pH Regimes Research Articles

Desorption of Antibiotics from Granular Activated Carbon during Water Treatment by Adsorption

Although desorption of adsorbed pharmaceuticals from granular activated carbon (GAC) may inadvertently lead to their partial discharge with adverse effects on aquatic environments, there have only been a few reports of this phenomenon. This study has investigated desorption of antibiotics vancomycin and rifampicin from activated carbon in aqueous media regarding contact time and pH regime. Various characterizations of the three types of GAC were investigated. Then, antibiotics were loaded on them via adsorption. Subsequently desorption and re-adsorption of antibiotics were quantified for a range of contact times and ambient pH values. Within the first hour of a reversed concentration gradient at neutral pH, desorption released 2% to 54% of previously adsorbed antibiotics to water, which were subsequently re-adsorbed within 24 hours to four weeks with less than 1% antibiotics remaining in the liquid phase. Lower desorption was positively associated with higher GAC mesopore content and larger specific surface area. Effects of the ambient pH regime varied between studied adsorbents. The results are evidence that mesopore content and pore size in relation to the kinetic diameter of adsorbate molecules are important determinants of the extent of antibiotic desorption from GAC and the rates of subsequent re-adsorption. Physisorption was the dominant mechanism involved in both processes. Observed proportions and rates of antibiotic desorption suggest that selection of GAC properties should also consider their effects on unintended desorption and the re-adsorption during treatment processes in order to minimize potential pollution discharge or promotion of antibiotic resistance during treatment processes.

Design of the Particle Size and Morphology of Hard Carbon Anode Materials for Sodium-Ion Batteries Through Hydrothermal Carbonization

With sodium-ion batteries (SIBs) finding widespread application, the demand grows for hard carbon, the most popular anode material for SIBs. Hydrothermal carbonization facilitates the production of hard carbon with desired characteristics from various sources. Despite the considerable volume of literature addressing this subject, there is a notable absence of investigations elucidating the relationship between synthesis conditions and the electrochemical characteristics of the product. Here we study systematically the influence of hydrothermal carbonization parameters on hard carbon characteristics and emphasize the potential of hard carbon as an anode material for SIBs. The initial Coulombic efficiency (ICE) is significantly affected by the particle size of the glucose-derived hard carbon, which, in turn, depends on glucose concentration in the initial solution, pH, and stirring regime. By optimizing the hydrothermal carbonization parameters, the ICE up to 91% and a good reversible capacity of ∼300 mAh g−1 in a half cell are achieved. Full cells with Na3(VO)2(PO4)2F cathode material demonstrate ICE of about 80% and reversible capacity of up to 100 mAh g−1 cath. Considering the effective performance of pouch-cell SIB prototypes based on Na3(VO)2(PO4)2F and hard carbon, hydrothermal carbonization of glucose yields hard carbon with the necessary characteristics required for its successful application in SIBs.

Solfataric Alteration at the South Sulfur Bank, Kilauea, Hawaii, as a Mechanism for Formation of Sulfates, Phyllosilicates, and Silica on Mars

Abstract Solfataric alteration at the South Sulfur Bank of the former Kilauea caldera produced opal, Mg- and Fe-rich smectites, gypsum, and jarosite through silica replacement of pyroclastic Keanakako’i ash and leaching of basaltic lavas. This site on the island of Hawaii serves as an analog for formation of several minerals found in altered deposits on Mars. Two distinct alteration environments were characterized in this study including a light-toned, high-silica, friable outcrop adjacent to the vents, and a bedded outcrop containing alternating orange/tan layers composed of smectite, gypsum, jarosite, hydrated silica, and poorly crystalline ferric oxide phases. This banded unit likely represents deposition of pyroclastic material with variations in chemistry over time that was subsequently altered via moderate hydrothermal and pedogenic processes and leaching of basaltic caprock to enhance the Si, Al, Mg, Fe, and Ca in the altered layers. In the light-toned, friable materials closest to the vents along the base of the outcrop glassy fragments were extensively altered to opal-A plus anatase. Lab measurements of samples returned from the field were conducted to replicate recent instruments at Mars and provide further characterization of the samples. These include elemental analyses, sample texture, XRD, SEM, VNIR/mid-IR reflectance spectroscopy, TIR emittance spectroscopy, and Mössbauer spectroscopy. Variations in the chemistry and mineralogy of these samples are consistent with alteration through hydrothermal processes as well as brines that may have formed through rain interacting with sulfuric fumes. Silica is present in all altered samples and the friable pyroclastic ash material with the strongest alteration contains up to 80 wt.% SiO2. Sulfate mineralization occurred at the South Sulfur Bank through fumarolic action from vents and likely included solfataric alteration from sulfuric gases and steam, as well as oxidation of sulfides in the basaltic caprock. Gypsum and jarosite are typically present in different layers of the altered wall, likely because they require different cations and pH regimes. The presence of both jarosite and gypsum in some samples implies high sulfate concentrations and the availability of both Ca2+ and Fe3+ cations in a brine percolating through the altered ash. Pedogenic conditions are more consistent with the observed Mg-smectites and gypsum in the tan layers, while jarosite and nontronite likely formed under more acidic conditions in the darker orange layers. Assemblages of smectite, Ca-sulfates, and jarosite similar to the banded orange/tan unit in our study are observed on Mars at Gale crater, Noctis Labyrinthus, and Mawrth Vallis, while high-silica outcrops have been identified in parts of Gusev crater, Gale crater, and Nili Patera on Mars.

Germination characteristics of Sorghum bicolor (L.) Moench. under different pH regimes after chemo-priming

Soil pH not only plays a regulatory role in seed germination but also influences seedling development, flowering, and crop yield. The study investigated the germination characteristics of sorghum [Sorghum bicolor (L.) Moench.] under varying pH to understand the potential ameliorative effects of seed priming using plant growth-promoting substances. Seeds were sown in Petri dishes with pH moistened solutions at 1, 3, 5, 7, 9, 11, and 13 respectively. These were replicated five times in the second stage, viable seeds were first primed in 150 ppm indole-3-acetic acid, gibberellic acid, and vitamin C before sowing in pH solutions. The experiment showed no significant changes in morphology or physiology of primed and unprimed seeds and no germination at extreme pH. However, there was a significant difference in the activity of enzymes, germination time, and speed as well as germination percentages of both primed and unprimed seeds. Although chemo-priming did not reverse the effect of pH, it was observed however that vitamin C had a significant effect on germination percentage at higher pH. Germination was observed to be impaired at extreme pH. Seeds did not respond to germination capacity suggesting an optimal pH range of 3 and 11 for germination without priming. However, priming did not show any improved germinability index. Seeds primed in the presence of light showed enhanced germination at pH 7. Generally, the germination index without priming showed better germination characteristics than primed seeds, which suggests pH interactions with primers may be a limiting factor.

Redefined ion association constants have consequences for calcium phosphate nucleation and biomineralization

Calcium orthophosphates (CaPs), as hydroxyapatite (HAP) in bones and teeth are the most important biomineral for humankind. While clusters in CaP nucleation have long been known, their speciation and mechanistic pathways to HAP remain debated. Evidently, mineral nucleation begins with two ions interacting in solution, fundamentally underlying solute clustering. Here, we explore CaP ion association using potentiometric methods and computer simulations. Our results agree with literature association constants for Ca2+ and H2PO4−, and Ca2+ and HPO42-, but not for Ca2+ and PO43− ions, which previously has been strongly overestimated by two orders of magnitude. Our data suggests that the discrepancy is due to a subtle, premature phase separation that can occur at low ion activity products, especially at higher pH. We provide an important revision of long used literature constants, where association of Ca2+ and PO43− actually becomes negligible below pH 9.0, in contrast to previous values. Instead, [CaHPO4]0 dominates the aqueous CaP speciation between pH ~6–10. Consequently, calcium hydrogen phosphate association is critical in cluster-based precipitation in the near-neutral pH regime, e.g., in biomineralization. The revised thermodynamics reveal significant and thus far unexplored multi-anion association in computer simulations, constituting a kinetic trap that further complicates aqueous calcium phosphate speciation.

Assessing the potential of C-phycocyanin as a natural colorant for non-alcoholic carbonated beverages

The multibillion-dollar carbonated beverage industry is currently facing questions from health-conscious consumers over negative health effects of such beverages. Decreasing consumption trends have forced companies to look for healthier choices for their products. C-phycocyanin CPC, a bright blue cyanobacterial pigment with anti-oxidant and other health benefits has been proposed as a candidate in edible drinks. We found that CPC is stable in a wide pH and temperature regime. Reaction kinetics for 12 weeks at 4 °C in non-alcoholic carbonated beverages (B1-B4) showed that B3 (sweetened, ~30 % degradation) best preserved CPC integrity while B1 (non-sweetened, ~87 % degradation) was ineffective. Other beverages (sweetened) could preserve ~ 49 % CPC integrity. Behnajady-Modirshahla-Ghanbary and first order kinetic models explained CPC degradation with and without preservative (sucrose), respectively. The ’consume-by’ times suggest possible refrigeration from ~ 13 hours to 27 days for various CPC-containing beverages. Results suggest CPC could be filter-sterilized and added to non-alcoholic beverages before being packaged in cans or tetra packs to avoid light exposure.Graphical abstract

The effect of in vitro simulated colonic pH gradients on microbial activity and metabolite production using common prebiotics as substrates

BackgroundThe interplay between gut microbiota (GM) and the metabolization of dietary components leading to the production of short-chain fatty acids (SCFAs) is affected by a range of factors including colonic pH and carbohydrate source. However, there is still only limited knowledge on how the GM activity and metabolite production in the gastrointestinal tract could be influenced by pH and the pH gradient increases along the colon.ResultsHere we investigate the effect of pH gradients corresponding to levels typically found in the colon on GM composition and metabolite production using substrates inulin, lactose, galactooligosaccharides (GOS), and fructooligosaccharide (FOS) in an in vitro colon setup. We investigated 3 different pH regimes (low, 5.2 increasing to 6.4; medium, 5.6 increasing to 6.8 and high, 6.0 increasing to 7.2) for each fecal inoculum and found that colonic pH gradients significantly influenced in vitro simulated GM structure, but the influence of fecal donor and substrate was more pronounced. Low pH regimes strongly influenced GM with the decreased relative abundance of Bacteroides spp. and increased Bifidobacterium spp. Higher in vitro simulated colonic pH promoted the production of SCFAs in a donor- and substrate-dependent manner. The butyrate producer Butyricimonas was enriched at higher pH conditions, where also butyrate production was increased for inulin. The relative abundance of Phascolarctobacterium, Bacteroides, and Rikenellaceae also increased at higher colonic pH, which was accompanied by increased production of propionate with GOS and FOS as substrates.ConclusionsTogether, our results show that colonic substrates such as dietary fibres influence GM composition and metabolite production, not only by being selectively utilized by specific microbes, but also because of their SCFA production, which in turn also influences colonic pH and overall GM composition and activity. Our work provides details about the effect of the gradients of rising pH from the proximal to distal colon on fermenting dietary substrates in vitro and highlights the importance of considering pH in GM research.

Modeling the Role in pH on Contaminant Sequestration by Zerovalent Metals: Chromate Reduction by Zerovalent Magnesium.

The role of pH in sequestration of Cr(VI) by zerovalent magnesium (ZVMg) was characterized by global fitting of a kinetic model to time-series data from unbuffered batch experiments with varying initial pH values. At initial pH values ranging from 2.0 to 6.8, ZVMg (0.5 g/L) completely reduced Cr(VI) (18.1 μM) within 24 h, during which time pH rapidly increased to a plateau value of ∼10. Time-series correlation analysis of the pH and aqueous Cr(VI), Cr(III), and Mg(II) concentration data suggested that these conditions are controlled by combinations of reactions (involving Mg0 oxidative dissolution and Cr(VI) sequestration) that evolve over the time course of each experiment. Since this is also likely to occur during any engineering applications of ZVMg for remediation, we developed a kinetic model for dynamic pH changes coupled with ZVMg corrosion processes. Using this model, the synchronous changes in Cr(VI) and Mg(II) concentrations were fully predicted based on the Langmuir-Hinshelwood kinetics and transition-state theory, respectively. The reactivity of ZVMg was different in two pH regimes that were pH-dependent at pH < 4 and pH-independent at the higher pH. This contrasting pH effect could be ascribed to the shift of the primary oxidant of ZVMg from H+ to H2O at the lower and higher pH regimes, respectively.

Molecular mechanisms and environmental adaptations of flagellar loss and biofilm growth of Rhodanobacter under environmental stress.

Biofilms aid bacterial adhesion to surfaces via direct and indirect mechanisms, and formation of biofilms is considered as an important strategy for adaptation and survival in suboptimal environmental conditions. However, the molecular underpinnings of biofilm formation in subsurface sediment/groundwater ecosystems where microorganisms often experience fluctuations in nutrient input, pH, and nitrate or metal concentrations are underexplored. We examined biofilm formation under different nutrient, pH, metal, and nitrate regimens of 16 Rhodanobacter strains isolated from subsurface groundwater wells spanning diverse levels of pH (3.5 to 5) and nitrates (13.7 to 146mM). Eight Rhodanobacter strains demonstrated significant biofilm growth under low pH, suggesting adaptations for survival and growth at low pH. Biofilms were intensified under aluminum stress, particularly in strains possessing fewer genetic traits associated with biofilm formation, findings warranting further investigation. Through random barcode transposon-site sequencing (RB-TnSeq), proteomics, use of specific mutants, and transmission electron microscopy analysis, we discovered flagellar loss under aluminum stress, indicating a potential relationship between motility, metal tolerance, and biofilm growth. Comparative genomic analyses revealed the absence of flagella and chemotaxis genes and the presence of a putative type VI secretion system in the highly biofilm-forming strain FW021-MT20. In this study we identified genetic determinants associated with biofilm growth under metal stress in a predominant environmental genus, Rhodanobacter, and identified traits aiding survival and adaptation to contaminated subsurface environments.

Low-Cost and Scalable Electrodes for Anodic Production of Hydrogen Peroxide Via 2e- Water Oxidation

Hydrogen peroxide (H2O2) is a crucial chemical that is widely utilized in various industrial processes. The conventional anthraquinone process for H2O2 production has limitations in terms of energy consumption, high costs, and waste generation [1]. An alternative, greener and more sustainable approach is the electrochemical production of H2O2 from oxygen and water using renewable energy. Our research group has been extensively investigating the two electron (2e-) water oxidation reaction (WOR) for production of H2O2 using various electrode materials, including metal oxides, commercial carbon materials, and boron-doped diamond (BDD) [2, 3]. We also investigated the role of carbonate ions (HCO3 - and CO3 2-) in the process of water oxidation to H2O2. The enhancing effect e of CO3 2- ions on anodic H2O2 production was studied in a continuous flow reactor, where the optimal flow rate, process configuration and cell design, and chemical stabilizer were determined. Among other parameters, chemical composition and pH regime of the electrolyte were found to be crucial.Recently, we explored the use of graphite bipolar plates (BPP) as a low-cost alternative to BDD electrodes for anodic H2O2 generation [4]. Three different commercial BPPs with varying fluoropolymer content were examined, and a correlation was found between fluoropolymer content and H2O2 generation. In that study we found that a BPP sample with high fluoropolymer content resulted in a stable H2O2 production for up to 100 hours at a current density of 200 mA cm–2, with a constant faradaic efficiency of 40%. The results demonstrate that low-cost commercial carbon electrode materials can selectively oxidize water to H2O2, enabling economically viable technical applications of anodic H2O2 production.

Dual contrast CEST MRI for pH-weighted imaging in stroke.

pH enhanced (pHenh ) CEST imaging combines the pH sensitivity from amide and guanidino signals, but the saturation parameters have not been optimized. We propose pHdual as a variant of pHenh that suppresses background signal variations, while enhancing pH sensitivity and potential for imaging ischemic brain injury of stroke. Simulation and in vivo rodent stroke experiments of pHenh MRI were performed with varied RF saturation powers for both amide and guanidino protons to optimize the contrast between lesion/normal tissues, while simultaneously minimizing signal variations across different types of normal tissues. In acute stroke, contrast and volume ratio measured by pHdual imaging were compared with an amide-CEST approach, and perfusion and diffusion MRI. Simulation experiments indicated that amide and guanidino CEST signals exhibit unique sensitivities across different pH ranges, with pHenh producing greater sensitivity over a broader pH regime. The pHenh data of rodent stroke brain demonstrated that the lesion/normal tissue contrast was maximized for an RF saturation power pair of 0.5 μT at 2.0 ppm and 1.0 μT at 3.6 ppm, whereas an optimal contrast-to-variation ratio (CVR) was obtained with a 0.7 μT saturation at 2.0 ppm and 0.8 μT at 3.6 ppm. In acute stroke, CVR optimized pHenh (i.e., pHdual ) achieved a higher sensitivity than the three-point amide-CEST approach, and distinct patterns of lesion tissue compared to diffusion and perfusion MRI. pHdual MRI improves the sensitivity of pH-weighted imaging and will be a valuable tool for assessing tissue viability in stroke.

Germination characteristics of Sorghum bicolor (L.) Moench under different pH regimes after chemopriming.

Germination characteristics of Sorghum bicolor (L.) Moench under different pH regimes after chemopriming.

Insights into the stress corrosion cracking propagation behavior of Alloy 690 and 316 L stainless steel in KOH versus LiOH oxygenated water

The stress corrosion cracking (SCC) propagation behavior of 20% cold worked 316 L stainless steel (SS) and Alloy 690 was investigated in high-temperature oxygenated water. No discernable effect was observed at the same pH level for LiOH or KOH. Increasing pH could dramatically enhance the crack growth rates (CGRs) due to the dissolution of Cr-rich oxide film and the weakening of passivity in high pH regimes. The similarities in SCC behavior and cracking characteristics indicate that the cracking mechanism of both austenite alloys occurs by a slip-dissolution model.

NADH and NADPH peroxidases as antioxidant defense mechanisms in intestinal sulfate-reducing bacteria

Animal and human feces typically include intestinal sulfate-reducing bacteria (SRB). Hydrogen sulfide and acetate are the end products of their dissimilatory sulfate reduction and may create a synergistic effect. Here, we report NADH and NADPH peroxidase activities from intestinal SRB Desulfomicrobium orale and Desulfovibrio piger. We sought to compare enzymatic activities under the influence of various temperature and pH regimes, as well as to carry out kinetic analyses of enzymatic reaction rates, maximum amounts of the reaction product, reaction times, maximum rates of the enzyme reactions, and Michaelis constants in cell-free extracts of intestinal SRB, D. piger Vib-7, and D. orale Rod-9, collected from exponential and stationary growth phases. The optimal temperature (35 °C) and pH (7.0) for both enzyme’s activity were determined. The difference in trends of Michaelis constants (Km) during exponential and stationary phases are noticeable between D. piger Vib-7 and D. orale Rod-9; D. orale Rod-9 showed much higher Km (the exception is NADH peroxidase of D. piger Vib-7: 1.42 ± 0.11 mM) during the both monitored phases. Studies of the NADH and NADPH peroxidases—as putative antioxidant defense systems of intestinal SRB and detailed data on the kinetic properties of this enzyme, as expressed by the decomposition of hydrogen peroxide—could be important for clarifying evolutionary mechanisms of antioxidant defense systems, their etiological role in the process of dissimilatory sulfate reduction, and their possible role in the development of bowel diseases.

Removal enhancement of dielectric barrier discharge reactor using heterogeneous gC3N4 catalyst modified by doping with oxygen and CuO

In this study, the hybrid process of the heterogeneous catalyst of CuO/O-gC3N4/dielectric barrier discharge is utilized to destruct aqueous dye solution. To recognize the property of the synthesized catalyst, a range of optical, morphological, electrochemical, and textural experiments were conducted. The experimental lab phase is comparatively completed between sole dielecteric barrier discharge reactor and combined with catalyst process for tartrazine aqueous dye removal. The variations of initial pH, pollutant concentration, catalyst concentration and flow regime were investigated. The research findings represent the best result for both processes obtained at a pH = 3, catalyst dosage of 800 mg/L, intensity power of 13.5 kV, and initial dye concentration of 10 mg/L. The addition of nanocomposite into the dielectric barrier discharge reactor strengthens the charge flux and increase radical generation within plasma medium for the degradation improvement. The radical scavenger investigation of process mechanism introduces OH as the key degradation radical for the dielectric barrier discharge reactor alone and combined with catalyst that are effectively involved through the entire processes, respectively.

Warmer and more acidic conditions enhance performance of an endemic low shore gastropod.

Changing ocean temperatures are predicted to challenge marine organisms, especially when combined with other factors, such as ocean acidification. Acclimation, as a form of phenotypic plasticity, can however, moderate the consequences of changing environments for biota. Our understanding of how altered temperature and acidification together influence species acclimation responses is, however, limited compared to responses to single stressors. This study investigated how temperature and acidification affected the thermal tolerance and righting speed of the Girdled Dogwhelk, Trochia cingulata (Linnaeus, 1771). Whelks were acclimated for two weeks to combinations of three temperatures (11°C: cold, 13°C: moderate and 15°C: warm) and two pH regimes (8.0: moderate and 7.5: acidic). We measured the temperature sensitivity of righting response by generating thermal performance curves from individual data collected at seven test temperatures and determined critical thermal minima (CTmin) and maxima (CTmax). We found that T. cingulata has a broad basal thermal tolerance range (∼38°C) and after acclimation to the warm temperature regime, both the optimal temperature for maximum righting speed and CTmax increased. Contrary to predictions, acidification did not narrow this population's thermal tolerance but increased CTmax. These plastic responses are likely driven by the predictable exposure to temperature extremes measured in the field which originate from the local tidal cycle and the periodic acidification associated with ocean upwelling in the region. This acclimation ability suggests that T. cingulata has at least some capacity to buffer the thermal changes and increased acidification predicted to occur with climate change.

Assessing the colloidal stability of copper doped ZIF-8 in water and serum

Colloidal formulations to treat cardiovascular conditions are urgently needed since diseases like atherosclerosis are a major societal burden and agonizing for affected individuals. Copper ions and zinc ions as well as correctly dosed nitric oxide (NO) have long been known to alleviate these pathologies. Herein, we present strategies for size-controlled crystallization of copper-doped Zeolitic Imidazolate Framework 8 (ZIF-8). The colloidal stability and structural integrity of copper-doped ZIF-8 was assessed in water and blood serum. Key findings of the present study include that structural integrity of colloidal copper doped ZIF-8 in blood serum is maintained over several days, while disintegration occurs more quickly in water. Further, we confirmed the known ability of copper-doped ZIF-8 micro-particles to convert blood borne s-nitrosothiols into nitric oxide for the presented colloidal formulations. Nitric Oxide conversion was more moderate and sustained in colloidal copper-doped ZIF-8 formulations compared to free copper ions in solution, which is crucial for many biomedical applications. Another key finding of the present study is that the onset of rapid structural disintegration of copper-doped ZIF-8 occurs at pH 5.5, which is a common physiological pH regime of atherosclerotic plaques. Colloidal particles are known to accumulate in atherosclerotic plaques and the presented system may be a valuable addition to the emerging field of nanomedicines for atherosclerosis treatment. The present study has evaluated the colloidal stability and structural integrity, establishing required material characteristics needed for biological evaluation of the material in future dedicated studies.

PH-Responsive Self-Assembled Compartments as Tuneable Model Protocellular Membrane Systems.

Prebiotically plausible single-chain amphiphiles are enticing as model protocellular compartments to study the emergence of cellular life, owing to their self-assembling properties. Here, we investigated the self-assembly behaviour of mono-N-dodecyl phosphate (DDP) and mixed systems of DDP with 1-dodecanol (DDOH) at varying pH conditions. Membranes composed of DDP showed pH-responsive vesicle formation in a wide range of pH with a low critical bilayer concentration (CBC). Further, the addition of DDOH to DDP membrane system enhanced vesicle formation and stability in alkaline pH regimes. We also compared the high-temperature behaviour of DDP and DDP:DDOH membranes with conventional fatty acid membranes. Both, DDP and DDP:DDOH mixed membranes possess packing that is similar to decanoic acid membrane. However, the micropolarity of these systems is similar to phospholipid membranes. Finally, the pH-dependent modulation of different phospholipid membranes doped with DDP was also demonstrated to engineer tuneable membranes with potential translational implications.

Monitoring the hydration behavior of hardened cement paste affected by different environmental pH regimes

The purpose of this paper is to investigate the hydration behavior of hardened Portland cement paste cured in different environmental pH values by compressive strength, XRD, TG-DTG and EIS. Meanwhile, a newly proposed equivalent circuit model is built to establish the correlation between the electrochemical parameters and compressive strength of cement paste. The results show that the matrix strength, hydration products and pore structure of hardened cement paste are significantly affected by different pH values. According to the in-situ nondestructive monitoring of EIS, the evaluating for the matrix strength of cement-based materials can be achieved by calculating the resistivity of discontinuous connected pores (Rcp) in the recommended equivalent circuit model.

Towards optimal inorganic carbon delivery to microalgae culture

Microalgae offer the potential to sequestrate CO2 and reduce the world's dependency on fossil fuels, thereby mitigating the greenhouse gas effect, which has resulted in climate change over time. Carbon is one of the critical nutrients for microalgae growth and product formation; the choice of carbon and pH control techniques has been identified as the key to improving the sustainability of microalgae cultivation. However, supplying CO2 in the gas phase is not cost-effective and could be counterproductive as a high percentage could be lost back to the atmosphere due to low solubility in the medium. Additionally, using conventional pH control techniques such as acid, base, and buffers is expensive at scale. This study assessed freshwater Chlorella sorokiniana cultivation using NaHCO3 solely as the inorganic carbon and for pH modulation. The investigation focuses on the effect of bicarbonate feed rates and culture starting pH in the acidic, neutral, and basic regimes on the pH modulation, biomass accumulation, and product yield in a fed-batch system. The final pH increased beyond the upper limit threshold for each pH regime, with the highest level of control achieved in the basic regime (7.50–8.48 ± 0.11). The maximum biomass accumulation reached 2.49 g/L and a doubling time of 49 h. Evaluation of the pigment showed a higher chlorophyll a content, 25.85 mg/L, similar to a CO2-fed culture and higher than the bicarbonate culture reported. The lipid contents showed a fatty acid composition suitable for biodiesel production with a higher percentage of saturated fatty acids (SFAs) (62.93 %–90.86 %) across all conditions. The sole use of bicarbonate for simultaneous inorganic carbon supply and pH control can be a cost-effective measure without compromising biomass and lipid productivities.