pH Buffering Effect Research Articles

Bidirectional pH Buffer Effect Facilitates High-Reversible Aqueous Zinc Ion Batteries.

Aqueous zinc ion batteries (AZIBs) stand out from the crowd of energy storage equipment for their superior energy density, enhanced safety features, and affordability. However, the notorious side reaction in the zinc anode and the dissolution of the cathode materials led to poor cycling stability has hindered their further development. Herein, ammonium salicylate (AS) is a bidirectional electrolyte additive to promote prolonged stable cycles in AZIBs. NH4 + and C6H4OHCOO- collaboratively stabilize the pH at the interface of the electrolyte/electrode and guide the homogeneous deposition of Zn2+ at the zinc anode. The higher adsorption energy of NH4 + compared to H2O on the Zn (002) crystal plane mitigates the side reactions on the anode surface. Moreover, NH4 + is similarly adsorbed on the cathode surface, maintaining the stability of the electrode. C6H4OHCOO- and Zn2+ are co-intercalation/deintercalation during the cycling process, contributing to the higher electrochemical performance of the full cell. As a result, with the presence of AS additive, the Zn//Zn symmetric cells achieved 700h of highly reversible cycling at 5mA cm-2. In addition, the assembled NH4V4O10(NVO)//Zn coin and pouch batteries achieved higher capacity and higher cycle lifetime, demonstrating the practicality of the AS electrolyte additive.

The precipitation mechanisms of scheelite from CO2-rich hydrothermal fluids: Insight from thermodynamic modeling

Scheelite and wolframite are two main tungsten-bearing ore minerals in tungsten deposits. Compared to wolframite formed mostly by NaCl–H2O fluids, scheelite in many but not all tungsten deposits is associated with CO2–bearing hydrothermal fluids, but its precipitation mechanisms from these fluids are poorly understood. The replacement of wolframite by scheelite is common among tungsten deposits where these two tungstates coexist, but how CO2, as the pH-buffering agent, affects their replacement remains unclear. To answer these questions, we first tested the pH-buffering effect of CO2 by comparing available experimental pH values of H2O–CO2±NaCl solutions at 200–280 °C and the corresponding thermodynamic modeling results. The mean absolute errors between the calculated and experimental pH values are 0.14 log units in H2O–CO2 solutions and 0.13 log units in H2O–CO2–NaCl solutions, indicating that the calculated acitivities of H+ in CO2-bearing solutions are reliable. Then, the solubilities of scheelite, scheelite-ferberite, and scheelite-hübnerite in NaCl–H2O–CO2 systems were modeled in this study. Our modeling results suggest that scheelite solubility in CO2-rich fluids is highly dependent on fluid pressure but is insensitive to fluid temperature. A decrease in fluid pressure from lithostatic to hydrostatic levels at a depth of 3–8 km causes CO2 escape and pH rise and precipitates over 70 % of tungsten contents in fluids on average. Therefore, CO2 escape is an efficient mechanism for precipitating scheelite from CO2–rich hydrothermal fluids. The independence of scheelite solubility on temperature at high pressures and the slightly retrograde solubility at low pressures allows CO2–rich hydrothermal fluids to carry a great amount of tungsten far away from its sources. This may be one of reasons why some scheelite deposits occur at greater distances (>500 m) from the granite or extend along its strike for several kilometers. Similar to the cases in NaCl–H2O systems, two mechanisms for scheelite replacing wolframite in CO2–rich fluids are identified, a single decrease in fluid pressure or simple cooling plus an increase in the ratios of total Ca contents to total Fe (or Mn) contents in fluids.

Salivary buffering capacity is correlated with umami but not sour taste sensitivity in healthy adult Japanese subjects

ObjectiveSaliva serves multiple important functions crucial for maintaining a healthy oral and systemic environment. Among them, the pH buffering effect, which is primarily mediated by bicarbonate ions, helps maintain oral homeostasis by neutralizing acidity from ingested foods. Therefore, higher buffering capacity, reflecting the ability to neutralize oral acidity, may influence taste sensitivity, especially for sour taste since it involves sensing H+ ions. This study aims to explore the relationship between salivary buffering capacity and taste sensitivities to the five basic tastes in healthy adult humans. DesignEighty seven healthy adult students participated in this study. Resting saliva volume was measured using the spitting method. The liquid colorimetric test was used to assess salivary buffering capacity. The whole-mouth taste testing method was employed to determine the recognition threshold for each tastant (NaCl, sucrose, citric acid, quinine-HCl, monosodium glutamate). ResultsTaste recognition thresholds for sour taste as well as sweet, salty, and bitter tastes showed no correlation with salivary buffering capacity. Interestingly, a negative relationship was observed between recognition threshold for umami taste and salivary buffering capacity. Furthermore, a positive correlation between salivary buffering capacity and resting saliva volume was observed. ConclusionsSalivary buffering capacity primarily influences sensitivity to umami taste, but not sour and other tastes.

Development and characterization of ceramic-polymeric hybrid scaffolds for bone regeneration: incorporating of bioactive glass BG-58S into PDLLA matrix

In recent years, there has been a notable surge of interest in hybrid materials within the biomedical field, particularly for applications in bone repair and regeneration. Ceramic-polymeric hybrid scaffolds have shown promising outcomes. This study aimed to synthesize bioactive glass (BG-58S) for integration into a bioresorbable polymeric matrix based on PDLLA, aiming to create a bioactive scaffold featuring stable pH levels. The synthesis involved a thermally induced phase separation process followed by lyophilization to ensure an appropriate porous structure. BG-58S characterization revealed vitreous, bioactive, and mesoporous structural properties. The scaffolds were analyzed for morphology, interconnectivity, chemical groups, porosity and pore size distribution, zeta potential, pH, in vitro degradation, as well as cell viability tests, total protein content and mineralization nodule production. The PDLLA scaffold displayed a homogeneous morphology with interconnected macropores, while the hybrid scaffold exhibited a heterogeneous morphology with smaller diameter pores due to BG-58S filling. The hybrid scaffold also demonstrated a pH buffering effect on the polymer surface. In addition to structural characteristics, degradation tests indicated that by incorporating BG-58S modified the acidic degradation of the polymer, allowing for increased total protein production and the formation of mineralization nodules, indicating a positive influence on cell culture.

Reduction-orientated selective removal of selenate by thiourea-functionalized polystyrene material

Efficient removal of trace selenate [Se(VI)] from contaminated water is still challenging because of the inevitable interference from the coexisting anions toward the adsorption or ion-exchange process. Herein, a bifunctional material (NCS@CMPS) was proposed for selective removal of Se(VI) from a complex matrix. NCS@CMPS was subtly prepared by grafting a chloromethylated polystyrene substrate (CMPS) with thiourea, resulting in reductive groups (C-SH and C=S) and adsorptive sites (–NH-, –NH2, and C=NH2+) anchored on the skeleton of CMPS. Batch studies demonstrated an excellent removal efficiency and anti-interference capabilities of NCS@CMPS toward Se(VI), even with very high levels of competing anions (chloride, sulfate, phosphate, nitrate, and bicarbonate) over a wide pH range (3 ∼11). The in-situ reductive removal and the unique pH-buffering effect of NCS@CMPS were responsible for the high selectivity and the wide applicability. The XPS analyses identified the removal mechanisms of concentrating, reducing, and sequestrating of Se species inside NCS@CMPS, where the majority of Se species was reduced to Se(IV) (80.9%). In column mode, NCS@CMPS can treat over 10,000 bed volumes (BV) of a simulated Se(VI) wastewater ([Se]ini = 200 μg/L) to below 10 μg/L, whereas the capacity of its substrate (i.e., CMPS) was only 28 BV. Additionally, the exhausted NCS@CMPS can be regenerated by NaBH4-NaOH-HCl treatment for repeated use. Moreover, the effectiveness of NCS@CMPS in treating actual industrial Se(VI) wastewater was also validated.

α-Zirconium hydrogenophosphate as a nano-container of 2-aminobenzimidazole for the corrosion protection of zinc in NaCl medium.

The development of a new generation of anticorrosion pigments for paints remains an important challenge to replace the usual sparingly-soluble pigments and thus avoid the dissemination of heavy metals in the environment and the formation of holes in polymer coatings. For this purpose, α-zirconium hydrogenophosphate (Zr(HPO4)2·H2O, denoted as α-ZrP) was intercalated with the corrosion inhibitor 2-aminobenzimidazole (ABIM). Various microstructural analyses have proven the insertion of ABIM in the interlayer space by an acid-base exchange reaction and allowed us to propose a structural model for the new ABIM-ZrP pigment. The anticorrosion properties on zinc of the ABIM-ZrP, characterized by electrochemical measurements in 0.1 M NaCl, are due to the release of ABIM molecules by an ion-exchange reaction and the pH-buffer effect of α-ZrP and the amine group of ABIM. Compared to the commercial aluminium tri-phosphate (ATP) pigment, an alkyd-polymer coating loaded with the ABIM-ZrP pigment shows very interesting electrochemical behaviour by avoiding the blistering of the polymer coating and the beginning of zinc corrosion. This effect may be due to both the tortuous effect brought by the platelet shape of the pigments and the release of ABIM once the water uptake of the polymer becomes significant.

Fermentative iron reduction buffers acidification and promotes microbial metabolism in marine sediments

Microbial iron reduction is a crucial process in natural ecosystems, contributing to the cycling of elements and supporting the biological activities of organisms. However, the significance of fermentative iron reduction in marine environments and microbial metabolism remains understudied compared with iron reduction coupled with respiration. The main objective of our study was to investigate the influence of fermentative iron reduction on microbial populations and marine sediment. Our findings revealed a robust iron-reducing activity in the enriched marine sediment, demonstrating a maximum ferrihydrite-reducing rate of 0.063 mmol/h. Remarkably, ferrihydrite reduction exhibited an intriguing pH-buffering effect through the release of OH+ and Fe2+ ions, distinct from fermentation alone. This effect resulted in substantial improvements in glucose consumption (71.4%), bacterial growth (48.1%), and metabolite production (80.8%). To further validate the acidification-buffering and metabolism-promoting effects of ferrihydrite reduction, we conducted iron-reducing experiments using a pure strain, Clostridium pasteurianum DMS525. The observed pH-buffering effect resulted from microbial iron reduction in marine sediment and has potential environmental implications by reducing CO2 emissions, mitigating acidification, and preserving the delicate balance of marine ecosystems.

Direct Imaging of Local pH Reveals Bubble-Induced Mixing in a CO2 Electrolyzer.

Electrochemical CO2 reduction poses a promising pathway to produce hydrocarbon chemicals and fuels without relying on fossil fuels. Gas diffusion electrodes allow high selectivity for desired carbon products at high current density by ensuring a sufficient CO2 mass transfer rate to the catalyst layer. In addition to CO2 mass transfer, the product selectivity also strongly depends on the local pH at the catalyst surface. In this work, we directly visualize for the first time the two-dimensional (2D) pH profile in the catholyte channel of a gas-fed CO2 electrolyzer equipped with a bipolar membrane. The pH profile is imaged with operando fluorescence lifetime imaging microscopy (FLIM) using a pH-sensitive quinolinium-based dye. We demonstrate that bubble-induced mixing plays an important role in the Faradaic efficiency. Our concentration measurements show that the pH at the catalyst remains lower at -100 mA cm-2 than at -10 mA cm-2, implying that bubble-induced advection outweighs the additional OH- flux at these current densities. We also prove that the pH buffering effect of CO2 from the gas feed and dissolved CO2 in the catholyte prevents the gas diffusion electrode from becoming strongly alkaline. Our findings suggest that gas-fed CO2 electrolyzers with a bipolar membrane and a flowing catholyte are promising designs for scale-up and high-current-density operation because they are able to avoid extreme pH values in the catalyst layer.

Nitrogen and Phosphorus Release Characteristics of Pipeline Sediments on Entering Different Water Bodies

Differences in the physical and chemical properties of reclaimed water (RW) and natural surface water (SW) lead to further differences in nitrogen and phosphorus release when pipeline sediments enter these water bodies. The release kinetics of nitrogen and phosphorus from pipe sediments with different particle sizes have been investigated. The results demonstrated that both SW and RW had a pH buffering effect after sediment addition, and the final pH (approximately 8.1) of RW was lower. The release of total phosphorus (TP) and ammonia nitrogen (NH4+-N) fitted the first-order kinetic model in which the release of TP reached equilibrium. TP release was inhibited in both SW and RW, with RW exhibiting the lowest (by a factor of 1.23~2.44) release (0.002 mg/g). The release of NH4+-N was promoted in both SW and RW; the maximum release in RW was 0.0188 mg/g. The amounts of NH4+-N released in SW and RW were 1.02–1.40 and 1.30–1.80 times that of the control group (CG), respectively. The percentage of TP and NH4+-N release in the three groups was highest in 75–154 μm pipe sediment, reaching 34.53% and 43.51% in SW and RW, respectively. These results can assist in the development of water quality evolution models for specific urban scenarios and provide important guidance for the precise regulation of water recharge quality during and after rainfall.

Effects of Mineral on Taxonomic and Functional Structures of Microbial Community in Tengchong Hot Springs via in-situ cultivation

Diverse mineralogical compositions occur in hot spring sediments, but the impact of minerals on the diversity and structure of microbial communities remains poorly elucidated. In this study, different mineral particles with various chemistries (i.e., hematite, biotite, K-feldspar, quartz, muscovite, aragonite, serpentine, olivine, barite, apatite, and pyrite) were incubated for ten days in two Tengchong hot springs, one alkaline (pH ~ 8.34) with a high temperature (~ 82.8 °C) (Gumingquan, short as GMQ) and one acidic (pH ~ 3.63) with a relatively low temperature (~ 43.3 °C) (Wenguangting, short as WGT), to determine the impacts of minerals on the microbial communities taxonomic and functional diversities. Results showed that the mineral-associated bacterial taxa differed from those of the bulk sediment samples in the two hot springs. The relative abundance of Proteobacteria, Euryarchaeota, and Acidobacteria increased in all minerals, indicating that these microorganisms are apt to colonize on solid surfaces. The α-diversity indices of the microbial communities on the mineral surfaces in the WGT were higher than those from the bulk sediment samples (p < 0.05), which may be caused by the stochastically adhering process on the mineral surface during 10-day incubation, different from the microbial community in sediment which has experienced long-term environmental and ecological screening. Chemoheterotrophy increased with minerals incubation, which was high in most cultured minerals (the relative contents were 5.8 − 21.4%). Most notably, the sulfate respiration bacteria (mainly related to Desulfobulbaceae and Syntrophaceae) associated with aragonite in the acidic hot spring significantly differed from other minerals, possibly due to the pH buffering effect of aragonite providing more favorable conditions for their survival and proliferation. By comparison, aragonite cultured in the alkaline hot spring highly enriched denitrifying bacteria and may have promoted the nitrogen cycle within the system. Collectively, we speculated that diverse microbes stochastically adhered on the surface of minerals in the water flows, and the physicochemical properties of minerals drove the enrichment of certain microbial communities and functional groups during the short-term incubation. Taken together, these findings thereby provide novel insights into mechanisms of community assembly and element cycling in the terrestrial hydrothermal system associated with hot springs.

Reductive ethylenediamine group immobilized in hybrid Pd-based nanocomposite for efficiently sequestrating selenate

Reductive sequestration of selenate [Se(VI)] has emerged as an effective and promising approach in consideration of the poor adsorptive selectivity toward Se(VI) by regular adsorption processes, where the adsorption efficiency for Se(VI) would be typically compromised by the coexisting anions, especially sulfate anion, which has similar structure and property as that of selenate. Herein, we propose a synergistic strategy of ion-exchange and catalytic reduction for this purpose; that is, a Pd-embedded hybrid nanocomposite (Pd-EDA@CMPS) was subtly assembled by in situ nucleating Pd-nanoparticle inside a porous polystyrene adsorbent possessing ethylenediamine (EDA) functional group, which is a reversible redox unit and served as electron donator for Se(VI) reduction, and the embedded Pd nanoparticle exhibited superior catalytic reduction activity and stability for sustainable use. The reduction product, i.e., Se(IV), was immediately in-situ sequestrated inside the hybrid nanocomposite. Macroscopic batch experiments verified the outstanding anti-interference of Se(VI) removal by Pd-EDA@CMPS against the ubiquitous competing anions such as sulfate, chloride, bicarbonate, and phosphate even with 100-times higher concentration. Furthermore, the notable applicability of Pd-EDA@CMPS in a wide pH range (i.e., 3.0 ∼ 11.0) was confirmed, and an interesting pH-buffering effect may be responsible for such a satisfied performance. Besides the excellent hydraulic properties and mechanical strength, the exhausted Pd-EDA@CMPS can be regenerated by successive treatment with NaOH and NaBH4 solution for reuse without obvious loss in capacity.

Understanding the Key Roles of pH Buffer in Accelerating Lignin Degradation by Lignin Peroxidase.

pH buffer plays versatile roles in both biology and chemistry. In this study, we unravel the critical role of pH buffer in accelerating degradation of the lignin substrate in lignin peroxidase (LiP) using QM/MM MD simulations and the nonadiabatic electron transfer (ET) and proton-coupled electron transfer (PCET) theories. As a key enzyme involved in lignin degradation, LiP accomplishes the oxidation of lignin via two consecutive ET reactions and the subsequent C-C cleavage of the lignin cation radical. The first one involves ET from Trp171 to the active species of Compound I, while the second one involves ET from the lignin substrate to the Trp171 radical. Differing from the common view that pH = 3 may enhance the oxidizing power of Cpd I via protonation of the protein environment, our study shows that the intrinsic electric fields have minor effects on the first ET step. Instead, our study shows that the pH buffer of tartaric acid plays key roles during the second ET step. Our study shows that the pH buffer of tartaric acid can form a strong H-bond with Glu250, which can prevent the proton transfer from the Trp171-H•+ cation radical to Glu250, thereby stabilizing the Trp171-H•+ cation radical for the lignin oxidation. In addition, the pH buffer of tartaric acid can enhance the oxidizing power of the Trp171-H•+ cation radical via both the protonation of the proximal Asp264 and the second-sphere H-bond with Glu250. Such synergistic effects of pH buffer facilitate the thermodynamics of the second ET step and reduce the overall barrier of lignin degradation by ∼4.3 kcal/mol, which corresponds to a rate acceleration of 103-fold that agrees with experiments. These findings not only expand our understanding on pH-dependent redox reactions in both biology and chemistry but also provide valuable insights into tryptophan-mediated biological ET reactions.

Co-digestion of food waste and hydrothermal liquid digestate: Promotion effect of self-generated hydrochars

Hydrothermal treatment (HTT) can efficiently valorize the digestate after anaerobic digestion. However, the disposal of the HTT liquid is challenging. This paper proposes a method to recover energy through the anaerobic co-digestion of food waste and HTT liquid fraction. The effect of HTT liquid recirculation on anaerobic co-digestion performance was investigated. This study focused on the self-generated hydrochars that remained in the HTT supernatant after centrifugation. The effect of the self-generated hydrochars on the methane (CH4) yield and microbial communities were discussed. After adding HTT liquids treated at 140 and 180 °C, the maximum CH4 production increased to 309.36 and 331.61 mL per g COD, respectively. The HTT liquid exhibited a pH buffering effect and kept a favorable pH for the anaerobic co-digestion. In addition, the self-generated hydrochars with higher carbon content and large oxygen-containing functional groups remained in HTT liquid. They increased the electron transferring rate of the anaerobic co-digestion. The increased relative abundance of Methanosarcina, Syntrophomonadaceae, and Synergistota was observed with adding HTT liquid. The results of the principal component analysis indicate that the electron transferring rate constant had positive correlationships with the relative abundance of Methanosarcina, Syntrophomonadaceae, and Synergistota. This study can provide a good reference for the disposal of the HTT liquid and a novel insight regarding the mechanism for the anaerobic co-digestion.

Exploring the impact of sodium salts on hydrotropic solubilization.

Some ionic liquids (ILs) were shown to display a strong ability to enhance the solubility of phenolic compounds through hydrotropy. However, evidence shows that salt ions in hydrotropic aqueous solutions may change the behavior of molecules by promoting possible interactions between the components of the system, thus causing changes in solubility. Herein, we study the impact of sodium salt anions on the hydrotropic dissolution of syringic acid using 1-butyl-3-methylimidazolium chloride ([C4mim]Cl) as a hydrotrope, with a focus on dicyanamide Na[N(CN)2] and thiocyanate Na[SCN] salts. Dynamic light scattering, Raman spectroscopy, and nuclear magnetic resonance spectroscopy were used to investigate how the mixture of IL-salts affects the solvation. The results obtained show that [C4mim]Cl is able to increase the solubility of syringic acid 80-fold. Despite their structural similarities, the presence of Na[N(CN)2] or Na[SCN] in an aqueous solution of [C4mim]Cl induced opposite solubility trends. The addition of Na[N(CN)2] promotes a higher ability to solubilize syringic acid than in the corresponding IL system due to a pH buffering effect, resulting in the deprotonation of the solute. The addition of Na[SCN], on the other hand, induces a relative decrease in syringic acid solubilization at higher concentrations of ILs due to the negative contribution of the NaCl formed by anion-exchange. These results emphasise the often overlooked pH contribution provided by ILs for biomolecule solubilisation whilst providing experimental insights into the structure of aqueous solutions of ionic liquids and the role it plays in the formation of IL-salt aggregates.

CaCO3 solubility in the process water of recycled containerboard mills

Abstract Water system closure in recycled containerboard mills may have reached a technical limit due to the accumulation of organic and inorganic contaminants in the process water. The specific water chemistry characteristics of recycled containerboard mills with restricted water systems were analyzed and a computer model was developed to simulate calcium carbonate solubility in the presence of volatile fatty acids under relevant mill conditions. A strong linear correlation between VFAs and calcium ions was found. The calcium carbonate dissolution mechanism, solubility, and precipitation were investigated. The reaction of VFAs with calcium carbonate results in the formation of bicarbonate and carbonic acid. By binding hydrogen ions, the carbonate has a pH buffering effect. The carbonic acid dissociates into water and CO2. Gaseous CO2 escapes from the water and leads to decarbonization. This mechanism is responsible for the uncoupling of pH from the concentration of VFAs, as well as from the concentration of dissolved calcium ions. The resulting lack of carbonates prevents the precipitation of calcium carbonate. The introduction of CO2 contained in the biogas produced in anaerobic biological water treatment reverses the dissolution mechanism and causes the precipitation of calcium carbonate. Concentrating technologies such as membrane filtration and evaporation may therefore meet the specific requirements for complete water system closure in recycled containerboard mills better than current commonly used biological treatment.

Dental Composites with Magnesium Doped Zinc Oxide Nanoparticles Prevent Secondary Caries in the Alloxan-Induced Diabetic Model.

Antibacterial restorative materials against caries-causing bacteria are highly preferred among high-risk patients, such as the elderly, and patients with metabolic diseases such as diabetes. This study aimed to enhance the antibacterial potential of resin composite with Magnesium-doped Zinc oxide (Mg-doped ZnO) nanoparticles (NPs) and to look for their effectiveness in the alloxan-induced diabetic model. Hexagonal Mg-doped ZnO NPs (22.3 nm diameter) were synthesized by co-precipitation method and characterized through ultraviolet-visible (UV-Vis), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) analysis. The Mg-doped ZnO NPs (1, 2.5 and 5% w/w) were then evaluated for antibacterial activity using a closed system in vitro biofilm model. Significant enhancement in the antibacterial properties was observed in composites with 1% Mg-doped ZnO compared to composites with bare ZnO reinforced NPs (Streptococcus mutans, p = 0.0005; Enterococcus faecalis, p = 0.0074, Saliva microcosm, p &lt; 0.0001; Diabetic Saliva microcosm, p &lt; 0.0001). At 1-2.5% Mg-doped ZnO NPs concentration, compressive strength and biocompatibility of composites were not affected. The pH buffering effect was also achieved at these concentrations, hence not allowing optimal conditions for the anaerobic bacteria to grow. Furthermore, composites with Mg-doped ZnO prevented secondary caries formation in the secondary caries model of alloxan-induced diabetes. Therefore, Mg-doped ZnO NPs are highly recommended as an antibacterial agent for resin composites to avoid biofilm and subsequent secondary caries formation in high-risk patients.

Disagreements Between Calorimetric and Van't Hoff Enthalpies of Adsorption II: Effect of pH and pH Buffers on Phenobarbital Adsorption to Activated Carbon

The reported inconsistencies between the van't Hoff equation and calorimetry hinder the utility of thermodynamics in biochemical and pharmaceutical research. A novel thermodynamic approach is developed herein for ligand adsorption with a focus on the interpretation of calorimetric data in the presence of concurrent proton exchange reactions. Such exchange reactions typically result in a pH-dependence of calorimetric measurements that obscures intrinsic binding enthalpies. It is shown that for the adsorption of phenobarbital to activated carbon, the measured calorimetric enthalpy is a result of three linked acid/base equilibria. A model was established to predict the intrinsic binding enthalpy using 1) the adsorbate's pKa and 2) the adsorbate's enthalpy of protonation. The observed calorimetric enthalpy of binding exhibited both pH and buffer-dependence and was between -5 and -42 kJ/mol. Meanwhile, the predicted intrinsic enthalpy (-25.1 kJ/mol) of binding was in excellent agreement with the measured intrinsic enthalpy (-25.6 kJ/mol). Corrections to the observed calorimetric enthalpies allowed comparisons with enthalpies obtained from the van't Hoff method. It is shown that the predicted intrinsic calorimetric enthalpy agrees well with the van't Hoff enthalpies in instances where observed enthalpies significantly deviated. This treatment is general and is not specific to phenobarbital or activated carbon.

Influence of the characteristics of paper mill sludges on their anaerobic digestion.

The objective of this study was to characterise the anaerobic degradation of three paper mill waste water treatment residues in the shape of sludges and to correlate this anaerobic digestion to the physico-chemical characteristics of the paper sludges. After a deep characterisation of each paper sludge in their initial stage, several parameters were analysed on each paper sludge in mesophilic conditions for 40-50 days: pH, conductivity, chemical oxygen demand, total organic acids and organic fibres degradation. A special care was taken to identify and quantify the volatile fatty acids (VFAs) produced by the digestion using gas chromatography coupled with a mass spectrometer. The results showed that in paper sludges, cellulose mainly degrades over time while the degradation of the other fibres (hemicellulose and lignin) is limited. Consequently, the greater the cellulose content in a paper sludge, the greater the digestion and formation of VFAs. However, not all the cellulose degrades because of a shielding effect of lignin on cellulose, and a pH buffering effect of the calcium carbonate present in the paper sludges limits the hydrolysis-acidogenesis step of the anaerobic digestion. Finally, the gas chromatography-mass spectrometry (GC-MS) investigations showed that acetic acid is the main VFA produced by the anaerobic digestion of paper sludges. This work helps predicting paper mill sludge evolution in the purpose of using them in circular economy.

Influence of augmentation of biochar during anaerobic co-digestion of Chlorella vulgaris and cellulose

The anaerobic co-digestion (AcoD) of microalgae is a prospective option for generating biomethane from renewable sources. This study investigates the effects of inoculum-to-substrate ratio (ISR), C/N ratio and biochar (BC) load on the AcoD of Chlorella vulgaris and cellulose. An initial augmentation of BC at ISR 0.5–0.9 and C/N ratio 10–30 offered a pH buffering effect and resulted in biomethane yields of 233–241 mL CH4/g VS, corresponding to 1.8–4.6 times the controls. BC addition ameliorated significantly AcoD, supporting the digestate stability at less favourable conditions. The effect of the process variables was further studied with a 23 factorial design and response optimisation. Under the design conditions, the variables had less influence over methane production. Higher ISRs and C/N ratios favoured AcoD, whereas increasing amounts of BC reduced biomethane yield but enhanced production rate. The factorial design highlighted the importance of BC-load on AcoD, establishing an optimum of 0.58 % (w/v).

Syngas biomethanation: effect of biomass-gas ratio, syngas composition and pH buffer

The concept of syngas biomethanation is attractive, however, it still needs improvement in optimizing the operational conditions. In the present study, syngas fermentations under different carbon monoxide (CO), carbon dioxide (CO2) and hydrogen (H2) compositions were conducted under two different biomass-gas ratio (BGR) systems. The results showed that high BGR enhanced the CO consumption rate, achieving a 60% enhancement with CO as the sole substrate. Stoichiometric H2 addition could successfully convert all the CO and CO2 to pure methane, however, higher H2 partial pressure might decline the CO consumption due to pH inhibition from consumption of bicarbonate. Microbial analysis showed different syngas composition could affect the bacteria community, while, archaea community was only slightly affected with Methanothermobacter as the dominant methanogen. This study provided strategy for efficient syngas biomethanation and deeper insight into effect of H2 addition on CO conversion under different BGR systems.