CO2 Biofixation Research Articles

Enhanced nutrient removal and bioenergy production in microalgal photobioreactor following anaerobic membrane bioreactor for decarbonized wastewater treatment

This study investigated the nutrient removal, decarbonization potentials, and bioenergy production (i.e., algal biomass and biogas) between a membrane photobioreactor (MPBR) and a sequencing photobioreactor (SPBR) as the post-treatment process of an anaerobic membrane bioreactor (AnMBR) for municipal wastewater treatment. All photobioreactors without aeration showed favourable performance on AnMBR effluent polishing and bioenergy production. In comparison, MPBRs achieved higher removal efficiencies with 98.4 %−99.1 % NH4-N and 74.8 %−88.4 % PO4-P removal compared to the SPBRs with 41.1 %−82.0 % NH4-N and 39.6 %−72.9 % PO4-P removal. MPBRs enhanced more nutrient utilization (24.9–49.3 g(N)/(m3·d) and 3.4–8.1 g(P)/(m3·d)) and CO2 assimilation (22.9–43.4 g(C)/(m3·d)), and concentrated more microalgae with 1.58–1.98 g/L higher than the SPBRs. Moreover, the MPBR effectively upgraded the biogas from AnMBR with superior methane percentage of 89.4 %−93.4 % due to its better CO2 biofixation. The MPBR, with better carbon, nitrogen and phosphorous removal and bioenergy production, following AnMBR is an attractive decarbonized technology for future sustainable wastewater treatment.

Sustainability and carbon neutralization trends in microalgae bioenergy production from wastewater treatment: A review

Reducing CO2 emissions using biomass is gaining popularity as an environmentally friendly strategy. Due to high growth rates, low production costs, and ability to withstand harsh conditions, microalgae have become quite popular. Microalgae may also undertake photosynthesis, converting CO2 and solar energy into sugar before becoming biomass, making them an excellent source of renewable and promising biofuels. CO2 sequestration and biofixation was utilized to compare the synthesis of biodiesel as a third-generation biofuel from various types of wastewater was also used as a source for the algal cultivation. This review article focuses on recent developments, research discoveries in the field of microalgal CO2 capture modification and the optimization of conversion efficiency. This review is intended to serve as a helpful and reference for the use of wastewater treatment with microalgae to collect CO2. The overarching objective of this study is to assist wastewater treatment systems in achieving carbon neutrality.

Assessment of CO2 biofixation and bioenergy potential of microalga Gonium pectorale through its biomass pyrolysis, and elucidation of pyrolysis reaction via kinetics modeling and artificial neural network.

This study investigates CO2 biofixation and pyrolytic kinetics of microalga G. pectorale using model-fitting and model-free methods. Microalga was grown in two different media. The highest rate of CO2 fixation (0.130g/L/day) was observed at a CO2 concentration of 2%. The pyrokinetics of the biomass was performed by a thermogravimetric analyzer (TGA). Thermogravimetric (TG) and derivative thermogravimetric (DTG) curves at 5, 10 and 20°C/min indicated the presence of multiple peaks in the active pyrolysis zones. The activation energy was calculated by different model-free methods such as Friedman, Flynn-Wall-Ozawa (FWO), Kissinger-Akahira-Sunose (KAS), and Popescu. The obtained activation energy which are 61.7-287kJ/mol using Friedman, 40.6-262kJ/mol using FWO, 35-262kJ/mol using KAS, and 66.4-255kJ/mol using Popescu showed good agreement with the experimental values with higher than 0.96 determination coefficient (R2). Moreover, it was found that the most probable reaction mechanism for G. pectorale pyrolysis was a third-order function. Furthermore, the multilayer perceptron-based artificial neural network (MLP-ANN) regression model of the 4-10-1 architecture demonstrated excellent agreement with the experimental values of the thermal decomposition of the G. pectoral. Therefore, the study suggests that the MLP-ANN regression model could be utilized to predict thermogravimetric parameters.

Design and characterization of a new pressurized flat panel photobioreactor for microalgae cultivation and CO2 bio-fixation

Microalgae-based biorefinery processes are gaining particular importance as a biotechnological tool for direct carbon dioxide fixation and production of high-quality biomass and energy feedstock for different industrial markets. However, despite the many technological advances in photobioreactor designs and operations, microalgae cultivation is still limited due to the low yields achieved in open systems and to the high investment and operation costs of closed photobioreactors. In this work, a new alveolar flat panel photobioreactor was designed and characterized with the aim of achieving high microalgae productivities and CO2 bio-fixation rates. Moreover, the energy efficiency of the employed pump-assisted hydraulic circuit was evaluated. The 1.3 cm thick alveolar flat-panels enhance the light utilization, whereas the hydraulic design of the photobioreactor aims to improve the global CO2 gas-liquid mass transfer coefficient (kLaCO2). The mixing time, liquid flow velocity, and kLaCO2 as well as the uniformity matrix of the artificial lighting source were experimentally calculated. The performance of the system was tested by cultivating the green microalga Acutodesmus obliquus. A volumetric biomass concentration equal to 1.9 g L−1 was achieved after 7 days under controlled indoor cultivation conditions with a CO2 bio-fixation efficiency of 64% of total injected CO2. The (gross) energy consumption related to substrate handling was estimated to be between 27 and 46 Wh m−3, without any cost associated to CO2 injection and O2 degassing. The data suggest that this pilot-scale cultivation system may constitute a relevant technology in the development of microalgae-based industrial scenario for CO2 mitigation and biomass production.

Exploring indigenous freshwater chlorophytes in integrated biophotovoltaic system for simultaneous wastewater treatment, heavy metal biosorption, CO2 biofixation and biodiesel generation

The study explored the combined photosynthetic activities of two green microalgal species, Tetradesmus obliquus and Tetradesmus reginae, on an integrated biophotovoltaic (BPV) platform for simultaneous wastewater treatment, toxic metal biosorption, carbon biofixation, bioelectricity generation and biodiesel production. The experimental setup comprised of a dual-chambered BPV with copper anode surrounded by T. obliquus in BG11 media, and copper cathode with T. reginae in municipal wastewater separated by Nafion 117 membrane. The study reported a maximum power density of 0.344 Wm−2 at a cell potential of 0.415 V with external resistance of 1000 Ω and 0.3268 V maximum open-circuit voltage. The wastewater electrical conductivity and pH increased from 583 ± 22 to 2035 ± 29.31 mS/cm and 7.403 ± 0.174 to 8.263 ± 0.055 respectively, signifying increased photosynthetic and electrochemical activities. Residual nitrogen, phosphorus, chemical oxygen demand, arsenic, cadmium, chromium and lead removal efficiencies by T. reginae were 100%, 80.68%, 71.91%, 47.6%, 88.82%, 71.24% and 92.96%, respectively. T. reginae accumulated maximum biomass of 0.605 ± 0.033 g/L with a CO2 biosequestration rate of 0.166 ± 0.010 gCO2/L/day and 42.40 ± 1.166% lipid content. Methyl palmitate, methyl undecanoate and 13-octadecenoic acid with relative abundances of 37.24%, 24.80% and 12.02%, respectively were confirmed.

Integrating eco-technological approach for textile dye effluent treatment and carbon dioxide capturing from unicellular microalga Chlorella vulgaris RDS03: a synergistic method

A pilot-scale treatment method was used in the present study to test the biosorption of textile dye from textile effluent and carbon dioxide using Chlorella vulgaris RDS03. The textile dye effluent treatment achieved that textile dye biosorption capacity (qmax) rate of 98.84% on 15 days of treatment using Chlorella vulgaris RDS03. The Langmuir and Freundlich isotherm kinetics model indicated that the higher R2 value 0.98. The microalga Chlorella vulgaris RDS03 was captured-96.86% of CO2 analyzed by CO2 utilization and biofixation kinetics, 4.65 mgmL−1 of biomass, 189.26 mgg−1 of carbohydrate, 233.89 mgg−1 of lipid, 4.3 mLg−1 of bioethanol and 4.9 mLg−1 of biodiesel produced. We performed fatty acid methyl ester (FAME) profiling using gas chromatography-mass spectrometry (GCMS). We found 40 types of biodiesel compounds, specifically myristic acid, pentadecanoic acid, octadecanoic acid, palmitic acid, and oleic acid. The high-performance liquid chromatography (HPLC) validated and analyzed the produced bioethanol. Novelty of the Research • Unicellular microalga Chlorella vulgaris RDS03 was isolated from the freshwater region and investigated their biosorption efficiency against hazardous synthetic azo textile dyes. • Chlorella vulgaris RDS03 ability to biosorption 96.86% of environmental polluted carbon dioxide • Treated biomass was used to produce ecofriendly, unpolluted and green energy such as biofuels (biodiesel and bioethanol)

A geographical source-sink matching for carbon capture and utilization deployment in Taiwan

To achieve the Paris Agreement's targets, Taiwan is actively working towards net-zero greenhouse gas emissions by 2050. In particular, carbon capture storage (CCS) and utilization (CCU) have been recognized as significant strategies to meet these goals. To foster the deployment of CCU technologies in Taiwan, this work presents a methodology to identify appropriate CO2 source-sink matching. Spatial analysis is used to tease out prospective source-sink matches, and spatially characterize and visualize potential clusters where opportunities for CCU deployment exist.In total, 6 clusters of facilities were identified and quantitatively characterized using geographical information system tools. They include main stationary CO2 sources (> 0.1 MtCO2 per year) from both the power sector and hard-to-abate industries, such as cement and steelmaking plants. Potential CO2 sinks comprise existing sites that currently use CO2, CO2 biofixation from microalgae farming, and CO2 mineralization from alkaline solid wastes. In addition to the annual 200 ktCO2 already used by industrial facilities, approximately 3 MtCO2 can be fixed by the mineralization process, and 7 ktCO2 biofixed through microalgae farming per year. These clusters may offer commercial synergies lowering the risk while achieving carbon and waste reduction and providing long-term CO2 storage in the case of mineral carbonation.

Genetic improvement of microalgae for enhanced carbon dioxide sequestration and enriched biomass productivity: Review on CO2 bio-fixation pathways modifications

Algae, carbon dioxide and wastewater are the most promising research topics in recent years. Integrated sustainable approaches on cultivating microalgae in both real-time and simulated wastewater with carbon dioxide (CO2) are experimented as environmentally feasible approach. However, in terms of high macromolecules rich biomass productivity (example: high lipid accumulated biomasses productivity for biofuel applications) are needed to achieve sustainable productivity. Hence, it is needed to improve photosynthesis process by which we can achieve higher CO2 sequestration and enriched biomass productivity. Therefore, on improving photosynthesis process, efficiency of enzymes involved in photosynthetic pathways needs to be enriched, light utilization range needs to be improved and majorly the release of captured CO2 needs to be minimized. These modifications are achievable through genetic engineering approaches in environmentally friendly way. Hence, this review provides the detailed potential strategies that helps in enhancing the microalgae-based CO2 fixation, technical insights into existing limitations and challenges, future research directions to achieve sustainable development.

Investigation of Hydrodynamic Parameters in an Airlift Photobioreactor on CO2 Biofixation by Spirulina sp.

The rise of CO2 concentration on Earth is a major environmental problem that causes global warming. To solve this issue, carbon capture and sequestration technologies are becoming more and more popular. Among them, cyanobacteria can efficiently sequestrate CO2, which is an eco-friendly and cost-effective way of reducing carbon dioxide, and algal biomass can be harvested as valuable products. In this study, the hydrodynamic parameters of an airlift photobioreactor such as gas holdup, mean bubble diameter and liquid circulation velocity were measured to investigate CO2 biofixation by Spirulina sp. The total gas holdup was found to increase linearly with the increase in the gas velocity from 0.185 to 1.936 cm/s. The mean bubble velocities in distilled water only and in the cyanobacterial culture on the first and sixth days of cultivation were 109.97, 87.98, and 65.89 cm/s, respectively. It was found that shear stress at gas velocities greater than 0.857 cm/s led to cyanobacterial death. After 7 days of batch culture, the maximum dry cell weight reached 1.62 g/L at the gas velocity of 0.524 cm/s, whereas the highest carbon dioxide removal efficiency by Spirulina sp. was 55.48% at a gas velocity of 0.185 cm/s, demonstrating that hydrodynamic parameters applied in this study were suitable to grow Spirulina sp. in the airlift photobioreactor and remove CO2.

CO2 biofixation at microalgae photobioreactors: hydrodynamics and mass transfer study

CO2 biofixation at microalgae photobioreactors: hydrodynamics and mass transfer study

Oleaginous Microalga Coccomyxa subellipsoidea as a Highly Effective Cell Factory for CO2 Fixation and High-Protein Biomass Production by Optimal Supply of Inorganic Carbon and Nitrogen.

Microalgae used for CO2 biofixation can effectively relieve CO2 emissions and produce high-value biomass to achieve “waste-to-treasure” bioconversion. However, the low CO2 fixation efficiency and the restricted application of biomass are currently bottlenecks, limiting the economic viability of CO2 biofixation by microalgae. To achieve high-efficient CO2 fixation and high-protein biomass production, the oleaginous microalga Coccomyxa subellipsoidea (C. subellipsoidea) was cultivated autotrophically through optimizing inorganic carbon and nitrogen supply. 0.42 g L−1 NaHCO3 supplemented with 2% CO2 as a hybrid carbon source resulted in high biomass concentration (3.89 g L−1) and productivity (318.33) with CO2 fixation rate 544.21 mg L−1 d−1 in shake flasks. Then, used in a 5-L photo-fermenter, the maximal protein content (60.93% DW) in batch 1, and the highest CO2 fixation rate (1043.95 mg L−1 d−1) with protein content (58.48% DW) in batch 2 of repeated fed-batch cultures were achieved under 2.5 g L−1 nitrate. The relative expression of key genes involved in photosynthesis, glycolysis, and protein synthesis showed significant upregulation. This study developed a promising approach for enhancing carbon allocation to protein synthesis in oleaginous microalga, facilitating the bioconversion of the fixed carbon into algal protein instead of oil in green manufacturing.

Evaluating application of photosynthetic microbial fuel cell to exhibit efficient carbon sequestration with concomitant value-added product recovery from wastewater: A review.

The emission of CO2 from industrial (24%) and different anthropogenic activities, like transportation (27%), electricity production (25%), and agriculture (11%), can lead to global warming, which in the long term can trigger substantial climate changes. In this regard, CO2 sequestration and wastewater treatment in tandem with bioenergy production through photosynthetic microbial fuel cell (PMFC) is an economical and sustainable intervention to address the problem of global warming and elevating energy demands. Therefore, this review focuses on the application of different PMFC as a bio-refinery approach to produce biofuels and power generation accompanied with the holistic treatment of wastewater. Moreover, CO2 bio-fixation and electron transfer mechanism of different photosynthetic microbiota, and factors affecting the performance of PMFC with technical feasibility and drawbacks are also elucidated in this review. Also, low-cost approaches such as utilization of bio-membrane like coconut shell, microbial growth enhancement by extracellular cell signalling mechanisms, and exploitation of genetically engineered strain towards the commercialization of PMFC are highlighted. Thus, the present review intends to guide the budding researchers in developing more cost-effective and sustainable PMFCs, which could lead towards the commercialization of this inventive technology.

Microalgae bioremediation and CO2 fixation of industrial wastewater

The present work evaluates the bioremediation potential of the microalgae Chlorella sp. cultivated in industrial wastewaters of a metallurgy facility for CO2 fixation. Its growth in wastewaters was investigated experimentally and growth rate was determined based on different dilutions. Taguchi's experimental design was carried out and values found in laboratory were compared to those of a mathematical model adjusted based on growth rate. Process efficiency was evaluated to reduce organic load, nutrient consumption, and cell count during the initial and final stages via microscopy. After the biological treatment, reduction percentages of 99% for COD (Chemical Oxygen Demand) and 95% for SS (Sedimentable Solids) were achieved, in addition to 86% and 93% of nutrient and cyanide removal, respectively, and average CO2 biofixation of 0.1854 gL-1d-1. These values are close to those found in literature for other cultivation media. It was also observed that biomass productivity and CO2 fixation data are in agreement with those obtained in other studies, thus evidencing the efficiency of Chlorella sp. microalgae and its high photosynthetic capacity.

Biofixation of Air Emissions and Biomass Valorization-Evaluation of Microalgal Biotechnology.

This research appraised the simultaneous biofixation, that is not quite common in scientific literature, of carbon dioxide (CO2) and nitric oxides (NOx) by microalgae species Chlorella vulgaris, Haematococcus pluvialis, and Scenedesmus subspicatus. The experimental design was established by five treatments with gas concentrations between control-0.04% of CO2, 5 to 15% of CO2, and 30 to 100ppm of NOx. Parameters such as pH, growth, productivity, lipids, protein, carbon/ nitrogen ratio, and astaxanthin were evaluated. For all species, the maximal growth and productivity were achieved with 5% of CO2 and 30ppm of NOx. Regarding protein content, for all the three species, better results were obtained at higher concentrations of CO2 and NOx. These results prove the microalgae capacity for CO2 and NOx biofixation and reuse of biomass as a source of high value-added products, such as lipids, proteins, and astaxanthin. These findings support the indication of these species for flue gas treatment process and use in biorefineries systems.

Marine biorefinery: an environmentally sustainable solution to turn marine biomass and processing wastes into value-added products and profits

Marine biorefinery: an environmentally sustainable solution to turn marine biomass and processing wastes into value-added products and profits

Promotion of Carbon Dioxide Biofixation through Metabolic and Enzyme Engineering

Carbon dioxide is a major greenhouse gas, and its fixation and transformation are receiving increasing attention. Biofixation of CO2 is an eco–friendly and efficient way to reduce CO2, and six natural CO2 fixation pathways have been identified in microorganisms and plants. In this review, the six pathways along with the most recent identified variant pathway were firstly comparatively characterized. The key metabolic process and enzymes of the CO2 fixation pathways were also summarized. Next, the enzymes of Rubiscos, biotin-dependent carboxylases, CO dehydrogenase/acetyl-CoA synthase, and 2-oxoacid:ferredoxin oxidoreductases, for transforming inorganic carbon (CO2, CO, and bicarbonate) to organic chemicals, were specially analyzed. Then, the factors including enzyme properties, CO2 concentrating, energy, and reducing power requirements that affect the efficiency of CO2 fixation were discussed. Recent progress in improving CO2 fixation through enzyme and metabolic engineering was then summarized. The artificial CO2 fixation pathways with thermodynamical and/or energetical advantages or benefits and their applications in biosynthesis were included as well. The challenges and prospects of CO2 biofixation and conversion are discussed.

Post-treatment of an aerated facultative pond with constructed wetland: First two years of operation in a dairy industry

In the present study, a horizontal subsurface flow constructed wetland (HSF-CW) with a surface area of 240 m2 and HRT of 2 days, was used in the post treatment of a facultative aerated pond. Application rates of 175 kg BOD5 ha−1 day−1 and 408 kg COD ha−1 day−1 can be considered admissible for HSF-CW operation following a facultative aerated pond. The system presented values for COD, BOD5 and TSS removal of 88%, 98.8% and 99.3%, respectively. The system supported operation at a solids application rate of 23.3 g TSS m−2 day−1 for two years without clogging. The species grown in the CW (Brachiaria ruziziensis) presented a biomass produtivity of between 1.86 and 2.55 kg m−2 y−1, providing CO2 biofixation of between 3.10 and 3.98 kg m−2 y−1. The present study, conducted over two years, indicates that the HSF-CW model employed, and the operational parameters proposed, can be used in post treatment for a pond system that is not operating satisfactorily.

Use of the cyanobacterium Spirulina platensis in cattle wastewater bioremediation

In the present study, the microalga Spirulina platensis (Arthrospira) was grown in two horizontal photobioreactors (HPBR) under two different irradiances (150 and 270 μmol m-2 s-2). Anaerobically digested cattle wastewater (ACWW) was used as substrate. The experiment was carried out in batches for a period of 8 days. The maximum specific growth rate of 0.347 day-1 and the doubling time of 2.08 days were obtained under the highest illumination of the culture. Dry biomass production reached maximum values between 2.17 g L-1 and 6.52 g L-1, with volumetric biomass productivities between 0.0812 and 0.5578 g L-1 day-1. Productivity per area was equal to 47.97 g m-2 d-1, which is the highest value recorded compared to those found in the literature consulted. As for CO2 biofixation, relevant values for reducing this gas in the atmosphere were obtained, ranging from 128.52 to 882.36 mg L-1 day-1. In terms of organic matter, 16.3-77% of BOD5 and 12.6-61.6% of COD were reduced. In the reduction of TS, TSS and VSS, values of 71.3-78.5%, 79.5-84.4% and 87.0-88.3%, respectively, were reached. NH4+ reduction was 32.5-98.3%, organic nitrogen reduction was 20.3-95.9% and total phosphorus reduction was 33.5-89.9%. The reductions of thermotolerant coliforms were between 71.7% and 99.9%. In view of the results found, it can be considered that the bioremediation of the effluent reached promising efficiencies, with the advantage of producing biomass with potential to obtain bioproducts of relevant economic value

Single-step integrated technology for enhanced CO2 biofixation and efficient lipid extraction in microalgal system including a water-immiscible solvent

The potential of microalgae for both carbon fixation and energy sustainability has been demonstrated. However, the low CO2 biofixation rate and high cost of lipid extraction restrict its large-scale development. This paper proposes a novel integrated technology for enhanced CO2 biofixation and efficient lipid extraction in microalgal system by adding water-immiscible solvent N-heptane over the culture medium. N-heptane can act as a ‘carbon sink’ and ‘extract agent’ without causing significant damage to microalgal cells. Specifically, N-heptane with the volume percentages of 4, 8, 12, 25 and 42 % was added to Chlorella sp. culture systems. Simulated flue gas containing 15 vol% CO2 in nitrogen gas was used as the sole carbon source. The maximum biomass concentration (0.84 g·L-1) and specific growth rate (0.23 d-1) were achieved with 12 % N-heptane. These values were higher than blank culture by 12.3 % (biomass concentration) and 56.9 % (specific growth rate). The CO2 biofixation rate increased with N-heptane to a maximum value of 220.2 mg·L-1·d-1, which was 64.7 % higher than that of the blank culture. Meanwhile, the system has a potential for the generation of biofuels with a maximum lipid amount of 2.82 g·gAlgae-1 in this single step approach.

Chlorella vulgaris cultivation in pilot-scale to treat real swine wastewater and mitigate carbon dioxide for sustainable biodiesel production by direct enzymatic transesterification

This study firstly addressed real swine wastewater (RSW) treatment by an indigenous Chlorella vulgaris MBFJNU-1 in 5-m3 outdoor open raceway ponds and then direct enzymatic transesterification of the resulting lipids from the wet biomass for sustainable biodiesel production. Compared to the control group, C. vulgaris MBFJNU-1 at 3% CO2 achieved higher microalgal biomass (478.5 mg/L) and total fatty acids content (21.3%), higher CO2 bio-fixation (63.2 mg/L/d) and lipid (9.1 mg/L/d) productivities, and greater nutrients removals (total nitrogen, 82.1%; total phosphorus, 28.4%; chemical oxygen demand, 37.1%). The highest biodiesel conversion (93.3%) was attained by enzymatic transesterification of wet disrupted Chlorella biomass with 5% lipase TL and 5% phospholipase PLA. Moreover, the enzymatic transesterification gave around 83% biodiesel conversion in a 15-L stirred tank bioreactor. Furthermore, the integrated process was a cost-effective approach to treat RSW and mitigate CO2 for microalgal biodiesel production, based on the mass and energy balances analysis.