CO2 Sparging Research Articles

Enhanced microbial electrosynthesis performance with 3-D algal electrodes under high CO2 sparging: Superior biofilm stability and biocathode-plankton interactions

Microbial electrosynthesis (MES) shows great promise for converting CO2 into high-value chemicals. However, cathode biofilm erosion by high CO2 sparging and the unclear role of plankton in MES hinders the continuous improvement of its performance. This study aims to enhance biofilm resistance and improve interactions between bio-cathode and plankton by upgrading waste algal biomass into 3-D porous algal electrode (PAE) with rough surface. Results showed that the acetate synthesis of PAE under 20 mL/min CO2 sparging (PAE-20) was up to 3330.61 mol/m3, 4.63 times that of carbon felt under the same conditions (CF-20). The microbial loading of PAE-20 biofilm was twice that of CF-20. Furthermore, higher cumulative abundance of functional microorganisms was observed in plankton of PAE-20 (55 %), compared to plankton of CF-20 (14 %), and enhanced biocathode-plankton interactions significantly suppressed acetate consumption. Thus, this efficient and sustainable 3-D electrode advances MES technology and offers new perspectives for waste biomass recycling.

Chain elongation in continuous microbial electrosynthesis cells: The effect of pH and precursors supply

Microbial electrosynthesis (MES) enables the production of carbon-neutral chemicals using CO2 as a carbon source. Acetic acid is the main MES product, but recent studies show the direct production of elongated carboxylic acids, e.g., butyric and caproic acid. However, the production of elongated acids in MES systems is still inefficient due to the low growth rates of acetogenic bacteria and to limited solventogenic rates. Subsequently, researchers have produced elongated carboxylic acids directly from acetic acid or have operated MES systems at low pH to favor solventogenesis. However, the effect the addition of different chain elongation precursors and the operation pH exerts in the bioelectrochemical production of elongated acids remains unclear. To investigate this, three pH-controlled MES systems were operated in this study with continuous liquid and gas supply. MES systems elongating acetic acid at pH 6 achieved higher butyric (0.71 vs. 0.42 g L−1) and caproic acid (0.71 vs. 0.42 g L−1) titers in the absence of CO2 sparging. Additionally, lowering the pH to 5 in the MES systems fed with CO2 and acetic acid improved the elongated acids titers, reaching 0.72 g L−1 butyric and 0.33 g L−1 caproic acid. The 16 S rRNA analysis showed the community was dominated by Oscillibacter at pH 6, and by Clostridium at pH 5. Furthermore, the first scanning electron microscopy pictures revealing biofilm stratification in MES cathodes were taken in this study, where homogeneous rod-shaped bacteria biofilm layers, in contact with the graphite cathode, were covered by heterogeneous biofilm layers.

Microbial electrolysis cells designed for BioH2 production: Potential improvements with carbon dioxide and nitrogen

The long-term feasibility and efficiency of microbial electrolysis cells (MECs) depend primarily upon several crucial parameters. However, they show promise for sustainably producing biohydrogen (bioH2). This study investigates a newly designed biohydrogen reactor by studying the effects of several variables on the production of bioH2, including applied voltage, electrode material, and gas sparging with CO2 and N2. The study aims to optimize the system for improved efficiency and production performance. The results of this study show that both electrode type and applied voltage affect bioH2 production where choosing the right inoculum has a significant impact on the catalytic efficiency. The aluminum electrodes significantly help produce the most bioH2 production at 2.0 V with 884 mL/L in 11.25 min, while emphasizing the significance of material characteristics. The reduced partial pressure from CO2 sparging, up to a point, improves bioH2 generation. The N2 gas sparging further demonstrates an increased efficiency where the ideal flow rates are dependent on the size of the MEC system. The highest bioH2 production rates for CO2 and N2 sparging are measured as 821 mL/L and 813 mL/L in 4.25 min and 11.50 min at a volume of 400 mL/min and 300 mL/min, respectively. The results of this study further advance our knowledge of and ability to optimize MEC systems for long-term, sustainable bioH2 production.

Low electric current in a bioelectrochemical system facilitates ethanol production from CO using CO-enriched mixed culture.

Fossil resources must be replaced by renewable resources in production systems to mitigate green-house gas emissions and combat climate change. Electro-fermentation utilizes a bioelectrochemical system (BES) to valorize industrial and municipal waste. Current electro-fermentation research is mainly focused on microbial electrosynthesis using CO2 for producing commodity chemicals and replacing petroleum-based infrastructures. However, slow production rates and low titers of metabolites during CO2-based microbial electrosynthesis impede its implementation to the real application in the near future. On the other hand, CO is a highly reactive gas and an abundant feedstock discharged from fossil fuel-based industry. Here, we investigated CO and CO2 electro-fermentation, using a CO-enriched culture. Fresh cow fecal waste was enriched under an atmosphere of 50% CO and 20% CO2 in N2 using serial cultivation. The CO-enriched culture was dominated by Clostridium autoethanogenum (≥89%) and showed electro-activity in a BES reactor with CO2 sparging. When 50% CO was included in the 20% CO2 gas with 10 mA applied current, acetate and ethanol were produced up to 12.9 ± 2.7 mM and 2.7 ± 1.1 mM, respectively. The coulombic efficiency was estimated to 148% ± 8% without an electron mediator. At 25 mA, the culture showed faster initial growth and acetate production but no ethanol production, and only at 86% ± 4% coulombic efficiency. The maximum optical density (OD) of 10 mA and 25 mA reactors were 0.29 ± 0.07 and 0.41 ± 0.03, respectively, whereas it was 0.77 ± 0.19 without electric current. These results show that CO electro-fermentation at low current can be an alternative way of valorizing industrial waste gas using a bioelectrochemical system.

Colloids with reversible stability switched by tris[2‐(dimethylamino)ethyl]amine

AbstractThe addition of salt can irreversibly disrupt the stability of both emulsions and polymer latex. The reversible conversion of amines into organic ammonium salts can be induced by CO2 stimulation, thereby enabling the switching of colloids. The switchable amine, tris[2‐(dimethylamino)ethyl]amine (Me6TRAN), was selected for the study. The electrical conductivity of an aqueous solution of Me6TRAN is modulated by the introduction and removal of CO2. The critical micelle concentration of sodium dodecyl benzene sulfonate (SDBS) was observed to decrease from 1.0 × 10−3 to 5.0 × 10−4 M upon the introduction of Me6TRAN, as confirmed by surface tension measurements conducted under CO2. The emulsion of crude oil, which comprised of SDBS and Me6TRAN, underwent reversible destruction and restoration upon exposure to CO2 and N2. The PMMA latex exhibited a clear phase separation subsequent to CO2 sparging, but attained homogeneity upon N2 sparging. This study is anticipated to introduce a novel avenue for emulsion or polymer latex that can undergo demulsification and emulsification through CO2 stimulation.

Fouling management in oceanic carbon capture via in-situ electrochemical bipolar membrane electrodialysis

To assist reaching net-zero emissions, the dissolved carbon in the ocean can be extracted to enable an indirect air capture. An electrochemical bipolar membrane electrodialysis (BPMED) is a sustainable method for such capture. The BPMED enables a pH-swing that manipulates the oceanic carbonate-equilibrium using electricity. However, at alkaline-pH, an in-situ process suffers from inorganic fouling within the stack, increasing the cost of capture. In the current work, we investigate fouling management strategies including fouling control (i.e., membrane- configuration and current-flow rate optimization) and fouling removal methods. Fouling removal methods including air and CO2(g) sparging, dissolved CO2 (aq) cleaning, back-pressure, flow rate increase, and acid-wash are investigated under accelerated fouling conditions. The stack configuration containing the BPM-AEM pairs shows 4 × lower fouling than the BPM-CEM stack, while the carbonate-extraction and faradaic efficiency are similar for both configurations. From the scaling removal methods, only the acid wash combined with the back-pressure removed all the inorganic fouling, recovering both the cell voltage and pressure drop to their initial values. Upon the air sparging, the total cell voltage and pressure drop increased even more due to the trapped gas inside the netted spacers. Cleaning via dissolved and gaseous CO2 decreases the cell pH, dissolving hydroxide/carbonate-based fouling, but decreases the carbonate-removal significantly which is not preferred. Applying the back-pressure and higher flow rates decelerated the scaling buildup but was not enough to remove the fouling. Using BPM-AEM stacks in combination with periodic acid cleaning has potential as resilient oceanic carbon removal via BPMED.

Bifunctional Ionic Deep Eutectic Electrolytes for CO2 Electroreduction.

CO2 is a low-cost monomer capable of promoting industrially scalable carboxylation reactions. Sustainable activation of CO2 through electroreduction process (ECO2R) can be achieved in stable electrolyte media. This study synthesized and characterized novel diethyl ammonium chloride−diethanolamine bifunctional ionic deep eutectic electrolyte (DEACl–DEA), using diethanolamine (DEA) as hydrogen bond donors (HBD) and diethyl ammonium chloride (DEACl) as hydrogen bond acceptors (HBA). The DEACl–DEA has −69.78 °C deep eutectic point and cathodic electrochemical stability limit of −1.7 V versus Ag/AgCl. In the DEACl–DEA (1:3) electrolyte, electroreduction of CO2 to CO2•– was achieved at −1.5 V versus Ag/AgCl, recording a faradaic efficiency (FE) of 94%. After 350 s of continuous CO2 sparging, an asymptotic current response is reached, and DEACl–DEA (1:3) has an ambient CO2 capture capacity of 52.71 mol/L. However, DEACl–DEA has a low faradaic efficiency <94% and behaves like a regular amine during the CO2 electroreduction process when mole ratios of HBA–HBD are greater than 1:3. The electrochemical impedance spectroscopy (EIS) and COSMO-RS analyses confirmed that the bifunctional CO2 sorption by the DEACl–DEA (1:3) electrolyte promote the ECO2R process. According to the EIS, high CO2 coverage on the DEACl–DEA/Ag-electrode surface induces an electrochemical double layer capacitance (EDCL) of 3.15 × 10–9 F, which is lower than the 8.76 × 10–9 F for the ordinary DEACl–DEA/Ag-electrode. COSMO-RS analysis shows that the decrease in EDCL arises due to the interaction of CO2 non-polar sites (0.314, 0.097, and 0.779 e/nm2) with that of DEACl (0.013, 0.567 e/nm2) and DEA (0.115, 0.396 e/nm2). These results establish for the first time that a higher cathodic limit beyond the typical CO2 reduction potential is a criterion for using any deep eutectic electrolytes for sustainable CO2 electroreduction process.

Accelerating mineral carbonation in hydraulic fracturing flowback and produced water using CO2-rich gas

Mineral carbonation is a Carbon Capture Utilization and Storage (CCUS) technique that can be used to remove or divert carbon dioxide (CO2) from the atmosphere and store it in carbonate minerals. Hydraulic fracturing flowback and produced water (FPW) is Ca- and Mg-rich wastewater generated by the petroleum industry that can be used to sequester CO2 in benign minerals. Here, we describe the rate and efficiency of mineral carbonation achieved by sparging 10% CO2/90% N2 gas into pH-adjusted FPW, collected from the Duvernay Formation in the Western Canadian Sedimentary Basin. Our results indicate that calcite (CaCO3) precipitated at the expense of brucite [Mg(OH)2] dissolution following CO2 injection; as such, no Mg-carbonate precipitates were formed. The carbonation reaction reached steady state within 1 h and 14.2% of the aqueous Ca in the FPW was precipitated as calcite, sequestering 1.56 ± 0.33 g CO2 L−1 of FPW. Our dissolved inorganic carbon measurements, geochemical models, and stable carbon isotope results indicate that CO2 mineralization can be maximized by maintaining solution at pH ≥ 10 during CO2 sparging. If all of the Ca and Mg in the FPW could be carbonated, it would offer a greater CO2 sequestration potential of 12.5 ± 0.3 g CO2 L−1.

Separate Reclamation of Oil and Surfactant from Oil-in-Water Emulsion with a CO2-Responsive Material.

Oil-in-water (O/W) emulsion is one type of oily wastewater produced by many industries. The treatment of and resource recovery from O/W emulsions are very challenging. Unlike bulk or floating oil, which can be successfully abstracted from wastewater by hydrophobic/oleophilic materials, the abstraction of emulsified oil is not easy because of its highly hydrophilic surface composed of dense surfactants. Separate reclamation of miscible oil and surfactant through a green approach is even more difficult. Here, we report that a CO2-responsive material can abstract emulsified oil and demulsify the oil droplets. Moreover, it can release the abstracted oil and surfactant separately. This material exhibited a very high adsorption capacity for emulsified oil (14 g g-1). Upon switching the surface wettability of the material under CO2 or synthetic flue gas sparging, coalesced oil was reclaimed while the surfactant was retained inside the pores. The hydrophobic character of the material was retrieved when CO2 was purged with nitrogen sparging or air heating. Then, the surfactant was reclaimed by elution with diluted alkali/ethanol. Oil and surfactant were thus separately reclaimed from the O/W emulsion. High rates of oil removal, oil recovery, and surfactant recovery were maintained during repeated adsorption/desorption operations. This work provides a potentially sustainable and green way for O/W emulsion treatment and resource recovery.

Multi-objective tailored optimization deciphering carbon partitioning and metabolomic tuning in response to elevated CO2 levels, organic carbon and sparging period.

Microalgae have garnered much contemplation as candidates to fix CO2 into valuable compounds. Although microalgae have been studied to produce various metabolites, they have not yet proved successful for commercialization. Since, handling such problems practically requires satisfying multiple parameters simultaneously, we put forth a multi-parameter optimization strategy to manipulate the carbon metabolism of Scenedesmus sp. to improve biomass production and enhance CO2 fixation to increase the production of fuel-related metabolites. The Box-Behnken design method was applied with CO2 concentration, CO2 sparging time and glucose concentration as independent variables; biomass and total fatty acid methyl ester (total FAME) content were analyzed as response variables. The strain is supplemented with both CO2 and glucose with an aim to enhance carbon flux and rechannel it towards carbon fixation. As per the results obtained in this study, Scenedesmus sp. could effectively exploit high CO2 concentration (15%) for longer duration under high concentration of glucose supplementation (9g/L) producing a biomass of 635.24±39.9μg/mL with a high total fatty acid methyl ester (FAME) content of 71.29±4.2μg/mg, significant acetyl-CoA carboxylase enzyme activity and a favorable fatty acid profile: 35.8% palmitic acid, 10.5% linoleic acid and 30.6% linolenic acid. The carbohydrate content was maximum at 10% CO2 sparged for the longest duration of 90min under glucose concentration of 9g/L. This study puts forth an optimal design that can provide evidence on comprehending the carbon assimilation mechanism to enhance production of biomass and biofuels and provide conditions to microalgal species to tolerate CO2 rich flue gas.

Microbiota associated with the large-scale outdoor cultivation of the cyanobacterium Synechococcus sp. PCC 7002

The model euryhaline cyanobacterium Synechococcus sp. PCC 7002 has potential as a platform for biotechnological applications because of its genetic amenability and fast growth rates. The purpose of this work was to measure the outdoor productivity metrics of Synechococcus sp. PCC 7002, which we tested by cultivation in 110 L flat-panel photobioreactors and 1025 L open raceway ponds at the Algae Testbed Public Private Partnership (ATP3) algae culturing testbed site at the Arizona Center for Algae Technology and Innovation (AzCATI). This work was carried out during the summer growing season when ambient temperatures and light availability are highest to support maximum photoautotrophic biomass yields. Modifications to the traditional A+ laboratory growth media for Synechococcus sp. PCC 7002 included the use of urea as a nitrogen source, and CO2 sparging for automated pH control in open ponds. Synechococcus showed robust growth in flat-panel photobioreactors, which are suited for the containment of modified organisms; however, cultivation in the open-raceway pond system was challenging due to pond crashes. We investigated the microbiota associated with Synechococcus pond cultures using Illumina amplicon sequencing of the 16S rRNA genes of bacteria and archaea and the 18S rRNA genes of microbial eukaryotes, to identify potential competitor and predator genera. These results pointed to likely predation of Synechococcus by a ciliated protozoan of the genus Euplotes. Development of crop protection strategies will be crucial for enabling the mass cultivation of Synechococcus in open pond systems.

Designing a Strategy for pH Control to Improve CHO Cell Productivity in Bioreactor.

Background:Drastic pH drop is a common consequence of scaling up a mammalian cell culture process, where it may affect the final performance of cell culture. Although CO2 sparging and base addition are used as common approaches for pH control, these strategies are not necessarily successful in large scale bioreactors due to their effect on osmolality and cell viability. Accordingly, a series of experiments were conducted using an IgG1 producing Chinese Hamster Ovary (CHO-S) cell culture in 30 L bioreactor to assess the efficiency of an alternative strategy in controlling culture pH.Methods:Factors inducing partial pressure of CO2 and lactate accumulation (as the main factors altering culture pH) were assessed by Plackett-Burman design to identify the significant ones. As culture pH directly influences process productivity, protein titer was measured as the response variable. Subsequently, Central Composite Design (CCD) was employed to obtain a model for product titer prediction as a function of individual and interaction effects of significant variables.Results:The results indicated that the major factor affecting pH is non-efficient CO2 removal. CO2 accumulation was found to be affected by an interaction between agitation speed and overlay air flow rate. Accordingly, after increasing the agitation speed and headspace aeration, the culture pH was successfully maintained in the range of 6.95–7.1, resulting in 51% increase in final product titer. Similar results were obtained during 250 L scale bioreactor culture, indicating the scalability of the approach.Conclusion:The obtained results showed that pH fluctuations could be effectively controlled by optimizing CO2 stripping.

Carboxylic acids production and electrosynthetic microbial community evolution under different CO2 feeding regimens

Microbial electrosynthesis (MES) is a potential technology for CO2 recycling, but insufficient information is available on the microbial interactions underpinning electrochemically-assisted reactions. In this study, a MES reactor was operated for 225 days alternately with bicarbonate or CO2 as carbon source, under batch or continuous feeding regimens, to evaluate the response of the microbial communities, and their productivity, to dynamic operating conditions. A stable acetic acid production rate of 9.68 g m-2 d-1, and coulombic efficiency up to 40%, was achieved with continuous CO2 sparging, higher than the rates obtained with bicarbonate (0.94 g m-2 d-1) and CO2 under fed-batch conditions (2.54 g m-2 d-1). However, the highest butyric acid production rate (0.39 g m-2 d-1) was achieved with intermittent CO2 sparging. The microbial community analyses focused on differential amplicon sequence variants (ASVs), allowing detection of ASVs significantly different across consecutive samples. This analysis, combined with co-occurence network analysis, and cyclic voltammetry, indicated that hydrogen-mediated acetogenesis was carried out by Clostridium, Eubacterium and Acetobacterium, whereas Oscillibacter and Caproiciproducens were involved in butyric acid production. The cathodic community was spatially inhomogeneous, with potential electrotrophs, such as Sulfurospirillum and Desulfovibrio, most prevalent near the current collector. The abundance of Sulfurospirillum positively correlated with that of Acetobacterium, supporting the syntrophic metabolism of both organisms.

Pilot outdoor cultivation of an extreme alkalihalophilic Trebouxiophyte in a floating photobioreactor using bicarbonate as carbon source

As an alternative carbon supply approach in the microalgae cultivation process, bicarbonate shows many advantages over the conventional method of CO2 sparging and may have great applicability in the future. However, the optimal bicarbonate concentrations for high biomass productivity and carbon utilization efficiency (CUE) are usually different, and a method to simultaneously achieve both of them is lacking. In this study, the CUE and biomass productivity of an isolated alkalihalophilic Trebouxiophyte in bicarbonate-based cultivation condition was investigated. The results showed that CUE decreased as the bicarbonate concentration increased, where the highest CUE of 96.7 ± 0.25% was achieved in a culture with 100 mmol L−1 bicarbonate, while the highest biomass density of 1.40 ± 0.01 g L−1 was produced in a 300 mmol L−1 bicarbonate culture. The bicarbonate concentration of 300 mmol L−1 was selected for a balance between CUE and biomass productivity. Under this concentration, the Trebouxiophyte cultured at high light intensity had higher CUE (46.01 ± 0.65%) and biomass productivity (0.80 g L−1 d−1) than those with 2% CO2. The outdoor cultivation in the floating photobioreactor produced a higher biomass concentration (0.603 g L−1), highest areal biomass productivity (10.1 g m−2 d−1), and CUE (22.61 ± 0.03%) than those in an open pond, which was 0.377 ± 0.01 g L−1, 5.36 g m−2 d−1 and 11.65 ± 0.01%. These results indicated that Trebouxiophyte can be efficiently produced with bicarbonate as the sole carbon source, and provided a good example to select a balanced bicarbonate concentration to simultaneously achieve high biomass productivity and CUE.

Feeding tricarboxylic acid cycle intermediates improves lactate consumption and antibody production in Chinese hamster ovary cell cultures.

Media components play an important role in modulating cell metabolism and improving product titer in mammalian cell cultures. To sustain cell productivity, highly active oxidative metabolism is desired. Here we explored the effect of tricarboxylic acid (TCA) cycle intermediates supplementation on lactate metabolism and productivity in Chinese hamster ovary fed-batch cultures. Direct addition of 5 mM alpha-ketoglutarate (α-KG), malic acid, or succinic acid in the basal medium did not have any significant impact on culture performance. On the other hand, feeding α-KG, malic acid, and succinic acid in the stationary phase, either as a single solution or as a mixture, significantly improved lactate consumption, reduced ammonium accumulation, and led to higher cell specific productivity and antibody titer (~35% increase for the best condition). Delivering those intermediates as an acidic solution for pH control eliminated CO2 sparging and accumulation. Feeding TCA cycle intermediates was also demonstrated to be superior to feeding lactic acid or pyruvic acid in titer improvement. Taken together, feeding TCA cycle intermediates was effective in improving lactate consumption and increasing product titer, which is likely due to enhanced oxidative metabolism in an extended duration.

Application of computational fluid dynamics to raceways combining paddlewheel and CO2 spargers to enhance microalgae growth

The present study investigated the effect of light intensity and mixing on microalgae growth in a raceway by comparing the performance of a paddlewheel to a combination of paddlewheel and CO2 spargers in a 20L raceway. The increase of light intensity was known to be able to increase the microalgal growth rate. Increasing paddlewheel rotation speed from 13 to 30rpm enhanced C.vulgaris growth by enhancing culture mixing. Simulation results using computational fluid dynamics (CFD) indicated that both the turnaround areas of the raceway and the area opposite the paddlewheel experienced very low flow velocities (dead zones) of less than 0.1m/min, which could cause cell settling and slow down growth. The simulated CFD velocity distribution in the raceway was validated by actual velocity measurements. The installation of CO2 spargers in the dead zones greatly increased flow velocity. The increase of paddlewheel rotation speed reduced the dead zones and hence increased algal biomass production. By complementing the raceway paddlewheel with spargers providing CO2 at 30mL/min, we achieved a dry cell weight of 5.2±0.2g/L, which was about 2.6 times that obtained without CO2 sparging.

Carbon dioxide fixation coupled with ammonium uptake by immobilized Scenedesmus obliquus and its potential for protein production

In this study, immobilized Scenedesmus obliquus (S. obliquus) was proposed to simultaneously alleviate the carbon dioxide (CO2) and ammonium (NH4+-N). Two trophic modes of autotrophy and mixotrophy were conducted by batch experiments with a period of 5 days. The results shown that NH4+-N could be removed more efficiently if algal cells were immobilized, and the trophic mode change had no significant effect on immobilized S. obliquus to NH4+-N removal under 5% CO2 sparging. Specifically, immobilized S. obliquus could remove NH4+-N completely at initial concentrations of 30 and 50 mg/L and reached about 80% removal rate of NH4+-N at the concentration of 70 mg/L under both trophic modes. The protein synthesis was its main removal mechanism and the dominant amino acid components including glutamic acid (Glu), cystine (Cys), arginine (Arg), methionine (Met) and lysine (Lys) were sensitive to NH4+-N assimilation.

Effects of crystalline nanocellulose on wastewater-cultivated microalgal separation and biomass composition

Microalgae are renewable and promising feedstock rich in biochemicals for biofuel and bioenergy production. The viability of this technology relies on the energy- and cost-efficient cultivation (culture medium used) and harvesting (coagulant applied) processes. The natural coagulant of crystalline nanocellulose modified with 1-(3-aminopropyl) imidazole (CNC-APIm) was demonstrated as a green and recyclable coagulant for microalgal harvesting. However, optimisation is still needed to ensure its applicability to microalgae cultivated on wastewaters, no effect on biomass composition, as well as cost-effective harvesting. In this study, microalgal growth and nutrient removal capacity of Chlorella vulgaris (C. vulgaris) were first investigated on two types of municipal wastewaters. C. vulgaris grew well on both primary and 30% (v/v) diluted centrate wastewaters with biomass productivities of 0.071 ± 0.005 and 0.062 ± 0.006 g/(L·d), respectively. High nitrogen and phosphorus removal efficiencies (91.1–100%) were obtained. Subsequently, the wastewater-cultivated C. vulgaris was harvested using a novel natural coagulant of crystalline nanocellulose modified with 1-(3-aminopropyl) imidazole (CNC-APIm). Based on the optimization results of the Design of Experiments driven response surface methodology approach, the optimal conditions for maximum HEs (86.5%) and RCs (38.5 g-algae/g-CNC) responses were determined for C. vulgaris under the following conditions: 0.02 g-CNC-APIm/g-algae of mass ratio, 5 s of CO2 sparging time, 8 min of air sparging time, and 50 ml/min of air flow rate. Moreover, no statistically significant differences were observed in the contents of carbohydrate, protein, lipid and fatty acids in the biomass harvested by centrifugation and CNC-APIm, respectively, suggesting that CNC-APIm would not impact the downstream microalgal application. According to the rough technical and economical estimation, CNC-APIm will be an alternative to conventional coagulants for commercial microalgal harvesting application.

Effective bioreactor pH control using only sparging gases.

pH control is critical in bioreactor operations, typically realized through a two-sided control loop, where CO2 sparging and base addition are used in bicarbonate-buffered media. Though a common approach, base addition could compromise culture performance due to the potential impact from pH excursions and osmolality increase in large-scale bioreactors. In this study, the feasibility of utilizing control of sparge gas composition as part of the pH control loop was assessed in Chinese hamster ovary (CHO) fed-batch cultures. Fine pH control was evaluated in multiple processes at different setpoints in small-scale ambr®250 bioreactors. Desired culture pH setpoints were successfully maintained via air sparge feedback control. As part of the pH control loop, air sparging was increased to improve CO2 removal automatically, hence increase culture pH, and vice versa. The effectiveness of this pH control strategy was seamlessly transferred from ambr®250 to 200 L scale, demonstrating scalability of the proposed methodology. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 35: e2743, 2019.

ATRP Catalyst Removal and Ligand Recycling Using CO2-Switchable Materials

We have designed three approaches to remove copper catalyst and recycle the ligands after atom transfer radical polymerizations, all based on using materials whose properties can be switched using only CO2 and any nonacidic gas (e.g., air, nitrogen, and argon) as triggers. The first approach involves use of a CO2-switchable solvent (Cy2NMe, N,N-dicyclohexylmethylamine) as the medium for the ATRP reaction. After addition of water to the polymerized reaction mixture and sparging with CO2, the polymer precipitates while the copper salt remains in the solvent. The second approach involves using a conventional ATRP solvent such as toluene to conduct the polymerization. Following polymerization, addition of water and CO2 sparging result in the ligand (Me6TREN) and copper salt transferring into the aqueous phase, while the polymer remains in the organic phase. Finally we demonstrate the effectiveness of the approach in ARGET ATRP using less ligand and copper salt. Residual copper in the polymer was <30 ppb using the switchable solvent and <15 ppb in toluene, while residual nitrogen was <90 ppm using the switchable solvent and <35 ppb in toluene. The feasibility of recovering and reusing the ligand for subsequent polymerizations is also established.