Influence of the CO2 absorbent monoethanolamine on growth and carbon fixation by the green alga Scenedesmus sp

Enhancing microbial CO2 electrocatalysis for multicarbon reduction in a wet amine-based catholyte

Microbial CO2 electroreduction (mCO2ER) offers a promising approach for producing high-value multicarbon reductants from CO2 by combining CO2 fixing microorganisms with conducting materials (i. e., cathodes). However, the solubility and availability of CO2 in an aqueous electrolyte pose significant limitations in this system. This study demonstrates the efficient production of long-chain multicarbon reductants, specifically carotenoids (~C40), within a wet amine-based catholyte medium during mCO2ER. Optimizing the concentration of the biocompatible CO2 absorbent, monoethanolamine (MEA), led to enhanced CO2 fixation in the electroautotroph bacteria. Molecular biological analyses revealed that MEA in the catholyte medium redirected the carbon flux towards carotenoid biosynthesis during mCO2ER. The faradaic efficiency of mCO2ER with MEA for carotenoid production was 4.5-fold higher than that of the control condition. These results suggest the mass transport bottleneck in bioelectrochemical systems could be effectively addressed by MEA-assissted mCO2ER, enabling highly efficient production of valuable products from CO2.

Nuclear mutagenesis and adaptive evolution improved photoautotrophic growth of Euglena gracilis with flue-gas CO2 fixation

To effectively improve biomass growth and flue-gas CO2 fixation of microalgae, acid-tolerant Euglena gracilis was modified with cobalt-60 γ-ray irradiation and polyethylene glycol (PEG) adaptive screening to obtain the mutant strain M800. The biomass dry weight and maximum CO2 fixation rate of M800 were both 1.47 times higher than that of wild strain, which was attributed to a substantial increase in key carbon fixation enzyme RuBisCO activity and photosynthetic pigment content. The high charge separation quantum efficiency in PSII reaction center, efficient light utilization and energy regulation that favors light conversion, were the underlying drivers of efficient photosynthetic carbon fixation in M800. M800 had stronger antioxidant capacity in sufficient high-carbon environment, alleviating lipid peroxidation damage. After adding 1 mM PEG, biomass dry weight of M800 reached 2.31 g/L, which was 79.1 % higher than that of wild strain. Cell proliferation of M800 was promoted, the apoptosis and necrosis rates decreased.

Carbon capture and utilization by algae with high concentration CO2 or bicarbonate as carbon source

Algae plays a key role in carbon capture and utilization (CCU) as it can capture and use the atmospheric CO2 for conversion of value-added products. Concentrated CO2 is common in flue gas and provides opportunities for algae cultivation. The drawbacks are mass transfer limitation, poor CO2 dissolution, and challenges to reach optimal levels for algal growth at given flue gas levels. Bicarbonate is flexible to be used as carbon source and owns the potential to enhance the efficiency of biological carbon fixation by algae. The requirements of algae strains are more stringent. To improve the industrial scale-up of CCU, system optimization is of great importance. More novel algal strains that can grow rapidly under harsh environment and provide valuable bio-products should be developed for large-scale production. Algae-driven CCU is promising for achieving carbon-neutrality.

Sustainability and carbon neutrality trends for microalgae-based wastewater treatment: A review

As the global economy develops and the population increases, greenhouse gas emissions and wastewater discharge have become inevitable global problems. Conventional wastewater treatment processes produce direct or indirect greenhouse gas, which can intensify global warming. Microalgae-based wastewater treatment technology can not only purify wastewater and use the nutrients in wastewater to produce microalgae biomass, but it can also absorb CO₂ in the atmosphere or flue gas through photosynthesis, which demonstrates great potential as a sustainable and economical wastewater treatment technology. This review highlights the multifaceted roles of microalgae in different types of wastewater treatment processes in terms of the extent of their bioremediation function and microalgae biomass production. In addition, various newly developed microalgae cultivation systems, especially biofilm cultivation systems, were further characterized systematically. The performance of different microalgae cultivation systems was studied and summarized. Current research on the technical approaches for the modification of the CO₂ capture by microalgae and the maximization of CO₂ transfer and conversion efficiency were also reviewed. This review serves as a useful and informative reference for the application of wastewater treatment and CO₂ capture by microalgae, aiming to provide a reference for the realization of carbon neutrality in wastewater treatment systems.

Paradigm shift in algal biomass refinery and its challenges

Microalgae have been studied and tested for over 70 years. However, biodiesel, the prime target of the algal industry, has suffered from low competitiveness and current steps toward banning the internal combustion engine all over the world. Meanwhile, interest in reducing CO₂ emissions has grown as the world has witnessed disasters caused by global warming. In this situation, in order to maximize the benefits of the microalgal industry and surmount current limitations, new breakthroughs are being sought. First, drop-in fuel, mandatory for the aviation and maritime industries, has been discussed as a new product. Second, methods to secure stable and feasible outdoor cultivation focusing on CO₂ sequestration were investigated. Lastly, the need for an integrated refinery process to simultaneously produce multiple products has been discussed. While the merits of microalgae industry remain valid, further investigations into these new frontiers would put algal industry at the core of future bio-based economy.

Enhancing CO2 utilization by a physical absorption-based technique in microalgae culture

Carbon dioxide supplementation is significant for cell growth in autotrophic cultures of microalgae. However, the CO₂ utilization efficiency is quite low in most processes. Aimed at this problem, six kinds of physical absorption enhancers were investigated to enhance the biological carbon sequestration of microalgae. By the addition of a small amount of CO₂ absorption enhancer, the total inorganic carbon concentration of the medium was significantly increased. In addition, the biomass productivity of Scenedesmus dimorphus was maximally increased by 63% by the addition of propylene carbonate in flask cultures. In cultures using an air-lift photobioreactor equipped with a pH-feedback control system to supply CO₂, the CO₂ consumption was maximally reduced by 71% with added polyethylene glycol dimethyl ether. This study indicates that the incorporation of physical absorption enhancers could be a promising approach to overcome the problems of low CO₂ utilization efficiency and high carbon source cost in algal biomass production.

Using polyethylene glycol to promote Nannochloropsis oceanica growth with 15 vol% CO2

CO₂ capture with microalgae has been put forward in response to global concern on greenhouse gas emission. However, the short residence time and slow diffusion of CO₂ in water limits the growth of microalgae. In order to improve CO₂ transfer from gas phase to liquid phase and utilization by algal cells, polyethylene glycol 200 (PEG 200) was used as CO₂ absorbent to promote growth of Nannochloropsis oceanica with the bubbling of 15 vol% CO₂. Total inorganic carbon (TIC) absorbed in culture medium remained constant at 5.6 mM when 15 vol% CO₂ was bubbled continuously. PEG 200 in the medium provided additional CO₂ absorption from 0.6 to 4.8 mM when PEG 200 concentration increased from 0.5 to 4 mM. The specific growth rate of N. oceanica reached the maximum (1.41 d^-1) with 1 mM PEG 200 in culture medium, which was 21.5% higher than the specific growth rate without PEG 200. About 79% of the increase in biomass was attributed to the increased TIC with more CO₂ dissolution in culture medium because of PEG 200, and about 21% was attributed to PEG 200 itself utilized as an organic carbon source. In conclusion, PEG 200 as a CO₂ absorbent can effectively capture flue-gas CO₂ for algal growth.

Enhancement of biofuel production by microalgae using cement flue gas as substrate

The cement industry generates a substantial amount of gaseous pollutants that cannot be treated efficiently and economically using standard techniques. Microalgae, a promising bioremediation and biodegradation agent used as feedstock for biofuel production, can be used for the biotreatment of cement flue gas. In specific, components of cement flue gas such as carbon dioxide, nitrogen, and sulfur oxides are shown to serve as nutrients for microalgae. Microalgae also have the capacity to sequestrate heavy metals present in cement kiln dust, adding further benefits. This work provides an extensive overview of multiple approaches taken in the inclusion of microalgae biofuel production in the cement sector. In addition, factors influencing the production of microalgal biomass are also described in such an integrated plant. In addition, process limitations such as the adverse impact of flue gas on medium pH, exhaust gas toxicity, and efficient delivery of carbon dioxide to media are also discussed. Finally, the article concludes by proposing the future potential for incorporating the microalgae biofuel plant into the cement sector.

Enhanced biomass productivity of Arthrospira platensis using zeolitic imidazolate framework-8 as carbon dioxide adsorbents

In order to improve CO₂ diffusion in algae solution and conversion into dissolved HCO₃^-, zeolitic imidazolate framework-8 (ZIF-8) with zinc cores as unsaturated metal sites was first used as CO₂ adsorbents. Flue gas CO₂ from coal-chemical industry can be adsorbed and can be made available throughout cultivation to promote biomass productivity of Arthrospira platensis. The ZIF-8 adsorbent with particle size of 719 nm performed the largest pore area of 351.8 m²/g, which promoted CO₂ conversion into HCO₃^- by 72.9% compared to control condition without ZIF-8. The increased HCO₃^- concentration enhanced thylakoid membrane proportion in cell cross-sectional area by 1.3 times to 78.3%, which resulted in enhancement of photosynthesis in A. platensis cells. Relative electron transport rate increased by 9.4% accordingly, which was attributed to the improvement of chlorophyll a concentration by 110%. The biomass productivity using ZIF-8 adsorbent with particle size of 719 nm markedly increased by 64.0%.

Fed-batch cultivation with CO2 and monoethanolamine: Influence on Chlorella fusca LEB 111 cultivation, carbon biofixation and biomolecules production

The aim of this study was to evaluate the interaction between the periodic addition of monoethanolamine (MEA) and CO₂ during the cultivation of Chlorella fusca LEB 111. For this purpose, MEA has been added in abiotic assays, followed by fed-batch cultures with that green alga and the absorbent. BG-11 medium shown a higher potential of CO₂ absorption with MEA addition, and the bicarbonate was the chemical species of carbon prevailing in the chemical equilibrium. The periodic addition of MEA did not reduce the kinetics of growth, promoted a higher accumulation of DIC (81.4 mg L^-1) in the medium and protein (44.0% w w^-1) and lipid (30.8% w w^-1) concentrations in the biomass of C. fusca LEB 111. Therefore, it was demonstrated that fed-batch culture with MEA increased CO₂ fixation and the biomolecule synthesis as proteins and lipids.

CO2 conversion by the integration of biological and chemical methods: Spirulina sp. LEB 18 cultivation with diethanolamine and potassium carbonate addition

The aim of this work was to evaluate if the addition of the chemical absorbents diethanolamine and potassium carbonate affects the CO₂ biofixation, growth and biomass composition of Spirulina sp. LEB 18. The association of the diethanolamine (DEA) and potassium carbonate (K₂CO₃) absorbents increased the dissolved inorganic carbon concentration in the cultivation medium, allowing greater CO₂ biofixation by the Spirulina. Higher biomass concentration (2.1 g L^-1) and maximum productivity (174.2 mg L^-1 d^-1) were observed with the mixture of 1.64 mmol L^-1 of DEA and 0.41 mmol L^-1 of K₂CO₃. In this cultivation condition, Spirulina sp. LEB 18 showed high protein content (58.8 w w^-1) and an increased carbohydrate concentration (23.7% w w^-1). The addition of these absorbent concentrations may be applied in the cultivation of Spirulina sp. LEB 18 to increase CO₂ biofixation and cell growth.

Green alga cultivation with monoethanolamine: Evaluation of CO2 fixation and macromolecule production

This study aimed to assess the growth of Chlorella strains isolated from adverse environments at various concentrations of monoethanolamine (MEA), evaluating the CO₂ fixation and macromolecule production. For this purpose, the green algae Chlorella sp. and Chlorella fusca LEB 111 were tested against five concentrations of MEA: 50, 75, 100, 200 and 300 mg L^-1. The strain C. fusca LEB 111 exhibited higher tolerance to MEA as well as higher accumulation of dissolved inorganic carbon and efficiency of CO₂ utilization (approximately 37.0% w w^-1) with the addition of 100 and 150 mg L^-1 of MEA. In addition, the highest carbohydrate productivity and the highest lipid productivity were obtained with 50 and 100 mg L^-1 of MEA, respectively. Thus, the absorbent increased the carbon concentration in the medium, and its use in culture can be exploited by C. fusca LEB 111 to produce higher macromolecule concentrations.

Magnesium aminoclay enhances lipid production of mixotrophic Chlorella sp. KR-1 while reducing bacterial populations

Improving lipid productivity and preventing overgrowth of contaminating bacteria are critical issues relevant to the commercialization of the mixotrophic microalgae cultivation process. In this paper, we report the use of magnesium aminoclay (MgAC) nanoparticles for enhanced lipid production from oleaginous Chlorella sp. KR-1 with simultaneous control of KR-1-associated bacterial growth in mixotrophic cultures with glucose as the model substrate. Addition of 0.01-0.1g/L MgAC promoted microalgal biomass production better than the MgAC-less control, via differential biocidal effects on microalgal and bacterial cells (the latter being more sensitive to MgAC's bio-toxicity than the former). The inhibition effect of MgAC on co-existing bacteria was, as based on density-gradient-gel-electrophoresis (DGGE) analysis, largely dosage-dependent and species-specific. MgAC also, by inducing an oxidative stress environment, increased both the cell size and lipid content of KR-1, resulting in a considerable, ∼25% improvement of mixotrophic algal lipid productivity (to ∼410mgFAME/L/d) compared with the untreated control.

CO2 Biofixation of Actinobacillus succinogenes Through Novel Amine-Functionalized Polystyrene Microsphere Materials

CO₂-derived succinate production was enhanced by Actinobacillus succinogenes through polystyrene (PSt) microsphere materials for CO₂ adsorption in bioreactor, and the adhesion forces between A. succinogenes bacteria and PSt materials were characterized. Synthesized uniformly sized and highly cross-linked PSt microspheres had high specific surface areas. After modification with amine functional groups, the novel amine-functionalized PSt microspheres exhibited a high adsorption capacity of 25.3 mg CO₂/g materials. After addition with the functionalized microspheres into the culture broth, CO₂ supply to the cells increased. Succinate production by A. succinogenes can be enhanced from 29.6 to 48.1 g L^-1. Moreover, the characterization of interaction forces between A. succinogenes cells and the microspheres indicated that the maximal adhesive force was about 250 pN. The amine-functionalized PSt microspheres can adsorb a large amount of CO₂ and be employed for A. succinogenes anaerobic cultivation in bioreactor for high-efficiency production of CO₂-derived succinate.

Carbon dioxide capture strategies from flue gas using microalgae: a review

Global warming and pollution are the twin crises experienced globally. Biological offset of these crises are gaining importance because of its zero waste production and the ability of the organisms to thrive under extreme or polluted condition. In this context, this review highlights the recent developments in carbon dioxide (CO2) capture from flue gas using microalgae and finding the best microalgal remediation strategy through contrast and comparison of different strategies. Different flue gas microalgal remediation strategies discussed are as follows: (i) Flue gas to CO2 gas segregation using adsorbents for microalgal mitigation, (ii) CO2 separation from flue gas using absorbents and later regeneration for microalgal mitigation, (iii) Flue gas to liquid conversion for direct microalgal mitigation, and (iv) direct flue gas mitigation using microalgae. This work also studies the economic feasibility of microalgal production. The study discloses that the direct convening of flue gas with high carbon dioxide content, into microalgal system is cost-effective.

Evaluation of photosynthetic efficacy and CO2 removal of microalgae grown in an enriched bicarbonate medium

Bicarbonate species in the aqueous phase is the primary source for CO₂ for the growth of microalgae. The potential of carbon dioxide (CO₂) fixation by Chlorella pyrenoidosa in enriched bicarbonate medium was evaluated. In the present study, effects of parameters such as pH, sodium bicarbonate concentration and inoculum size were assessed for the removal of CO₂ by C. pyrenoidosa under mixotrophic condition. Central composite design tool from response surface methodology was used to validate statistical methods in order to study the influence of these parameters. The obtained results reveal that the maximum removal of CO₂ was attained at pH 8 with sodium bicarbonate concentration of 3.33 g/l, and inoculum size of 30 %. The experimental results were statistically significant with R ² value of 0.9527 and 0.960 for CO₂ removal and accumulation of chlorophyll content, respectively. Among the various interactions, interactive effects between the parameters pH and inoculum size was statistically significant (P < 0.05) for CO₂ removal and chlorophyll accumulation. Based on the studies, the application of C. pyrenoidosa as a potential source for carbon dioxide removal at alkaline pH from bicarbonate source is highlighted.

Spirulina cultivation with a CO2 absorbent: Influence on growth parameters and macromolecule production

The objective of this study was to select a concentration of CO2 absorbents to supplement Spirulina sp. LEB 18 cultivation and to evaluate the effect of these compounds on the growth and production of macromolecules. Three initial biomass concentrations (X0), eight concentrations of monoethanolamine (MEA), and three NaOH concentrations were tested. The selected MEA concentrations did not inhibit the growth of Spirulina and doubled the dissolved inorganic carbon concentration in the assay medium in relation to the concentration of NaOH. The protein concentration in the biomass grown with MEA was, on average, 17% higher than that obtained with NaOH. Thus, it was found that MEA did not reduce the productivity of Spirulina sp. LEB 18, and its use can be further explored as a means for converting the carbon dissolved in the medium to biomolecules.

Utilisation of tris(hydroxymethyl)aminomethane as a gas carrier in microalgal cultivation to enhance CO2utilisation and biomass production

CO₂supplementation is usually a limiting factor in microalgal culture systems, especially when flue gases are used as the carbon source.

Chemical absorption and CO2 biofixation via the cultivation of Spirulina in semicontinuous mode with nutrient recycle

The chemical absorption of carbon dioxide (CO2) is a technique used for the mitigation of the greenhouse effect. However, this process consumes high amounts of energy to regenerate the absorbent and to separate the CO2. CO2 removal by microalgae can be obtained via the photosynthesis process. The objective of this study was to investigate the cultivation and the macromolecules production by Spirulina sp. LEB 18 with the addition of monoethanolamine (MEA) and CO2. In the cultivation with MEA, were obtained higher results of specific growth rate, biomass productivity, CO2 biofixation, CO2 use efficiency, and lower generation time. Besides this, the carbohydrate concentration obtained at the end of this assay was approximately 96.0% higher than the control assay. Therefore, Spirulina can be produced using medium recycle and the addition of MEA, thereby promoting the reduction of CO2 emissions and showing potential for areas that require higher concentrations of carbohydrates, such as in bioethanol production.

Cascade enzymatic reactions for efficient carbon sequestration

Thermochemical processes developed for carbon capture and storage (CCS) offer high carbon capture capacities, but are generally hampered by low energy efficiency. Reversible cascade enzyme reactions are examined in this work for energy-efficient carbon sequestration. By integrating the reactions of two key enzymes of RTCA cycle, isocitrate dehydrogenase and aconitase, we demonstrate that intensified carbon capture can be realized through such cascade enzymatic reactions. Experiments show that enhanced thermodynamic driving force for carbon conversion can be attained via pH control under ambient conditions, and that the cascade reactions have the potential to capture 0.5 mol carbon at pH 6 for each mole of substrate applied. Overall it manifests that the carbon capture capacity of biocatalytic reactions, in addition to be energy efficient, can also be ultimately intensified to approach those realized with chemical absorbents such as MEA.

Amines and amine-related compounds in surface waters: a review of sources, concentrations and aquatic toxicity

This review compiles available information on the concentrations, sources, fate and toxicity of amines and amine-related compounds in surface waters, including rivers, lakes, reservoirs, wetlands and seawater. There is a strong need for this information, especially given the emergence of amine-based post-combustion CO2 capture technologies, which may represent a new and significant source of amines to the environment. We identify a broad range of anthropogenic and natural sources of amines, nitrosamines and nitramines to the aquatic environment, and identify some key fate and degradation pathways of these compounds. There were very few data available on amines in surface waters, with reported concentrations often below detection and only rarely exceeding 10 μg/L. Reported concentrations for seawater and reservoirs were below detection or very low, while for lakes and rivers, concentrations spanned several orders of magnitude. The most prevalent and commonly detected amines were methylamine (MA), dimethylamine (DMA), ethylamine (EA), diethylamine (DEA) and monoethanolamine (MEAT). The paucity of data may reflect the analytical challenges posed by determination of amines in complex environmental matrices at ambient levels. We provide an overview of available aquatic toxicological data for amines and conclude that at current environmental concentrations, amines are not likely to be of toxicological concern to the aquatic environment, however, the potential for amines to act as precursors in the formation of nitrosamines and nitramines may represent a risk of contamination of drinking water supplies by these often carcinogenic compounds. More research on the prevalence and toxicity of amines, nitrosamines and nitramines in natural waters is necessary before the environmental impact of new point sources from carbon capture facilities can be adequately quantified.

The contamination and control of biological pollutants in mass cultivation of microalgae

The potential of microalgae as a biomass feedstock for biofuels, bioproducts and as a technological solution for CO(2) fixation is subject to intense academic and industrial researches. However, current microalgal mass culture technologies have failed to produce bulk volume of microalgal biomass at low cost, because the contaminations of biological pollutants become a big constraint in mass cultivation and impede the industrial process. Here the transmission routes, contamination mechanisms of biological pollutants both in open ponds and photobioreactors are described and recent attempts to overcome the barrier are reviewed. What worth noting, unlike conventional microbial fermentation which uses a pure monoculture, the cultivation of microalgae is a complicated symbiotic system of microalgae-bacterial-zooplankton where the target microalgae dominate, cross infection or contamination by biological pollutants is inevitable and it will require much further research. Further investigation and development of control methods are necessary, particularly microalgal strain selection.