Development of suitable photobioreactors for CO2 sequestration addressing global warming using green algae and cyanobacteria

CO₂ sequestration by cyanobacteria and green algae are receiving increased attention in alleviating the impact of increasing CO₂ in the atmosphere. They, in addition to CO₂ capture, can produce renewable energy carriers such as carbon free energy hydrogen, bioethanol, biodiesel and other valuable biomolecules. Biological fixation of CO₂ are greatly affected by the characteristics of the microbial strains, their tolerance to temperature and the CO₂ present in the flue gas including SO_X, NO_X. However, there are additional factors like the availability of light, pH, O₂ removal, suitable design of the photobioreactor, culture density and the proper agitation of the reactor that will affect significantly the CO₂ sequestration process. Present paper deals with the photobioreactors of different geometry available for biomass production. It also focuses on the hybrid types of reactors (integrating two reactors) which can be used for overcoming the bottlenecks of a single photobioreactor.     

The enzyme system for the entrance of 14CO2 in the dark CO2-fixation of brown algae

High activity of phosphoenolpyruvate (PEP)-carboxykinase, orADP: oxalacetate (OAA) carboxy-lyase activity (a kind of EC4. 1. 1. 32) was discovered in enzyme extracts or partiallypurified preparations obtained from the brown algae, Eiseniabicyclis, Dictyota dichotoma, Spatoglossum pacificum; and Hizikiafusiformis. Enzyme activities were determined by measuring theradioactivity incorporated in the products of dark ¹⁴CO₂-fixationand by spectrophotometric determinations. Except for the lowactivity of "malic enzyme" (EC 1. 1. 1.40), no activities ofother carboxylases, i.e. PEP-carboxylase, PEP-carboxytransphosphorylase,and pyruvate carboxylase could be detected in algal extractsprepared under various conditions. Malate dehydrogenase (EC1. 1. 1. 37), fumarase (EC 4. 2. 1. 2), and glutamic: oxalacetictransaminase (EC 2. 6. 1. 1) were also detected. The algal PEP-carboxykinase required ADP and Mn²⁺ for maximumactivity in the carboxylation reaction; and ATP and Mn²⁺, butnot GTP, for maximum activity in both the decarboxylation andOAA-¹⁴CO₂-exchange reactions. The optimum pH of purified PEP-carboxykinase was in the regionof 7.0 to 7.3 in both the carboxylation and decarboxylationreactions, and its Km values for HCO₃^–, PEP, and ADP were10 mM, 0.3 mM, and 0.07 mM, respectively, in the carboxylationreaction, and values for OAA and ATP were 0.05 mM and 0.4 mM,respectively, in the decarboxylation reaction. Furthermore,the decarboxylation reaction was markedly inhibited by 20 mMHCO₃^–. The physiological role of PEP-carboxykinase as the enzyme responsiblefor the entrance reaction of the dark CO₂-fixation is discussed. ¹ Contributions from the Shimoda Marine Biological Station ofTokyo Kyoiku University, No. 236. This work was supported inpart by a Grant-in-Aid for Co-operative Research from the Ministryof Education, Japan and Matsunaga Science Foundation (to T.Ikawa). ² Present address: Department of Antibiotics, the National Instituteof Health, Shinagawa, Tokyo, Japan. (Received February 22, 1972; )     

Optimal schedule for monitoring a plant incursion when detection and treatment success vary over time

Management of an invasive plant species can be viewed as two separate and successive processes. The first, survey, aims to find infested areas and remove individuals. The second, monitoring, consists of repeated visits to these areas in order to prevent possible re-emergence. As detection probability may vary over time, the timing and number of monitoring visits can dramatically impact monitoring efficacy. We explore the optimal timing and number of monitoring visits, by focusing on one infested site. Our decision-analysis framework defines an optimal monitoring schedule which accounts for a time-dependent probability of detection, based on the presence/absence of a flower. We use this framework to investigate the optimal monitoring schedule for Hieracium aurantiacum, an invasive species in the Australian Alps and many other countries. We also perform a sensitivity analysis to draw more general conclusions. For H. aurantiacum eight monitoring visits (compared to 12 visits in the current program) are sufficient to obtain a 99% monitoring efficacy. When four or fewer visits to a site are allowed, it is optimal to visit during the high season, when the weed is likely to initiate flowering. Any extra visits should be scheduled in the early season, before the plants flower. The sensitivity analysis shows that increasing the detection probability early in the season has a greater impact than increasing it late in the season. An effective treatment method increases the value of site visits late in the season, when the detection probability is higher. Our decision-analysis framework can assist invasive species managers to reduce or reallocate management resources by determining the minimum number of monitoring visits required to satisfy an acceptable risk of re-emergence.     

Increased temperatures may safeguard the nutritional quality of crops under future elevated CO2 concentrations

Iron (Fe) and zinc (Zn) deficiencies are a global human health problem that may worsen by the growth of crops at elevated atmospheric CO₂ concentration (eCO₂). However, climate change will also involve higher temperature, but it is unclear how the combined effect of eCO₂ and higher temperature will affect the nutritional quality of food crops. To begin to address this question, we grew soybean (Glycine max) in a Temperature by Free‐Air CO₂ Enrichment (T‐FACE) experiment in 2014 and 2015 under ambient (400 μmol mol^?1) and elevated (600 μmol mol^?1) CO₂ concentrations, and under ambient and elevated temperatures (+2.7°C day and +3.4°C at night). In our study, eCO₂ significantly decreased Fe concentration in soybean seeds in both seasons (?8.7 and ?7.7%) and Zn concentration in one season (?8.9%), while higher temperature (at ambient CO₂ concentration) had the opposite effect. The combination of eCO₂ with elevated temperature generally restored seed Fe and Zn concentrations to levels obtained under ambient CO₂ and temperature conditions, suggesting that the potential threat to human nutrition by increasing CO₂ concentration may not be realized. In general, seed Fe concentration was negatively correlated with yield, suggesting inherent limitations to increasing seed Fe. In addition, we confirm our previous report that the concentration of seed storage products and several minerals varies with node position at which the seeds developed. Overall, these results demonstrate the complexity of predicting climate change effects on food and nutritional security when various environmental parameters change in an interactive manner.     

CO2 Transport and photosynthetic productivity of a continuous culture of algae

The photosynthetic activity of a continuous culture of the microalga Chlorella vulgaris as it is influenced by the CO₂ concentration in the aerating air at different light levels is discussed. It is shown that the characteristic of this behavior is mainly determined by the CO₂ transport from the air to the algal cell. Therefore the critical CO₂ concentration necessary for optimal growth of a particular alga cannot be given in general, as it differs over a very wide range depending on the dispersion system used in the culture vessel. By analyzing experimental data by means of a mathematical model the overall transport coefficient in a well stirred system for the CO₂ transport from the air bubble to the algal cell and the “actual” CO₂ kinetics, can be calculated within reasonable limits of accuracy.     

Rising atmospheric CO2 may affect oil quality and seed yield of sunflower (Helianthus annus L.)

The impact of rising atmospheric CO₂ on crop productivity and quality is very important for global food and nutritional security under the changing climatic scenario. A study was conducted to investigate the effect of elevated CO₂ on seed oil quality and yield in a sunflower hybrid DRSH 1 and variety DRSF 113, raised inside open top chambers and exposed to elevated CO₂ (550 ± 50 µl l^?1). Elevated CO₂ exposure significantly influenced the rate of photosynthesis, seed yield and the quality traits in both hybrid and variety. Plants grown under elevated CO₂ concentration showed 61–68 % gain in biomass and 35–46 % increase in seed yield of both the genotypes, but mineral nutrient and protein concentration decreased in the seeds. The reduction in seed protein was up to 13 %, while macro and micronutrients decreased drastically (up to 43 % Na in hybrid seeds) under elevated CO₂ treatment. However, oil content increased significantly in DRSF 113 (15 %). Carbohydrate seed reserves increased with similar magnitudes in both the genotypes under elevated CO₂ treatment (13 %). Fatty acid composition in seed oil contained higher proportion of unsaturated fatty acids (oleic and linoleic acid) under elevated CO₂ treatment, which is a desirable change in oil quality for human consumption. These findings conclude that rising atmospheric CO₂ in changing future climate can enhance biomass production and seed yield in sunflower and alter their seed oil quality in terms of increased concentration of unsaturated fatty acids compared with saturated fatty acids and lower seed proteins and mineral nutrients.     

Thymidine incorporation is highly predictive of colony formation and can be used for high-throughput screening

The primary goal of anticancer chemotherapy is to kill cancer cells. Therefore, it is of critical importance that any assay that is used to determine the toxicity of a potential anticancer drug accurately measures viability. While colony formation is widely regarded as the most accurate measure of viability following drug treatment, it is laborious, time consuming, and difficult to carry out with non-adherent cells. For these reasons, it is not suitable for moderate- to high-throughput screening applications. We sought to identify a convenient and reliable assay that would accurately reproduce colony formation results and be amenable to high-throughput applications. Here, we describe a modification of the 3H-thymidine incorporation assay that meets these criteria. The assay can be carried out in 96-well plates with minimal handling of reagents and media. It can be performed with non-adherent and adherent cell lines. Most importantly, LC50 values obtained with this assay show excellent agreement with colony formation results. Taken together, these advantages make the modified 3H-thymidine incorporation assay well suited for high-throughput viability assays in anticancer drug discovery and development.     

The possible roles of algae in restricting the increase in atmospheric CO2 and global temperature

ABSTRACT

Anthropogenic inputs are increasing the CO₂ content of the atmosphere, and the CO₂ and total inorganic C in the surface ocean and, to a lesser degree, the deep ocean. The greenhouse effect of the increased CO₂ (and, to a lesser extent, other greenhouse gases) is very probably the major cause of present global warming. The warming increases temperature of the atmosphere and the surface ocean to a greater extent than the deep ocean, with shoaling of the thermocline, decreasing nutrient flux to the surface ocean where there is greater mean photosynthetic photon flux density. These global changes influence algae in nature. However, it is clear that algae are important, via the biological pump, in decreasing the steady state atmospheric and ocean surface CO₂, and thus decreasing radiative forcing, a reduction enhanced by algal increases in albedo. As well as these natural processes there are possibilities that algae can, with human intervention, partly offset the increase in atmospheric CO₂. One possibility is to grow algae as sources of fuel for transport, in principle providing an energy source that is close to CO₂-neutral. The other possibility is to increase the role of algae in sequestering CO₂ as organic C over periods of hundreds or more years in the deep ocean and marine sediments and/or increasing albedo and decreasing radiative forcing of temperature. There are problems, currently unresolved, in the economically viable production of algal biofuels without carbon trading subsidies. Enhanced algal CO₂ sequestration also has costs, both in resource input (phosphorus (P) from high P content rocks, a limited resource with a competing use as an agricultural fertilizer) and adverse environmental effects. For example, ocean anoxic zones producing N₂O and increased algal production of short-lived halocarbons by algae that both, through breakdown, destroy O₃ and increase UV flux to the Earth’s surface.     

Use of macroalgae for marine biomass production and CO2 remediation: a review

Biomass production from macroalgae has been viewed as important mainly because of the need for pollution abatement. Environmental considerations will increasingly determine product and process acceptability and drive the next generation of economic opportunity. Some countries, including Japan, are actively promoting "green" technologies that will be in demand worldwide in the coming decades. Should an international agreement on CO₂-reduction be ratified, its effective use for energy production would be of high priority. This report shows that macroalgae have great potential for biomass production and CO₂ bioremediation. Macroalgae have high productivity, as great or greater than the most productive land plants, and do not compete with terrestrial crops for farm land. The review focuses on recent data on productivity, photosynthesis, nutrient dynamics, optimization and economics. Biomass from macroalgae promises to provide environmentally and economically feasible alternatives to fossil fuels. Nevertheless, the techniques and technologies for growing macroalgae on a large-scale and for converting feedstocks to energy carriers must be more fully developed.     

Rewinding the tape: selection of algae adapted to high CO2 at current and pleistocene levels of CO2

Selective history is thought to constrain the extent and direction of future adaptation by limiting access to genotypes that are advantageous in a novel environment. Populations of Chlamydomonas previously selected at high CO2 were either backselected at ambient levels of CO2, or selected at levels of CO2 that last occurred during glaciation in the Pleistocene. There was no effect of selective history on adaptation to either level of CO2, and the high CO2 phenotypes were evolutionarily reversible such that fitness in ambient CO2 returned to values seen in controls. CO2 uptake affinity improved relative to the ancestor in both ambient and glacial CO2, although wild-type regulation of CO2 uptake, which deteriorated during previous selection at high CO2, was not restored by selection at lower levels of CO2. Trade-offs in both CO2 uptake affinity and growth were seen after selection at any given level of CO2. Adaptation to ambient and glacial-era levels of CO2 produced a range of phenotypes, suggesting that chance rather than selective history contributes to the divergence of replicate populations in this system.     

Expression, reconstruction and characterization of codon-optimized carbonic anhydrase from Hahella chejuensis for CO2 sequestration application

The high production of functional carbonic anhydrase (CA) is required for practical CO₂ sequestration application mediated by CA. Here, the synthetic gene based on Escherichia coli codon usage of new α-type CA (HC-aCA) of Hahella chejuensis, a Korea marine microorganism, was highly expressed in E. coli. We obtained a high yield of functional HC-aCA by denaturing/refolding process and incorporating zinc ion into its active site. The refolded HC-aCA displayed a half-deactivation temperature of 60 °C with maximal activity at 50 °C, and had high pH stability in alkali condition with maximal activity at pH 10.0. The esterase activity of HC-aCA almost doubled at high salt concentration ranging from 0.67 to 2.0 M NaCl. HC-aCA catalyzed the conversion of CO₂ to CaCO₃ as calcites form in the presence of Ca²⁺. The refolded HC-aCA could be a promising candidate for the development of efficient CA-based CO₂ sequestration processes.     

Expression and characterization of a codon-optimized alkaline-stable carbonic anhydrase from Aliivibrio salmonicida for CO2 sequestration applications

Bioprocess and Biosystems Engineering - The CO2 mineralization process, accelerated by carbonic anhydrase (CA) was proposed for the efficient capture and storage of CO2, the accumulation of which...     

Tracking plant preference for higher‐quality mycorrhizal symbionts under varying CO2 conditions over multiple generations

The symbiosis between plants and root‐colonizing arbuscular mycorrhizal (AM) fungi is one of the most ecologically important examples of interspecific cooperation in the world. AM fungi provide benefits to plants; in return plants allocate carbon resources to fungi, preferentially allocating more resources to higher‐quality fungi. However, preferential allocations from plants to symbionts may vary with environmental context, particularly when resource availability affects the relative value of symbiotic services. We ask how differences in atmospheric CO₂‐levels influence root colonization dynamics between AMF species that differ in their quality as symbiotic partners. We find that with increasing CO₂‐conditions and over multiple plant generations, the more beneficial fungal species is able to achieve a relatively higher abundance. This suggests that increasing atmospheric carbon supply enables plants to more effectively allocate carbon to higher‐quality mutualists, and over time helps reduce lower‐quality AM abundance. Our results illustrate how environmental context may affect the extent to which organisms structure interactions with their mutualistic partners and have potential implications for mutualism stability and persistence under global change.     

A large impact of tropical biomass burning on CO and CO2 in the upper troposphere

A large interannual variation of biomass burning emissions from Southeast Asia is associated with the ENSO events. During 1997/98 and 1994 El Nino years, uncontrolled wildfires of tropical rainforests and peat lands in Indonesia were enlarged due to a long drought. Enhanced CO injection into the upper troposphere from the intense Indonesian fires was clearly observed in the 8-year measurements from a regular flask sampling over the western Pacific using a JAL airliner between Australia and Japan. This airliner observation also revealed that upper tropospheric CO2 cycle largely changed during the 1997 El Nino year due partly to the biomass burning emissions. Widespread pollution from the biomass burnings in Southeast Asia was simulated using a CO tracer driven by a 3D global chemical transport model. This simulation indicates that tropical deep convections connected to rapid advection by the subtropical jet play a significant role in dispersing biomass-burning emissions from Southeast Asia on a global scale.     

A large impact of tropical biomass burning on CO and CO2 in the upper troposphere

A large interannual variation of biomass burning emissions from Southeast Asia is asso-ciated with the ENSO events. During 1997/98 and 1994 El Nino years, uncontrolled wildfires of tropical rainforests and peat lands in Indonesia were enlarged due to a long drought. EnhancedCO injection into the upper troposphere from the intense Indonesian fires was clearly observed in the 8-year measurements from a regular flask sampling over the western Pacific using a JAL air-liner between Australia and Japan. This airliner observation also revealed that upper tropospheric CO_2 cycle largely changed during the 1997 El Nino year due partly to the biomass burning emis-sions. Widespread pollution from the biomass burnings in Southeast Asia was simulated using aCO tracer driven by a 3D global chemical transport model. This simulation indicates that tropical deep convections connected to rapid advection by the subtropical jet play a significant role in dis-persing biomass-burning emissions from Southeast Asia on a global scale.     

The production of phytoliths in China's grasslands: implications to the biogeochemical sequestration of atmospheric CO2

Among the most promising approaches of long‐term atmospheric CO₂ sequestration is terrestrial biogeochemical carbon sequestration. One of the most promising terrestrial biogeochemical carbon sequestration mechanisms is the occlusion of carbon within phytoliths, the silicified features that deposit within plant tissues. Using phytolith content‐biogenic silica content transfer function obtained from our investigation, in combination with published silica content and above‐ground net primary productivity (ANPP) data of China's grasslands, we estimated the production of phytoliths and phytolith‐occluded carbon (PhytOC) in grasslands. The results show that the average above‐ground phytolith production rates of China's grasslands (10.9 10⁶ t yr^?1 or 1.45% of world grasslands) are much lower than those of other grasslands (e.g. North American nonwoody grasslands) mainly because of much lower ANPP. Assuming a median content of PhytOC of 1.5%, the average above‐ground PhytOC production rates of China's grasslands and world grasslands are estimated to be 0.6 10⁶ t CO₂ yr^?1 and 41.4 10⁶ t CO₂ yr^?1, respectively. The management of grasslands to maximize ANPP has the potential to result in considerable quantities of phytoliths and securely bio‐sequestered carbon.     

Enhanced inorganic carbon uptake by Chlorella sp. IMMTCC-2 under autotrophic conditions for lipid production and CO2 sequestration

To achieve sustainable production of biofuel from microalgae, a well-optimized and sustained biomass production is prerequisite. The major factor determining the higher productivity of algae is the availability and uptake of CO₂ for biomass growth. In this study, an improved CO₂ sequestration method leading to improved biomass yields has been investigated. The ability of OH^? ions in fixing dissolved CO₂ in form of HCO ₃ ^? in algal growth medium was studied using a Chlorella sp. and scaled-up in a photobioreactor. It was observed that a critical concentration of 0.005?M OH^? is required for HCO ₃ ^? formation and utilization by algae. HCO ₃ ^? uptake was enhanced by 70.8% (in presence of 0.01?M NaOH) with a sixfold increase in growth rate compared with only CO₂ system. In mineral carbon systems such as NaHCO₃ and Na₂CO₃, increase in HCO ₃ ^? uptake was enhanced by 65.4% and 63.4%, respectively. The maximum rate of CO₂ fixation of 6.6?mg?L^?1?h^?1 was obtained with 0.01?M NaOH which was 1.5 times compared with mineral carbon sources. The biomass from scale-up experiment contained 16.3% lipid (by weight) of which 75% is unsaturated fatty acids (in total lipids). This supports the idea that fixing the dissolved CO₂ in the form of bicarbonate using alkali helps in increased biomass productivity rather than CO₂ itself, forms a precursor for biodiesel, and increases CO₂ sequestration in a cyclic process.     

The outcome is in the assumptions: analyzing the effects on atmospheric CO2 levels of increased use of bioenergy from forest biomass

Recently, several studies have quantified the effects on atmospheric CO₂ concentration of an increased harvest level in forests. Although these studies agreed in their estimates of forest productivity, their conclusions were contradictory. This study tested the effect of four assumptions by which those papers differed. These assumptions regard (1) whether a single or a set of repeated harvests were considered, (2) at what stage in stand growth harvest takes place, (3) how the baseline is constructed, and (4) whether a carbon‐cycle model is applied. A main finding was that current and future increase in the use of bioenergy should be studied considering a series of repeated harvests. Moreover, the time of harvest should be determined based on economical principles, thus taking place before stand growth culminates, which has implications for the design of the baseline scenario. When the most realistic assumptions are used and a carbon‐cycle model is applied, an increased harvest level in forests leads to a permanent increase in atmospheric CO₂ concentration.