Presence Of Bicarbonate Ions Research Articles

The unique allosteric property of crocodilian haemoglobin elucidated by cryo-EM

The principal effect controlling the oxygen affinity of vertebrate haemoglobins (Hbs) is the allosteric switch between R and T forms with relatively high and low oxygen affinity respectively. Uniquely among jawed vertebrates, crocodilians possess Hb that shows a profound drop in oxygen affinity in the presence of bicarbonate ions. This allows them to stay underwater for extended periods by consuming almost all the oxygen present in the blood-stream, as metabolism releases carbon dioxide, whose conversion to bicarbonate and hydrogen ions is catalysed by carbonic anhydrase. Despite the apparent universal utility of bicarbonate as an allosteric regulator of Hb, this property evolved only in crocodilians. We report here the molecular structures of both human and a crocodilian Hb in the deoxy and liganded states, solved by cryo-electron microscopy. We reveal the precise interactions between two bicarbonate ions and the crocodilian protein at symmetry-related sites found only in the T state. No other known effector of vertebrate Hbs binds anywhere near these sites.

Innovative strategy for the effective utilization of coal waste slag in the Fenton-like process for the degradation of trichloroethylene

In response to environmental concerns at the global level, there is considerable momentum in the exploration of materials derived from waste that are both sustainable and eco-friendly. In this study, CS-Fe (carbon, silica, and iron) composite was synthesized from coal gasification slag (CGS) and innovatively applied as a catalyst to activate PS (persulfate) for the degradation of trichloroethylene (TCE) in water. Scanning electron microscope (SEM), fourier transmission infrared spectroscopy (FTIR), energy dispersive x-ray spectroscopy (EDS), brunauer, emmet, and teller (BET) technique, and x-ray diffractometer (XRD) spectra were employed to investigate the surface morphology and physicochemical composition of the CS-Fe composite. CS-Fe catalyst showed a dual nature by adsorption and degradation of TCE simultaneously, displaying 86.1% TCE removal in 3 h. The synthesized CS-Fe had better adsorption (62.1%) than base material CGS (36.4%) due to a larger BET surface area (770.8 m2 g−1), while 24.0% TCE degradation was recorded upon the activation of PS by CS-Fe. FTIR spectra confirmed the adsorption and degradation of TCE by investigating the used and fresh samples of CS-Fe catalyst. Scavengers and Electron paramagnetic resonance (EPR) analysis confirmed the availability of surface radicals and free radicals facilitated the degradation process. The acidic nature of the solution favored the degradation while the presence of bicarbonate ion (HCO3−) hindered this process. In conclusion, these results for real groundwater, surfactant-added solution, and degradation of other TCE-like pollutants propose that the CS-Fe composite offers an economically viable and favorable catalyst in the remediation of organic contaminants within aqueous solutions. Further investigation into the catalytic potential of coal gasification slag-based carbon materials and their application in Fenton reactions is warranted to effectively address a range of environmental challenges.

Fenton-like water disinfection using fixed-bed reactor filled with a CoFe2O4 catalyst: Mechanisms, the impact of anions, electromagnetic heating, and toxicity evaluation

This work is a pioneering study demonstrating a promising breakthrough in water disinfection using a cobalt ferrite catalyst in a fixed bed. The performance of CoFe2O4 in E. coli inactivation is due to HO• radicals generated in the Fe3+/Fe2+ and Co3+/Co2+ redox cycles. In contrast to existing reports using cobalt ferrite nanoparticles, the bulk cobalt ferrite provides long-lasting catalytic performance in a flow reactor. The positively charged surface of cobalt ferrite attracts negatively charged E. coli membranes, which enhances disinfection. The CoFe2O4 catalyst was synthesized by the flow co-precipitation method, which allows obtaining kilogram quantities needed for industrial applications. The efficiency of E. coli inactivation was studied as a function of H2O2 concentration. For the first time, the reactor with a CoFe2O4 catalyst was additionally boosted by an electromagnetic field to decompose H2O2 and inactivate bacteria. The electromagnetically heated CoFe2O4/H2O2 system provides a significant 6 log bacterial inactivation. Importantly, cobalt ferrite is very stable under operating conditions. Only a negligible leaching of Fe and Co ions was observed. The presence of inorganic anions was beneficial for the bacterial inactivation. Ecotoxicological analysis revealed the absence of the toxicity of the treated water after using CoFe2O4/H2O2 with electromagnetic heating in the presence of bicarbonate ions. The results show that the magnetic cobalt ferrite is a promising, durable, heterogeneous catalyst for large-scale water disinfection.

Fluoride leaching from tuff breccia and its removal by natural and commercial adsorbents

In Japan, the concentration of fluoride (F−) leached from rocks, such as tuff breccia, excavated in tunnel construction projects often exceeds the Japanese environmental standard of 0.8 mg/L. Because of this, proper disposal methods are necessary for managing F−-bearing excavated rocks. One effective solution based on circular economy is the use of an adsorption layer system. This system can simultaneously prevent the migration of F− released from excavated rocks and allow the recycling of this construction waste material. To determine the most suitable material for the disposal of excavated F−-bearing tuff breccia from a tunnel construction in Hokkaido, Japan, four types of natural geological materials (S-1, S-2, S-3, and S-4) obtained near the tunnel construction site, as well as three types of commercial adsorbents (calcium (Ca), magnesium (Mg), and CaMg adsorbents) were selected for evaluation. The batch adsorption test results showed that S-1 and S-4 had high adsorption capacities for F−, and the adsorption process followed the Langmuir isotherm. The adsorption of F− to the natural adsorbents was strongly influenced by the pH and the presence of bicarbonate ions (HCO3−), but unaffected by chloride (Cl−) and sulfate (SO42−). There was also a strong positive correlation between the abundance of amorphous aluminum (Al) and iron (Fe) extracted and the adsorption of F−, indicating the importance of ion exchange reactions associated with surface OH− in immobilizing F−. Meanwhile, the Mg-bearing adsorbent exhibited the highest adsorption affinity for F− among the commercial adsorbents. This was attributed to adsorption through electrostatic interactions and coprecipitation with magnesium hydroxide (Mg(OH)2) formed during the hydration of magnesium oxide (MgO). To effectively incorporate these adsorbents into the adsorption layer system, parameters such as permeability and residence time need to be determined in order to maximize the retention of F− through adsorption, ion exchange and coprecipitation reactions.

Clay peptization and clay swelling inhibition in the presence of carbonic acid, bicarbonate and carbonate ions and calcium ions

Relevance. The need to ensure the integrity of the wellbore, composed of clay rocks, and the stability of drilling fluid when drilling in conditions of carbon dioxide and bicarbonate aggression. Aim. To determine experimentally the effect of carbonic acid, bicarbonate and carbonate ions on clay depending on the presence of calcium ions in the dispersion medium. Objects. Water contaminated with carbonic acid, bicarbonate and carbonate ions with different equivalent concentrations of calcium ions. Methods. Inhibitory and peptizing properties of the objects of study in relation to the clay rock were studied by the method of clay swelling when it was in the water under study (on the Zhigacha-Yarov device); methods of chemical analysis (complexometric and acid-base titration) and potentiometry were used to control water composition and properties. Results. The peptizing and inhibiting properties of drilling fluid depend significantly on the form of carbonic acid present in the dispersion medium and the equivalent content of calcium ions (Ca2+). It was found that carbonic acid (H2CO3) contributes to clay inhibition (coagulation), bicarbonate ions (HCO3–) and carbonate ions (CO32–) – clay peptization. Calcium ions (Ca2+) do not have an inhibitory effect in the presence of carbonic acid (H2CO3) – hydrogen ions (H+) displace exchangeable cations from the interlayer space of clays and, due to their small diameter, independently inhibit clay swelling. In the presence of bicarbonate ions (HCO3–), calcium ions (Ca2+) also do not have an inhibitory effect – bicarbonate ions (HCO3–), being in a dispersion medium, draw calcium ions (Ca2+) from the clay surface, increasing the thickness of the electrical double layer. In the presence of carbonate ions (CO32–) the calcium ions (Ca2+) precipitate and effectively prevent clay peptization only in the presence of hydroxide ions (OH–). The authors proved experimentally that calcium ions (Ca2+) in the presence of hydroxide ions (OH–) have a better inhibitory ability than hydrogen ions (H+) of dissociated carbonic acid (H2CO3). A mechanism was proposed for inhibiting the swelling of clays by calcium ions (Ca2+) in the presence of hydroxide ions (OH-), based on the adsorption of the hydrated calcium ion (Ca2+) on a silica tetrahedral sheet due to the preliminary protonation of its oxygen atoms by water molecules. The conditions required for clay effective peptization are formulated: [CO32–]≥0; [OH–]>0, [Ca2+]=0, pH>11.5; for clay swelling inhibition: [CO32–]=0; [OH–]>0, [Ca2+]>0 and pH>11.5.

Dexamethasone degradation in aqueous medium by a thermally activated persulfate system: Kinetics and transformation products

Dexamethasone (DEX) is a synthetic steroid hormone that, owing to its endocrine disruptive effects, has the potential to be detrimental. DEX must be successfully removed during drinking water treatment to preserve human and aquatic animals' health. This study investigates the thermally activated persulfate (TAP) process for the efficient decomposition of DEX. The effectiveness of several variables such as pH, persulfate dose, DEX concentration, reaction temperature, and water matrices was studied. Removal of 500 μg/L DEX reached 100 % by using 100 mg/L of persulfate in ultrapure water (pH = 7) at 50 °C, within 45 min of reaction time. DEX removal usually followed exponential decay. The removal efficiency of DEX in the TAP process was pH-dependent, as 61 % of DEX was removed at a pH value of 9. In contrast, complete degradation was achieved under acidic and near neutral conditions.Moreover, environmentally relevant degradation experiments showed that, in principle, the presence of bicarbonate ions and humic acid had a negative effect on DEX decomposition by reducing the percentage removal of the target compound by >50 %. Six transformation products derived from DEX oxidation were identified using high-resolution LC-MS. TAP system could be proposed as a promising application for removing steroid hormones n real water matrices after process optimization in real conditions.

Corrosion Response of Carbon Steel Exposed to Dynamic H2S Aqueous Solution in the Presence of Bicarbonate Ions and Natural Aeration

Corrosion Response of Carbon Steel Exposed to Dynamic H2S Aqueous Solution in the Presence of Bicarbonate Ions and Natural Aeration

Computational Exploration of the Mechanism of Critical Steps in the Biomimetic Synthesis of Preuisolactone A, and Discovery of New Ambimodal (5 + 2)/(4 + 2) Cycloadditions.

Computational studies with ωB97X-D density functional theory of the mechanisms of the steps in Trauner's biomimetic synthesis of preuisolactone A have elaborated and refined mechanisms of several unique processes. An ambimodal transition state has been identified for the cycloaddition between an o-quinone and a hydroxy-o-quinone; this leads to both (5 + 2) (with H shift) and (4 + 2) cycloaddition products, which can in principle interconvert via α-ketol rearrangements. The origins of periselectivity of this ambimodal cycloaddition have been investigated computationally with molecular dynamics simulations and tested further by an experimental study. In the presence of bicarbonate ions, the deprotonated hydroxy-o-quinone leads to only the (5 + 2) cycloaddition adduct. A new mechanism for a benzilic acid rearrangement resulting in ring contraction is proposed.

Adaptive strategies to minimise iron limiting stress under climate change scenario: A study pertinent to iron stress response of two soybean (Glycine max (L.) Merr.) Genotypes

The response of soybean genotypes to iron deficiency stress under elevated CO2 and temperature condition could be guided by three critical rhizospheric processes viz. proton (H+) extrusion, root exudation and ferric chelate reductase (FCR) activity. In the present study, the iron efficient and responsive (FeER) genotype recorded an impressive performance over iron inefficient and responsive (FeIR) genotype in counteracting iron deficiency stress but experienced modest stress caused by the combined interaction between the genotype (G), environment (E) and HCO3- ion (B). The antagonistic interaction between Fe2+ with HCO3- ion resulted in greater iron stress. Plants grown in the absence of bicarbonate have significantly higher total chlorophyll content (1.79±0.04 mg g-1, mean ± SE) than plants grown in presence of bicarbonate (1.48 ± 0.06 mg g-1). To warfare the constraints in Fe availability, especially under more stressed e-[CO2+T] environmental condition in the presence of bicarbonate ion, the root system of iron efficient genotype of soybean (FeER) exuded out significantly higher amount of low molecular weight organic acids. Furthermore, the presence of bicarbonate ion in the nutrient solution exacerbated the iron deficiency stress and consequently resulted in higher proton extrusion (~1.2 fold increase), lower ferric chelate reductase activity (~1.3 fold decrease) and higher organic acid exudation (up to ~1.9 fold increase in malic acid). The intra-specific variability between contrasting genotypes and their response to elevated CO2 and temperature could be exploited to remediate emerging Fe deficiency of soybean plants under climate change scenario.

Investigating the effect of bicarbonate ion on the structure and strength of calcium silicate-based dental restorative material—Biodentine

Investigating the effect of carbonation on the strength and structure of calcium silicate-based cement (Biodentine™) in the presence of bicarbonate ion. Cylindrical samples of Biodentine (N = 120) were prepared and cured in deionised water (DW) or bicarbonate solution (BC) for 1 and 2days and 1, 2 and 4weeks. After storage, the compressive strength of cured samples was tested using a universal testing machine, and carbonate was quantified on the surface or within the structure of samples using Raman and Fourier transform infrared spectroscopy, respectively. Levels of calcium and silicon ions and pH were measured after each storage duration, and 4-week-old samples were imaged using scanning electron microscopy. Cement's compressive strength was significantly higher after curing in BC for 2days. This was associated with significantly higher levels of carbonate on the surface of the cement but not within its structure. Levels of calcium and silicon ions and pH in BC dropped significantly after 1day and remained at a steady lower level. The pH and calcium ion levels dropped gradually over 4weeks in DW, unlike the silicon ion level that maintained a steady higher level than in BC. Our results indicate that Biodentine exhibited higher strength in the presence of bicarbonate, which can be explained by the carbonation process that encouraged the formation of calcium carbonate on the cement's surface. Carbonation should be of more consideration when studying calcium silicate-based cements, with curing and testing conditions closer to the intraoral conditions.

U(VI) removal efficiency by natural pyrite under the oxygen-rich conditions with/without bicarbonate present

Natural pyrite, as an ubiquitous mineral in the reducing environments, shows great potential on the treatment of wastewater polluted by heavy metals. In the present work, a dynamic leaching experiment was carried out to investigate the removal efficiency of U(VI) by natural pyrite under the oxygen rich conditions with/without bicarbonate ions. Experimental results shows that pyrite oxidation can significantly remove U(VI) from the solution under the oxygen rich conditions with/without bicarbonate ions. With the absence of bicarbonate ions, U(VI) concentration decreases from 50 mg/L to 20 mg/L with the removal rate up to 60%; with the presence of bicarbonate ions, U(VI) concentration decreases from 50 mg/L to 30 m/L with the removal rate up to 40%, indicating that natural pyrite can be an effective material to treat high-uranium groundwater under the oxygen-rich conditions with bicarbonate present or not.

Simple spectrophotometric assay for measuring catalase activity in biological tissues

BackgroundThe details of a precise, accurate, and sensitive spectrophotometric method for measuring catalase activity are presented here. The assay was established for biological samples and depends on the rapid formation of a stable and colored carbonato-cobaltate (III) complex. Samples exhibiting catalase activity are incubated with hydrogen peroxide solution for 2 min prior to rapid mixing of the incubation enzymatic reaction mixture with cobalt-bicarbonate reagent, which assesses non-reacting hydrogen peroxide. Catalase activity is always directly proportional to the rate of dissociation of hydrogen peroxide. Hydrogen peroxide acts to oxidize cobalt (II) to cobalt (III) in the presence of bicarbonate ions; this process ends with the production of a carbonato-cobaltate (III) complex ([Co (CO3)3]Co). The formed end product has two maximum absorbance peaks: 440 nm and 640 nm. The 440-nm peak has been utilized for assessing catalase activity.ResultsThe catalase activity results of the current method for erythrocyte lysate homogenates were computationally identical to those of the dichromate method (r = 0.9950). The coefficient of variation was calculated to determine the imprecision of the current assay. The within-run and between-run results were 2.96 and 3.83%, respectively.ConclusionThis method is appropriate for analyzing bacteria, red blood cells and liver and kidney tissue homogenates.

Diagnosis of Copper Corrosion in Fresh Water By Combining Amperometry and Potentiometry

Copper is used for tubes of absorption-refrigerator machines because it has good corrosion resistance and thermal conductivity. However, it has been reported that a leakage accident occurs due to pitting corrosion inside copper tubes in flowing fresh water[1]. The occurrence of pitting corrosion of copper is caused by the presence of bicarbonate ions which affect scale formation and aggressive anions such as chloride and sulfate ions. Therefore, the corrosion diagnosis method of copper using electrochemical measurements in fresh water has been reported in Japan[2]. This method can discriminate the corrosion type of copper by using a potentiodynamic polarization and galvanostatic polarization, and the corrosion map 3D can be created based on the results of electrochemical measurements and the pH of test solution. In the previous report[2], the current density at 0.2 V vs. SSE in the potentiodynamic polarization curve can separate the corrosion type of copper. Therefore, in this study, a new corrosion diagnosis method of copper by using corrosion map 3D was proposed by combining potentiostatic polarization of 0.2 V vs. SSE and galvanostatic polarization since the corrosion map 3D can be easily created by using the current density obtained by the potentiostatic polarization of 0.2 V vs. SSE. In this study, simulated test waters with eight compositions were made using a pure water and analytical grade of sodium bicarbonate, sodium chloride and sodium sulfate. As a measuring device, a small potentiogalvanostat (TOHO TECHNICAL RESEARCH, PPS1) was used. Experiments were carried out with a three-electrode system. The copper electrode was used as working electrode, the platinum wire was used as counter electrode and the saturated silver/silver chloride electrode (DKK-TOA, HS-205C) was used as reference electrode. The procedures for measurement is described as follows: the potentiostatic polarization at 0.2 V vs. SSE for 10 min, the galvanostatic polarization at 500 µA cm-2 for 10 min and the electrode surface was observed by optical microscope (KEYENCE, VHX-200). From the observation results of the electrode surface using the optical microscope, pitting corrosion was observed at No.2 and No.7, general dissolution at No.3, No.4, No.6 and No.8 and no corrosion at No.1 and No.5. Fig. 1 shows the corrosion map 3D created by the electrochemical measurements. The axes of corrosion map 3D were the potential of copper electrode after 10 min by galvanostatic polarization at 500 µA cm-2, the current density by potentiostatic polarization at 0.2 V vs. SSE and pH of the test solution. The plots of corrosion map 3D agreed with the observation results of the electrode surface, indicating the possibility of simple corrosion diagnosis by combining amperometry and potentiometry.

Kinetics of the Bicarbonate-Assisted Oxidation of Diethyl Sulfide by Hydrogen Peroxide and Sodium Peroxoborate

The kinetics of oxidation of diethyl sulfide (Et2S) is studied in aqueous solutions of hydrogen peroxide and sodium peroxoborate (Na2[В2(О2)2(ОН)4]) in the presence of bicarbonate ions by means of gas−liquid distribution. The kinetics is investigated in a broad range of pH. Data show that the oxidation of Et2S by sodium peroxoborate in the range of pH 6−12 is mediated by such reactive species as hydrogen peroxide, hydrogen peroxide anions, and mono (B(O2H)(OH) $$_{3}^{ - }$$ ) and diperoxoborate (B(O2H)2(OH) $$_{2}^{ - }$$ ) anions. The rate of Et2S oxidation increases in the presence of bicarbonate, due to the additional reaction pathways mediated by monoperoxocarbonate species.

Improved volume stability of mortar bars exposed to magnesium sulfate in the presence of bicarbonate ions

The effect of the simultaneous occurrence of sulfate and bicarbonate ions in magnesium containing solutions was investigated for a CEM I and CEM III/B mortar under laboratory conditions. The presence of bicarbonate ions, which is common in natural waters, prevents the typical expansion and surface erosion of CEM I mortars and the surface deterioration of CEM III/B mortars. The chemical effect of the bicarbonate ions is twofold. The precipitation of CaCO3 lowers the availability of CaO for the formation of additional sulfate bearing phases like ettringite and gypsum. The second effect is the reduction of supersaturation of the pore solution with respect to ettringite. The absence of deterioration is linked to the formation of only small amounts of ettringite and to the absence of gypsum in the affected zones. Thermodynamic modeling suggests that relatively small bicarbonate concentrations suffice to prevent damage, contribute to the scarcity of damage under natural exposure conditions and to the diversity of results under laboratory exposure conditions.

Characterization of a two component system, Bas1213‐1214, important for oxidative stress in Bacillus anthracis

Microbial colonization is an outcome of appropriate sensing and regulation of its gene expression. Bacillus anthracis adapts and thrives in its environment through complex regulatory mechanisms, among them, the two component systems (TCS). Many bacteria respond to the oxygen fluctuations via TCS. In the present work, a previously uncharacterized TCS, Bas1213-1214, of B. anthracis with a probable role in oxygen sensing has been characterized as a functional TCS. A substantial increase in the expression of Bas1213 was observed during the stationary growth phase, in presence of bicarbonate ions, and under oxidative stress thereby speculating the role of Bas1213 in toxin production and adaptive responses. Electrophoretic mobility shift assay (EMSA) and ANS assay highlighted autoregulation of the system. Identification of Bas1213 regulon further suggested its regulatory function in metabolism and adaptive responses. A marked reduction in sporulation was observed on overexpression of Bas1213 in B. anthracis which can be correlated with the augmented expression of sporulation kinase D. Additionally, Bas1213 was shown to regulate catalase, and ABC transporter (mntH) further implicating its essential role during oxidative stress. Finally, crucial residues involved in the DNA binding activity of Bas1213 were also identified. This study reports that the role of Bas1213-1214 in the regulation of metabolism and adaptive responses during oxidative stress. Both sporulation and response to environmental oxygen are important for the maintenance of B. anthracis lifecycle, therefore, characterization of Bas1213-1214 provides a step closer toward understanding the regulatory network governing in B. anthracis.

Chemistry and Chemical Equilibrium Dynamics of BMAA and Its Carbamate Adducts.

Beta-N-methylamino-L-alanine (BMAA) has been demonstrated to contribute to the onset of the ALS/Parkinsonism-dementia complex (ALS/PDC) and is implicated in the progression of other neurodegenerative diseases. While the role of BMAA in these diseases is still debated, one of the suggested mechanisms involves the activation of excitatory glutamate receptors. In particular, the excitatory effects of BMAA are shown to be dependent on the presence of bicarbonate ions, which in turn forms carbamate adducts in physiological conditions. The formation of carbamate adducts from BMAA and bicarbonate is similar to the formation of carbamate adducts from non-proteinogenic amino acids. Structural, chemical, and biological information related to non-proteinogenic amino acids provide insight into the formation of and possible neurological action of BMAA. This article reviews the carbamate formation of BMAA in the presence of bicarbonate ions, with a particular focus on how the chemical equilibrium of BMAA carbamate adducts may affect the molecular mechanism of its function. Highlights of nuclear magnetic resonance (NMR)-based studies on the equilibrium process between free BMAA and its adducts are presented. The role of divalent metals on the equilibrium process is also explored. The formation and the equilibrium process of carbamate adducts of BMAA may answer questions on their neuroactive potency and provide strong motivation for further investigations into other toxic mechanisms.

Activated alumina for the removal of fluoride ions from high alkalinity groundwater: New insights from equilibrium and column studies with multicomponent solutions

Highlights - Constant mass bottle-point method revealed that fluoride equilibrium uptake was unfavourable on alumina. - Fluoride sorption required modelling by multilayer isotherm expressions. - Both sorption mechanism and loading capacity of fluoride ions related to solution pH. - High alkalinity solutions required pH adjustment using HCl and not H2SO4. - Activated alumina suitable for reducing fluoride levels in groundwater to meet regulatory guidelines. Abstract This study focussed on the differences in sorption behaviour of fluoride on activated alumina, between simple sodium fluoride solutions and multicomponent groundwater samples with high alkalinity. It was our hypothesis that: fluoride uptake may be inhibited by the presence of bicarbonate ions: the separation mechanism may involve multiple pathways which have not been identified previously due to inappropriate bottle-point approaches; groundwater pH is critical; and methods of pH modification are important. Equilibrium studies of alkaline UOP-A201 alumina with sodium fluoride solutions showed that the isotherm was unfavourable in character (due to competition with hydroxyl species) in contrast to existing literature which suggested it was favourable. The monolayer capacities of the alumina depended upon pH, with fluoride uptakes of 6.63, 29.8, and 23.78 g F/kg alumina predicted at pH values of 8, 6, and 4, respectively. Evidence for multilayer sorption was apparent at pH 8 and 4, and as such the Aranovich Donohue model successfully simulated isotherm behaviour. Column studies of sodium fluoride solutions resulted in diminished operational fluoride loadings (1.05–1.29 g F/kg alumina) due possibly to high pH of the exchange environment. Adjustment of solution pH using sulphuric acid was detrimental to fluoride uptake due to competitive interactions between fluoride and sulphate ions for adsorption sites. In a column study, fluoride was effectively removed from an acid dosed groundwater sample from the Surat Basin in Queensland, with almost 800 bed volumes of water treated prior to break through of the 2 mg/L discharge limit. The groundwater was pre-treated with hydrochloric acid (ca. pH 5.2) to decompose high concentrations of bicarbonate ions which reduce fluoride uptake. Operating capacity of the alumina was 2.94 g F/kg alumina which was substantially less than fluoride capacities estimated from equilibrium isotherms but greater than column studies with sodium fluoride solutions.

Unraveling the Reactivity of Minium toward Bicarbonate and the Role of Lead Oxides Therein

Understanding the reactivity of (semiconductor) pigments provides vital information on how to improve conservation strategies for works of art to avoid rapid degradation of the pigments. This study focuses on the photoactivity of minium (Pb3O4), a semiconductor pigment that gives rise to strong discoloration phenomena upon exposure to various environmental conditions. For demonstrating its photoactivity, an electrochemical setup with a minium-modified graphite electrode (C|Pb3O4) was used. It is confirmed that minium is a p-type semiconductor that is photoactive during illumination and becomes inactive in the dark. Raman measurements confirm the formation of degradation products. The photoactivity of a semiconductor pigment is partly defined by the presence of lead oxide (PbO) impurities; these introduce new states in the original band gap. It will be experimentally evidenced that the presence of PbO particles in minium leads to an upward shift of the valence band that reduces the band gap. Thus, upon photoexcitation, the electron/hole separation is more easily initialized. The PbO/Pb3O4 composite electrodes demonstrate a higher reductive photocurrent compared to the photocurrent registered at pure PbO or Pb3O4-modified electrodes. Upon exposure to light with energy close to and above the band gap, electrons are excited from the valence band to the conduction band to initialize the reduction of Pb(IV) to Pb(II), resulting in the initial formation of PbO. However, in the presence of bicarbonate ions, a significantly higher photoreduction current is recorded because the PbO reacts further to form hydrocerussite. Therefore, the presence of bicarbonates in the environment stimulates the photodecomposition process of minium and plays an important role in the degradation process.

Process Research on Advanced Treatment of Yeast Wastewater Through Enhanced Catalytic Ozonation

After the secondary treatment of yeast wastewater, the chemical oxygen demand(COD) usually remains very high (approximately 800–1500mg/L) in this effluent, which contains various degradation-resistant substances. Because of the presence of bicarbonate ions, which are the inhibitor of ·OH free radical chain reaction, the direct ozonation of a secondary effluent treatment is limited. In this study, the addition of calcium hydroxide as a pretreatment not only eliminates adverse effects of bicarbonate ions on chain reaction of hydroxyl free radical's generation, but also enhances the indirect ozonation by increasing the pH value up to 11. At the same time, heterogeneous catalytic ozonation treatment is also conducted on the secondary effluent of yeast wastewater by the use of manganese sand (containing manganese dioxide as an effective constituent).The COD of the raw water is reduced to 389 mg/L from 853 mg/L, and the total removal rate reaches 54%. Process analysis is conducted on the pH value, OxidationReduction Potential (ORP) value, and the concentration of dissolved ozone through an online monitoring system. A control method is also proposed to strengthen the catalytic ozonation technology by combining the ozone consumption and COD removal variation.