No abstract

This study reports that the combination of Cu(II) with hydroxylamine (HA) (referred to herein as Cu(II)/HA system) in situ generates H2O2 by reducing dissolved oxygen, subsequently producing reactive oxidants through the reaction of Cu(I) with H2O2. The external supply of H2O2 to the Cu(II)/HA system (i.e., the Cu(II)/H2O2/HA system) was found to further enhance the production of reactive oxidants. Both the Cu(II)/HA and Cu(II)/H2O2/HA systems effectively oxidized benzoate (BA) at pH between 4 and 8, yielding a hydroxylated product, p-hydroxybenzoate (pHBA). The addition of a radical scavenger, tert-butyl alcohol, inhibited the BA oxidation in both systems. However, electron paramagnetic resonance (EPR) spectroscopy analysis indicated that (•)OH was not produced under either acidic or neutral pH conditions, suggesting that the alternative oxidant, cupryl ion (Cu(III)), is likely a dominant oxidant.

Oxidation by persulfates at elevated temperatures (thermally activated persulfates) disintegrates bacterial cells and extracellular polymeric substances (EPS) composing waste-activated sludge (WAS), facilitating the subsequent sludge dewatering. The WAS disintegration process by thermally activated persulfates exhibited different behaviors depending on the types of persulfates employed, that is, peroxymonosulfate (PMS) versus peroxydisulfate (PDS). The decomposition of PMS in WAS proceeded via a two-phase reaction, an instantaneous decomposition by the direct reaction with the WAS components followed by a gradual thermal decay. During the PMS treatment, the WAS filterability (measured by capillary suction time) increased in the initial stage but rapidly stagnated and even decreased as the reaction proceeded. In contrast, the decomposition of PDS exhibited pseudo first-order decay during the entire reaction, resulting in the greater and steadier increase in the WAS filterability compared to the case of PMS. The treatment by PMS produced a high portion of true colloidal solids (<1 μm) and eluted soluble and bound EPS, which is detrimental to the WAS filterability. However, the observations regarding the dissolved organic carbon, ammonium ions, and volatile suspended solids collectively indicated that the treatment by PMS more effectively disintegrated WAS compared to PDS, leading to higher weight (or volume) reduction by postcentrifugation.

No abstract

Oxidative degradation of six representative microcystins (MCs) (MC-RR, -LR, -YR, -LF, -LW, and -LA) by potassium permanganate (KMnO; Mn(VII)) was investigated, focusing on the temperature- and pH-dependent reaction kinetics, the effect of dissolved organic matter (DOM), and the oxidation mechanisms. Second-order rate constants for the reactions of the six MCs with Mn(VII) ( k) were determined to be 160.4-520.1 M s (MC-RR > -LR ≈ -YR > -LF ≈ -LW > -LA) at pH 7.2 and 21 °C. The k values exhibited activation energies ranging from 15.1 to 22.4 kJ mol. With increasing pH from 2 to 11, the k values decreased until pH 5, and plateaued over the pH range of 5-11, except for that of MC-YR (which increased at pH > 8). Species-specific second-order rate constants were calculated using predicted p K values of MCs. The oxidation of MCs in natural waters was accurately predicted by the kinetic model using k and Mn(VII) exposure (∫[Mn(VII)]dt) values. Among different characteristics of DOM in natural waters, UV, SUVA, and the abundance of humic-like substances characterized by fluorescence spectroscopy exhibited good correlation with ∫[Mn(VII)]dt. A thorough product study of MC-LR oxidation by Mn(VII) was performed using liquid chromatography-mass spectrometry.