CO2 Fixation Capacity Research Articles

Optimizing carbonation reaction parameters of calcium carbide slag in acidic/alkaline environment enhancing CO2 mineralization efficiency

Carbide slag (CS) is a typical alkaline solid waste with Ca(OH)2 as its main component, exhibiting a high capacity for CO2 mineralization. Currently, the methods for CS mineralization of CO2 include direct and indirect mineralization which the initial pH of the reaction system plays a crucial role in the mineralization process. In this study, we explored the effects of alkaline and acidic environments on the carbonation reaction between CS and CO2 and optimized the related reaction parameters. The alkaline system involved dissolving CS followed by introducing CO2, while the acidic system involved introducing CO2 first, followed by either one-time or intermittent addition of CS. We studied the dissolution behavior and reaction processes of CO2 and CS in both systems. The results showed that the carbonation reaction could be completed in the alkaline system. However, in the acidic system, the carbonation reaction is uncompleted with one-time addition of small amount of CS (solid–liquid ratio of 1:100) especially intermittent addition of CS. On the contrary, one-time addition of sufficient CS into acidic solution forming high solid-to-liquid ratio suspension (solid–liquid ratio of 5:100 and 10:100) resulted in thoroughly completion of the carbonation. More importantly, the CO2 fixation capacity, reaction rate, Ca2+ extraction, size distribution and phase structure of obtained calcite was superior to that of the alkaline system. This study demonstrates that although the acidic environment is unfavorable for the dissolution of CS and the leaching of Ca2+, the reaction can still proceed to completion at a faster rate under optimized conditions. This finding might promote the practical utilization of industrial solid waste for CO2 sequestration and enhance its scale-up application.

Inorganic salt starvation improves the polysaccharide production and CO2 fixation by Porphyridium purpureum.

The microalgae industry shows a promising future in the production of high-value products such as pigments, phycoerythrin, polyunsaturated fatty acids, and polysaccharides. It was found that polysaccharides have high biomedical value (such as antiviral, antibacterial, antitumor, antioxidative) and industrial application prospects (such as antioxidants). This study aimed to improve the polysaccharides accumulation of Porphyridium purpureum CoE1, which was effectuated by inorganic salt starvation strategy whilst supplying rich carbon dioxide. At a culturing temperature of 25°C, the highest polysaccharide content (2.89g/L) was achieved in 50% artificial seawater on the 12th day. This accounted for approximately 37.29% of the dry biomass, signifying a 25.3% increase in polysaccharide production compared to the culture in 100% artificial seawater. Subsequently, separation, purification and characterization of polysaccharides produced were conducted. Furthermore, the assessment of CO2 fixation capacity during the cultivation of P. purpureum CoE1 was conducted in a 10L photobioreactor. This indicated that the strain exhibited an excellent CO2 fixation capacity of 1.66g CO2/g biomass/d. This study proposed an efficient and feasible approach that not only increasing the yield of polysaccharides by P. purpureum CoE1, but also fixing CO2 with a high rate, which showed great potential in the microalgae industry and Bio-Energy with Carbon Capture and Storage.

Light‐use efficiency for coral reef communities and benthic functional types

AbstractCoral reef metabolism is dominated by benthic photoautotrophic communities that comprise varying combinations of algae, coral, and sand. Rates of daily gross primary production (GPP) for these benthic functional types (BFTs) are remarkably consistent across biogeographical regions, supporting the idea that reefs exhibit modal metabolism. Most variability in reported rates likely arises from differences in light availability. In fact, GPP is a linear function of incident photosynthetically active radiation (PAR), the fraction of PAR absorbed (fAPAR) by photoautotrophic organisms or communities, and light‐use efficiency (ε), which parameterizes photosynthesizers' biochemical capacity for CO2 fixation: GPP = ε × fAPAR × PAR. On time scales of days to weeks, fAPAR and ε are far more stable than PAR. ε is a critical parameter, because it represents productive response integrated across all environmental conditions, other than light. If BFTs exhibit consistent GPP across wide geographic ranges, then their εs must also be consistent. The aim of this study was to estimate ε for algae, coral, and sand. Using data collected during NASA's CORAL mission in 2016–2017, ε was calculated for 32 mixed communities at Lizard Island, Australia (10); Kāne'ohe Bay, Hawai'i (8); Guam (6); and Palau (8). Nonnegative least squares was used to solve for ε of each BFT, producing values of 0.038, 0.060, and 0.016 C photon−1 for algae, coral, and sand, respectively. These values can be used in light‐driven models of reef metabolism. Further work is necessary to refine these estimates and, importantly, to explore how ε is affected by environmental conditions.

Enhanced resuscitation of anammox granular sludge by adding folate: A perspective from the growth factor

Quick resuscitation of preserved anammox granular sludge (AnGS) is crucial for its engineering applications. In this study, the stimulation effect and its mechanism of folate addition on resuscitation of AnGS after the long-term cryopreservation were investigated. The folate addition was found to enhance the recovery of AnGS activity to 76.4% of the original level on the 8th day, which was 28.1% higher than the folate-free group (CK). The folate addition could also promote the community recovery of AnGS, in which the live cells and abundance of anammox bacteria (AnAOB) were 10.2% and 14.0% higher than those in the CK in the early phase of resuscitation. Besides, the folate addition was revealed to stimulate the AnAOB recovery of AnGS, with higher activity and cell number by 58.7% and 40.9% than those in the CK. Furthermore, the mechanism of folate stimulation was proposed on the resuscitation of preserved AnGS. The exogenous folate addition could enhance the CO2 fixation capacity of AnAOB, which further accelerated both activity and cell number recovery of AnAOB, leading to the strong stimulation effect on the resuscitation of AnGS. These findings could offer valuable insights for optimizing and innovating the preservation technology of AnGS.

Analysis of Net Primary Productivity Variation and Quantitative Assessment of Driving Forces-A Case Study of the Yangtze River Basin.

Net primary productivity (NPP) can indirectly reflect vegetation's capacity for CO2 fixation, but its spatiotemporal dynamics are subject to alterations to some extent due to the influences of climate change and human activities. In this study, NPP is used as an indicator to investigate vegetarian carbon ability changes in the vital ecosystems of the Yangtze River Basin (YRB) in China. We also explored the NPP responses to climate change and human activities. We conducted a comprehensive analysis of the temporal dynamics and spatial variations in NPP within the YRB ecosystems from 2003 to 2020. Furthermore, we employed residual analysis to quantitatively assess the contributions of climate factors and human activities to NPP changes. The research findings are as follows: (1) Over the 18-year period, the average NPP within the basin amounted to 543.95 gC/m2, displaying a noticeable fluctuating upward trend with a growth rate of approximately 3.1 gC/m2; (2) The areas exhibiting an increasing trend in NPP account for 82.55% of the total study area. Regions with relatively high stability in the basin covered 62.36% of the total area, while areas with low stability accounted for 2.22%, mainly situated in the Hengduan Mountains of the western Sichuan Plateau; (3) NPP improvement was jointly driven by human activities and climate change, with human activities contributing more significantly to NPP growth. Specifically, the contributions were 65.39% in total, with human activities contributing 59.28% and climate change contributing 40.01%. This study provides an objective assessment of the contributions of human activities and climate change to vegetation productivity, offering crucial insights for future ecosystem development and environmental planning.

Microalgal co-cultivation -recent methods, trends in omic-studies, applications, and future challenges.

The burgeoning human population has resulted in an augmented demand for raw materials and energy sources, which in turn has led to a deleterious environmental impact marked by elevated greenhouse gas (GHG) emissions, acidification of water bodies, and escalating global temperatures. Therefore, it is imperative that modern society develop sustainable technologies to avert future environmental degradation and generate alternative bioproduct-producing technologies. A promising approach to tackling this challenge involves utilizing natural microbial consortia or designing synthetic communities of microorganisms as a foundation to develop diverse and sustainable applications for bioproduct production, wastewater treatment, GHG emission reduction, energy crisis alleviation, and soil fertility enhancement. Microalgae, which are photosynthetic microorganisms that inhabit aquatic environments and exhibit a high capacity for CO2 fixation, are particularly appealing in this context. They can convert light energy and atmospheric CO2 or industrial flue gases into valuable biomass and organic chemicals, thereby contributing to GHG emission reduction. To date, most microalgae cultivation studies have focused on monoculture systems. However, maintaining a microalgae monoculture system can be challenging due to contamination by other microorganisms (e.g., yeasts, fungi, bacteria, and other microalgae species), which can lead to low productivity, culture collapse, and low-quality biomass. Co-culture systems, which produce robust microorganism consortia or communities, present a compelling strategy for addressing contamination problems. In recent years, research and development of innovative co-cultivation techniques have substantially increased. Nevertheless, many microalgae co-culturing technologies remain in the developmental phase and have yet to be scaled and commercialized. Accordingly, this review presents a thorough literature review of research conducted in the last few decades, exploring the advantages and disadvantages of microalgae co-cultivation systems that involve microalgae-bacteria, microalgae-fungi, and microalgae-microalgae/algae systems. The manuscript also addresses diverse uses of co-culture systems, and growing methods, and includes one of the most exciting research areas in co-culturing systems, which are omic studies that elucidate different interaction mechanisms among microbial communities. Finally, the manuscript discusses the economic viability, future challenges, and prospects of microalgal co-cultivation methods.

Advancement of Abiotic Stresses for Microalgal Lipid Production and Its Bioprospecting into Sustainable Biofuels

The world is currently facing global energy crises and escalating environmental pollution, which are caused by the extensive exploitation of conventional energy sources. The limited availability of conventional energy sources has opened the door to the search for alternative energy sources. In this regard, microalgae have emerged as a promising substitute for conventional energy sources due to their high photosynthetic rate, high carbohydrate and lipid content, efficient CO2 fixation capacity, and ability to thrive in adverse environments. The research and development of microalgal-based biofuel as a clean and sustainable alternative energy source has been ongoing for many years, but it has not yet been widely adopted commercially. However, it is currently gaining greater attention due to the integrated biorefinery concept. This study provides an in-depth review of recent advances in microalgae cultivation techniques and explores methods for increasing lipid production by manipulating environmental factors. Furthermore, our discussions have covered high lipid content microalgal species, harvesting methods, biorefinery concepts, process optimizing software tools, and the accumulation of triglycerides in lipid droplets. The study additionally explores the influence of abiotic stresses on the response of biosynthetic genes involved in lipid synthesis and metabolism. In conclusion, algae-based biofuels offer a viable alternative to traditional fuels for meeting the growing demand for energy.

Carbon sequestration performance, enzyme and photosynthetic activity, and transcriptome analysis of algae-bacteria symbiotic system after antibiotic exposure

Wastewater treatment technology based on algae-bacteria successfully combines pollutant purification, CO2 reduction and clean energy production to provide new insights into climate solutions. In this study, the reciprocal mechanisms between algae and bacteria were explored through physiological and biochemical levels of algae cells and differentially expressed genes (DEGs) based on the performance of immobilized algae-bacteria symbiotic particles (ABSPs) for CO2 fixation. The results showed that ABSPs promoted the CO2 fixation capacity of microalgae. The enhanced growth capacity and photosynthetic activity of algal cells in ABSPs are key to promoting CO2 uptake, and the stimulation of photosynthetic system and the promotion of Calvin cycle were the main contributors to enhanced carbon sequestration. These findings will provide guidance for carbon reduction using immobilized ABSS as well as deciphering the algae-bacteria reciprocal mechanism.

Effects of stabilizers on CO2 fixation capacity in neutralization of alkali construction sludge

Construction sludge, generated from tunneling and piling, is typically in a liquid state. It can be improved via physical treatments, such as dehydration, and/or chemical treatments, using stabilizers, in order to to be recycled as construction material. To adjust the strength of sludge, chemical treatments are often preferred. However, chemical treatments frequently result in alkali leaching. Methods to reduce alkalinity by curing the alkaline sludge under CO2 gas at a certain concentration have been proposed in Japan. In recent years, technologies that utilize CO2 to improve the quality of cementitious material have received considerable attention in terms of carbon capture. Therefore, the effects of stabilizers on the CO2 fixation capacity of alkaline sludge during pH neutralization were investigated in this study. Accelerated carbonation and carbonate content measurement tests were conducted to detect the CO2 content fixed in alkaline sludge specimens treated with various stabilizers. The test results showed that the fixed maximum CO2 content per gram of dry mass of sludge, (mCO2)max, increased with the calcium oxide (CaO) content of the stabilizer(s) per gram of dry sludge, CCaO. However, the rate of increase in (mCO2)max with CCaO was significantly affected by the type of stabilizer used. In the case of quicklime (QL), the ratio of (mCO2)max to CCaO was approximately 0.5, whereas, in the cases of fly ash (FA) and steel slag (SS), the ratio was approximately 0.25. The ratios for biomass ash and paper sludge ash were between that for QL and that for FA and SS. Detailed analyses of the test results suggest that the CaO content per gram of stabilizer(s) in the sludge, C*CaO, can provide an estimate of the fixed maximum amount of CO2 per gram of stabilizer(s) in the sludge, (m*CO2)max. However, other factors, including the amount of water-soluble Ca, should be considered for a precise evaluation. Additionally, the experimental results showed that the decrease in pH owing to neutralization increases with the increasing CCaO. However, the type of stabilizer did not significantly affect the relationship between the degree of CO2 fixation and the degree of neutralization.

Photosynthetic living building material: Effect of the initial population of cyanobacteria on fixation of CO2 and mechanical properties

Living building materials are regarded as environmentally friendly due to their minimal greenhouse gas emissions during the manufacturing process. In this study, a living building material (LBM) composed of sand, gelatin, and cyanobacteria was molded into 20 mm cubes with varying initial inoculation of cyanobacteria (1, 10, 100 units of biomass based on chlorophyll content). The atmospheric CO2 fixation capacity, compressive strength, gelatin desiccation, microbial viability, and CaCO3 content of the LBM cubes were measured during a 28-day curing period in the light chamber. The results indicated a positive correlation between the initial number of microbes, the rate of CO2 fixation, and the rate of microbial growth. The compressive strength of the cubes was primarily influenced by gelatin desiccation until day 7, and by microbial mineral precipitation, which fortified the gelatin scaffold after day 7.

Light-independent regulation of algal photoprotection by CO2 availability

Photosynthetic algae have evolved mechanisms to cope with suboptimal light and CO2 conditions. When light energy exceeds CO2 fixation capacity, Chlamydomonas reinhardtii activates photoprotection, mediated by LHCSR1/3 and PSBS, and the CO2 Concentrating Mechanism (CCM). How light and CO2 signals converge to regulate these processes remains unclear. Here, we show that excess light activates photoprotection- and CCM-related genes by altering intracellular CO2 concentrations and that depletion of CO2 drives these responses, even in total darkness. High CO2 levels, derived from respiration or impaired photosynthetic fixation, repress LHCSR3/CCM genes while stabilizing the LHCSR1 protein. Finally, we show that the CCM regulator CIA5 also regulates photoprotection, controlling LHCSR3 and PSBS transcript accumulation while inhibiting LHCSR1 protein accumulation. This work has allowed us to dissect the effect of CO2 and light on CCM and photoprotection, demonstrating that light often indirectly affects these processes by impacting intracellular CO2 levels.

Study of carbon fixation and carbon partitioning of evolved Chlorella sp.'s strain under different carbon dioxide conditions

Algal biotechnology is a powerful tool for CO2 fixation. Rapid CO2 fixation and carbon partitioning are both important questions in the field of algal biotechnology. Adaptive laboratory evolution has been applied for improving the tolerance of microalgae to high concentration of CO2. A new strategy should be proposed to improve the CO2 fixation capacity and efficiency of ALE under non-stress conditions. An evolved strain, AE1, was obtained after 31 cycles (>157 generations) of adaptive evolution under 1% CO2 condition. The growth profiles and carbon partitioning were investigated for the evolved strain under 1%, 10% and 30% CO2 conditions. It was confirmed that AE1 could tolerate 10% CO2 but 30% CO2 inhibited the growth of AE1. Increasing CO2 concentration led to the increase of total protein contents and decrease of total lipid contents while the carbohydrate contents were not significantly varied at day 11. The biomass components and free fatty acids in starting strain, AE1 and AE10 evolved strain under 10% CO2 conditions were investigated. It was indicated that the metabolic phenotype of AE1 was different to those of starting strain and AE10 based on principal component analysis. It is also proved that the selection of environmental stress and strategy in adaptive evolution is very essential. The current study presents novel information of CO2 fixation and carbon partitioning of microalgae. It is confirmed that ALE could improve the CO2 fixation capacity of microalgae and it is helpful to establish new approach for carbon neutrality.

Advancement pathway of biochar resources from macroalgae biomass: A review

Macroalgae, with short growth cycles, and high CO2 fixation capacity, are third-generation biomass mainstays that play an essential role as a global carbon sink. Macroalgal biochar plays a crucial role in soil improvement, pollutant adsorption, electrodes, and capacitors, and it has already contributed to both ecological and economic fields. However, the physicochemical properties of macroalgal biochar are challenging to control, and the way macroalgal biochar is pyrolyzed and activated largely determines its physicochemical properties and areas of application. In this study, five standard methods (conventional pyrolysis, hydrothermal carbonization, microwave pyrolysis, co-pyrolysis, and drying) for the pyrolysis of macroalgal biochar and two activation methods (physical and chemical) are reviewed to screen for optimal preparation and activation methods under different conditions and in different application contexts. The conventional pyrolysis process is mature and simple, but the yield is low, which is suitable for industrial production. Hydrothermal carbonization can reduce the content of alkali metals in biochar without prior drying. Microwave pyrolysis has low energy consumption and uniform product properties, which is suitable for biochar with high stability requirements. Co-pyrolysis is a low-cost pyrolysis method if suitable co-pyrolysis materials can be found. The drying ash content is high, but the surface performance is weak, which is generally used as pretreatment. From laboratory to practical applications, macroalgal biochar still needs to be investigated in terms of cost reduction, yield improvement, and optimization of preparation and activation methods.

ASSESSMENT OF BIOFUEL PRODUCTION TECHNOLOGIES FROM MICROALGAE AND ORGANIC WASTE

Today, the processing of organic matter, such as organic waste or microalgae, is an important way to renewable energy sources. To maintain a prosperous life of the population, it is critical that renewable sources of energy be found. Problem statement. In the near future, mineral and organic reserves of the earth's interior will cease to meet the growing energy needs of civilization. Already today, technologies have emerged that allow the production of fossil fuels based on many plant species. But the cultivation of such crops leads to depletion of land resources. In other words, the top and thin fertile layer of humus is gradually depleted, which can lead to the use of millions or billions of hectares of arable land. And here to replace usual terrestrial cultures come microalgae. Research methodology. The study was based on the analysis of theoretical studies and comparison of different types of biological fuels from plant-type and microalgae, at the economic, environmental and social levels. Results and discussion. Biodiesel from microalgae is a third generation fuel obtained by processing vegetable raw materials. It is known that algae are characterized by a high content of fatty acids, which are the basis for the production of biodiesel. Microalgae are very cheap and, at the same time - highly productive raw materials. One hectare of microalgae produces 30 times more biofuel than one hectare of soybeans. At the same time, biofuel from algae is 5-10% more energy-intensive than biodiesel from vegetable oils. In addition, microalgae grow quite rapidly. For example, algae, which is 80% composed of substances similar in origin to oil, grows in 10 days, while the same algae, which is 30% composed of substances similar in origin to oil, grows in only 3 days. Another advantage of using algae is the fact that, unlike growing other types of plant materials, they do not need to be fed and fertilized - they use carbon dioxide (CO2) for growth. The higher the concentration of carbon dioxide, the faster they are cultivated. Thus, the cultivation of microalgae can solve several problems: the problem of the greenhouse effect; the problem of employment of sown areas; the problem of shortages of traditional fuels and many other equally important problems. Conclusion. Organic susstance as microalgae have been experimented as a potential feedstock for biofuel generation in current era owing to its’ rich energy content, inflated growth rate, inexpensive culture approaches, the notable capacity of CO2 fixation, and O2 addition to the environment. The implementation of the technology of biofuel production from organic waste also warns of danger, first of all for people. By reducing free waste, use it as a secondary material and benefit from it. Integrated waste management technology includes successive steps that take into account the environmental, economic and social spheres of life.

Role of autotrophic microbes in organic matter accumulation in soils degraded by erosion

AbstractAtmospheric CO2 fixation by autotrophic microbes has been investigated in various habitats, but little is known about the microbial CO2 fixation capacity in soil degraded by erosion. To fill the knowledge gap about the role of autotrophic microbes in organic matter accumulation in degraded soil, the microbial CO2 fixation rate was estimated in nondegraded, lightly degraded, and severely degraded soils using 13C stable isotope tracing technique. The influences of soil physical properties, nutrient contents, and autotrophic bacterial community on the microbial CO2 fixation capacity were investigated using a structural equation model. The results showed that soil degradation significantly reduced the autotrophic bacterial abundance. However, a higher species diversity and a more complex cooccurrence network of autotrophic bacterial taxa were observed in the lightly degraded soil than in the nondegraded and severely degraded soils. Interestingly, the microbial CO2 fixation rates in the lightly and severely degraded soils were 2.15‐ and 1.52‐times higher than those in the nondegraded soil, respectively. The annual organic carbon fixed by autotrophic microbes exceeded 2.05% of the total organic carbon in the degraded soil, suggesting that autotrophic microbes play a vital role in organic matter accumulation in degraded soil. The structural equation model showed that soil nutrients other than the autotrophic bacterial community are the key factor affecting the microbial CO2 fixation capacity. The negative effect of soil nutrients on the CO2 fixation capacity indicates that autotrophic microbes exert a more important function at the initial stage of the restoration of degraded soil.

Higher Photochemical Quenching and Better Maintenance of Carbon Dioxide Fixation Are Key Traits for Phosphorus Use Efficiency in the Wheat Breeding Line, RAC875.

Maintaining carbohydrate biosynthesis and C assimilation is critical under phosphorus (P) deficiency as inorganic P (Pi) is essential for ATP synthesis. Low available P in agricultural soils occurs worldwide and fertilizer P sources are being depleted. Thus, identifying biosynthetic traits that are favorable for P use efficiency (PUE) in crops is crucial. This study characterized agronomic traits, gas exchange, and chlorophyll traits of two wheat genotypes that differ in PUE. RAC875 was a P efficient genotype and Wyalkatchem was a P inefficient genotype. The plants were grown in pots under growth room conditions at two P levels; 10 mg P kg–1 soil (low P) and 30 mg P kg–1 soil (adequate P) and gas exchange and chlorophyll fluorescence were measured at the vegetative and booting stages using a portable photosynthesis system (LI-6800, LI-COR, United States). Results showed significant differences in some agronomic traits between the two wheat genotypes, i.e., greater leaf size and area, and a higher ratio of productive tillers to total tillers in RC875 when compared with Wyalkatchem. The CO2 response curve showed Wyalkatchem was more severely affected by low P than RAC875 at the booting stage. The relative ratio of the photosynthetic rate at low P to adequate P was also higher in RAC875 at the booting stage. Photochemical quenching (qP) in RAC875 was significantly higher when compared with Wyalkatchem at the booting stage. Maintaining CO2 fixation capacity under low P and higher qP would be associated with P efficiency in RAC875 and measuring qP could be a potential method to screen for P efficient wheat.

Garden post-transplant effects of pre-transplant plug cell volume and growing medium quality (as abiotic stresses) in Impatiens walleriana

Abstract Although much is known about the production of bedding plants, including Impatiens walleriana, little has been documented on their post-production performance. Thus, the aim of this work was to understand how pre-transplant crop management related to root restrictions imposed by plug cell volume and substrate quality affects the post-production performance related to biomass accumulation. To this end, we tested four plug cell volumes, as well as four growing media with significantly different physical and chemical properties, during nursery and pot culture. We also evaluated the difference between use and nonuse of synthetic cytokinin spray (benzyl aminopurine, BAP), a proven stress alleviator. Our novelty data validated the previous hypothesis and showed that plant quality and garden performance are dependent on these potential stress sources. The physiological mechanisms involved included differences in leaf area expansion (estimated mainly by relative leaf area expansion rate) and differences in CO2 fixation capacity (estimated by net assimilation rate). The sum of these responses determined significant differences in total fresh and dry weight during pot culture, which were amplified when plants were transplanted to a field bed. Spraying plants with synthetic cytokinin early during nursery allowed overriding of most root restriction abiotic stresses related to plug cell volume and growing media; therefore, synthetic cytokinin constitutes a tool to improve the yield of bedding plants (at the grower's level) and garden performance.

Aspergillus sp. assisted bioflocculation of Chlorella MJ 11/11 for the production of biofuel from the algal-fungal co-pellet

In recent times to address the energy issues, the use of microalgal feedstock as third generation biofuel has gained significance due to sustainability and feasibility. Compared to terrestrial plants, it has a higher growth rate and superior CO2 and sunlight fixation capacity; along with higher lipid content. However, a major bottleneck which impedes the mass production of microalgal oil is the high cost of harvesting. Therefore, energy efficient and eco-friendly harvesting techniques are crucial to improve the economic viability of algal biofuel production. In this study, pellet forming Aspergillus sp. was evaluated for the efficient biomass recovery of Chlorella sp. MJ11/11 through the process of fungal pelletization. The effect of different process factors like: rotational speed of the shaker, pH, nutrients and cationic agent concentrations in the media on biomass recovery were evaluated. When algae: fungi were used in 1:3 w/w ratios, more than 90% harvesting efficiency was obtained at pH 3 within 5 h. Fourier transform infrared spectroscopy analysis showed changes in the C-H and C-N groups indicating their role in co-pelletization process. The CHNS characterization of the co-pellet showed an improved C/N ratio, with a high heating value of 19.55 MJ Kg−1. The lipid and biomass concentration of the co-pellet was 332 mg L−1 and 2.37 ± 0.12 g L−1 respectively. Also, the X-ray diffraction analysis indicated an increase in the amorphous property of the co-pellet; demonstrating the suitability of the algal fungal co-pellet as a substrate for biofuel production.

Review on carbon dioxide fixation coupled with nutrients removal from wastewater by microalgae

The application of microalgae in carbon dioxide (CO2) fixation coupled with wastewater treatment has been regarded as a promising and cutting-edge technology in recent years, but it still faces some problems. The CO2 fixation capacity and nutrients removal capacity of microalgae should be considered simultaneously under various environmental conditions. Moreover, breeding microalgae using a photobioreactor is required and critical for CO2 fixation and wastewater treatment. In addition, the related influenced factors, mechanisms and kinetics of CO2 fixation and nutrients removal by microalgae remains complex and unclear. Thus, this work provides an updated review of the literature regarding the application of microalgae in the remediation of wastewaters from different sources coupled with CO2 fixation, discusses the main interactions between biological or environmental factors and how they can influence nutrient removal and CO2 fixation efficiencies, and further focuses on their mechanisms and kinetics. It is found that blue-green algae are most suitable to fix CO2 integrating treated wastewater, but more microalgal strains with excellent anti-fouling performance, tolerance to high concentrations of CO2 and NH3–N performance need to be screened. Additionally, wastewater and gas conditions during the cultivation process should be optimized in research and applications, and development of innovative photobioreactors with low cost is also required. Furthermore, modelling mainly focuses on estimating biomass yield, nutrient removal rates and CO2 fixation rates, while laboratory modelling results deviated from the natural modelling results. Finally, this paper also provides insight into what should be done in future work to support the development of CO2 fixation coupled with wastewater treatment by microalgae.

Vertical distribution pattern of cbb genes and bacterial CO2 fixing potential in the South China sea

In this study, the cbb genes which encode the key enzymes in the Calvin cycle were used as functional markers to investigate the distribution pattern of CO2 fixing potential of autotrophic bacteria at different depths of the South China Sea (SCS). The results revealed that cbb gene abundance was similar between the surface and the deep layer of SCS, over two fold higher than the middle layer. The types of cbb genes showed dramatically different distributions with depths. Metagenomic amplicon sequencing revealed that Synechococcus was the main genus containing cbb genes in the surface layer, along with Rubrivivax and Limnohabitans in the middle, and unclassified Epsilonproteobacteria in the deep. Furthermore, the surface layer had the highest CO2 fixing potential due to that Synechococcus had a high CO2 fixation capacity and relatively high autotrophic growth rate. The difference in the distribution of bacterial species and therefore cbb types with depths was potentially affected by the variation in light intensity and concentration of dissolved oxygen, inorganic carbon and reducing substances.