CO2 Supplementation Research Articles

The MpsAB Bicarbonate Transporter Is Superior to Carbonic Anhydrase in Biofilm-Forming Bacteria with Limited CO2 Diffusion.

ABSTRACTCO2 and bicarbonate are required for carboxylation reactions, which are essential in most bacteria. To provide the cells with sufficient CO2, there exist two dissolved inorganic carbon supply (DICS) systems: the membrane potential-generating system (MpsAB) and the carbonic anhydrase (CA). Recently, it has been shown that MpsAB is a bicarbonate transporter that is present not only in photo- and autotrophic bacteria, but also in a diverse range of nonautotrophic microorganisms. Since the two systems rarely coexist in a species but are interchangeable, we investigated what advantages the one system might have over the other. Using the genus Staphylococcus as a model, we deleted the CA gene can in Staphylococcus carnosus and mpsABC genes in Staphylococcus aureus. Deletion of the respective gene in one or the other species led to growth inhibition that could only be reversed by CO2 supplementation. While the S. carnosus Δcan mutant could be fully complemented with mpsABC, the S. aureus ΔmpsABC mutant was only partially complemented by can, suggesting that MpsAB outperforms CA. Interestingly, we provide evidence that mucus biofilm formation such as that involving polysaccharide intercellular adhesin (PIA) impedes the diffusion of CO2 into cells, making MpsAB more advantageous in biofilm-producing strains or species. Coexpression of MpsAB and CA does not confer any growth benefits, even under stress conditions. In conclusion, the distribution of MpsAB or CA in bacteria does not appear to be random as expression of bicarbonate transporters provides an advantage where diffusion of CO2 is impeded.IMPORTANCE CO2 and bicarbonate are required for carboxylation reactions in central metabolism and biosynthesis of small molecules in all bacteria. This is achieved by two different systems for dissolved inorganic carbon supply (DICS): these are the membrane potential-generating system (MpsAB) and the carbonic anhydrase (CA), but both rarely coexist in a given species. Here, we compared both systems and demonstrate that the distribution of MpsAB and/or CA within the phylum Firmicutes is apparently not random. The bicarbonate transporter MpsAB has an advantage in species where CO2 diffusion is hampered—for instance, in mucus- and biofilm-forming bacteria. However, coexpression of MpsAB and CA does not confer any growth benefits, even under stress conditions. Given the clinical relevance of Staphylococcus in the medical environment, such findings contribute to the understanding of bacterial metabolism and thus are crucial for exploration of potential targets for antimicrobials. The knowledge gained here as exemplified by staphylococcal species could be extended to other pathogenic bacteria.

Sustainable Hydrates for Enhanced Carbon Dioxide Capture from an Integrated Gasification Combined Cycle in a Fixed Bed Reactor.

An increase in temperature of up to 2 °C occurs when the amount of CO2 reaches a range of 450 ppm. The permanent use of mineral oil is closely related to CO2 emissions. Maintaining the sustainability of fossil fuels and eliminating and reducing CO2 emissions is possible through carbon capture and storage (CCS) processes. One of the best ways to maintain CCS is hydrate-based gas separation. Selected type T1-5 (0.01 mol % sodium dodecyl sulphate (SDS) + 5.60 mol % tetrahydrofuran (THF), with the help of this silica gel promotion was strongly stimulated. A pressure of 36.5 bar of CO2 is needed in H2O to investigate the CO2 hydrate formation. Therefore, ethylene glycol monoethyl ether (EGME at 0.10 mol %) along with SDS (0.01 mol %) labeled as T1A-2 was used as an alternative to THF at the comparable working parameters in which CO2 uptake of 5.45 mmol of CO2/g of H2O was obtained. Additionally, it was found that with an increase in tetra-n-butyl ammonium bromide (TBAB) supplementation of CO2, the hydrate and operating capacity of the process increased. When the bed height was reduced from 3 cm to 2 cm with 0.1 mol % TBAB and 0.01% SDS (labelled as T3-2) in fixed bed reactor (FBR), the outcomes demonstrated a slight expansion in gas supply to 1.54 mmol of CO2/g of H2O at working states of 283 K and 70 bar. The gas selectivity experiment by using the high-pressure volume analysis through hydrate formation was performed in which the highest CO2 uptake for the employment of silica contacts with water in fuel gas mixture was observed in the non-IGCC conditions. Thus, two types of reactor configurations are being proposed for changing the process from batch to continuous with the employment of macroporous silica contacts with new consolidated promoters to improve the formation of CO2 hydrate in the IGCC conditions. Later, much work should be possible on this with an assortment of promoters and specific performance parameters. It was reported in previous work that the repeatability of equilibrium moisture content and gas uptake attained for the sample prepared by the highest rates of stirring was the greatest with the CIs of ±0.34 wt % and ±0.19 mmol of CO2/g of H2O respectively. This was due to the amount of water occluded inside silica gel pores was not an issue or in other words, vigorous stirring increased the spreadability. The variation of pore size to improve the process can be considered for future work.

Evaluation of high rate ponds operational and design strategies for algal biomass production and domestic wastewater treatment

This study evaluated the effect of high rate ponds (HRPs) depth on algal biomass production during domestic wastewater treatment. HRPs were evaluated for 20, 30, and 40 cm depths, with and without CO2 supplementation. In addition, 40 cm deep HRP with ultraviolet (UV) pre-disinfection was evaluated. The concentration of chlorophyll-a as a function of time for each evaluated condition was represented by logistic models that were after submitted to cluster analysis. The 20 cm HRPs presented higher chlorophyll-a concentration, reaching a maximum of 5.8 and 4.3 mg L−1, in the HRPs with and without CO2 addition, respectively. Ammonia nitrogen and soluble phosphorus were greater removed in shallower HRPs. The addition of CO2 influenced the nutrient removal processes, optimizing nutrient recovery by biomass assimilation. HRP configuration did not influence organic matter removal (~40% of removal efficiency in all HRPs), predominant microalgae genera (Chlorella sp. and Scenedesmus), and E. coli inactivation (removal of ~2 log units), except for the 20 cm HRP without CO2 that had removal of 4 log units due to high pH values. For HRPs with CO2 addition and UV pre-disinfection, the models for 40 cm were grouped together with those obtained for 30 cm HRPs, indicating the same behavior for chlorophyll-a production as a function of time. Thus, it can be concluded that the evaluated strategies represent alternatives for reducing HRP area requirements. Moreover, results may represent advancement and major contributions for HRP design criteria.

Technologies for improving microalgae biomass production coupled to effluent treatment: A life cycle approach

Algal biomass production in wastewater is a promising value-adding alternative that should be coupled to the treatment system. The technical aspects of cultivation systems for improved biomass yield have been widely reported in the literature; yet, their environmental performance can still be further studied and compared. This study evaluated the environmental impacts associated with the production of 1 kg of biomass grown in high-rate ponds, with domestic effluent as culture media. Seven systems with three approaches to cultivation were modeled through the life cycle assessment method: using effluent pre-treated with ultraviolet disinfection; with supplementation from industrial CO2 and with exhaust gas from gasoline combustion; coupled with a biofilm reactor for biomass attached growth. Environmental impacts were also compared to a base cultivation using the ReCiPe method, for 13 impact categories. The environmental impacts were reduced at least 30% by using wastewater as a water and nutrient source, with systems reaching negative impact values. The only exception was eutrophication categories, with the highest normalized impacts along with toxicity-related categories. The system using CO2 supply from exhaust gas from gasoline combustion had the best performance in 11 categories, reducing impacts in at least 56% compared to a base cultivation scenario. The most impactful process was industrial CO2 supplementation, followed by biofilm. Coupling industrial CO2 supply and hybrid systems for increased biomass productivity did not compensate environmentally, increasing impacts up to 227%. Scenario evaluations were performed for increased and worsened performance of CO2 supply rates (±40%) and biofilm reactor lifespan (±20 days). Opportunities to improve lie in the use of recovered gas from different industries and different support materials for the attached growth of biomass in hybrid systems.

Recycle of nitrogen and phosphorus in hydrothermal liquefaction biochar from Galdieria sulphuraria to cultivate microalgae

Hydrothermal liquefaction (HTL) of G. sulphuraria (GS) has been demonstrated to produce energy-dense biocrude oil, water-soluble chemicals, and biochar. The recycling of nutrients from HTL water-soluble chemicals for algae cultivation has been demonstrated. The current study evaluated the feasibility of using HTL biochar, a by-product to recover nutrients and use the nutrients to cultivate microalgae without inhibition. GS biomass was liquefied to produce biocrude oil, biochar, water phase, and gasses under subcritical water conditions (300 °C, 15 MPa & 30 min). The N and P content in the HTL biochar were ~5.27 wt.% and ~15.98 wt.%, respectively. Both nutrients were leached from the biochar at varied pH values with ~40.23% of phosphate and ~70.01% of ammoniacal nitrogen recovery obtained at a pH of 0.5. The leached phosphates and ammoniacal nitrogen were added to N and P free Cyanidium medium (CM) for cultivating GS. Growth experiments were carried out in microtiter plates and culture tube reactors at 40 °C and with CO₂ (2–3%) supplementation. Similar growth rates were observed in cultures supplemented with the leached nutrients when compared to controls in standard CM growth media proving the absence of inhibition in the former. Comprehensive characterization of HTL biochar by Inductively Coupled Plasma Optical Emission Spectrometry, bomb calorimeter, and Scanning Electron Microscope is also presented. This study confirmed the feasibility of recovering nutrients from GS biochar and using these nutrients to cultivate algae successfully without inhibition, thus supporting reduced steps for recycling, process optimization, and HTL technology commercialization.

Insights into the influence of CO2 supplement on phycoremediation and lipid accumulation potential of microalgae: An exploration for biodiesel production

An economic and environmentally friendly approach for sustainable wastewater treatment, CO 2 abatement, and resource recovery via assimilation into biomass would be — Phycoremediation. Thus an attempt was made to investigate the effect of CO 2 gas supplement on an ozone pre-treated tannery effluent (OPTE) accustomed microalgae Nannochloropsis oculata , Chlorella vulgaris, and Chlorella sorokiniana for their nutrient removal efficiency, biomass productivity, CO 2 fixing rate, lipid content, and fatty acid composition in OPTE. The experiments were conducted in a glass reactor maintained at optimized cultivation conditions within the algal chamber. In which, the CO 2 gas was supplied intermittently through a glass tube immersed in the reactor. Among the species studied, C.sorokiniana has revealed its better performance towards nutrient removal i.e. NH 4 + -N (96%) and o-PO 4 3 − (100%) with the maximum biomass yield and CO 2 fixation rate of 2.1 ± 0.15 g/L and 0.48 g CO 2 / L/d respectively. While the results recommended the N. oculata for biodiesel production owing to its maximum lipid accumulation potential (51%) and lipid yield (703 ± 2.8 mg/L). Further, the predicted biodiesel properties of N. oculata were good associations with the standard biodiesel quality. Thus, the phycoremediation of OPTE with the supplement of CO 2 can be considered as a sustainable treatment method owing to the recovery of value-added biomass for biodiesel production. • CO 2 supplement has a significant influence on phycoremediation and lipid content. • C.sorokiniana revealed better performance towards nutrient removal — C, N & P. • The maximum biomass yield and CO 2 fixation rate were attained with C.sorokiniana . • FAME profile suggested N. oculata — a suitable feedstock for biodiesel production. • The predicted biodiesel properties were in line with the standard biodiesel quality.

A novel nanoemulsion-based microalgal growth medium for enhanced biomass production

BackgroundMicroalgae are well-established feedstocks for applications ranging from biofuels to valuable pigments and therapeutic proteins. However, the low biomass productivity using commercially available growth mediums is a roadblock for its mass production. This work describes a strategy to boost algal biomass productivity by using an effective CO2 supplement.ResultsIn the present study, a novel nanoemulsion-based media has been tested for the growth of freshwater microalgae strain Chlorella pyrenoidosa. Two different nanoemulsion-based media were developed using 1% silicone oil nanoemulsion (1% SE) and 1% paraffin oil nanoemulsion (1% PE) supplemented in Blue-green 11 media (BG11). After 12 days of cultivation, biomass yield was found highest in 1% PE followed by 1% SE and control, i.e., 3.20, 2.75, and 1.03 g L−1, respectively. The chlorophyll-a synthesis was improved by 76% in 1% SE and 53% in 1% PE compared with control. The respective microalgal cell numbers for 1% PE, 1% SE and control measured using the cell counter were 3.00 × 106, 2.40 × 106, and 1.34 × 106 cells mL−1. The effective CO2 absorption tendency of the emulsion was highlighted as the key mechanism for enhanced algal growth and biomass production. On the biochemical characterization of the produced biomass, it was found that the nanoemulsion-cultivated C. pyrenoidosa had increased lipid (1% PE = 26.80%, 1% SE = 23.60%) and carbohydrates (1% PE = 17.20%, 1% SE = 18.90%) content compared to the control (lipid = 18.05%, carbohydrates = 13.60%).ConclusionsThis study describes a novel nanoemulsion which potentially acts as an effective CO2 supplement for microalgal growth media thereby increasing the growth of microalgal cells. Further, nanoemulsion-cultivated microalgal biomass depicts an increase in lipid and carbohydrate content. The approach provides high microalgal biomass productivity without altering morphological characteristics like cell shape and size as revealed by field emission scanning electron microscope (FESEM) images.Graphical abstract

Cysteiniphilum marinum sp. nov., isolated from coastal seawater.

Six aerobic Gram-negative bacteria were isolated from seawater in Guangdong Province, P.R. China. Cells were observed to be Gram-negative, aerobic, non-motile and non-spore forming. Growth of the designated type strain 19X3-30T occurred at a temperature range of 14-37°C (optimum, 28°C), a pH range of 6.0-8.0 (optimum, pH 7) and up to 7.5% NaCl (optimum, 1.5%; w/v), and was enhanced by CO2 and L-cysteine supplementation. The major polar lipids identified in strain 19X3-30T were diphosphatidylglycerol, phosphatidylethanolamine and phosphatidylglycerol. The principal cellular fatty acids profile showed the presence of anteiso-C15:0, anteiso-C17:0 and C18:0 (> 8% of total fatty acids), and the respiratory quinone was ubiquinone 8 (UQ-8). According to the analysis of 16S rRNA gene sequences, these strains represented a novel species within the family Fastidiosibacteraceae, sharing maximum similarities with Cysteiniphilum litorale DSM 101832T (96.6%) and Cysteiniphilum halobium DSM 103992T (95.3%). Phylogenetic dendrograms based on 16S rRNA gene and protein marker genes from the genomic sequences both indicated that the strains formed a monophyletic lineage closely linked to the genus Cysteiniphilum, which was also supported by the UPGMA dendrogram based on the MALDI-TOF MS profile. The genomic DNA G + C contents of six strains ranged from 38.0% to 38.1%. Based on different taxonomic genomic metrics, phylogeny and phenotypic features, we propose that the strains warrant the assignment to a novel species, for which the name Cysteiniphilum marinum sp. nov. is proposed. The type strain is 19X3-30T (= KCTC 82154T = CGMCC 1.18585T).

A sustainable process train for a marine microalga-mediated biomass production and CO2 capture: A pilot-scale cultivation of Nannochloropsis salina in open raceway ponds and harvesting through electropreciflocculation

Major challenges in cultivation, harvesting, CO2 capture and downstream processing of microalgae biomass have to be confronted for successful commercial deployment. This study explored a sustainable process train to mass-produce a native marine algal strain, Nannochloropsis salina, for biocrude production and CO2 capture. The microalga was cultivated in a 3-m2 raceway pond with manual agitation, 10-m2 raceway ponds with and without CO2 supplementation and a 120-m2 pond with CO2 supplementation using carbonation column reactor (CCR). During the above experiments, the areal productivities obtained ranged from 7.5 to 34.4 g m−2 d−1 and the lipid content was between 29 and 80%. This study also demonstrated a novel 10 KLPD (kilolitres per day) capacity electropreciflocculation (ePF) reactor (∼0.56–0.78 KWh/KL) and filter press for biomass harvesting with 98.24% efficiency. The CO2 capture of N. Salina estimated was in the range of 45.38–208.12 tons ha−1 y−1, and the average was 95.39 tons ha−1 y−1. The cost estimated based on the 120-m2 pond trials was $3.46/kg of dry algal biomass. Thus the findings provide immense scope for future research on large-scale cultivation of Nannochloropsis salina for biofuel production and carbon capture applications.

Anaerobic digestate abattoir effluent (ADAE), a suitable source of nutrients for Arthrospira platensis cultivation

Untreated as well as partially treated anaerobic digestate abattoir effluent (ADAE) were used for the cultivation of Arthrospira platensis in this study. The effect of CO2 addition on the biomass productivity, nutrient removal efficiency and biochemical composition were also investigated. Arthrospira platensis exhibited significant improved growth in raw ADAE when alkalinity of the medium was adjusted to 6.3 g L−1 using NaHCO3. Addition of CO2 resulted in 20% increase in biomass productivity and higher ammoniacal nitrogen removal rate (99.0%) when compared to the cultures with no CO2 supplementation. No significant differences were found in protein (50.2%) and phycocyanin (12.0%) content of A. platensis cultivated in raw ADAE supplemented with HCO3− and that grown in synthetic Zarrouk medium. This study demonstrated that raw ADAE can be successfully used as culture media for A. platensis when its alkalinity is adjusted using bicarbonate. Such an approach would reduce the need of freshwater and external synthetic nutrients for A. platensis cultivation if the aim is to produce reclaimable water as well as biomass rich in protein content and phycocyanin for potential use as an animal and aquaculture feed.

Assessment of the performance of an anoxic-aerobic microalgal-bacterial system treating digestate

The performance of an anoxic-aerobic microalgal-bacterial system treating synthetic food waste digestate at 10 days of hydraulic retention time via nitrification-denitrification under increasing digestate concentrations of 25%, 50%, and 100% (v/v) was assessed during Stages I, II and III, respectively. The system supported adequate treatment without external CO2 supplementation since sufficient inorganic carbon in the digestate was available for autotrophic growth. High steady-state Total Organic Carbon (TOC) and Total Nitrogen (TN) removal efficiencies of 85–96% and 73–84% were achieved in Stages I and II. Similarly, PO43−-P removals of 81 ± 15% and 58 ± 4% were recorded during these stages. During Stage III, the average influent concentrations of 815 ± 35 mg TOC·L−1, 610 ± 23 mg TN·L−1, and 46 ± 11 mg PO43−-P·L−1 induced O2 limiting conditions, resulting in TOC, TN and PO43−-P removals of 85 ± 3%, 73 ± 3%, and 28 ± 16%, respectively. Digestate concentrations of 25% and 50% favored nitrification-denitrification mechanisms, whereas the treatment of undiluted digestate resulted in higher ammonia volatilization and hampered nitrification-denitrification. In Stages I and II, the microalgal community was dominated by Chlorella vulgaris and Cryptomonas sp., whereas Pseudoanabaena sp. was more abundant during Stage III. Illumina sequencing revealed the presence of carbon and nitrogen transforming bacteria, with dominances of the genera Gemmata, Azospirillum, and Psychrobacter during Stage I, II, and III, respectively. Finally, the high settleability of the biomass (98% of suspended solids removal in the settler) and average C (42%), N (7%), P (0.2%), and S (0.4%) contents recovered in the biomass confirmed its potential for agricultural applications, contributing to a closed-cycle management of food waste.

Influence of Nitrogen to Phosphorus Ratio and CO2 Concentration on Lipids Accumulation of Scenedesmus dimorphus for Bioenergy Production and CO2 Biofixation.

The potential of Scenedesmus dimorphus microalgae for CO2 biofixation and lipid biosynthesis for bioenergy applications was evaluated in this study. Batch experiments were conducted using synthetic tertiary municipal wastewater samples at several nitrogen to phosphorus (NP) ratios (1 : 1 to 8 : 1) and CO2 concentrations (∼0%, 2%, 4%, and 6% CO2 in supplied air). Scenedesmus dimorphus was cultivated for 25 days and the growth is highly dependent on the CO2 concentration and the NP ratio. An NP ratio of 2 : 1 produces a biomass yield of 733 mg/L when the microalga culture was supplied with air enriched with 2% CO2 . The maximum CO2 biofixation rate of 49.6 mg L-1 d-1 is at an NP ratio of 8 : 1 with 4% CO2 . A colorimetric technique depending on sulpho-phospho-vanillin (SPV) was utilized for the determination of the intracellular lipid content. The highest lipid content of 31.6% as the dry weight of the biomass is at an NP ratio of 1 : 1 and 6% CO2 . These results indicate that supplementation of suitable CO2 with favorable NP ratio has a considerable effect on lipid accumulation in the microalgae Scenedesmus dimorphus biomass.

Engineering an efficient H2 utilizing Escherichia coli platform by modulation of endogenous hydrogenases

Abstract H2 is extensively available from geological reservoirs, industrial byproducts or natural processes, which makes H2 an ideal supplemental substrate providing additional reductive equivalents for increasing anaerobic fermentation efficiency. While it has been applied broadly in industrial and pharmaceutical fileds, Escherichia coli was not shown to efficiently utilize hydrogen. To construct a versatile biological platform for efficient utilization of H2, the endogenous hydrogenase genes of E. coli were investigated. Consequently, overexpression of the endogenous hydrogenases Hyd-1 and Hyd-2 induced respective 26.5 % and 36.7 % increases of succinate yield, indicating that both Hyd-1 and Hyd-2 contributed to the increased pool of reductive equivalents. Additionally, simultaneously modulating the expression of hya and hyb genes by introducing the strong promoter P10 resulted in the higher yield of succinate. To further improve the utilization of H2, pathway of rTCA cycle and CO2 supplementation were engineered in the strain ZL014(pBTCA), which produced the highest succinate yield of 1.50 mol per mol glucose. Our work successfully engineered a novel E. coli platform that could efficiently utilize H2, which could be employed to construct a variety of microbial cell factories requiring substantial amounts of reductive equivalents.

Greenhouse Carbon Dioxide Supplementation with Irrigation and Fertilization Management of Geranium and Fountain Grass

Increase in ambient carbon dioxide (CO2) concentration is beneficial for plant growth due to increased photosynthesis and water use efficiency. A greenhouse study was conducted to investigate how supplemented CO2 influences optimal irrigation and fertilization management for production of two ornamental plants. Two identical greenhouses were used, with one having CO2 supplementation and the other serving as the control with ambient CO2 concentration. Tensiometer-based irrigation treatments were applied at soil tensions of –5, –10, and –15 kPa with 0-, 3-, 6-, or 9-g controlled-release fertilizer rates applied in factorial with irrigation treatments. Plugs of geranium ‘Pinto Premium Rose Bicolor’ and fountain grass were grown under experimental conditions for 12 and 16 weeks, respectively. The results showed that CO2 supplementation increased the dry weight of geranium ‘Pinto Premium Rose Bicolor’ and fountain grass by 35% and 39%, respectively. Under the two driest irrigation regimes (–10 and –15 kPa), photosynthesis of geranium ‘Pinto Premium Rose Bicolor’ increased with CO2 supplementation compared with the ambient condition. Similarly, for fountain grass, the moderately watered (–10 kPa) treatment had a greater rate of photosynthesis with greater fertilizer rates of 6 or 9 g. CO2 supplementation resulted in increased water use efficiency of both species, whereas rate of transpiration was lower only in fountain grass. Among different fertilizer rates, 6- or 9-g fertilizer rates had greater values for dry weight, number of flowers, and stomatal conductance in both species. Therefore, it can be concluded that CO2 supplementation can help in efficient use of water for greenhouse production of ornamental plants.

Production of algal oil from power plant algae

ABSTRACT Algae growing in the thermal power plant environment are considered as waste for the power industry. But the algal biomass could act as efficient CO2-bio-sequester as they are adapted to grow under high CO2 concentration and the algal oil extracted from those algae is a cheap source of bio-diesel or green energy, thus mitigating the environmental pollution and conversion of ‘waste-to-wealth’. The present study aims at the production of bio-oil from a macro-alga, Pithophora varia collected and identified from water bodies of a thermal-power-plant in India. The oil productivity of the alga can be correlated with the biomass growth. The alga was cultivated in Erlenmeyer-flasks with external CO2 supplementation of 0.15 mole fraction in air. The light intensity 10,897 lux was incident on the flask’s wall when placed under sunlight for 8 h. Simultaneously, oil yield of 18.7% has been measured before subjecting the alga to the growth and starvation phase. An increase in oil-yield was measured on day 9 for both growth (26.2%) and starvation phases (29.3%). During growth phase, initiation of conversion of reserve food materials to lipid granules advocates for the oil yield. But the increment in lipid productivity during the starvation phase might have resulted due to nutrient deficiency and initiation of the stimulation of lipid-synthetic pathways towards the formation of triacylglceride.

On-demand release of CO2 from photothermal hydrogels for accelerating skin wound healing

Acceleration of skin wound healing is an important aspect of wound treatment. The use of carbon dioxide (CO2) has been recognized as one of the most effective ways to improve microcirculation and to benefit wound healing, while the need of the specialized equipment and the uncontrollable delivery of gas CO2 might restrict such strategy in wide applications. Herein, we develop a photothermal hydrogel for the on-demand and localized delivery of CO2 to accelerate skin wound healing by combining thermoresponsive block copolymer (BCP) of Pluronic F127 and carbon nanoparticles (CNPs) with amino groups, which can be used for loading CO2 precursor of bicarbonate for controlled release. We show that by rationally optimizing the content of the thermoresponsive BCP in the photothermal hydrogel, a liquid-to-solid transition triggered by the body temperature can be achieved. Under light irradiation, the CNPs can convert light into heat, triggering the decomposition of the bicarbonate, and the photothermal hydrogel can thus locally release CO2 in the wound site. Wound healing can be accelerated by improving local microcirculation disturbance and increasing tissue oxygen concentration. This study provides a new opportunity for local CO2 supplement for accelerating wound healing.

Supplemental CO2 improves oxygen saturation, oxygen tension, and cerebral oxygenation in acutely hypoxic healthy subjects.

Oxygen is viewed in medicine as the sole determinant of tissue oxygenation, though carbon dioxide homeostasis is equally important and clinically often ignored. The aims of this study were as follows: (a) to examine the effects of different acute hypoxic conditions on partial pressure of arterial oxygen (PaO2), arterial oxygen saturation of hemoglobin (SaO2), and regional cerebral saturation of hemoglobin (rSO2); and (b) to evaluate supplemental CO2 as a tool to improve oxygenation in acutely hypoxic individuals. We hypothesized that exposure to gas mixtures with added CO2 would improve oxygenation in hypoxic human subjects. Twenty healthy subjects were exposed to 5‐min intervals of two gas mixtures: hypoxic gas mixture containing 8% oxygen, and a CO2‐enriched mixture containing 8% oxygen plus either 3% or 5% CO2. Ten subjects received the 3% CO2‐enriched mixture, and the remaining 10 subjects received the 5% CO2‐enriched mixture. The order of exposure was randomized. Blood gases, pulse oximetry, end‐tidal CO2, and cerebral oximetry were measured. Compared to the purely hypoxic gas group, PaO2 was increased in the 3% and 5% CO2‐enriched groups by 14.9 and 9.5 mmHg, respectively. Compared to pure hypoxia, SaO2 was increased in the 3% and 5% CO2‐enriched groups by 16.8% and 12.9%, respectively. Both CO2‐enriched gas groups had significantly higher end‐exposure rSO2 and recovered to baseline rSO2 within 1 min, compared to the pure hypoxic gas group, which returned to baseline in 5 min. These results suggest that in acutely hypoxic subjects, CO2 supplementation improves blood oxygen saturation and oxygen tension as well as cerebral oxygenation measures.

Special issue in honour of Prof. Reto J. Strasser - Photosynthesis response of microalgae (Tetradesmus wisconsinensis) to different inorganic carbon sources probed with chlorophyll fluorescence analysis

Bicarbonate is an alternative carbon source for production of photosynthetic microalgae, although sparging of CO2-enriched gas is commonly practised, its efficiency seems to be scarcely considered. This study evaluated the photosynthetic activities of microalgae (Tetradesmus wisconsinensis) using chlorophyll fluorescence under different concentrations of bicarbonate (HCO3-) and CO2. Chlorophyll fluorescence analysis showed noticeable difference in photosynthetic activity between the bicarbonate (HCO3-) and CO2 supplied cultures. The JIP-test parameters obtained for the cultures supplemented by HCO3- or CO2 were distinct, but of similar values in quantum yield of PSII. The typical polyphasic rise, called the OJIP curves, showed a typical difference between the treatments at the J and I inflection of the fluorescence transient curve. Both HCO3- (20 mM) and CO2 (5%, v/v) gave higher biomass yield than the other carbon regimes, i.e., 673 ± 12 and 658 ± 11 mg L-1, respectively. We concluded that bicarbonate resulted in similar photosynthetic yield as CO2 supplementation.

Special issue in honour of Prof. Reto J. Strasser - A comparative chlorophyll a fluorescence study on isolated cells and intact leaves of Bouteloua gracilis (blue grama grass)

Bouteloua gracilis (blue grama grass) is one of the most drought and grazing tolerant plants in the short-grass ecosystem. To obtain information on their photosystem activities, we measured the fast (< 1 s) chlorophyll a fluorescence transient (the OJIP curve) from their leaves, and isolated cells grown photoautotrophically in suspension in a culture medium, or with added sucrose. One of our goals was to study the effect of different sucrose concentrations (0, 0.15, 0.3, and 3%) on PSII activity in isolated cells. Our results on cells suspended in culture medium, using the JIP-test, showed a decrease in PSII activity at increasing sucrose concentrations, while the photoautotrophic cells showed an optimal PSII activity, close to that of the leaves. Further, our data on cells grown in 0, 0.15, and 0.3% sucrose, but with added CO2, and measured while the cells were deposited on filter paper, indicate that supplementary CO2 can increase the PSII activity in the presence of sucrose, although further research is necessary to understand these results.

Nutrient and pathogen removal from anaerobically treated black water by microalgae

The demand for systems that efficiently and sustainably recover value-added compounds and materials from waste streams is a major challenge. The use of wastewater as a source for recovery of carbon and nutrients is an attractive and sustainable alternative. In this study, anaerobically treated black water was treated in photobioreactors (PBRs) inoculated with Chlorella sorokiniana, and the process was investigated in terms of phosphorus and nitrogen removal, biomass growth, and the removal of pathogens. The consumption of bicarbonate (alkalinity) and acetate (volatile fatty acids) as carbon sources by microalgae was investigated. The average nutrient removal achieved was 66% for N and 74% for P. A high consumption of alkalinity (83%) and volatile organic acids (76%) was observed, which suggests that these compounds were used as a source of carbon. The biomass production was 73 mg L−1 day−1, with a mean biomass of 0.7 g L−1 at the end of the batch treatment. At the end of the experiments, a log removal/inactivation of 0.51 log for total coliforms and 2.73 log for Escherichia coli (E. coli) was observed. The configuration used, a flat-panel PBR operated in batch mode without CO2 supplementation, is a cost-effective and environmentally sustainable method for recovering of nutrients and production of algal biomass.