Biological Sequestration Research Articles

Assessing the potential of a genetically modified Parachlorella kessleri-I with low CO2 inducible proteins for enhanced biomass and biofuel productivity

The biological process is one of the promising approaches for CO2 capture and storage. Recently, biological sequestration using microalgae has gained much interest due to its capability to utilize CO2 as a carbon source to generate valorizable biomass. This algal biomass further can be used as a feedstock for bioenergy and different value-added products. Here, we have heterogeneously overexpressed the low CO2 inducible proteins (LCIA & LCIB) from Chlamydomonas reinhardtii in the marine alga Parachlorella kessleri-I. Incorporation of these two genes boosted the endogenous CCM leading to a hybrid system and improved overall carbon acquisition. The combination of these CCM proteins enhanced the supply of inorganic carbon to RuBisCO with positive effects on growth and biomass productivity. Biochemical analyses revealed that the hybrid CCM in P. kessleri-I was characterised by 2- fold higher carbonic anhydrase activity, increased starch, and 2X more lipid yield in comparison to wild type (WT) strain. Moreover, the semi-continuous cultivation of GM strain with supply of 1 % CO2 led to around 60 % rise in the overall biomass productivity. These traits also persisted in scale-up studies leading to 2X more biomass productivity in the GM strain than WT in 100 L PBR. A comparative life-cycle assessment underlines the sustainability of the process of carbon capture and both biofuel and biochar production from P. kessleri-I with a hybrid CCM.

Novel paradigm of light and CO2 feeding to improve the ‎ co-production of ‎astaxanthin and polyunsaturated fatty acids in Haematococcus ‎pluvialis

This study aimed to develop an innovative paradigm of lighting and CO2 flow rate in dilution and photoinduction stages of H. pluvialis cultivation to overcome the cell number reduction and stimulate the astaxanthin and polyunsaturated fatty acids accumulation joined by carbon bio-sequestration. The appropriate paradigm of lighting to reach the maximum cell number, astaxanthin concentration, and astaxanthin content in the dilution and photoinduction stages was obtained 2-fold (300 µmol/m2/s) and 6-fold (900 µmol/m2/s) of the final light intensity in the phototrophy stage (150 µmol/m2/s), respectively. Under the inventive lighting paradigm, feeding the 225 mL/L/min CO2 recorded optimum consequences in the dilution and photoinduction stages. The cell number, astaxanthin productivity, lipid content, polyunsaturated fatty acid and CO2 bio-fixation rate at the end of the photoinduction stages by lighting/CO2 balance were 94 %, 96 %, 32 %, 61 % and 40 % higher than control, respectively. Additionally, the levels of omega-6 fatty acids and omega-3 fatty acids were 70 % and 73 % higher than the control, respectively. This substantial increase was achieved by maintaining an optimal ratio of omega-6 to omega-3 fatty acids (3.05). Furthermore, to maximize the cell growth of microalgae and enhance the accumulation of valuable metabolites through CO2 bio sequestration, it is recommended to focus on the CO2 flow rate parameter instead of the CO2 percentage. That is affected by both the CO2 percentage and the aeration rate. Our findings provide a promising cost-effective and ecofriendly approach to improve the co-production of astaxanthin and polyunsaturated fatty acids in H. pluvialis.

Cultivation Of Spirulina Platensis for carbon dioxide bio sequestration in hybrid photobioreactor with real-time monitoring system

Innovative methods for effectively sequestering significant amounts of carbon dioxide (CO2) are required to address the ongoing problem of greenhouse gas emissions, which have increased in tandem with industrial development. Optimisation of the performance of the photobioreactor remains a challenge, despite the potential of using photobioreactors and cyanobacteria for bio sequestration. A potential solution lies in the development of a hybrid photobioreactor design. Thus, this study aims to develop a hybrid design of the photobioreactor equipped with tailor-made real-time monitoring system known as FCB2022 for cultivating Spirulina platensis. The performance is evaluated by monitoring real-time data such as pH, dissolved oxygen (DO), and temperature, alongside assessing the growth kinetic of cyanobacterium, CO2 sequestration, oxygen release rate and mass carbon balance. These assessments are conducted under varying photon flux densities (PFD) of 100µmol/ (m2.s), 200µmol/ (m2.s), and 300µmol/ (m2.s). The result demonstrates that FCB2022 exhibited high hydrodynamic performance with parameters like mixing time, circulation time, Reynold number, and empty bed residence time showing favourable values. The optimal ranges for temperature, pH, and dissolved oxygen are determined to be between 23.56 and 29.11 ⁰C, 9.03–9.58, and 6.57–6.89 mgO2/L, respectively. Under the conditions of 15% CO2 and PFD of 300µmol/ (m2.s), the specific growth rates reach 0.36±0.004 /day and maximum biomass concentration attains 1.52±0.03 kg/m3. Notably, the PFD of 300µmol/ (m2.s) yields the highest conversion of carbon into biomass, ranging from 1.09×10−02 kg to 1.26×10−02 kg, representing the yield of 31–83% in each CO2 injection treatment.

Carbon Balance of a Carboxylic Farm

Biological sequestration was studied as a compensatory measure to reduce greenhouse gas emissions. The article offers carboxylic farms set up on the example of the developed model in temperate climate. Its technological parameters were substantiated: plant species – Scotch pine (Pinus sylvestris), planting density – 8200 pieces/ha, life cycle – 40 years. At the end of the life cycle of a carboxylic farm, it is recommended to use the resulting wood in the pulp and paper industry, as well as the pyrolysis of mill culls with the release of carbonizates as a by-product fuel, sorbents for water purification and a composting structurer. The assessment of greenhouse gas emissions at all stages of the life cycle of a carbon farm showed that a significant part of the emissions occurs in the post-operational period and amounts to about 14 % of greenhouse gas uptake in CO2 equivalent.

New approach to soil management focusing on soil health and air quality: one earth one life (critical review).

Soil plays a key role in ecosphere and air quality regulation. Obsolete environmental technologies lead to soil quality loss, air, water, and land systems pollution. Pedosphere and plants are intertwined with the air quality. Ionized O2 is capable to intensify atmosphere turbulence, providing particulate matter (PM2.5) coalescence and dry deposition. Addressing environmental quality, a Biogeosystem Technique (BGT*) heuristic transcendental (nonstandard and not direct imitation of nature) methodology has been developed. A BGT* main focus is an enrichment of Earth's biogeochemical cycles through land use and air cleaning. An intra-soil processing, which provides the soil multilevel architecture, is one of the BGT* ingredients. A next BGT* implementation is intra-soil pulse continuously discrete watering for optimal soil water regime and freshwater saving up to 10-20 times. The BGT* comprises intra-soil dispersed environmentally safe recycling of the PM sediments, heavy metals (HMs) and other pollutants, controlling biofilm-mediated microbial community interactions in the soil. This provides abundant biogeochemical cycle formation and better functioning of the humic substances, biological preparation, and microbial biofilms as a soil-biological starter, ensuring priority plants and trees nutrition, growth and resistance to phytopathogens. A higher underground and aboveground soil biological product increases a reversible C biological sequestration from the atmosphere. An additional light O2 ions photosynthetic production ensures a PM2.5 and PM0.1 coalescence and strengthens an intra-soil transformation of PM sediments into nutrients and improves atmosphere quality. The BGT* provides PM and HMs intra-soil passivation, increases soil biological productivity, stabilizes a climate system of the earth and promotes a green circular economy.

Carbon dioxide removal–What’s worth doing? A biophysical and public need perspective

Carbon dioxide removal (CDR) has become a focal point for legislators and policymakers who are pursuing strategies for climate change mitigation. This paper employs a policy framework of collective biophysical need to examine two broad categories of CDR methods being subsidized and advanced by the United States and other countries: mechanical capture and biological sequestration. Using published data on these methods, we perform a biophysical input-outcome analysis, focusing on the U.S., and compare methods on the basis of three criteria: effectiveness at net carbon removal, efficiency at a climate-relevant scale, and beneficial and adverse co-impacts. Our findings indicate that biological methods have a superior return on resource inputs in comparison to mechanical methods. Biological methods are both more effective and more resource efficient in achieving a climate-relevant scale of CO2 removal. Additionally, the co-impacts of biological methods are largely positive, while those of mechanical methods are negative. Biological methods are also far less expensive. Despite their disadvantages and a track record of failure to date, mechanical CDR methods continue to receive large subsidies from the US government while biological sequestration methods do not. To achieve more optimal CDR outcomes, policymakers should evaluate CDR methods’ effectiveness, efficiency, and biophysical co-impacts. We present tools for this purpose.

Carbon-free hydrogen and bioenergy production through integrated carbon capture and storage technology for achieving sustainable and circular economy– A review

Drastic changes in climatic conditions accelerate the need for the implementation of emission reduction techniques to restrict global warming. Conventional technologies do face severe drawbacks in reducing carbon emissions. Carbon neutrality is considered as the most essential concept as it can alleviate the issues of greenhouse gas emissions while deriving energy and fuels from fossil origin. Several reduction technologies are proposed in the recent past, in which the integration of renewable energy resources such as solar and wind power are signified. The review aims to provide an understanding of the technology transition to attain carbon neutrality through production of carbon-free energies such as hydrogen and bioenergy. Despite the chemical and physical sequestration methods, the biological sequestration technique is given special attention for the mitigation of CO2 emissions by utilizing photosynthetic microalgae. Of numerous microalgae, Chlorella vulgaris, a common eukaryotic microalga found in freshwater showed a maximum CO2 fixation rate of about 3.35 g/L/d with 10 % CO2 input. Apart from capturing and storing carbon in the geological site, the concept of utilizing and converting carbon into valuable byproducts is described elaborately. The possibilities for utilizing renewable energy sources for carbon-free energy production through unique prototypes are reviewed and elaborated. It mainly aids to utilize renewable resources more than conventional, which significantly minimizes the carbon footprint. The integration of bioenergy, carbon capture and storage concepts with renewable energy sources extends opportunities to minimize emissions and transition towards carbon neutrality and indeed can aid in achieving carbon negativity. The aforementioned concept was reported to produce about 12.5 million tons ton of hydrogen with 133 million tons of CO2 recovery. An innovative prototype to resolve emission issues other than CO2 was also addressed. Illustrations of the artificial photosynthesis process, convective vortex system and integrated multi energy system are disc proposed innovative carbon reduction technologies' economic feasibility and environmental outlook technologies are reviewed and presented.

Carbon content, carbon fixation yield and dissolved organic carbon release from diverse marine nitrifiers.

Nitrifying microorganisms, including ammonia-oxidizing archaea, ammonia-oxidizing bacteria, and nitrite-oxidizing bacteria, are the most abundant chemoautotrophs in the ocean and play an important role in the global carbon cycle by fixing dissolved inorganic carbon (DIC) into biomass. The release of organic compounds by these microbes is not well quantified, but may represent an as-yet unaccounted source of dissolved organic carbon (DOC) available to marine food webs. Here, we provide measurements of cellular carbon and nitrogen quotas, DIC fixation yields and DOC release of 10 phylogenetically diverse marine nitrifiers. All investigated strains released DOC during growth, representing on average 5-15% of the fixed DIC. Changes in substrate concentration and temperature did not affect the proportion of fixed DIC released as DOC, but release rates varied between closely related species. Our results also indicate previous studies may have underestimated DIC fixation yields of marine nitrite oxidizers due to partial decoupling of nitrite oxidation from CO2 fixation, and due to lower observed yields in artificial compared to natural seawater medium. The results of this study provide critical values for biogeochemical models of the global carbon cycle, and help to further constrain the implications of nitrification-fueled chemoautotrophy for marine food-web functioning and the biological sequestration of carbon in the ocean.

Overview: Recent advances in the understanding of the northern Eurasian environments and of the urban air quality in China – a Pan-Eurasian Experiment (PEEX) programme perspective

Abstract. The Pan-Eurasian Experiment (PEEX) Science Plan, released in 2015, addressed a need for a holistic system understanding and outlined the most urgent research needs for the rapidly changing Arctic-boreal region. Air quality in China, together with the long-range transport of atmospheric pollutants, was also indicated as one of the most crucial topics of the research agenda. These two geographical regions, the northern Eurasian Arctic-boreal region and China, especially the megacities in China, were identified as a “PEEX region”. It is also important to recognize that the PEEX geographical region is an area where science-based policy actions would have significant impacts on the global climate. This paper summarizes results obtained during the last 5 years in the northern Eurasian region, together with recent observations of the air quality in the urban environments in China, in the context of the PEEX programme. The main regions of interest are the Russian Arctic, northern Eurasian boreal forests (Siberia) and peatlands, and the megacities in China. We frame our analysis against research themes introduced in the PEEX Science Plan in 2015. We summarize recent progress towards an enhanced holistic understanding of the land–atmosphere–ocean systems feedbacks. We conclude that although the scientific knowledge in these regions has increased, the new results are in many cases insufficient, and there are still gaps in our understanding of large-scale climate–Earth surface interactions and feedbacks. This arises from limitations in research infrastructures, especially the lack of coordinated, continuous and comprehensive in situ observations of the study region as well as integrative data analyses, hindering a comprehensive system analysis. The fast-changing environment and ecosystem changes driven by climate change, socio-economic activities like the China Silk Road Initiative, and the global trends like urbanization further complicate such analyses. We recognize new topics with an increasing importance in the near future, especially “the enhancing biological sequestration capacity of greenhouse gases into forests and soils to mitigate climate change” and the “socio-economic development to tackle air quality issues”.

Integrated Approach for Carbon Sequestration and Wastewater Treatment Using Algal–Bacterial Consortia: Opportunities and Challenges

Increasing concentrations of carbon dioxide (CO2), one of the important greenhouse gases, due to combustion of fossil fuels, particularly burning coal, have become the major cause for global warming. As a consequence, many research programs on CO2 management (capture, storage, and sequestration) are being highlighted. Biological sequestration of CO2 by algae is gaining importance, as it makes use of the photosynthetic capability of these aquatic species to efficiently capture CO2 emitted from various industries and converting it into algal biomass as well as a wide range of metabolites such as polysaccharides, amino acids, fatty acids, pigments, and vitamins. In addition, their ability to thrive in rugged conditions such as seawater, contaminated lakes, and even in certain industrial wastewaters containing high organic and inorganic nutrients loads, has attracted the attention of researchers to integrate carbon capture and wastewater treatment. Algae offer a simple solution to tertiary treatments due to their nutrient removal efficiency, particularly inorganic nitrogen and phosphorus uptake. The algal–bacterial energy nexus is an important strategy capable of removing pollutants from wastewater in a synergistic manner. This review article highlights the mechanism involved in biological fixation of CO2 by microalgae, their cultivation systems, factors influencing algal cultivation in wastewater and CO2 uptake, the effect of co-cultivation of algae and bacteria in wastewater treatment systems, and challenges and opportunities.

Chromium bioremediation from river Yamuna using cyanobacteria at white and red illumination wavelengths

Industrial waste from thermal power plants and tanneries discharged into natural water bodies contaminate water and limit its usage for drinking and irrigation purposes. Heavy metals present in the water are detrimental to health. Removal of such heavy metals is a necessity due to their non-biodegradability in the environment. Chromium (Cr) imparts high toxicity to water in two valence states - Cr (III) and Cr (VI). Microalgae possess a mechanism for uptake of both trivalent and hexavalent Cr and deposit them in the polymeric form of trivalent Cr. This work emphasizes on the process of bio enrichment of Cr (III) in microalgae Spirulina sp. NCIM5143. The first stage involves acclimatizing the strain to high concentrations of Cr (up to 80 mg/L) in the Yamuna River water and Zarrouk's medium used as cultivation media. This was achieved by a serial increase of Cr in the increment of 20 mg/L in each batch. A Cr (III) removal of 88.1% in the Yamuna medium and 87% in the Zarrouk's medium was obtained, whereas a Cr (VI) removal of 74% in the Yamuna medium and 83.1% in the Zarrouk's medium was obtained. A complete removal of 100% was observed when red LED was used along with the production of pigments chlorophyll and phycocyanin. Hence, Spirulina sp. proved to be an excellent scavenger of Cr (III) and Cr (VI) ions and for the production of value-added pigments. Also, Spirulina sp. assisted Cr (III) and Cr (VI) bio sequestration has no detrimental effects on environment.

Analyzing and optimizing the carbon utilization and lipid yield at different light intensities for Scenedesmus arcuatus

Microalgae, the photosynthetic microorganism growing abundantly in marine and aquatic ecosystems, are potential source for biological sequestration of CO2. The carbon uptake differs in the presence of other nutrients, light intensity etc. The biomass yield of Scenedesmus arcuatus var capitatus was studied based on the Face Centred Central Composite design (FCCD) of Response Surface Methodology (RSM) for nitrate, phosphate and carbonate under different conditions (laboratory, room and sunlight conditions). Various pre-treatments (osmotic shock, autoclaving, microwave and ultrasonication) were employed to find the best method for maximum lipid yield. The biomass yield reached a maximum of 1 g/L under sunlight conditions of nitrate concentration 500 ppm and carbonate 2000 ppm. The laboratory conditions resulted in a biomass yield of 0.59 g/L at 500 ppm nitrate, 1000 ppm carbonate and 250 ppm phosphate. Under room conditions, the yield was very low (0.11 g/L). Osmotic shock resulted in higher lipid yield than the other pre-treatment methods. The ability of Scenedesmus arcuatus to uptake high carbon under sunlight conditions and to adapt to high light intensity and fluctuations in light intensity concludes that this species is suitable for large-scale open pond cultivation for CO2 sequestration and production of metabolites.

Salinity reduction of brackish water using a chemical photosynthesis desalination cell.

In this study, a chemical photosynthesis desalination cell (CPDC) was investigated for saltwater desalination. The cell consisted of three main parts: (1) an anodic compartment where the oxidation reaction occurs, releasing electrons, (2) a cathode compartment where the required soluble oxygen is provided by microalgae photosynthesis, and (3) an electrodialysis desalination cell installed between the cathode and anode. In the anode, a novel idea was adopted to shorten the desalination duration and increase the salinity rate using a chemical oxidation reaction in combination with the biocathode. The CPDC contributed to the carbon dioxide biological sequestration (reducing air pollution), produced microalgae biomass as a source of renewable energy and generated electricity. In the investigated CPDC, microalgae were used to supply the required oxygen solution as an electron acceptor. The metal anode-microalgae biocathode battery could provide the required energy for electrodialysis. In addition, some extra electricity was generated with a maximum excess power density of 32.4W/m3 per volume of the net anodic compartment, 16.2W/m3 per volume of the net cathodic compartment, and 3.07W/m2 of membrane surface area. This study confirms the benefits of microalgae as a sustainable biocathode in microbial desalination cells (MDCs) to supply electron acceptors in an environmental-friendly manner. Compared to photosynthetic microbial desalination cells (PMDCs), the CPDC decreased the desalination time by a factor of about 4. Besides, the NaCl removal was about 69% for 12g/L NaCl concentration in the CPDC, higher than other MDCs. In addition, as a new operational factor, the internal resistance variations were determined by electrochemical impedance spectroscopy in different case studies. The results demonstrated for the first time the possibility of applying a new desalination cell (i.e. CPDC) for water desalination and power generation which only uses a source of chemical reaction and microalgae photosynthesis without the need for an external power source.

Construction of an integrated technology system for control agricultural non-point source pollution in the Three Gorges Reservoir Areas

Agricultural non-point source pollution (NPSP) is becoming a severe threat and seriously restricting the sustainable development of agricultural economy and rural environment in the Three Gorges Reservoir Areas (TGRA). However, limited studies have focused on agricultural NPSP management in TGRA, especially for integrated technology systems with TGRA characteristics. An integrated slopping land/paddy field/hydro-fluctuation belt eco-system (SPHES) was constructed using best management practices in this study. Evaluation results of the SPHES at the comprehensive test demonstration zone showed that ecological engineering interception technologies on slopping land can reduce 80–90 % of sediment, 20–30 % of nitrogen (N), and 25–35 % of phosphorus (P), respectively. The utility of interception and absorption technology under ridge cropping pattern in paddy fields can effectively control inorganic N in sewage and P in external sewage within one week. Biological sequestration technologies of N and P in hydro-fluctuation belt can intercept 30–50 % of total N, 65–95 % of total P, and 75–90 % of sediments. In summary, the comprehensive removal rate of pollutants in agricultural NPSP exceeded 89 % using this eco-system. The work presented here provides the construction of this integrated eco-system for agricultural NPSP controlling, thereby applying to all small watersheds in the TGRA to control and manage agricultural NPSP. This integrated technology system has broad prospects for promotion and application in similar ecological areas.

Major role of particle fragmentation in regulating biological sequestration of CO2 by the oceans.

A critical driver of the ocean carbon cycle is the downward flux of sinking organic particles, which acts to lower the atmospheric carbon dioxide concentration. This downward flux is reduced by more than 70% in the mesopelagic zone (100 to 1000 meters of depth), but this loss cannot be fully accounted for by current measurements. For decades, it has been hypothesized that the missing loss could be explained by the fragmentation of large aggregates into small particles, although data to test this hypothesis have been lacking. In this work, using robotic observations, we quantified total mesopelagic fragmentation during 34 high-flux events across multiple ocean regions and found that fragmentation accounted for 49 ± 22% of the observed flux loss. Therefore, fragmentation may be the primary process controlling the sequestration of sinking organic carbon.

Optimization of Nutrients for the Growth of Scenedesmus Sp. By Response Surface Methodology

Microalgae, the photosynthetic microorganisms growing abundantly in various ecosystems are not just weeds but a potential source for sequestration of CO2. Biological sequestration of CO2 by microalgae is much more significant from the physical and chemical methods as it produces biomass (source of biofuels) apart from sequestering CO2.The growth of microalgae depends upon and requires optimum concentration of light intensity, temperature, nutrients, concentration of inoculum to produce higher yield of biomass as well its byproducts. The present study aims to optimize the nutrients using RSM for growth of microalgae, Scenedesmus sp, which was isolated locally. The other parameters such as light intensity (160 µE/m2 /s), temperature (250 C) and light/dark cycle (12/12) were maintained constant to reveal the nutrient effect on the biomass growth. The nutrients studied were nitrate (urea (0-500 ppm)), phosphate (potassium dihydrogen phosphate (0-500 ppm)), and bicarbonate ((potassium hydrogen carbonate (0-2000 ppm)). Face Centered Central Composite Design (FCCD) of 15 runs was obtained using Design Expert 8.0.7.1 (Trail version). The higher yield of biomass was obtained at optimized nutrient concentrations of 0 ppm nitrate, 250 ppm phosphate, and 1000 ppm bicarbonate. The response equation (biomass yield) as a function of nitrate, phosphate and carbonate concentrations was obtained which helps to identify the effect of various composition. The RSM technique will help to identify the best combination of nutrients for the growth of Scenedesmus sp.

Systematic Variation in Marine Dissolved Organic Matter Stoichiometry and Remineralization Ratios as a Function of Lability

Remineralization of organic matter by heterotrophic organisms regulates the biological sequestration of carbon, thereby mediating atmospheric CO2. While surface nutrient supply impacts the elemental ratios of primary production, stoichiometric control by remineralization remains unclear. Here we develop a mechanistic description of remineralization and its stoichiometry in a marine microbial ecosystem model. The model simulates the observed elemental plasticity of phytoplankton and the relatively constant, lower C:N of heterotrophic biomass. In addition, the model captures the observed decreases in the C:N of more labile dissolved organic matter (DOM) and the C:N of its remineralization with depth, which are driven by a switch in the dominant source of DOM from phytoplankton to heterotrophic biomass. Only a model version with targeted remineralization of N‐rich components is able to simulate the observed profiles of preferential remineralization of N relative to C and the elevated C:N of bulk DOM. The model suggests that more labile substrates are associated with C‐limited heterotrophic growth and not with preferential remineralization, while less labile substrates are associated with growth limited by processing rates and with preferential remineralization. The resulting patterns of variable remineralization stoichiometry mediate the extent to which a proportional increase in carbon production resulting from changes in phytoplankton stoichiometry can increase the efficiency of the biological pump. Results emphasize the importance of understanding the physiology of both phytoplankton and heterotrophs for anticipating changes in biologically driven ocean carbon storage.

Fixation of CO2, electron donor and redox microenvironment regulate succinic acid production in Citrobacter amalonaticus

Biological sequestration of CO2 for generating value added products is an emerging strategy. Succinic acid (SA) is an important C4 building block chemical, and its biological production via CO2 sequestration, holds many practical applications. This study presents an in-depth insight on SA production using isolated strain belonging to genus Citrobacter, more closely related to Citrobacter amalonaticus by considering critical process parameters such as different carbon sources at various initial concentrations, buffering agent (NaHCO3) concentrations and different pH conditions. The effect of H2 gas as an electron donor and availability of CO2 during SA production was also evaluated. The results from this work demonstrated that the isolated strain depicted the ability to utilize diverse carbon sources and highest SA production was achieved with sucrose as a substrate, indicating that reduced carbon substrates help in maximizing the redox potential. Incorporation of CO2 and H2 not only enhanced the production of SA but also affected the total acids profile favoring the production of SA over lactic, formic and acetic acids. Additional supply of CO2 and H2 led to maximum SA production of 12.07 gL−1, productivity of 0.36 gL−1 h−1 and SA yield of 48.5%. In control operation when no gases were supplied and in other test conditions where either of the gases were supplied, lactic acid was the major end product followed by acetic acid. The positive effect of CO2 for SA production provides scope for sustainable integration of SA and the CO2-generating biofuel industries or industrial side streams.

Application of a new ceramic hydrophobic membrane for providing CO2 in algal photobioreactor during cultivation of Arthrospira sp.

Biological sequestration of CO2 using microalgal route emerges as a promising option due to its cleaner approach which can be used to produce various forms of bioenergy. The current study reports on development of a new ceramic hydrophobic membrane and its application in an algal photobioreactor towards an efficient dissolution of CO2 during cultivation of Arthrospira sp. Clay-alumina based ceramic capillary support elements were coated with bentonite clay and surface modified using polydimethyl siloxane (PDMS) to impart hydrophobicity. The prepared membrane indicated pore size of 5.0nm with around 35.3% porosity and contact angle of 147°. A two-element membrane module having 150mm length, 3.16 outer diameter and 2.16mm inner diameter was used as a nano bubble sparger to provide CO2 in 1L of the culture medium and an enhanced overall mass transfer coefficient of about 38×10−4m/s was obtained using 19.5% CO2 gas mixture and 0.23m/s gas velocity. The membrane was efficient in removal of dissolved oxygen produced during photosynthesis, resulting in higher algal growth and higher CO2 sequestration. Algal growth of about 178.2g(dwt)/m3/day were obtained at 24h interval of CO2 supply in the photobioreactor and subsequent CO2 sequestration obtained was 13.99g/m3/h. Under optimized growth conditions the produced biomass yielded biodiesel content of about 5.82% of dry weight of algae. Application of the ceramic hydrophobic membrane thus enables enhanced mass transfer coefficient and dissolved oxygen removal efficiency making it suitable in photobioreactor application towards algal bio-sequestration of CO2 and subsequent biomass and biofuel production.

Studies on the effect of wind speed on loss of carbon dioxide during bio sequestration

Microalgal technology is one of the most promising technologies to eliminate the anthropogenic CO2 and to create a benign environment. Carbon dioxide is bubbled into the microalgae reactors during bio sequestration process. Since CO2 concentration in the atmosphere is very less, mass transfer occur naturally from the reactor to the atmosphere. The possibility of losses to the atmosphere occurs due to the higher flow rate, lower fixation rate of the species and also due to the wind speed available at the particular locations. The objective of the study is to evaluate the CO2 loss due to the different wind speeds in an open pond reactor. The wind velocities in the range of 2.7 m/s to 10.5 m/s on the percentage loss of carbon dioxide were studied. The results indicate that higher the wind speed, higher the CO2 loss to the atmosphere. The gas transfer velocity was evaluated at each wind speed. The empirical relation was determined relating the wind speed and gas transfer velocity. The developed correlation was verified satisfactorily for the percentage loss of carbon dioxide in the open air. Based on the wind speed available at any location, the rate of CO2 loss could be predicted from the correlation.