DECOMPOSITION OF 4-NITROPHENOL BY OZONATION IN A HOLLOW FIBER MEMBRANE REACTOR

Efficient reactive blue 19 decolorization by the comparison of ozonation membrane contacting process and Fenton oxidation

The decolorization of Reactive Blue 19 (RB 19) wastewater by an ozonation membrane contactor and Fenton oxidation was studied. The aims of the study were to investigate the affecting parameters and to compare the performance of RB 19 decolorization by two different processes. The results showed that Fe²⁺ and H₂O₂ concentrations for Fenton oxidation and ozone concentration with different membranes for the membrane contacting process played the most important roles in RB 19 decolorization. The optimum conditions for RB 19 decolorization by Fenton oxidation were initial pH 3.0, 1.5 mM H₂O₂ and 0.25 mM Fe²⁺; in contrast, the optimum conditions for the membrane contactor were initial pH 11 and 40 mg L⁻¹ ozone concentration. Under these conditions, the decolorization of RB 19 by the membrane contactor was almost completed and was higher than by Fenton and photo-Fenton oxidations for 90 min. The decolorizations of RB 19 by Fenton and photo-Fenton oxidations were constant after 30 min, but the decolorization of RB 19 by ozonation with a membrane contactor gradually increased via ozone consumption until 90 min operation, which was higher than that of Fenton oxidations. The use of a PVDF-PAM membrane in the membrane contactor resulted in higher decolorization efficiency than a PVDF membrane. The results demonstrated a COD removal efficiency of 63% by an ozonation membrane contacting process using PVDF-PAM, which was lower than that of Fenton oxidation (73%), but resulted in higher BOD₅/COD and NO₃⁻ and SO₄²⁻ releases. Under these conditions, the ozonation membrane contacting process showed the lowest electric energy consumption.

The decolorization of Reactive Blue 19 (RB 19) wastewater by an ozonation membrane contactor and Fenton oxidation was studied.

Facile synthesis of magnetic Co3O4/BFO nanocomposite for effective reduction of nitrophenol isomers

Co₃O₄/BiFeO₃ nanocomposite catalysts were synthesized by a facile hydrothermal method following the impregnation process. The nanocomposite was successfully characterized by powder X-ray diffraction(XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), nitrogen adsorption desorption isotherms and X-ray photoelectron spectroscopic (XPS) analysis. The as-synthesized Co₃O₄/BiFeO₃ nanocomposites were tested as a catalyst in the reduction of nitrophenol isomers with NaBH₄ at room temperature. The results indicate that the as-prepared Co₃O₄/BiFeO₃ nanocomposites are an efficient recyclable catalyst for the reduction of nitrophenol isomers. The reduction kinetics for all the reactions follows the pseudo-first order. The rate reduction of nitrophenols followed the order 3NP > 2NP > 4NP.

Application of a ceramic membrane contacting process for ozone and peroxone treatment of micropollutant contaminated surface water

This study investigates the performance of membrane-based ozonation and peroxone processes, regarding the transformation of carbamazepine (CBZ), benzotriazole (BZT), p-chlorobenzoic acid (pCBA) and atrazine (ATZ) in natural surface waters, as well as the formation of bromates. Ozonation, performed with the use of ceramic membrane contactor, was able to diminish CBZ concentration below 0.1 μM at 0.4 mg O₃/mg DOC, i.e. presenting >90% removal rate, whereas the transformation of BZT, pCBA and ATZ was not exceeded 70%, 57% and 49%, respectively, under the same experimental conditions. The addition of H₂O₂ reduced the removal efficiency of CBZ, since up to -8% transformation values were observed at 0.1 mg O₃/mg DOC. In contrast, the transformation of ozone-resistant compounds pCBA and ATZ was slightly improved by approximately 5-10%, at 0.8 mg O₃/mg DOC. Membrane-based oxidative treatment of surface water resulted to high bromate concentrations (49 μg/L and 28 μg/L for ozone and peroxone process, respectively, at 0.8 mg O₃/mg DOC). The results obtained by using the membrane contactor were also compared with the corresponding from conventional batch experiments. These results suggest that the implementation of membrane contactors with the highest possible inner surface per volume along with the use of low ozone gas concentration are required to improve the removal of micropollutants and diminish bromate formation.

Impact of O3 or O3/H2O2 treatment via a membrane contacting system on the composition and characteristics of the natural organic matter of surface waters

The present study aims to evaluate changes in the structure-composition of natural organic matter (NOM) that occur after the application of bubbleless ozonation or peroxone treatment of surface waters. The oxidation experiments (using 0.5-2 mg O3/mg DOC, or 2:1 O₃:H₂O₂ molar ratio) were performed in a continuous mode, using a tubular ceramic membrane contactor. Fluorescence spectroscopy (emission-excitation matrix) and liquid chromatography-organic carbon detection (LC-OCD) were mainly used for the detailed DOC characterization. In brief, the application of single ozonation resulted to high reduction of humic-like peak fluorescence intensities (50-85%) and also to the formation of two new peaks in the region of protein-like components. The co-addition of H₂O₂ did not present the anticipated increase in the reduction of fluorescence intensity; however, it resulted to the further oxidation of protein-like fluorophores. LC-OCD measurements confirmed the decrease of average molecular weight of NOM during ozone treatment, due to the gradual degradation of biopolymers (14-23%) and humic substances (11-17%) towards building blocks and low molecular weight (LMW) neutrals. Advanced oxidation process (AOP) treatment by the mixture O₃/H₂O₂ resulted in the simultaneous decrease of building blocks and LMW neutral concentrations. Conventional batch ozonation and AOP experiments were conducted using ozone-saturated solutions to investigate the effect of different contacting patterns. The results revealed that the different reaction pathways followed during bubbleless and conventional batch experiments may also influence the formation of NOM oxidation intermediates.

Investigation of the synergistic effects for p-nitrophenol mineralization by a combined process of ozonation and electrolysis using a boron-doped diamond anode

Electrolysis and ozonation are two commonly used technologies for treating wastewaters contaminated with nitrophenol pollutants. However, they are often handicapped by their slow kinetics and low yields of total organic carbon (TOC) mineralization. To improve TOC mineralization efficiency, we combined electrolysis using a boron-doped diamond (BDD) anode with ozonation (electrolysis-O3) to treat a p-nitrophenol (PNP) aqueous solution. Up to 91% TOC was removed after 60 min of the electrolysis-O3 process. In comparison, only 20 and 44% TOC was respectively removed by individual electrolysis and ozonation treatment conducted under similar reaction conditions. The result indicates that when electrolysis and ozonation are applied simultaneously, they have a significant synergy for PNP mineralization. This synergy can be mainly attributed to (i) the rapid degradation of PNP to carboxylic acids (e.g., oxalic acid and acetic acid) by O3, which would otherwise take a much longer time by electrolysis alone, and (ii) the effective mineralization of the ozone-refractory carboxylic acids to CO2 by OH generated from multiple sources in the electrolysis-O3 system. The result suggests that combining electrolysis with ozonation can provide a simple and effective way to mutually compensate the limitations of the two processes for degradation of phenolic pollutants.