Treatment options for tannery wastewater II: integrated chemical and biological oxidation

This is the second of two papers each dealing with a specific technological option for replacing the Fenton's reagent with simpler processes for treating industrial wastewater. In particular, the paper reports the results of an investigation aimed to check, at lab scale, the effectiveness of an alternative wastewater treatment combining biological degradation and chemical oxidation with ozone. The treatment was carried out in a lab scale hybrid reactor fed with the biological stage effluent of a plant treating the wastewater of a large tanning district in Central Italy whose residual COD result still higher than the Italian COD Maximum Allowable Concentration (MAC) value (i.e., 160 mgO2/L) The results are very promising, considering that a removal efficiency of 41% (as COD) has been achieved by treating an influent characterized by a COD content fully biorefractory. In addition, the proposed treatment presents the significant advantage of no additional sludge production, as happens with commonly utilized tertiary processes (i.e. Fenton), that is characterized by high chemical sludge production.     

Thermodynamic parameters for the binding of polycarboxylic anions by fully methyl substituted linear polyammonium cations

Enthalpy changes for the binding of malonate, citrate, 1,2,3-propanetricarboxylate and 1,2,3,4-butanetetracarboxylate by fully methyl substituted linear polyammonium cations (with the general formula C3nNnH(8n + 2)n+, with n = 1,2,3) were determined calorimetrically. Enthalpy changes were also determined for the binding of malonate by unsubstituted polyammonium cations (with the general formula C2(n - 1)NnH(6n - 2)n+, n = 1...6). delta H0/kJ mol-1 values are always positive and strongly dependent on the charges involved in the formation reaction. Mean values for delta G0 and T delta S0 were obtained as a function of the charge product zeta = Zanion/ Zcation: -delta G0/kJmol-1 = (4.0 +/- 0.4) zeta, T delta S0/kJmol-1 = (5.9 +/- 0.1) zeta (substituted polyamines), and -delta G0/kJmol-1 = (3.5 +/- 0.2) zeta, T delta S0/kJmol-1 = (5.0 +/- 0.4) zeta (unsubstituted polyamines). For both classes of amines it was found that T delta S0 vs. delta G0 is linear with a correlation coefficient of r = 0.9618. Crude approximation gives -delta G0/kJmol-1 = (7.0 +/- 0.4) n-1, T delta S0/kJmol-1 = (10.0 +/- 0.8) n-1 for unsubstituted amines and -delta G0/kJmol-1 = (8.0 +/- 0.8) n-1, T delta S0/kJmol-1 = (11.8 +/- 2.0) n-1 (n = number of possible salt bridges, or single interactions) for substituted amines.     

Substituent effects in the mass spectra of diethyl phenyl phosphates

The mass spectra of diethyl phenyl phosphates show substituent effects with electron-donating groups favouring the molecular ion M⁺˙, and the [M? C₂H₄]⁺˙, [M – 2C₂H₄]⁺˙ and [XPhOH]⁺˙ ions. The [PO₃C₂H₆]⁺ (m/z 109) and [PO₃H₂]⁺ (m/z 81) ions are favoured by electron-withdrawing groups. Results suggest that the formation of the [XPhC₂H₃]⁺˙ ion involves rearrangement of C₂H₃ to the position ortho to the phosphate group. Ortho effects are also observed.     

Dissociation Constants for Citric Acid in NaCl and KCl Solutions and their Mixtures at 25 °C

The constants for the dissociation of citric acid (H₃C) have been determined from potentiometric titrations in aqueous NaCl and KCl solutions and their mixtures as a function of ionic strength (0.05–4.5 mol-dm^–3) at 25 °C. The stoichiometric dissociation constants (K_i^*)

A convenient tool for studying the stability of proteins and nucleic acids

The aim of this work is to discuss the thermodynamic properties, obtained by differential scanning calorimetry (DSC), of the thermal transition of proteins and nucleic acids and to analyze these data using statistical thermodynamic relations. The denaturation of the ordered, specific structures of biological macromolecules is a cooperative process and in many cases the macromolecules undergo a two-state transition. Differential scanning calorimetry, giving direct thermodynamic information, has proved to be very useful in clarifying the energetics of macromolecule transitions and in characterizing their thermal stability. Here, various examples are discussed: i) the equilibrium thermal denaturation of ribonuclease A, a model for the use of DSC by following the temperature-unfolding of the proteins, a monomolecular transition; ii) the equilibrium thermal dissociation of a DNA double helix in two strands, an example of how DSC is used to follow a bimolecular process; iii) an example of the use of DSC for studying the melting of unimolecular and tetramolecular DNA quadruple-helices.     

Simultaneous determination of alkali, alkaline earths and ammonium in natural waters by ion chromatography

An ion chromatographic method has been developed for the determination of alkali (Li(+), Na(+), K(+)), alkaline earths (Ca(2+), Mg(2+), Ba(2+), Sr(2+)) and ammonium ion in waters. The usual difficulties encountered during traditional cation-exchange separations (incomplete resolution for Na(+) and NH(4) (+) present in disproportionate concentration ratios) have been overcome tuning the selectivity of the separation by the introduction of 18-crown-6 ether in the mobile phase using an IonPac CS12A (150x3 mm id) column. After a detailed study of the effect of mobile phase components on separation, a gradient elution from 26 mM methanesulphonic acid (MSA) with a step change at 9 min to 60 mM MSA (0.5 mM 18-crown-6) provided the required baseline separation for the eight selected analytes. The method developed provides the advantage of the determination, in the same analytical run, also of strontium and barium, which is usually performed by spectroscopic techniques. Within-day and between-day repeatability have been assessed, observing between-day RSD included between 0.3 and 1.8% for retention times and 0.6 and 7.2% for peak areas. The method has been finally tested for the analysis of water samples of different provenience (well, tanks, water system) and results compared with those obtained by the laboratory in charge of the control of drinking water for the city of Torino (Italy).     

Dioxouranium(VI)-Carboxylate Complexes. Interaction of {\rm OU}_{2}^{2+} with 1,2,3,4,5,6-Benzenehexacarboxylate (Mellitate) in 0 ≤ I(NaCl a q ) ≤ 1.0 mol·L −1

The formation constants of dioxouranium(VI)—1,2,3,4,5,6-benzenehexacarboxy- late [mellitate(6?)] complexes were determined in NaCl aqueous solutions at 0.1 ≤ I ≤ 1.0 mol·L^?1 and t = 25 ^°C by ISE-[H⁺] glass-electrode potentiometry. The speciation model obtained at each ionic strength includes the following species: ML^4?, MLH^3?, MLH₂ ^{2 ?}, MLH₃ ^?, M₂L^2?, MLOH^5? and ML(OH)₂ ^6? (M = UO₂ ^{2 +} and L^6? = mellitate). The ionic strength dependence of the protonation constants of mellitate and of the metal-ligand complexes was investigated using the SIT (Specific Ion Interaction Theory) approach. Formation constants at infinite dilution are [for the generic equilibrium $p{\rm UO}_{\rm 2}^{{\rm 2 + }} + q({\rm L}^{{\rm 6} - }) + r{\rm H}^{\rm + }\rightleftharpoons({\rm UO}_{\rm 2}^{{\rm 2 +}})_p({\rm L})_q {\rm H}_r^{(2p - 6q + r)};\,\beta _{pqr}$ ]: log₁₀ β ₁₁₀ = 10.155, log₁₀ β ₁₁₁ = 16.084, log₁₀ β ₁₁₂ = 20.749, log₁₀ β ₁₁₃ = 24.038, log₁₀ β ₂₁₀ = 17.936, log₁₀ β _11?1 = 2.327 and log₁₀ β _11?2 = ?6.804. Simple linear relationships between the formation constants and the stoichiometric coefficients of reactants are reported. The sequestering capacity of mellitate towards UO₂ ²⁺ was quantified using a sigmoid Boltzman-type equation.     

Matrix-assisted laser desorption/ionization time-of-flight investigation of Nylon 6 and Nylon 66 thermo-oxidation products

Matrix-assisted laser desorption/ionization mass spectrometry (MALDI) was used to determine the structure of the molecules produced in the thermo-oxidative degradation of Nylon 6 and Nylon 66, at 180 degrees C and 250 degrees C in air. The MALDI spectra of the thermo-oxidized nylons provide information on the structure and end groups of the oligomers produced in the oxidation process. Our results show that the thermo-oxidation of both Ny6 and Ny66 proceeds through a hydrogen abstraction and subsequent formation of hydroperoxide intermediates. The latter decompose, yielding oligomers containing aldehydes, amides and methyl terminal groups. The aldehydes undergo further oxidation to produce carboxylic end groups. The formation of cyclopentanone terminal groups is also observed in the case of Nylon 66. Oligomers with structures deriving from Norrish-type degradation processes were not detected here for either Ny6 or Ny66.     

Effect of Ionic Strength and Temperature on the Protonation of Oxidized Glutathione

The protonation constants for oxidized glutathione, H _i−1L^(4−i+1)−, K _i ^H=[H _i L⁽⁴⁻ⁱ⁾⁻]/[H _i−1L^(4−i+1)−][H⁺] i=1,2,…,6 have been measured at 5, 25 and 45 °C as a function of the ionic strength (0.1 to 5.4 mol⋅[kg(H₂O)]⁻¹) in NaCl solutions. The effect of ionic strength on the measured protonation constants has been used to determine the thermodynamic values (K _i ^H0) and the enthalpy (ΔH _i ) for the dissociation reaction using the SIT model and Pitzer equations. The SIT (ε) and Pitzer parameters (β ⁽⁰⁾, β ⁽¹⁾ and C) for the dissociation products (L⁴⁻, HL³⁻, H₂L²⁻, H₃L⁻, H₄L, H₅L⁺, H₆L²⁺) have been determined as a function of temperature. These results can be used to examine the effect of ionic strength and temperature on glutathione in aqueous solutions with NaCl as the major component (body fluids, seawater and brines).     

Thermodynamics (Solubility and Protonation Constants) of Risedronic Acid in Different Media and Temperatures (283.15–318.15 K)

Potentiometric measurements were carried out to study the protonation constants of risedronic acid (RA) in NaCl_(aq), (CH₃)₄NCl_(aq) and (C₂H₅)₄NI_(aq) at different ionic strengths and temperatures (283.15 ≤ T/K ≤ 318.15). In the same conditions, solubility measurements were also performed. Calorimetric measurements were done in NaCl to determine the protonation enthalpy values at I = 0.15 mol·dm^?3 and 298.15 K. Generally, the proton binding process was endothermic and the driving force was entropic in nature. The values of the protonation constants determined in NaCl_(aq) are lower than those obtained in the two tetraalkylammonium salts. The medium effect was interpreted using different thermodynamic models in terms of variation of the activity coefficients with ionic strength (Debye–Hückel type and SIT), or formation of weak complexes between risedronate (Ris^4?) and the ions of the supporting electrolytes. Specific interaction coefficients (ε) and the stability of five (CH₃)₄N⁺/Ris^4? (at different temperatures and ionic strengths) species are reported. The total solubility of risedronic acid is higher in NaCl_(aq) than in the other two ionic media and, in all cases, increases with increasing temperature. Setschenow and activity coefficients of the neutral species were also computed in all ionic media.