Effect of carbon source and metal toxicity for potential acid mine drainage (AMD) treatment with an anaerobic sludge using sulfate-reduction

This study compares sulfate-reduction performance in an anaerobic sludge with different carbon sources (ethanol, acetate, and glucose). Also, the toxic effect of copper was evaluated to assess its feasibility for possible acid mine drainage (AMD) treatment. Serological bottles with 1.5 g VSS/L and 150 mL of basal medium (0.67 g COD/g SO₄^2- at a 7-8 pH) were used to determine the percentage of electron equivalents, maximum specific methanogenic (SMA), and sulfide generation activities (SGA). The copper effect was evaluated in a previously activated sludge in batch bioassays containing different concentrations of copper (0-50 mg/L), 3 gVSS/L, and 150 mL of basal medium (0.67 g COD/g SO₄^2-). Carbon source bioassays with glucose obtained the best results in terms of the SGA (1.73 ± 0.34 mg S^2-/g VSS•d) and SMA (10.41 mg COD-CH₄/g VSS•d). The electron flow in the presence of glucose also indicated that 21.29 ± 5.2% of the metabolic activity of the sludge was directed towards sulfidogenesis. Copper toxicity bioassays indicated that a considerable decline in metabolic activity occurs above 10 mg/L. The 20%IC, 50%IC, and 80%IC were 4.5, 14.94, and 35.31 mg Cu/L. Compared to the other carbon sources tested, glucose proved to be a suitable electron donor since it favors sulfidogenesis. Finally, copper concentrations above 15 mg/L inhibited metabolic activity in the toxicity bioassays.

WITHDRAWN: Reply to Comment by Sierra Rayne and Kaya Forest on "Ab initio study of the structural, electronic, and thermodynamic properties of linear perfluorooctane sulfonate (PFOS) and its branched isomers"

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Ab initio study of the structural, electronic, and thermodynamic properties of linear perfluorooctane sulfonate (PFOS) and its branched isomers

Structural, electronic, and thermodynamic properties of linear perfluorooctane sulfonate (PFOS) and its trifluoromethyl-branched isomers (i.e. 1-CF(3)- to 6-CF(3)-PFOS) were theoretically studied by means of ab initio density functional theory (DFT) calculations with the B3LYP functional and a 6-31++G(d,p) basis set. The anionic form of linear PFOS and its trifluromethyl-branched isomers were considered for the initial construction of the computational models; subsequently, H(+), Li(+), and Na(+) were added as counter-ions to study their effect on the properties under investigation. Insignificant changes with respect to the anions were observed in the structure of both the protonated and salt forms due to the presence of these counter-ions. However, important differences in the electrostatic potential maps as well as HOMO and LUMO molecular orbitals were observed for the various forms of PFOS. The linear and branched PFOS ions were identified as the most suitable compounds for interacting with charged species. Furthermore, in the linear anion, it was observed that the LUMO orbital is diffused along the whole fluoro-carbon chain, whereas it is localized to the region close to the ternary carbon in the 4-CF(3)-PFOS, 5-CF(3)-PFOS, and 6-CF(3)-PFOS isomers. The higher accessibility of the LUMO orbital in these branched anions suggests that they have a higher probability of reacting with free radicals when compared with the linear counterpart. This behavior is reflected in the experimental observation that only the branched PFOS isomers were susceptible to reductive defluorination by reduced vitamin B(12) as we previously reported. The relative stability of the linear and branched PFOS in their different forms computed by comparing their calculated Gibbs free energy showed that 1-CF(3)-, 6-CF(3)-, and linear PFOS are the most favorable structures from a thermodynamic point of view.