organic load (0.105385), indicating that this concentration provided the most favorable conditions for the flourishing of microalgae. The results demonstrated the effectiveness of the microalgal treatment in removing the remaining nutrients and organic load, achieving a 92.5% reduction in ammonia, a 94.1% reduction in nitrate, and complete removal of phosphate (100%). The algal treatment also showed remarkable reductions in COD (96.5%) and BOD (96.1%). These findings underscore the potential of fungi, yeast, and Nile River microalgae in the growth and impact on livestock wastewater, with the additional benefit of bioethanol production.

Methods to protein and peptide extraction from microalgae: a systematic review

Currently, there is a demand for protein sources that do not use soil management or animal breeding. Among these sources we highlight the microorganisms, such cyanobacteria and microalgae, which have a simple growth using light, CO2, water and some mineral salts to generate high protein production. The extraction of these proteins depends on the method used. The most used methods for extracting bio-functional proteins are mechanical, chemical and enzymatic. The aim of this work is to analyze the protein extraction methods in microalgae using Scielo, ScienceDirect and NCBI (PubMed) electronic databases that made it possible to select original studies published in the last five years (2018-2023). A total of 2707 articles, 25 of which were selected for further analysis and subjected to risk of bias assessment. The genera Chlorella, Scenedesmus and Nannochloropsis were the most studied due to their high protein content. Mechanical methods and chemical hydrolysis are the most used methods, achieving an extraction yield of 46.0 % and 64.0 %, respectively. The best extraction results are obtained with a combination of methods, reaching up to 80.0 % yield. However, some aspects need to be observed to choose an ideal protein extraction method.

Enhancing immobilized Chlorella vulgaris growth with novel buoyant barium alginate bubble beads

Microalgae immobilization in alginate beads shows promise for biomass production and water pollution control. However, carrier instability and mass transfer limitations are challenges. This study introduces buoyant barium alginate bubble beads (BABB), which offer exceptional stability and enhance Chlorella vulgaris growth. In just 12 days, compared to traditional calcium alginate beads, BABB achieved a 20 % biomass increase while minimizing cell leakage and simplifying harvesting. BABB optimization involved co-immobilization with BG-11 medium, enrichment of CO2 in internal bubbles, and the integration of Fe nanoparticles (FeNPs). In the open raceway pond reactor, these optimizations resulted in a 39 % increase in biomass over 7 days compared to the unoptimized setup in closed flasks. Furthermore, enhancements in pigment and organic matter production were observed, along with improved removal of ammonia nitrogen and phosphate. These results highlight the overall advantages of BABB for microalgae immobilization, offering a scientific foundation for their effective utilization.

Growth of Scenedesmus obliquus in anaerobically digested swine wastewater from different cleaning processes for pollutants removal and biomass production

Anaerobically digested swine wastewater (ASW) purification by microalgae provides a promising strategy for nutrients recovery, biomass production and CO2 capture. However, the characteristics of ASW from different cleaning processes vary greatly. At present, the cultivation of microalgae in ASW from different manure cleaning processes is rarely investigated and compared. That may bring uncertainty for microalgae growth using different ASW in large-scale application. Thus, the ASW from three cleaning processes were tested for cultivating microalgae, including manure dry collection (I), water flushing (II) and water submerging processes (III). The characteristics of ASW from three manure cleaning processes varied greatly such as nutrient and heavy metals levels. High concentration of ammonia and copper in ASW significantly inhibited microalgae growth. Fortunately, the supply of high CO2 (10%) effectively alleviated negative influences, ensuring microalgal growth at low dilution ratio. The characteristics of three ASW resulted in significant differences in microalgae growth and biomass components. The maximal biomass production in optimal diluted ASW-I, II and III reached 1.46 g L-1, 2.19 g L-1 and 2.47 g L-1, respectively. The removal of organic compounds, ammonia and phosphorus by optimal microalgae growth in diluted ASW-I, II and III was 50.6%/94.2%/64.7%, 63.7%/82.3%/57.6% and 83.2%/91.7%/59.7%, respectively. The culture in diluted ASW-I, II and III obtained the highest lipids production of 12.1 mg L-1·d-1, 16.5 mg L-1·d-1 and 19.4 mg L-1·d-1, respectively. The analysis of lipids compositions revealed that the proportion of saturated fatty acids accounted for 36.4%, 32.4% and 27.9 % in optimal diluted ASW-I, II and III, as ideal raw materials for biodiesel production.

Abiotic factors improving fatty acid profiling of freshwater indigenous microalgae isolated from Kumaun region of Uttarakhand, India

Microalgae have grabbed huge attention as a potential feedstock for biofuel production in response to the rise in energy consumption and the energy crisis. In the present study, indigenous microalgal strains were isolated from four freshwater lakes in the Kumaun region, Uttarakhand, India. Based on growth and lipid profiles, the four best-performing isolates were selected for further experiments. Initial identification of isolates was done by morphological observations, which were further validated by molecular identification using ITS sequencing. The screened cultures were subjected to abiotic stress conditions (varying concentrations of nitrogen and different temperatures) to monitor the biomass, lipid accumulation, and biochemical compositions (chlorophyll and carotenoids). The quantification of fatty acids was checked via gas chromatographic analysis. The strains were identified as KU_MA3 Chlamydopodium starrii, KU_MA4 Tetradesmus nygaardii, KU_MA5 Desmodesmus intermedius, and KU_MA6 Tetradesmus nygaardii. KU_MA3 Chlamydopodium starrii showed the best results in terms of growth and lipid production at 21 °C and 0.37 g/L NaNO2 concentration. The percentage of fatty acid methyl esters (FAMEs) attained >80% and met the standard for biodiesel properties. The strain has the potential to attain higher biomass and accumulate higher lipid content, and after some more studies, it can be used for upscaling processes and large-scale biodiesel production.

Nitrogen and phosphorus stress as a tool to induce lipid production in microalgae

Microalgae, capable of accumulating large amounts of lipids, are of great value for biodiesel production. The high cost of such production stimulates the search for cultivation conditions that ensure their highest productivity. Reducing the content of nitrogen and phosphorus in the culture medium is widely used to change the content and productivity of lipids in microalgae. Achieving the right balance between maximum growth and maximum lipid content and productivity is the primary goal of many experimental works to ensure cost-effective biodiesel production from microalgae. The content of nitrogen and phosphorus in nutrient media for algal cultivation after converted to nitrogen (-N) and phosphorus (-P) lies in an extensive range: from 0.007 g L- 1 to 0.417 g L- 1 and from 0.0003 g L- 1 to 0.227 g L- 1 and N:P ratio from 0.12:1 to 823.33:1. When studying nutritional stress in microalgae, no single approach is used to determine the experimental concentrations of nitrogen and phosphorus. This precludes the possibility of correct interpretation of the data and may lead to erroneous conclusions. This work results from the systematisation of information on using nitrogen and phosphorus restriction to increase the lipid productivity of microalgae of different taxonomic and ecological groups to identify future research directions. The results of 301 experiments were included in the analysis using the principal components method. The investigation considered various divisions and classes: Cyanobacteria, Rhodophyta, Dinophyta, Haptophyta, Cryptophyta, Heterokontophyta/Ochrophyta (Bacillariophyceae, Eustigmatophyceae, Xanthophyceae), Chlorophyta, and also the ratio N:P, the time of the experiment, the light intensity during cultivation. Based on the concentrations of nitrogen and phosphorus existing in various nutrient media, a general scheme for designating the supply of nutrient media for nitrogen (as NO3- or NH4+, N g L- 1) and phosphorus (as РO4-, P g L- 1) has been proposed: replete -N (˃0.4 g L- 1), moderate -N (0.4-0.2), moderate N-limitation (0.19-0.1), strong N-limitation (˂0.1), without nitrogen (0), replete -Р (˃0.2), moderate -P (0.2-0.02), moderate P-limitation (0.019-0.01), strong P-limitation (˂0.01), without phosphorus (0).

The genomes of Vischeria oleaginous microalgae shed light on the molecular basis of hyper-accumulation of lipids

BACKGROUND

With the urgent need to reduce carbon emissions, and the dwindling reserves of easily exploitable fossil fuel, microalgae-based biofuels that can be used for transport systems and CO₂ abatement have attracted great attention worldwide in recent years. One useful characteristic of microalgae is their ability to accumulate high levels of lipid content, in particular under conditions of nitrogen deprivation, with numerous species identified so far. However, a trade-off between levels of lipid accumulation and biomass productivity hinders the commercial applicability of lipids from microalgae. Here, we sequenced the genomes of Vischeria sp. CAUP H4302 and Vischeria stellata SAG 33.83, which can accumulate high content of lipids rich in nutraceutical fatty acids and with excellent biomass yield in nitrogen-limiting culture.

RESULTS

A whole-genome duplication (WGD) event was revealed in V. sp. CAUP H4302, which is a rare event in unicellular microalgae. Comparative genomic analyses showed that a battery of genes encoding pivotal enzymes involved in fatty acids and triacylglycerol biosynthesis, storage polysaccharide hydrolysis, and nitrogen and amino acid-related metabolisms are expanded in the genus Vischeria or only in V. sp. CAUP H4302. The most highlighted is the expansion of cyanate lyase genes in the genus Vischeria, which may enhance their detoxification ability against the toxic cyanate by decomposing cyanate to NH₃ and CO₂, especially under nitrogen-limiting conditions, resulting in better growth performance and sustained accumulation of biomass under the aforementioned stress conditions.

CONCLUSIONS

This study presents a WGD event in microalgae, providing new insights into the genetic and regulatory mechanism underpinning hyper-accumulation of lipids and offering potentially valuable targets for future improvements in oleaginous microalgae by metabolic engineering.

Exploiting AGPase genes and encoded proteins to prioritize development of optimum engineered strains in microalgae towards sustainable biofuel production

Although ADP glucose pyrophosphorylase (AGPase), with two large subunits (ls) and two small subunits (ss), is a promising knockout target for increasing the neutral lipid content, the details regarding the sequence-structure features and their distribution within metabolic system in microalgae is rather limited. Against this backdrop, a comprehensive genome-wide comparative analysis on 14 sequenced microalgal genomes was performed. For the first time the heterotetrameric structure of the enzyme and the interaction of the catalytic unit with the substrate was also studied. Novel findings of the present study includes: (i) at the DNA level, the genes controlling the ss are more conserved than those controlling the ls; the variation in both the gene groups is mainly due to exon number, exon length and exon phase distribution; (ii) at protein level, the ss genes are more conserved relative to those for ls; (III) three putative key consensus sequences 'LGGGAGTRLYPLTKNRAKPAV', 'WFQGTADAV' and 'ASMGIYVFRKD' were ubiquitously conserved in all the AGPases; (iv) molecular dynamics investigations revealed that the modeled AGPase heterotetrameric structure, from oleaginous algae Chlamydomonas reinharditii, was completely stable in real time environment; (v) The binding interfaces of catalytic unit, ssAGPase, from C. reinharditii with α-D-glucose 1-phosphate (αGP) was also analyzed. The results of the present study have provided system-based insights into the structure-function of the genes and encoded proteins, which provided clues for exploitation of variability in these genes that, could be further utilized to design site-specific mutagenic experiments for engineering of microalgal strains towards sustainable development of biofuel.

Genetic engineering to enhance microalgal-based produced water treatment with emphasis on CRISPR/Cas9: A review

In recent years, the increased demand for and regional variability of available water resources, along with sustainable water supply planning, have driven interest in the reuse of produced water. Reusing produced water can provide important economic, social, and environmental benefits, particularly in water-scarce regions. Therefore, efficient wastewater treatment is a crucial step prior to reuse to meet the requirements for use within the oil and gas industry or by external users. Bioremediation using microalgae has received increased interest as a method for produced water treatment for removing not only major contaminants such as nitrogen and phosphorus, but also heavy metals and hydrocarbons. Some research publications reported nearly 100% removal of total hydrocarbons, total nitrogen, ammonium nitrogen, and iron when using microalgae to treat produced water. Enhancing microalgal removal efficiency as well as growth rate, in the presence of such relevant contaminants is of great interest to many industries to further optimize the process. One novel approach to further enhancing algal capabilities and phytoremediation of wastewater is genetic modification. A comprehensive description of using genetically engineered microalgae for wastewater bioremediation is discussed in this review. This article also reviews random and targeted mutations as a method to alter microalgal traits to produce strains capable of tolerating various stressors related to wastewater. Other methods of genetic engineering are discussed, with sympathy for CRISPR/Cas9 technology. This is accompanied by the opportunities, as well as the challenges of using genetically engineered microalgae for this purpose.

Fourth generation biofuel from genetically modified algal biomass for bioeconomic development

Biofuels from microalgae have promising potential for a sustainable bioeconomy. Algal strains' oil content and biomass yield are the most influential cost drivers in the fourth generation biofuel (FGB) production. Genetic modification is the key to improving oil accumulation and biomass yield, consequently developing the bioeconomy. This paper discusses current practices, new insights, and emerging trends in genetic modification and their bioeconomic impact on FGB production. It was demonstrated that enhancing the oil and biomass yield could significantly improve the probability of economic success and the net present value of the FGB production process. The techno-economic and socioeconomic burden of using genetically modified (GM) strains and the preventive control strategies on the bioeconomy of FGB production is reviewed. It is shown that the fully lined open raceway pond could cost up to 25% more than unlined ponds. The cost of a plastic hoop air-supported greenhouse covering cultivation ponds is estimated to be US 60,000$ /ha. The competitiveness and profitability of large-scale cultivation of GM biomass are significantly locked to techno-economic and socioeconomic drivers. Nonetheless, it necessitates further research and careful long-term follow-up studies to understand the mechanism that affects these parameters the most.

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.

A review on unit operations, challenges, opportunities, and strategies to improve algal based biodiesel and biorefinery

Globally, the demand for energy is increasing with an emphasis on green fuels for a sustainable future. As the urge for alternative fuels is accelerating, microalgae have emerged as a promising source that can not only produce high lipid but many other platform chemicals. Moreover, it is a better alternative in comparison to conventional feedstock due to yearlong easy and mass cultivation, carbon fixation, and value-added products extraction. To date, numerous studies have been done to elucidate these organisms for large-scale fuel production. However, enhancing the lipid synthesis rate and reducing the production cost still remain a major bottleneck for its economic viability. Therefore, this study compiles information on algae-based biodiesel production with an emphasis on its unit operations from strain selection to biofuel production. Additionally, strategies to enhance lipid accumulation by incorporating genetic, and metabolic engineering and the use of leftover biomass for harnessing bio-products have been discussed. Besides, implementing a biorefinery for extracting oil followed by utilizing leftover biomass to generate value-added products such as nanoparticles, biofertilizers, biochar, and biopharmaceuticals has also been discussed.

Analysis and Modeling of Innovations in the Global Microalgae Lipids Market

Microalgae lipids offer numerous advantages over those of plants and animals, enabling the sustainable commercialization of high value-added products in different markets. Although these markets are in a vertiginous annual expansion, technological life cycle modeling is a tool that has been rarely used for microalgae. Life cycle modeling is capable of assisting with decision-making based on data and is considered as a versatile model, usable in multiple software analyzing and diagnostic tasks. Modeling technological trends makes it possible to categorize the development level of the market and predict phase changes, reducing uncertainties and increasing investments. This study aims to fill this gap by performing a global analysis and modeling of microalgal lipid innovations. The Espacenet and Orbit platforms were used by crossing the keywords “microalgae”, “lipid*”, and the IPC code C12 (biochemistry and microbiology). Different sigmoid growth models were used in the present study. A successive repetition of the Chlorella genus category was found in the keyword clusters regarding extraction and separation of lipids. The life cycle S curve indicates a market starting at the maturity phase, where the BiDoseResp model stands out. The main countries and institutions at the technological forefront are shown, as well as potential technological domains for opening new markets.

Light Stress after Heterotrophic Cultivation Enhances Lutein and Biofuel Production from a Novel Algal Strain Scenedesmus obliquus ABC-009

Scenedesmus obliquus ABC-009 is a microalgal strain that accumulates large amounts of lutein, particularly when subjected to growth-limiting conditions. Here, the performance of this strain was evaluated for the simultaneous production of lutein and biofuels under three different modes of cultivation - photoautotrophic mode using BG-11 medium with air or 2% CO₂ and heterotrophic mode using YM medium. While it was found that the highest fatty acid methyl ester (FAME) level and lutein content per biomass (%) were achieved in BG-11 medium with CO₂ and air, respectively, heterotrophic cultivation resulted in much higher biomass productivity. While the cell concentrations of the cultures grown under BG-11 and CO₂ were largely similar to those grown in YM medium, the disparity in the biomass yield was largely attributed to the larger cell volume in heterotrophically cultivated cells. Post-cultivation light treatment was found to further enhance the biomass productivity in all three cases and lutein content in heterotrophic conditions. Consequently, the maximum biomass (757.14 ± 20.20 mg/l/d), FAME (92.78 ± 0.08 mg/l/d), and lutein (1.006 ± 0.23 mg/l/d) productivities were obtained under heterotrophic cultivation. Next, large-scale lutein production using microalgae was demonstrated using a 1-ton open raceway pond cultivation system and a low-cost fertilizer (Eco-Sol). The overall biomass yields were similar in both media, while slightly higher lutein content was obtained using the fertilizer owing to the higher nitrogen content.

Valorisation of algal biomass to value-added metabolites: emerging trends and opportunities

Algal biomass is a promising feedstock for sustainable production of a range of value-added compounds and products including food, feed, fuel. To further augment the commercial value of algal metabolites, efficient valorization methods and biorefining channels are essential. Algal extracts are ideal sources of biotechnologically viable compounds loaded with anti-microbial, anti-oxidative, anti-inflammatory, anti-cancerous and several therapeutic and restorative properties. Emerging technologies in biomass valorisation tend to reduce the significant cost burden in large scale operations precisely associated with the pre-treatment, downstream processing and waste management processes. In order to enhance the economic feasibility of algal products in the global market, comprehensive extraction of multi-algal product biorefinery is envisaged as an assuring strategy. Algal biorefinery has inspired the technologists with novel prospectives especially in waste recovery, carbon concentration/sequestration and complete utilisation of the value-added products in a sustainable closed-loop methodology. This review critically examines the latest trends in the algal biomass valorisation and the expansive feedstock potentials in a biorefinery perspective. The recent scope dynamics of algal biomass utilisation such as bio-surfactants, oleochemicals, bio-stimulants and carbon mitigation have also been discussed. The existing challenges in algal biomass valorisation, current knowledge gaps and bottlenecks towards commercialisation of algal technologies are discussed. This review is a comprehensive presentation of the road map of algal biomass valorisation techniques towards biorefinery technology. The global market view of the algal products, future research directions and emerging opportunities are reviewed.

Production of microalgae with high lipid content and their potential as sources of nutraceuticals

In the current global scenario, the world is under a serious dilemma due to the increasing human population, industrialization, and urbanization. The ever-increasing need for fuels and increasing nutritional problems have made a serious concern on the demand for nutrients and renewable and eco-friendly fuel sources. Currently, the use of fossil fuels is creating ecological and economic problems. Microalgae have been considered as a promising candidate for high-value metabolites and alternative renewable energy sources. Microalgae offer several advantages such as rapid growth rate, efficient land utilization, carbon dioxide sequestration, ability to cultivate in wastewater, and most importantly, they do not participate in the food crop versus energy crop dilemma or debate. An efficient microalgal biorefinery system for the production of lipids and subsequent byproduct for nutraceutical applications could well satisfy the need. But, the current microalgal cultivation systems for the production of lipids and nutraceuticals do not offer techno-economic feasibility together with energy and environmental sustainability. This review article has its main focus on the production of lipids and nutraceuticals from microalgae, covering the current strategies used for lipid production and the major high-value metabolites from microalgae and their nutraceutical importance. This review also provides insights on the future strategies for enhanced microalgal lipid production and subsequent utilization of microalgal biomass.

GRAPHICAL ABSTRACT

Cultivation of two Chlorella species in Open sewage contaminated channel wastewater for biomass and biochemical profiles: Comparative lab-scale approach

Open sewage contaminated channel wastewater (OSCCW) has high pollutant loads, responsible for eutrophication, when mixed with various channels of urban communities. But, these pollutants can be converted and recovered into useful end products with the help of algal species. In this study, two species of Chlorella (C. vulgaris and C. pyrenoidosa) were selected and investigated for the production of algal biomass and nutrient removal efficiencies with 50% concentration of OSCCW, in a comparative way at lab-scale. Chlorella sp. cultivated in OSCCW have removed nitrate (76.9-78.8%) and phosphate (67.6-79.7%) whereas COD (72.4-76.2%) and BOD (62.3-72.4%) respectively. Correlation analysis was investigated between physico-chemical parameters and biochemical profile of both species to analyze the positive and negative correlation between two variables. The bio-chemical profile and biomass productivity of both species of Chlorella were observed well on the basis of productivity of biomass (60.1, 56.5 mg/l/d), carbohydrate (15.71, 8.82 mg/l/d), protein (11.21, 15.82 mg/l/d), lipid (20.8, 17.5 mg/l/d) and chlorophyll (0.78, 0.67 mg/l/d) in OSCCW. The maximum lipid content (34.6%) was obtained with C. pyrenoidosa as compared to C. vulgaris. Findings also support that OSCCW is well-off with nutrient resources, which can be suitable alternative for algal biomass production and remediated wastewater can be used for animal and fish farming type activities.

Assessment on the oil accumulation by knockdown of triacylglycerol lipase in the oleaginous diatom Fistulifera solaris

Microalgae are promising producers of biofuel due to higher accumulation of triacylglycerol (TAG). However, further improvement of the lipid metabolism is critical for feasible application of microalgae in industrial production of biofuel. Suppression of lipid degradation pathways is a promising way to remarkably increase the lipid production in model diatoms. In this study, we established an antisense-based knockdown (KD) technique in the marine oleaginous diatom, Fistulifera solaris. This species has a capability to accumulate high content of lipids. Tgl1 KD showed positive impact on cell growth and lipid accumulation in conventional culture in f/2 medium, resulting in higher oil contents compared to wild type strain. However, these impacts of Tgl1 KD were slight when the cells were subjected to the two-stage growth system. The Tgl1 KD resulted in slight change of fatty acid composition; increasing in C14:0, C16:0 and C16:1, and decreasing in C20:5. This study indicates that, although Tgl1 played a certain role in lipid degradation in F. solaris, suppression of only a single type of TAG lipase was not significantly effective to improve the lipid production. Comprehensive understanding of the lipid catabolism in this microalga is essential to further improve the lipid production.

Immobilized Microalgae-Based Photobioreactor for CO2 Capture (IMC-CO2PBR): Efficiency Estimation, Technological Parameters, and Prototype Concept

Microalgae-mediated CO2 sequestration has been a subject of numerous research works and has become one of the most promising strategies to mitigate carbon dioxide emissions. However, feeding flue and exhaust gas into algae-based systems has been shown to destroy chloroplasts, as well as disrupt photosynthesis and other metabolic processes in microalgae, which directly limits CO2 uptake. CO2 biosequestration in existing photobioreactors (PBRs) is also limited by the low biomass concentration in the growth medium. Therefore, there is a real need to seek alternative solutions that would be competitive in terms of performance and cost-effectiveness. The present paper reports the results of experiments aimed to develop an innovative trickle bed reactor that uses immobilized algae to capture CO2 from flue and exhaust gas (IMC-CO2PBR). In the experiment, ambient air enriched with technical-grade CO2 to a CO2 concentration of 25% v/v was used. The microalgae immobilization technology employed in the experiment produced biomass yields approximating 100 g DM/dm3. A relationship was found between CO2 removal rates and gas volume flux: almost 40% of CO2 was removed at a feed of 25 dm3 of gas per hour, whereas in the 200 dm3/h group, the removal efficiency amounted to 5.9%. The work includes a determination of basic process parameters, presentation of a developed functional model and optimized lighting system, proposals for components to be used in the system, and recommendations for an automation and control system for a full-scale implementation.

Prospects of Microalgae for Biomaterial Production and Environmental Applications at Biorefineries

Microalgae are increasingly viewed as renewable biological resources for a wide range of chemical compounds that can be used as or transformed into biomaterials through biorefining to foster the bioeconomy of the future. Besides the well-established biofuel potential of microalgae, key microalgal bioactive compounds, such as lipids, proteins, polysaccharides, pigments, vitamins, and polyphenols, possess a wide range of biomedical and nutritional attributes. Hence, microalgae can find value-added applications in the nutraceutical, pharmaceutical, cosmetics, personal care, animal food, and agricultural industries. Microalgal biomass can be processed into biomaterials for use in dyes, paints, bioplastics, biopolymers, and nanoparticles, or as hydrochar and biochar in solid fuel cells and soil amendments. Equally important is the use of microalgae in environmental applications, where they can serve in heavy metal bioremediation, wastewater treatment, and carbon sequestration thanks to their nutrient uptake and adsorptive properties. The present article provides a comprehensive review of microalgae specifically focused on biomaterial production and environmental applications in an effort to assess their current status and spur further deployment into the commercial arena.