Use of catalytic wet air oxidation (CWAO) for pretreatment of high-salinity high-organic wastewater.

Catalytic wet air oxidation (CWAO) coupled desalination technology provides a possibility for the effective and economic degradation of high salinity and high organic wastewater. Chloride widely occurs in natural and wastewaters, and its high content jeopardizes the efficacy of Advanced oxidation process (AOPs). Thus, a novel chlorine ion resistant catalyst B-site Ru doped LaFe1-xRuxO3-δ in CWAO treatment of chlorine ion wastewater was examined. Especially, LaFe0.85Ru0.15O3-δ was 45.5% better than that of the 6%RuO2@TiO2 (commercial carrier) on total organic carbon (TOC) removal. Also, doped catalysts LaFe1-xRuxO3-δ showed better activity than supported catalysts RuO2@LaFeO3 and RuO2@TiO2 with the same Ru content. Moreover, LaFe0.85Ru0.15O3-δ has novel chlorine ion resistance no matter the concentration of Cl- and no Ru dissolves after the reaction. X-ray diffraction (XRD) refinement, X-ray photoelectron spectroscopy (XPS), transmission electron microscope (TEM), and X-ray absorption fine structure (XAFS) measurements verified the structure of LaFe0.85Ru0.15O3-δ. Kinetic data and density functional theory (DFT) proved that Fe is the site of acetic acid oxidation and adsorption of chloride ions. The existence of Fe in LaFe0.85Ru0.15O3-δ could adsorb chlorine ion (catalytic activity inhibitor), which can protect the Ru site and other active oxygen species to exert catalytic activity. This work is essential for the development of chloride-resistant catalyst in CWAO.

Preparation of three dimensional bimetallic Cu-Ni/NiF electrodes for efficient electrochemical removal of nitrate nitrogen.

It still remains a hotspot and great challenge to efficiently remove the nitrate nitrogen from high salt wastewater. Herein, a novel three dimensional porous bimetallic copper-nickel alloy electrode was fabricated with Ni foam (NiF) as substrate. The physicochemical and electrochemical characterization results showed Cu-Ni/NiF electrode possessed the smaller particle size (0.3-1.0 µm) and electrode film resistance comparing with Ni/NiF and Cu/NiF electrodes. Besides, higher double layer capacitance (Cdl) for Cu-Ni/NiF electrode indicated more electrochemical active sites could be used in the electrochemical nitrate nitrogen (NO3--N) removal. The electrochemical experiments showed the Cu-Ni/NiF electrode had the optimal NO3--N reduction ability and almost 100% NO3--N removal could be achieved with 30 min. All NO3--N removal processes were in accord with the pseudo-first-order reaction kinetics completely. The gaseous nitrogen selectivity for Cu-Ni/NiF electrode could reach 80.9% within 300 min. Stability assessment experiments indicated the Cu-Ni/NiF electrode all kept an excellent stability with Na2SO4 or NaCl electrolyte and the Cl- addition could significantly improve the gaseous nitrogen selectivity. Finally, a possible removal mechanism of NO3--N was proposed. This work offered a direction for designing non-noble bimetallic electrodes for nitrate removal.

Synergetic electrocatalytic degradation of isophorone by active oxygen species generated in the gas diffusion electrode and PbO2 anode.

Significant efforts have been made to achieve efficient H2O2 generation via oxygen reduction reaction (ORR). Here, the acetylene black (AB)-based gas diffusion electrodes (GDEs) modified by PTFE were fabricated and applied in a closed autoclave for H2O2 generation for the first time. The surface morphology, BET, XPS, cyclic voltammetry curves and linear scanning voltammetry curves of GDEs were all characterized. Additionally, the H2O2 generation experiments of GDEs and the relationship between H2O2 yield and BET surface area (SBET), double layer capacitance (Cdl) were all investigated. It could be found that the SBET and Cdl of GDEs kept a good linear relationship with H2O2 content, and 2#GDE (AB:PTFE = 1:3) possessed the optimal H2O2 generation capacity. Also, the effect of oxygen pressure and current density on H2O2 production was evaluated detailedly, indicating higher oxygen pressure was beneficial to the H2O2 generation and the preferable current density was 20 mA cm-2 due to the side reactions. And all the H2O2 electro-generation experiments exhibited a higher oxygen utilization efficiency (0.77%-2.93%). Finally, the efficient and synergetic electro-catalytic degradation of isophorone was achieved by self-made PbO2 anode and GDE.

Fabrication of boron-doped diamond films electrode for efficient electrocatalytic degradation of cresols.

The choice of anode materials has a significant influence on the electrocatalytic degradation of organics. Accordingly, the electrocatalytic activity of several active anodes (Ti/Ru-Ir, Ti/Ir-Ta, Ti/Pt) and non-active anodes (Ti/PbO2, Ti/SnO2, Si/BDD (boron-doped diamond)) was compared by electrocatalytic degradation of m-cresol. The results indicated Si/BDD electrode had the strongest mineralization ability and the lowest energy consumption. And the order of the activity of m-cresol degradation was as follows: Si/BDD > Ti/SnO2>Ti/PbO2>Ti/Pt > Ti/Ir-Ta > Ti/Ru-Ir. Also their intermediate products were compared. The effects of experimental parameters on electrocatalytic degradation of m-cresol with Si/BDD electrode showed m-cresol conversion was affected slightly by the electrode spacing and electrolyte concentration, but affected greatly by the temperature and current density. And smaller electrode spacing and current density, higher electrolyte concentration and temperature were beneficial to reduce energy consumption. Their degradation processes were all accord with the pseudo-first-order reaction kinetics completely. In addition, the results of electrocatalytic degradation of m, o, p-cresol indicated there was almost no significant difference on conversion rate between cresols isomers with the current density of 30 mA cm-2. However, the influence of group position was shown when the current density was reduced to 10 mA cm-2 and cresols conversion followed the sequence of m-cresol ≈ o-cresol > p-cresol.

A novel isophorone wastewater treatment technology-wet electrocatalytic oxidation and its degradation mechanism study.

How to solve the poisoning and loss of catalysts in catalytic wet air oxidation (CWAO) process remains a great challenge. In this work, an electric field was introduced into wet air oxidation (WAO) process for the efficient degradation of isophorone (IP) wastewater for the first time, named as wet electrocatalytic oxidation (WEO) process. Different composite electrodes including Ti/PbO2, Ti/Pt, Ti/Ru-Ir and Ti/Ir-Ta electrode were selected as the anodes of WEO technique and the results showed that the total organic carbon (TOC) removal via WEO process with PbO2 anode (89.56 %) was much higher than CWAO equipped with noble metal catalyst (Ru/TiZrO4, 75.0 %). Additionally, the current efficiency of WEO process was 85.6 %, which was significantly better than that of EO process (12.1 %). A response surface methodology was applied to elucidate the effects of reaction conditions on IP degradation. Analysis of response surface model showed TOC removal were markedly affected (p ≤ 0.01) by the reaction time (t), temperature (T), current density (ID), T2 and ID2, and also determined (p ≤ 0.05) by the interactions of T with t and ID respectively. In addition, a synergistic effect was proved to take place in WEO process with synergistic effect factor f of 1.2 at optimized conditions. As an advanced wastewater treatment technology, WEO integrates the advantages of both electro-catalytic oxidation (EO) and WAO.