CO2 Removal Rate Research Articles

COF-5/Pebax mixed-matrix membranes with enhanced CO2 removal ability for ECCO2R system

Extracorporeal CO2 removal (ECCO2R) is a type of extracorporeal life support (ECLS) technology. It aims to remove carbon dioxide (CO2) from small flow of the blood and correct hypercapnia and related acidosis. The ECCO2R system removes CO2 retained in the patient’s body through the gas-blood exchange membranes, which in use, blood flows on the outside of the membrane, and the inside of the membrane is for gas flow. Existing ECCO2R system generally improves the emission rate of CO2 by the increase of the gas flow rate. However, there is a problem that O2 is simultaneously taken out, which will reduce the blood O2 concentration. Therefore, the gas-blood exchange membranes should not only increase the CO2 removal rate by the improvement of CO2/O2 selectivity, but also retain more O2 in the blood and then maintain the oxygen saturation of the blood. In present work, a method was proposed to fabricate COF-5/Pebax mixed matrix membranes (MMMs) on the PMP surface for enhancing CO2/O2 selectivity, which was increased from 0.96 to 5.57. The CO2 removal ability of COF-5/Pebax MMM was tested by blood circulation, and it was found that the CO2 removal effect was increased 10.9% than that of the pristine membranes. The O2 concentration was maintained at a higher level, about 1.69 times that of the pristine membranes. In contrast to the pristine PMP membrane, blood compatibility of COF-5/Pebax MMMs was improved because protein adhesion decreased by 44.75%. The results of cytotoxicity test and rabbit pyrogen test exhibited that the prepared COF-5/Pebax MMM presented great biosafety. Overall, the proposed COF-5/Pebax MMM has good performance in ECCO2R system and attractive potential for medical application.

Dynamics of bio-based carbon dioxide removal in Germany

Bio-based carbon dioxide removal encompasses a range of (1) natural sink enhancement concepts in agriculture and on organic soils including peatlands, and in forestry, (2) bio-based building materials, and (3) bioenergy production with CO2 capture and storage (BECCS). A common database on these concepts is crucial for their consideration in strategies and implementation. In this study, we analyse standardised factsheets on these concepts. We find different dynamics of deployment until 2045: for CO2 removal rates from the atmosphere, natural sink enhancement concepts are characterised by gradually increasing rates, followed by a saturation and potentially a decrease after few decades; forest-related measures ramp up slowly and for construction projects and bioenergy plants, annually constant removal rates are assumed during operation which drop to zero afterwards. The expenses for removing 1 t CO2 from the atmosphere were found to be between 8 and 520 € t CO2−1, which arises from high divergence both in capital and operational expenditures among the concepts. This high variability of expenses seems to suggest the more cost-effective concepts should be implemented first. However, aspects from economics, resource base and environmental impacts to social and political implications for Germany need to be considered for developing implementation strategies. All concepts investigated could be deployed on scales to significantly contribute to the German climate neutrality target.

A novel cryogenic-thermochemical approach for clean hydrogen production from industrial flue gas streams with carbon capture and storage

The present work aims to develop a novel integrated energy system for clean hydrogen production from the industrial flue gas stream. The particular system incorporates a cryogenic distillation unit for H2S and CO2 separation and a thermochemical cycle for hydrogen production. The industrial flue gaseous mixture is considered a major feedstock for the present system. H2S is retrieved from the waste gaseous stream and fed to the two-step sulfur looping thermochemical cycle to perform clean hydrogen production. In this way, clean hydrogen production, elemental sulfur production, carbon capture, and storage are achieved. The entire integrated energy system is simulated in the Aspen Plus process simulator and is investigated thermodynamically in terms of energy and exergy performances. Various parametric studies are conducted to assess the significance of operating parameters on the system performance. The H2S and CO2 removal rates from the waste feed stream are found to be 85.55 % and 84.62 %. The H2S conversion into hydrogen is determined to be 66.67 %. The energy and exergy efficiencies of the two-step thermochemical cycle are found to be 53.93 % and 23.69 %, respectively. The parametric studies show that the hydrogen production rates of 3.63 kmol/h, 2.46 kmol/h, and 1.78 kmol/h are achieved at sulfurization temperatures of 200 °C, 300 °C, and 500 °C, respectively. The study further concludes that 44.60 % of the total input exergy is lost due to the presence of irreversibilities within the system. The overall energy and exergy efficiencies of the integrated energy system are found to be 82.99 % and 55.39 %, respectively.

Expert perspectives on ECCO2R for acute hypoxemic respiratory failure: consensus of a 2022 European roundtable meeting

BackgroundBy controlling hypercapnia, respiratory acidosis, and associated consequences, extracorporeal CO2 removal (ECCO2R) has the potential to facilitate ultra-protective lung ventilation (UPLV) strategies and to decrease injury from mechanical ventilation. We convened a meeting of European intensivists and nephrologists and used a modified Delphi process to provide updated insights into the role of ECCO2R in acute respiratory distress syndrome (ARDS) and to identify recommendations for a future randomized controlled trial.ResultsThe group agreed that lung protective ventilation and UPLV should have distinct definitions, with UPLV primarily defined by a tidal volume (VT) of 4–6 mL/kg predicted body weight with a driving pressure (ΔP) ≤ 14–15 cmH2O. Fourteen (93%) participants agreed that ECCO2R would be needed in the majority of patients to implement UPLV. Furthermore, 10 participants (majority, 63%) would select patients with PaO2:FiO2 > 100 mmHg (> 13.3 kPa) and 14 (consensus, 88%) would select patients with a ventilatory ratio of > 2.5–3. A minimum CO2 removal rate of 80 mL/min delivered by continuous renal support machines was suggested (11/14 participants, 79%) for this objective, using a short, double-lumen catheter inserted into the right internal jugular vein as the preferred vascular access. Of the participants, 14/15 (93%, consensus) stated that a new randomized trial of ECCO2R is needed in patients with ARDS. A ΔP of ≥ 14–15 cmH2O was suggested by 12/14 participants (86%) as the primary inclusion criterion.ConclusionsECCO2R may facilitate UPLV with lower volume and pressures provided by the ventilator, while controlling respiratory acidosis. Since recent European Society of Intensive Care Medicine guidelines on ARDS recommended against the use of ECCO2R for the treatment of ARDS outside of randomized controlled trials, new trials of ECCO2R are urgently needed, with a ΔP of ≥ 14–15 cmH2O suggested as the primary inclusion criterion.

CO2 mineralization and heavy metal leaching of multi-source ashes from municipal solid waste incineration

Mineralization holds great promise in simultaneously fixing CO2 and treating ash from the municipal solid waste incineration (MSWI). However, characteristics of CO2 mineralization and heavy metal leaching largely depends on the generation process of ashes. Herein, we report a systematic evaluation on the direct aqueous carbonation of multi-source MSWI ashes and leaching behavior of heavy metals before and after mineralization. Influencing factors for CO2 mineralization are determined to follow the order of CO2 concentration > temperature > solid–liquid ratio > stirring speed. Spray tower fly ash from the semi-dry process and bag filter fly ash from the dry process exhibit better sequestration capacities of 82.3 g-CO2/kg-ash and 150.9 g-CO2/kg-ash with a maximum CO2 removal rate of 0.117 mmol/s and 0.191 mmol/s among all ashes. Moreover, leaching concentration of Pb/Cu/As/Ni/Hg in six MSWI ashes all decreases significantly after CO2 mineralization. These findings could provide guidance for the potential intensive utilization of MSWI ashes in CO2 mitigation.

Carbonic anhydrase immobilized on Zn(II)-geopolymer membrane for CO2 capture

Inorganic membranes are widely used in water filtration and gas separation due to their many advantages. In this work, we proposed an innovative approach for enzyme immobilization using a geopolymer based tubular inorganic membrane (GM) as a carrier. The GM has abundant mesopores, excellent mechanical strength and strong stability for continuous flow systems in biocatalysis field, and carbonic anhydrase (CA) was successfully loaded into this mesoporous membrane using adsorption-crosslinking method, relying on the excellent ion exchange capacity of geopolymers and large number of hydroxyl groups naturally present in the membrane's mesopores. The results of the immobilization experiments showed that the immobilized enzyme composite membrane (GZnM-CA) could achieve 63.7% enzyme recovery. This is a significant improvement over the enzyme recoveries obtained on organic membranes which are typically less than 50%. In stability tests, the membrane retained more than 90.0% relative activity after 10 consecutive uses. In the CO2 capture assay, the CO2 capture efficiency developed dramatically under the catalytic of GZnM-CA. To our delight, the membrane has excellent separation capability for CO2 gas mixtures, especially at low CO2 concentrations, achieving 99.90% CO2 removal rate, and this result can be maintained for a long period of time in a pH = 8.0 environment.

Passive direct air capture using calcium oxide powder: The importance of water vapor

Calcium oxide (CaO; lime) looping is a proposed technology with the potential to capture gigatonnes of carbon dioxide (CO2) from the atmosphere to help mitigate climate change. The importance of water in carbonation reactions is widely understood as it is needed for mineral and CO2 dissolution and carbonate precipitation. However, the effects of water vapor on CaO carbonation pathways and rates have yet to be elucidated in a systematic manner. Here, we examine the impact of relative humidity (RH) on CO2 removal using CaO powder at 20% to 95% RH. Higher RH resulted in faster hydration rates, forming Ca(OH)2 (portlandite); however, passivation limited carbonation in all experiments, with the greatest carbonation occurring at 80% RH (65% CaCO3; calcite). Thus, CaO powder is highly prone to passivation when using RH to drive hydration and carbonation. In RH swing experiments, RH was changed at different times (hours or days) and by different amounts (e.g., 40–99%). Humidity swings can yield >85% CaCO3 when complete CaO hydration at a low RH (<40%) occurs before carbonation at a high RH (∼99%). Importantly, separating these two processes yields nearly complete carbonation. In this case, we achieved a CO2 removal rate of 1 t CO2 for every 1.95 t of Ca(OH)2 per day.

Investigation of the indoor CO2 removal efficiency and fresh air energy savings of living walls in office spaces

Elevated indoor CO2 levels might have adverse effects on human health. However, conventional physical and chemical methods for indoor CO2 removal face the challenges of high energy consumption, low efficiency at low CO2 concentrations, and high costs. Furthermore, the introduction of outdoor air to lower indoor CO2 concentrations results in significant HVAC energy consumption. Aligning with office hours and the natural light cycle, the utilization of photosynthesis in living walls (LWs) offers an energy-efficient and sustainable solution for the mitigation of high CO2 levels in office spaces. This study experimentally investigates the impacts of the carbon fixation pathways, light flux density, and substrate moisture content on the CO2 removal rate of LWs in two identical rooms. The findings provide practical suggestions for plant species selection, lighting design, and irrigation management in office spaces to enhance the CO2 removal efficiency of LWs. Additionally, the fresh air energy-saving effects of LWs under different scenarios are accurately simulated in EnergyPlus. The results demonstrate that choosing C3 plants over CAM plants in LWs yields higher CO2 removal efficiency. The activation of artificial lighting is recommended when the surface light flux density of LWs drops below the light compensation point (LCP), ensuring favorable conditions for growth. In a 30-m2 office room accommodating two and three occupants, LWs can respectively reduce the demand for fresh air by 13.9 %–38.5 % and decrease fresh air energy consumption by 11.2 %–28.2 %.

Effects of unilateral superimposed high-frequency jet ventilation on porcine hemodynamics and gas exchange during one-lung flooding.

Superimposed high-frequency jet ventilation (SHFJV) is suitable for respiratory motion reduction and essential for effective lung tumor ablation. Fluid filling of the target lung wing one-lung flooding (OLF) is necessary for therapeutic ultrasound applications. However, whether unilateral SHFJV allows adequate hemodynamics and gas exchange is unclear. To compared SHFJV with pressure-controlled ventilation (PCV) during OLF by assessing hemodynamics and gas exchange in different animal positions. SHFJV or PCV was used alternatingly to ventilate the non-flooded lungs of the 12 anesthetized pigs during OLF. The animal positions were changed from left lateral position to supine position (SP) to right lateral position (RLP) every 30 min. In each position, ventilation was maintained for 15 min in both modalities. Hemodynamic variables and arterial blood gas levels were repeatedly measured. Unilateral SHFJV led to lower carbon dioxide removal than PCV without abnormally elevated carbon dioxide levels. SHFJV slightly decreased oxygenation in SP and RLP compared with PCV; the lowest values of PaO2 and PaO2/FiO2 ratio were found in SP [13.0; interquartile range (IQR): 12.6-5.6 and 32.5 (IQR: 31.5-38.9) kPa]. Conversely, during SHFJV, the shunt fraction was higher in all animal positions (highest in the RLP: 0.30). In porcine model, unilateral SHFJV may provide adequate ventilation in different animal positions during OLF. Lower oxygenation and CO2 removal rates compared to PCV did not lead to hypoxia or hypercapnia. SHFJV can be safely used for lung tumor ablation to minimize ventilation-induced lung motion.

Open adsorption system for atmospheric CO2 capture: Scaling and sensitivity analysis

Open adsorption process of gas mixtures involves complex heat and mass transfer mechanisms. Understanding of the physical mechanisms and their impacts on the adsorption process from gas mixtures is vital. In this study, a detailed analysis of an open CO2 adsorption from CO2/N2 mixtures using zeolite 13X-APG was investigated. Key physical mechanisms (unsteady, diffusive, convective, and component source, etc.) involved were scrutinized, and their order of magnitudes relative to the system energy complex were determined. The influences of these physical mechanisms on the equilibrium and dynamic nature throughout the capture were quantified. The validated computational fluid dynamics (CFD) simulations for the same adsorption domain were carried out to verify the rationality of the scaling method. The adsorption time, tad; the maximum average temperature, T‾max; CO2 removal rate, Rre,CO2; equilibrium pressure drop, ΔPeq on different scale parameters and their sensitivity were investigated. The maximum relative sensitivity to porosity was found to be −0.945, 0.0235, −0.357, and −5.33 for tad, T‾max, Rre,CO2 and ΔPeq, respectively. It is observed that heat transfer by the conduction mechanism inside the bed significantly influences all scale parameters, except for ΔPeq. This work will contribute to a better understanding of the atmospheric CO2 adsorption and provide guidance for the design optimization.

Evaluation of CO2 removal rate of ECCO2R for a renal replacement therapy platform in an experimental setting.

A critical parameter of extracorporeal CO2 removal (ECCO2R) applications is the CO2 removal rate (VCO2). Low-flow venovenous extracorporeal support with large-size membrane lung remains undefined. This study aimed to evaluate the VCO2 of a low-flow ECCO2R with large-size membrane lung using a renal replacement therapy platform in an experimental animal model. Twelve healthy pigs were placed under mechanical ventilation and connected to an ECCO2R-CRRT system (surface area = 1.8 m2; OMNIset®, BBraun, Germany). Respiratory settings were reduced to induce two degrees of hypercapnia. VCO2 was recorded under different combinations of PaCO2 (50-69 or 70-89 mm Hg), extracorporeal blood flow (ECBF; 200 or 350 mL/min), and gas flow (4, 6, or 10 L/min). VCO2 increased with ECBF at all three gas flow rates. In severe hypercapnia, the increase in sweep gas flow from 4 to 10 L/min increased VCO2 from 86.38 ± 7.08 to 96.50 ± 8.71 mL/min at an ECBF of 350 mL/min, whereas at ECBF of 200 mL/min, any increase was less effective. But in mild hypercapnia, the increase in sweep gas flow result in significantly increased VCO2 at two ECBF. VCO2 increased with PaCO2 from 50-69 to 70-89 mm Hg at an ECBF of 350 mL/min, but not at ECBF of 200 mL/min. Post-membrane lung PCO2 levels were similar for different levels of premembrane lung PCO2 (p = 0.08), highlighting the gas exchange diffusion efficacy of the membrane lung in gas exchange diffusion. In severe hypercapnia, the reduction of PaCO2 elevated from 11.5% to 19.6% with ECBF increase only at a high gas flow of 10 L/min (p < 0.05) and increase of gas flow significantly reduced PaCO2 only at a high ECBF of 350 mL/min (p < 0.05). Low-flow venovenous extracorporeal ECCO2R-CRRT with large-size membrane lung is more efficient with the increase of ECBF, sweep gas flow rate, and the degree of hypercapnia. The influence of sweep gas flow on VCO2 depends on the ECBF and degree of hypercapnia. Higher ECBF and gas flow should be chosen to reverse severe hypercapnia.

Effect of experimental boundary conditions and treatment-time on the electro-desalination of soils.

This study investigates the effect of boundary conditions and treatment-time on the electro-desalination of artificially-contaminated soil. The effect of ion exchange membranes (IEM), calcium chloride (CaCl2), and ethylenediaminetetraacetic acid (EDTA)on the removal of salt (i.e., Na+, Cl-, and Ca2+) and metal (i.e., Co2+ and Fe2+) ions from the soil by electrokinetic (EK) was studied. The outcomes demonstrate that an increase in treatment-time decreases the electroosmosis and ion removal rate, which might be attributed to the formation of acid-base fronts in soil, except in the IEM case. Because a high pH jump and electroosmotic flow (EOF) of water were not observed within the soil specimen due to the IEM, the removal of ions was only by diffusion and electromigration. The collision of acid-base fronts produced a large voltage gradient in a narrow soil region with a reduced electric field (EF) in its remaining parts, causing a decrease in EOF and ion transportby electromigration. The results showed that higher electroosmosis was observed by using CaCl2 and EDTA; thus, the removal rate of Co2+, Na+, and Ca2+ was greater than Cl- due to higher EOF. However, for relatively low EOF, the removal of Cl- exceeded that of Co2+, Na+, and Ca2+, possibly due to a lack of EOF. In addition, the adsorption of Fe2+ in soil increased with treatment-time due to the corrosion of the anode during all EK experiments except in the case of IEM, where an anion exchange membrane (AEM)was introduced at the anode-soil interface.

Novel S-scheme Bi24O31Cl10/Bi7Fe2Ti2O17Cl heterojunction for efficient and stable photocatalytic activities

The strategy to boost photocatalytic activities toward CO2 reduction and organic pollutants degradation is still a key challenge for novel Sillén–Aurivillius oxyhalides. In this work, an S-scheme heterojunction of Bi24O31Cl10 and Bi7Fe2Ti2O17Cl is designed for CO2 reduction and organic pollutants degradation. The as-synthesized 5 % Bi24O31Cl10/Bi7Fe2Ti2O17Cl (BOC/BFTOC-5) composites depict an appealing CO2 reduction and removal rate for RhB organic pollutants in comparison with pristine Bi24O31Cl10 and Bi7Fe2Ti2O17Cl oxyhalides. This fascinating photocatalytic performance could be ascribed to the synergic effect of the enhanced visible light adsorption and photo-generated carriers separation derived from the Bi24O31Cl10/Bi7Fe2Ti2O17Cl heterojunction. Simultaneously, the trapping experiments confirm that the main active species during the catalytic process are the photo-generated hole (h+) and the hydroxy free radical (·OH). This work aims at providing an S-scheme heterojunction via Bi-based oxyhalides for efficient photocatalytic activity.

Carbon Capture and Storage Optimization with Machine Learning

This study examines the potential for enhancing carbon capture and storage (CCS) processes by machine learning to markedly improve performance across diverse capture methods, including as absorption, adsorption, membrane separation, and cryogenic distillation. Through the systematic adjustment of critical operating parameters, including temperature, pressure, flow rates, and sorbent characteristics using machine learning algorithms, we saw significant improvements in CO₂ collection efficiency. The use of optimum operating parameters, namely a temperature range of 40-60°C for absorption and a pressure range of 3-5 bar for adsorption, resulted in a 30% enhancement in capture efficiency. Moreover, machine learning models, namely Random Forest and Support Vector Machines (SVM), achieved a maximum enhancement of 20% in forecasting ideal operating parameters for membrane separation and cryogenic systems. Reduced cycle durations in adsorption processes, facilitated by predictive modeling, resulted in a 15% improvement in CO₂ removal rates. The models’ capacity to forecast sorbent regeneration conditions led to a 10% decrease in energy use. Machine learning algorithms adeptly optimized process-specific parameters, including material composition and flow dynamics, enhancing membrane performance by 18% and cryogenic systems by 12%. These results highlight the significance of using machine learning to customize CCS methods for particular materials and situations, facilitating more sustainable, efficient, and scalable carbon capture systems.

The Mining Industry's Role in Enhanced Weathering and Mineralization for CO2 Removal.

Enhanced weathering and mineralization (EWM) aim to remove carbon dioxide (CO2) from the atmosphere by accelerating the reaction of this greenhouse gas with alkaline minerals. This suite of geochemical negative emissions technologies has the potential to achieve CO2 removal rates of >1 gigatonne per year, yet will require gigatonnes of suitable rock. As a supplier of rock powder, the mining industry will be at the epicenter of the global implementation of EWM. Certain alkaline mine wastes sequester CO2 under conventional mining conditions, which should be quantified across the industry. Furthermore, mines are ideal locations for testing acceleration strategies since tailings impoundments are contained and highly monitored. While some environmentally benign mine wastes may be repurposed for off-site use─reducing costs and risks associated with their storage─numerous new mines will be needed to supply rock powders to reach the gigatonne scale. Large-scale EWM pilots with mining companies are required to progress technology readiness, including carbon verification approaches. With its knowledge of geological formations and ore processing, the mining industry can play an essential role in extracting the most reactive rocks with the greatest CO2 removal capacities, creating supply chains, and participating in life-cycle assessments. The motivations for mining companies to develop EWM include reputational benefits and carbon offsets needed to achieve carbon neutrality.

A Thermodynamics Model for the Assessment and Optimisation of Onboard Natural Gas Reforming and Carbon Capture

The paper examines pre-combustion carbon capture technology (PreCCS) for liquefied natural gas (LNG) propelled shipping from thermodynamics and energy efficiency perspectives. Various types of LNG reformers and CCS units are considered. The steam methane reformer (SMR) was found to be 20% more energy efficient than autothermal (ATR) and methane pyrolysis (MPR) reactors. Pressure swing adsorption (PSA) had a lower energy requirement than membrane separation (MEM), cryogenic separation (CS), and amine absorption (AA) in pre-combustion carbon capture, with PSA needing 0.18 kWh/kg CO2. An integrated system combining SMR and PSA was proposed using waste heat recovery (WHR) from the engine, assuming similar efficiency for LNG and H2 operation, and cooling and liquefying of the CO2 by the LNG. The SMR-PSA system without WHR had an overall efficiency of 33.4% (defined as work at the propeller divided by the total LNG energy consumption). This was improved to 41.7% with WHR and gave a 65% CO2 emission reduction. For a higher CO2 reduction, CCS from the SMR heater could additionally be employed, giving a maximum CO2 removal rate of 86.2% with 39% overall energy efficiency. By comparison, an amine-based post-engine CCS system without reforming could reach similar CO2 removal rates but with 36.6% overall efficiency. The advantages and disadvantages and technology readiness level of PreCCS for onboard operation are discussed. This study offers evidence that pre-combustion CCS can be a serious contender for maritime propulsion decarbonization.Graphical

Numerical modelling and process simulation of a post-combustion CO2 capture pilot plant based on a membrane contactor unit

Hollow fiber membrane contactors (HFMC) have gained prominence in post-combustion CO2 capture applications due to their potential for high mass transfer rates, compactness, modularity and versatility. In this work, two pilot plant design have been proposed, an innovative solution which foresees the membrane contactor as CO2 absorption reactor, and a conventional one based on a packed column absorber. A one-dimensional model based on the resistance-in-series method has been developed for the membrane module and validated against experimental data from literature. The other process units have been simulated in Aspen Plus V11. According to the model results the membrane contactor unit is able to guarantee same levels of CO2 removal rates with improved energy performances compared to the conventional packed column absorber. In particular, if the same reactor volume is considered for the two absorber configurations, a reduction in the specific reboiler duty (SRD) of 8.5% is estimated. On the other hand, if the same liquid-to-gas (L/G) ratio is applied, the HFMC is able to guarantee a required reactor volume almost halved (45% reduction). These substantial improvements of the CO2 capture process could lead to lower investment cost and better economic indicators of the CO2 capture plant.

The effect of initial inoculation amount of microalgae on synergistic purification of biogas slurry

ABSTRACT In this study, Chlorella and Scenedesmus were inoculated in biogas slurry medium with initial inoculum (OD680) of 0.05, 0.1, 0.2, and 0.3, respectively, and 5% CO2 was continuously injected. The study aimed to examine the carbon sequestration capacity of Chlorella and Scenedesmus, as well as the effectiveness of removing pollutants such as TN, TP, and COD in biogas slurry medium. Additionally, an economic efficiency analysis of energy consumption was conducted. The group with an initial inoculum (OD680) of 0.3 for both types of microalgae exhibited better tolerance to pollutants, entered the logarithmic growth stage earlier, promoted nutrient removal, achieved higher energy efficiency, and reduced carbon emissions compared to the other groups. The highest carbon sequestration rates were 18.03% for Chlorella and 11.05% for Scenedesmus. Furthermore, Chlorella demonstrated corresponding nutrient removal efficiencies of 83.03% for TN, 99.84% for TP, and 90.06% for COD, while Scenedesmus exhibited removal efficiencies of 66.35% for TN, 98.74% for TP, and 77.71% for COD. The highest energy efficiency for pollutants and CO2 removal rates for Chlorella were 49.51 ± 2.20 and 9.91 ± 0.44 USD−1, respectively. In conclusion, the findings demonstrate the feasibility of using microalgae for simultaneous purification of biogas and biogas slurry.

Modelling Selective CO2 Absorption and Validation via Photosynthetic Bacteria and Chemical Adsorbents for Methane Purification in Anaerobic Fermentation Bioreactors.

This study delves into advanced methane purification techniques within anaerobic fermentation bioreactors, focusing on selective CO2 absorption and comparing photosynthetic bacteria (PNSB) with chemical adsorbents. Our investigation demonstrates that MgO-Mg(OH)2 composites exhibit remarkable CO2 selectivity over CH4, substantiated through rigorous bulk and surface modelling analyses. To address the challenges posed by MgCO3 shell formation on MgO particles, hindering CO2 transport, we advocate for the utilisation of MgO-Mg(OH)2 composites. In on-site experiments, these composites, particularly saturated MgO-Mg(OH)2 solutions (S2), achieved an astonishing 100% CO2 removal rate within a single day while preserving CH4 content. In contrast, solid MgO powder (S3) retained a mere 5% of CH4 over a 10 h period. Although PNSB (S1) exhibited slower CO2 removal, it excelled in nutrient recovery from anaerobic effluent. We introduce a groundbreaking hybrid strategy that leverages S2's swift CO2 removal and S1 PNSB's nutrient recovery capabilities, potentially resulting in a drastic reduction in bioreactor processing time, from 10 days when employing S1 to just 1 day with the use of S2. This represents a remarkable efficiency improvement of 1000%. This pioneering strategy has the potential to revolutionise methane purification, enhancing both efficiency and sustainability. Importantly, it can be seamlessly integrated into existing bioreactors through an additional CO2 capture step, offering a promising solution for advancing biogas production and promoting sustainable waste treatment practices.

MEA-based CO2 capture: a study focuses on MEA concentrations and process parameters

CO2 capture using monoethanolamine (MEA) is one of the important decarbonization options and often considered as a benchmark, while the optimal MEA contraction and systematic process study are still lacking. In this work, firstly, the MEA concentrations between 15 and 30 wt% were studied from both process simulations with Aspen Plus and experimental measurements in the pilot-scale. 20 wt% MEA was identified as the preferable solution. Subsequently, a systematic analysis was conducted for CO2 capture using 20 wt% MEA with/without CO2 compression to study how various parameters, including gas flow rate, CO2 concentration, and CO2 removal rate, affected the energy demand and techno-economic performances quantitatively. The influence of each parameter on both energy demand and cost showed an obvious non-linear relationship, evidencing the importance of systematic analysis for further study on decarbonization. The evaluation indicated that the regeneration heat required the largest portion of energy demand. The economic analysis showed that the capital cost was more sensitive to the selected parameters than the operational cost, while the operational cost created a major change in the overall cost. In addition, the gas flow rate and CO2 concentration were the main parameters affecting the cost, rather than the CO2 removal rate. Finally, it was suggested that, for a new plant, CO2 capture showed the minimum investment cost per ton CO2 when operating the plant on a large scale, high CO2 concentration, and high CO2 removal rate; for an existing plant, the capture preferred to run with the high CO2 removal rate.