Rate Constant Kh Research Articles

Electrochemical fingerprinting of cephalosporin antibiotics and its applications for investigations of hydrolysis behavior

Cephalosporin, as one of the most widely used antibiotics, study of its hydrolysis process is important for predicting their environmental persistence. Two critical factors are considered has the first priority, which are hydrolysis rate constant (kh) and half-life (t1/2). To date, many efforts have been made by using various analytical techniques to obtain the data for calculating kh and t1/2. However, the typical techniques such as UV/vis spectrophotometry and liquid chromatography are of significant challenges like low accuracy and timely operations. Herein, we explored an electrochemical method by identifying the characteristic peaks with the same parent nuclear structure through square wave voltammetry (SWV). This proposed electrochemical fingerprinting was able to track the hydrolysis of intact cephalosporin molecules, β-lactam ring, and transformation product. The kh and t1/2 of cefadroxil (CDX) under pH = 7 and 25 °C by electrochemical (0.0640 d−1 and 11.0 d) were consistent with those of high-performance liquid chromatography-UV/vis (HPLC-UV/vis) (0.0660 d−1 and 10.7 d). The t1/2 ranged from 3.40 to 36.2 d, 7.33 d–43.7 d and 9.63 d–45.3 d for base-catalyzed, neutral pH and acid-catalyzed hydrolysis hydrolyzed, respectively, indicating that base-catalyzed hydrolysis rates were the greatest under alkaline conditions. Meanwhile, hydrolysis rates increased 2.50–3.60-fold for every 10 °C raise in temperature. Besides, the electrochemical fingerprinting could realize cephalosporin and β-lactam ring hydrolysis rates close to 100% in-situ hydrolysis process monitoring. This present work provides a powerful technology for understanding the environmental fate and predicting the environmental behavior of antibiotics with fast, high accuracy, specific recognition, and in situ monitoring.

Spent coffee grounds anaerobic digestion: Investigating substrate to inoculum ratio and dilute acid thermal pretreatment

Spent coffee grounds have the potential of being used in further bioprocesses to produce materials and fuels. In Norway, the relative abundance and ease of collection of this waste substrate make it a candidate for investigation. For this study, the substrate-to-inoculum ratio as well as a combined dilute acid-thermal pretreatment were assessed by a series of biochemical methane potential assays using spent coffee grounds as a substrate. Reactors with substrate-to-inoculum ratio 2 demonstrated a relatively low hydrolysis rate constant (kh) and comparatively high volatile fatty acids/alkalinity concentrations rendering them inapt to produce bio-CH4. Pretreatment was conducted over varying contact times (15–45 min), dilute acid concentrations (1.5–2.5 %, v/v), and liquid-to-solid ratios (10–20 %, v/w) and evaluated using response surface methodology. To determine bio-CH4 yield, pretreatment time and the interaction between acid concentration and liquid-to-solid ratio are considered significant variables, suggesting a shared importance. Chemical oxygen demandremoval is primarily contingent upon changes in liquid-to-solid ratio. Finally, Fourier-transform infrared spectroscopy of the discarded solid phase showed that the major functional groups are still widely present in the coffee grounds even after pretreatment was applied. A better understanding of the biodegradability profile of spent coffee grounds as a function of substrate-to-inoculum ratio is achieved.

Factors Governing Reactivity and Selectivity in Hydrogen Atom Transfer from C(sp3)-H Bonds of Nitrogen-Containing Heterocycles to the Cumyloxyl Radical.

A kinetic study of the hydrogen atom transfer (HAT) reactions from nitrogen-containing heterocycles (secondary and tertiary lactams, 2-imidazolidinones, 2-oxazolidinones, and succinimides) to the cumyloxyl radical has been carried out employing laser flash photolysis with ns time resolution. HAT occurs from the C–H bonds that are α to nitrogen, activated by hyperconjugative overlap with the N–C=O π system. In the lactam series, the second-order HAT rate constant (kH) was observed to decrease by a factor of ∼4 going from the five- and six-membered ring derivatives to the eight-membered ones, a behavior that was rationalized on the basis of a reduced extent of hyperconjugative activation associated to the greater flexibility of the larger rings compared to the smaller ones. In the five-membered-ring substrate series, the kH values were observed to increase by >3 orders of magnitude on going from succinimide to 2-imidazolidinones, a behavior that was explained in terms of the divergent contribution of hyperconjugative activation and deactivating electronic effects determined by ring functionalities. The results are discussed in the framework of the development of HAT-based C–H bond functionalization procedures.

Effect of Magnesium Ion on the Radical-Scavenging Rate of Pterostilbene in an Aprotic Medium: Mechanistic Insight into the Antioxidative Reaction of Pterostilbene.

Pterostilbene (PTS), a methylated analog of resveratrol (RSV), has recently attracted much attention due to its enhanced bioavailability compared to RSV. However, little is known about the radical-scavenging mechanism of PTS. In this study, we investigated the effect of Mg(ClO4)2 on the scavenging reaction of galvinoxyl radical (GO•) by PTS in acetonitrile (MeCN). GO• was used as a model for reactive oxygen radicals. The second-order rate constant (kH) for the GO•-scavenging reaction by PTS was more than threefold larger than that by RSV, although thermodynamic parameters, such as the relative O–H bond dissociation energies of the phenolic OH groups, ionization potentials, and HOMO energies calculated by the density functional theory are about the same between PTS and RSV. The oxidation peak potential of PTS determined by the cyclic voltammetry in MeCN (0.10 M Bu4NClO4) was also virtually the same as that of RSV. On the other hand, no effect of Mg (ClO4)2 on the kH values was observed for PTS, in contrast to the case for RSV. A kinetic isotope effect of 3.4 was observed when PTS was replaced by a deuterated PTS. These results suggest that a one-step hydrogen-atom transfer from PTS to GO• may be the rate-determining step in MeCN.

Mesophilic condition is more conducive to methane production yield and tylosin removal on tylosin fermentation dreg anaerobic digestion

Anaerobic digestion (AD) of antibiotic fermentation dreg is effective because of its satisfactory methanogenic performance and antibiotic removal rate. Thermophilic AD, an important branch, has not been studied. This study explored the effects of mesophilic and thermophilic AD on tylosin fermentation dreg (TFD) alone-digestion and co-digestion with food waste. The methane production (245–420 mL/g-VS) of mesophilic AD was 20.7%–28.6% higher than thermophilic AD, but the maximum methane production rate (RM), lag period (λ), and hydrolysis rate constant (kh) of thermophilic AD were 1.81, 0.236 and 3.16 times higher than those of mesophilic AD, respectively. However, the residual tylosin in mesophilic AD was always higher than that in thermophilic AD. The addition of food waste increased the methane production rate and yield under both temperature conditions. Therefore, due to the higher rate and yield of methane production, mesophilic AD, especially co-digestion, is more suitable for the treatment of TFD.

Quantifying the Pathophysiology of Beta-Thalassemia Using a Novel in-Silico Model of Red Blood Cell Production and Lifespan

Background: From a qualitative perspective the pathophysiology of beta-thalassemia (BT) is generally well understood. Reduction in hemoglobin (Hb) beta-chain synthesis relative to the normal rate of alpha-chain synthesis causes a free alpha-chain excess (ACE) that is toxic to the RBC and its precursors. Circulating RBCs are hemolyzed in the spleen, shortening their lifespan from the normal value of 120 days. RBC precursors in the bone marrow undergo early apoptosis leading to reduced RBC production relative to other anemic states (so called “ineffective erythropoiesis”). Together with low MCH levels these mechanisms lead to Hb levels ranging from 10 - 12 g/dL in BT trait, 7 - 10 g/dL in non-transfusion dependent (NTD) BT, below 7 g/dL in transfusion-dependent (TD) BT at baseline and above 9 - 10.5 g/dL in TD patients receiving regular transfusions administered every 2 to 5 weeks. To quantify the mechanisms responsible for the different BT phenotypes and the response to transfusion in TD patients, we have developed an in-silico model of RBC production and lifespan.Methods: The theoretical amount of ACE per cell was estimated by assuming that the alpha-chain level corresponds to an MCH of 30 pg and the non-alpha chain level (beta, gamma and delta chains) corresponds to the MCH of the BT phenotype, which varies from ~12 to 20 pg in TD BT to ~16 to 23 pg in NTD BT and ~18 to 24 pg in BT trait. The in-silico model consists of a bone marrow module - representing the production and aging of reticulocytes, Hb synthesis and entry to the bloodstream (equivalent to the RBC production rate, PRBC); a circulation module - representing the total blood volume (TBV), conversion of reticulocytes to mature RBCs, attainment of the final MCH, normal aging of RBCs, and a hemolytic process in BT (with rate constant kH that depends on the ACE level); and a transfusion module - representing the volume of transfused blood (VTF) with hematocrit H, a normal RBC age-distribution, and a separate hemolytic process (with rate constant kH_Tf). Reticulocyte lifespans in the bone marrow and circulation were set to ~3 days and ~1 day, respectively, but can vary oppositely at high PRBC (stress erythropoiesis). A key assumption of the model is that PRBC is down-regulated by the Hb level according to a sigmoidal Hill function, which was calibrated using PRBC data from normal subjects and patients with sickle cell disease, and was assumed to have a maximum value 10-fold the normal PRBC rate. In BT the PRBC function is also modulated by a factor FBT, dependent on the ACE level. Additional data from BT patients were used to derive the kH and FBT values. The model was expressed in ordinary differential equations using the Berkeley Madonna platform (Version 8.3.18).Results: To simulate the spectrum of BT phenotypes, MCH levels were varied from 15 pg to the normal value of 30 pg and the ACE levels, kH and FBT values were computed from the model. The simulated steady-state dependences of Hb vs. MCH (Figure 1A) and Reticulocyte count vs. Hb level (Figure 1B) are in good agreement with published literature data. For virtual patients (VPs) with MCH levels of 23, 21 and 18 pg, typical of BT trait, NTD and TD phenotypes, respectively, the estimated ACE levels were 0.22, 0.28 and 0.38 fmole/cell; kH values were 0.01, 0.019 and 0.037 day-1 and values of FBT were 0.65, 0.6 and 0.55. The effective RBC lifespans for these VPs were 68, 47 and 23 days, respectively. Regular transfusions (VTF = 15 mL/kg; H = 0.6) were simulated over 24 weeks for a TD VP (MCH = 18 pg; baseline Hb = 6.61 g/dL) to maintain the Hb level above 9 g/dL. In Figure 2A, where kH_Tf = 0 (no hemolysis of transfused blood), the transfusion interval stabilizes at 3.71 weeks. In Figure 2B, where kH_Tf = 0.0165 day-1(an effective RBC lifespan of 50.7 days), the transfusion interval stabilizes at 2 weeks. Reticulocyte counts decrease markedly in both cases. To achieve a ~3 g/dL increment in the Hb level, TBV must equal 100 mL/kg (~40% greater than normal).Conclusions: Our in-silico model explains the phenotypic variation of Hb levels and reticulocyte counts in BT in terms of the effects of ACE on the hemolysis rate constant (kH) and the fractional reduction in RBC production (FBT). The 2-week transfusion interval required in some patients to maintain Hb above 9 g/dL is explained by a shortened lifespan of the transfused blood. More clinical data would be helpful to confirm and refine these observations to better understand the key drivers of disease pathology in BT. [Display omitted] DisclosuresMazer:Roche: Employment, Equity Ownership. Hermosilla:Roche: Employment. Koerner:Roche: Employment.

Pyrolysis of 1-methylnaphthalene involving water: Effects of Fe-bearing minerals on the generation, C and H isotope fractionation of methane from H2O-hydrocarbon reaction

Water (H2O) and minerals involved organic-inorganic reactions are critical for hydrocarbon evolution in sedimentary basins and deep in the Earth. The mechanism and isotope fractionation for H2O-mineral-hydrocarbon interactions remain unclear. In this study, isothermal pyrolysis of 1-methylnaphthalene (1-MNa) involving H2O and three Fe-bearing minerals (pyrite–FeS2, magnetite–Fe3O4, and siderite–FeCO3), was conducted using a gold-tube system at 330–400 °C and a pressure of 50 MPa. It was observed that the presence of FeS2 and Fe3O4 led to an increase in the yield of hydrocarbon gases (C1-5). The isomeric ratios (iC4/nC4 and iC5/nC5) were much higher in the presence of Fe-minerals. In addition, 13C of methane (CH4) in pyrolysis with H2O-FeS2 and H2O-Fe3O4 was evidently more depleted than that in pyrolysis with only water. Kinetic calculations and carbon isotope fractionation revealed that FeS2 and Fe3O4 enhanced the H2O-hydrocarbon reaction via either ionic or free radical mechanisms at elevated temperatures. Moreover, the presence of FeS2 and Fe3O4 promoted hydrogen (H) transfer from H2O, causing the enrichment in the 2H of CH4. Furthermore, we first established a correlation between the H transfer rate constant (kH) and temperature (T): ln kH = −27.545 × 1000/T + 27.077. On this basis, it can be deduced that the time needed for equilibrium H transfer from H2O to CH4 at 200 °C and 400 °C with Fe-bearing minerals is approximately 4.8 Ma and 54.4 d, respectively.

Elaboration of carbon paste electrode containing pentadentate Nickel-(II) Schiff base complex: Application to electrochemical oxidation of thiosulfate in alkaline medium

A Nickel Schiff base complex, insoluble in water, was synthesized and used as modifier. A Nickel Schiff base modified carbon paste electrode MCPE was build. The electrodes were characterized by scanning electron microscopy (SEM), energy dispersive X-Ray spectroscopy (EDXS), cyclic voltammetry and chronoamperometry. The modifier is elctroactive, a well defined redox couple of NiIII/NiII in alkaline medium was made in evidence. It presents a quasi-reversible system with electron transfer coefficient (0.38) and electron transfer rate of 4.5 s−1. The electrogenerated NiIII species on the surface of the electrode act as an excellent catalyst toward thiosulfate oxidation reaction with a chemical rate constant Kh equal to 23,6 M−1s−1. The different techniques involved in this study qualify our modified electrode as sensitive, reliable and very stable for thiosulfate analysis.

Disintegration, In vitro Dissolution, and Drug Release Kinetics Profiles of k-Carrageenan-based Nutraceutical Hard-shell Capsules Containing Salicylamide

AbstractThe release of drugs from solid drug delivery materials has been studied intently in recent years. Quantitative analyses achieved from in vitro dissolution becomes easier if a zero-order mathematical model is used. Non-gelatin nutraceutical hard-shell capsules of zero size (approximately 0.7-0.8 cm) were produced from carrageenan-based natural polymers, namely carrageenan-alginate (CA) and carrageenan-starch (CS). Disintegration, dissolution and zero-order drug release kinetics of hard-shell capsules containing 100 mg of salicylamide were studied. The disintegration time of CA and CS were observed to be less than 30 min for both CA and CS. In vitro dissolution profile showed that the percentage dissolution of CA capsules was better at pH 4.5, while that of CS was poor at pH 1.2, 4.5 and 6.8. Determination of drug release kinetics profiles of carrageenan-based hardshell capsules utilized the Noyes-Whitney and Peppas-Sahlin modification rules for zero-order. The drug release from carrageenan-based capsules followed zero-order kinetics, especially at pH 6.8, and was compared to the Higuchi model. Salicylamide in CA hard-shell capsules at a pH 6.8 had a release rate constant (kH) of 2.91 %(ppm/ ppm) min-1/2, while the release rate constant of CS was 0.36 %(ppm/ppm) min-1.

Simultaneous Determination of Four DNA bases at Graphene Oxide/Multi-Walled Carbon Nanotube Nanocomposite-Modified Electrode.

In this study, we developed a modified glassy carbon electrode (GCE) with graphene oxide, multi-walled carbon nanotube hybrid nanocomposite in chitosan (GCE/GO-MWCNT-CHT) to achieve simultaneous detection of four nucleobases (i.e., guanine (G), adenine (A), thymine (T) and cytosine (C)) along with uric acid (UA) as an internal standard. The nanocomposite was characterized using TEM and FT-IR. The linearity ranges were up to 151.0, 78.0, 79.5, 227.5, and 162.5 µM with a detection limit of 0.15, 0.12, 0.44, 4.02, 4.0, and 3.30 µM for UA, G, A, T, and C, respectively. Compared to a bare GCE, the nanocomposite-modified GCE demonstrated a large enhancement (~36.6%) of the electrochemical active surface area. Through chronoamperometric studies, the diffusion coefficients (D), standard catalytic rate constant (Ks), and heterogenous rate constant (Kh) were calculated for the analytes. Moreover, the nanocomposite-modified electrode was used for simultaneous detection in human serum, human saliva, and artificial saliva samples with recovery values ranging from 95% to 105%.

Unveiling the biotic and abiotic mechanisms of solids concentration affecting hydrolysis and acidogenesis during sludge thermophilic anaerobic fermentation

Abstract The biotic factors (bacterial abundance, enzyme activity) and abiotic factors (sludge disintegration, organics solubilization) in sludge thermophilic fermentation at various solids concentrations were investigated to clarify the effects on hydrolysis and volatile fatty acids (VFAs) production. The results show that with the solids concentration increasing from volatile suspended solids (VSS) 5–40 g/L, the abiotic effects of particles disintegration played a leading role in hydrolysis, resulting in the decrease of hydrolysis rate constant (kH) (from 0.1181 to 0.0623) and solids degradation ratio (from 55.19% to 36.63%), while the biotic effects dominated above VSS20, reinforcing bacterial abundance and hydrolase activity. The maximal soluble chemical oxygen demand (SCOD) production yield positively correlated with VSS, and the value for VSS40 (436.52 mg/g VSSfed) increased by 50% over VSS5 (298.21 mg/g VSSfed). Additionally, the solubilization and conversion of carbohydrates were respectively enhanced by 2.6-folds and 13.4-folds at higher VSS, while for proteins they almost decreased by 50%. The VFAs production was comprehensively affected by the carbon substrate, ammonium and acid-forming enzyme, with the highest accumulation yield (232.17 mg CODVFA/g VSSfed) for VSS30; meanwhile, a higher percentage of acetate and n-butyrate but lower of propionate were achieved with VSS increasing.

Synergistic effect from anaerobic co-digestion of food waste and Sophora flavescens residues at different co-substrate ratios.

When food waste (FW) undergoes anaerobic digestion, the hydrolysis rate is rapid, and thus causes system instability. Sophora flavescens residues (SFRs) are rich in complex hydrolysed substances, such as lignocellulosic material. When combined FW and SFRs can effectively improve the stability of digestion systems and increase biogas yields. In this work, batch anaerobic experiments were conducted at different co-substrate ratios to investigate the performance of co-digestion and the synergistic effect of FW and SFRs. The co-digestion of the two substrates exerted synergistic effects on biogas production and the highest synergy was 120.8%. After digestion, the ratio of hydrolysed chemical oxygen demand (COD) to the entire COD (RCODH) of the co-digestion group was 1.08 times that of the single FW group, which indicated the co-digestion promoted the hydrolysis of substrates. Moreover, the hydrolysis rate constant (kh) of co-digestion group increased by 4.10 times in comparison with that of the single FW group, which indicated the co-digestion increased the hydrolysis rate. In other words, the synergistic effect mainly occurred in the hydrolysis acidification process.

Improved Methane Production Using Lignocellulolytic Enzymes from Trichoderma koningiopsis TM3 Through Co-digestion of Palm Oil Mill Effluent and Oil Palm Trunk Residues

The efficacy of concentrated enzymes from Trichoderma koningiopsis TM3 in hydrolyzing palm oil mill effluent (POME) and oil palm trunk residues (OPTr) at 40 and 50 °C was evaluated prior to methane fermentation. POME hydrolysate containing total sugar concentration of 15.40 g L−1 was obtained from enzymatic hydrolysis using 15 Unit g−1 TVS at 50 °C for 18 h incubation with the hydrolysis yield of 0.35 g total sugars g−1 TVS. The OPTr hydrolysate contained slightly higher total sugar concentration (18.90 g L−1) with the hydrolysis yield of 0.85 g total sugars g−1 TVS under the same condition. Methane production from POME hydrolysate was 6.29% higher than the raw POME. Co-digestion of POME hydrolysate with OPTr gave the maximum methane yield (369 ml CH4 g−1 VS-added) with the increase of 9.28% compared to the raw POME. The methane production rate (Rmax) and the hydrolysis rate constant (kh) of the co-digestion of POME hydrolysate with OPTr were 1.2-fold higher than those of the POME hydrolysate. PCR-DGGE analysis revealed that Clostridium sp. and Petrimonas sp. were dominated bacteria while Methanosarcina sp. and Methanospirillum sp. played an important role in methane production. These results indicated that enzymatic pretreatment and co-digestion of POME hydrolysate with OPTr could improve methane yield from anaerobic fermentation of POME.

Hydrolysis and interactions of d-cellobiose with polycarboxylic acids

The hydrolysis of cellulose model compound d-cellobiose was studied with a series of eight common polycarboxylic acids and two monocarboxylic acids in aqueous medium using 0.500 mmol -COOH/L at 170 °C. The maleic acid showed the highest catalytic activity with turnover frequency (TOF) of 29.5 h−1. The interaction of carboxylic acids with d-cellobiose in DMSO‑d6 was studied by determination of the pseudo first-order rate constant kH of anomeric -OH exchange rate in cellobiose using 1H NMR spectroscopy. The maleic, oxalic and citric acids showed infinitely large kH values indicating very strong interactions with d-cellobiose. The next highest interactions were found with phthalic acid (kH = 248.8 Hz). The FT-IR studies showed significant carboxylic acid C=O stretching frequency shifts (ΔνC=O) of 12, 13 and 10 cm−1 for maleic, oxalic and acetic acids respectively in mixtures with d-cellobiose.

Photoreduction of 3,6-Di-tert-Butyl-o-Benzoquinones in the Presence of N,N-Dimethylanilines in Binary Solvent Mixtures

The effect of the composition and dielectric characteristics of binary solvent mixtures on the photoreduction rate constant (kH) of 3,6-di-tert-butyl-o-benzoquinone and its 4-cyano derivative in the presence of three N,N-dimethylanilines has been studied. It has been found that for the pair 3,6-di-tert-butyl-o-benzoquinone–N,N-dimethylaniline, the free energy electron transfer of which is ΔGe = +0.11 eV, ln kH is proportional to the difference of the reciprocals of experimentally determined optical and static permittivities for the toluene–acetonitrile and benzene–N,N-dimethylformamide blends. For quinone–amine pairs, which have ΔGe ≠ +0.11 eV, kH is maximal in toluene and benzene and decreases with the increasing amount of the polar component in the solvent mixture, with lnkH being inversely proportional to the permittivity of the medium.

Impact of trace element supplementation on mesophilic anaerobic digestion of food waste using Fe-rich inoculum

Trace elements (TEs) play an indispensable role in enhancing the stability of anaerobic digestion (AD) of food waste (FW). Significant research on AD of FW with TE supplementation has been conducted with low Fe content inoculum. However, the use of Fe-rich inoculum is inevitable due to chemical phosphorous removal from wastewater in North America. We conducted comprehensive mesophilic batch tests to investigate the effect of TEs (Fe, Ni, Co, Se, and Mo) on FW digestion inoculated with Fe-rich sludge (≥ 1000mg FeL-1). This paper presents the impact of supplementing various concentrations of TEs on specific methanogenic activity (SMA), maximum specific methane production rate (SMPRmax), and apparent hydrolysis rate constant (Kh). The addition of TEs adversely impacted methanogenic activity by 20 to 58% in the SMA tests. The effects of individual and mixed supplementation of TEs on the SMPRmax and Kh during FW digestion were negligible; exceptions include Fe, Mo, and Co. Final soluble TE concentrations were 10-29% of the initial soluble TEs. The high Fe concentration in the inoculum reduces the bioavailable fraction of added TEs via coprecipitation. Contrary with many literature reports indicating the need to supplement TE to improve FW digestion efficiency, with Fe-rich sludges, FW digestion does not require TE supplementation.

Correlation between hydrolysis rate constant and chemical composition of energy crops

Besides biogas yield, the kinetic of biogas production in a biomethane potential (BMP) test also provides important information for feedstock characterization. In this study, fodder analysis and BMP tests with high temporal resolution were performed in order to identify statistical correlations between the hydrolysis rate constant (kh) and the chemical composition of various energy crops. Different species and cultivars of energy crops were analyzed in order to develop a broadly applicable regression model for the prediction of kh. Two independent datasets (222 samples in total) were used, one for the calibration of the model and one for its validation. The results indicated that the analytical parameters non-fiber carbohydrates and crude protein were statistically suitable for a multiple linear regression model for the prediction of kh. Furthermore, a first-order kinetic model and the proposed regression models can be utilized for the prediction of the biogas production in a BMP test. The proposed approach offers a fast and reliable prediction of the biogas production rate and allows a feedstock assessment according to their biogas potential.

Effect of coagulant on acidogenic fermentation of sludge from enhanced primary sedimentation for resource recovery: Comparison between FeCl3 and PACl

FeCl3 and PACl as coagulants in chemically enhanced primary sedimentation (CEPS) were compared in terms of their efficiencies in removing pollutants from wastewater and their effects on the acidogenic fermentation of CEPS sludge for resource recovery. PACl was found to be more effective than FeCl3 for removing suspended solids by CEPS, with around 20% higher removal efficiency. However, the coagulated Al-sludge experienced more difficulty and had lower efficiency than Fe-sludge in organic hydrolysis and acidogenesis. The batch fermentation results showed that FeCl3 dosed at 10–30mg Fe/Lsewage had little influence on sludge hydrolysis and volatile fatty acid (VFA) production, whereas an obvious inhibitory effect was observed for PACl in organic hydrolysis of the sludge. The specific hydrolysis rate constant (Kh,P) for sludge fermentation decreased from 0.0321 for the sludge without PACl to 0.017 for the Al-sludge obtained at a dosage of 24mgAl/Lsewage. Compared to the Al-sludge, the Fe-sludge had a much higher VFA yield and significant PO4–P release during the sludge fermentation, which is attributed to the reduction of Fe(III) to Fe(II) under anaerobic conditions and the resulting disintegration of sludge flocs. By simple pH adjustment of the fermented Fe-sludge supernatant, up to 31% of the phosphorus in wastewater can be recovered in the form of vivianite as P fertilizers. VFAs produced in the supernatant are valuable organic carbon resources that can be recovered for beneficial uses.

Effect of solvent nature on the photoreduction kinetics of substituted benzoquinones

Effect of the solvent nature on the kinetics of photoreduction of substituted benzoquinones in the presence of hydrogen donors has been studied. It has been found that the effective photoreduction rate constant (kH) for quinones decreases with an increase in solvent polarity. For the 3,6-di-tert-butylbenzoquinone–1,2-N,N-dimethylaniline pair, the dependence of ln kH on the difference of the reciprocals of optical and static solvent permitivities (1/e ∞–1/e0) is stepwise with a break point corresponding to CH2Cl2. A similar relationship lnkH = f(1/e ∞–1/e0) is observed for the p-chloranil–mesitylene pair. In the study of the photoreduction kinetics for a series of seven o-benzoquinones in the presence of p-derivatives of N,N-dimethylaniline in CH2Cl2, it has been found that the dependence of kH on the free energy of electron transfer (ΔGe) has a maximum for the 3,6-di-tert-butylquinone-1,2–N,N-dimethylaniline pair at ΔGe = 0.11 eV.

Fabrication and characterization of highly-ordered Zinc Oxide nanorods on gold/glass electrode, and its application as a voltammetric sensor

A novel voltammetric determination of amoxicillin (AMX) sensor has been fabricated, using zinc oxide nanorods (ZnO NRs) grown directly on gold/glass electrode. To prepare an electrode, ZnO NRs were directly grown on Au sputtered (thickness: 100nm) glass substrate (gold/glass electrode) with hydrothermal method. The directly synthesized ZnO NRs on the electrode expressively increases NRs attachment vertically, and increase its specific surface area. ZnO NRs/gold/glass electrode was characterized by field emission electron microscopy (FESEM), X-ray diffractometer (XRD) techniques, and this study has shown that the grown nanostructures are highly dense, uniform, and exhibited good crystal quality. The performance of the electrode was characterized with cyclic voltammetry (CV) and chronoamperometry (CA). The parameters of charge transfer coefficient (α), diffusion coefficient (D), electrode surface area (A), and catalytic rate constant (kh) were determined, and the results were studied. The electro catalytic current of AMX was found to have a linear relation to concentration over the range of 5×10−6 M–250×10−6 M (n=6). The good performance of the electrode is due to more immobilization on the well-aligned ZnO NRs arrays, and direct electron conduction between the ZnO NRs and the electrodes. Further, the sensor also showed a promising application for detecting AMX in capsule sample. The ease of fabrication, acceptable stability, and low cost of the modified electrode are the promising features of the proposed sensor.